Inorganic chemistry of the main group elements vol 2

The Alkali Metals Alloys and Intermetallic Compounds Solvation of Alkali-metal Ions Aqueous Solvation Non-aqueous Solvation Ions Compounds containing Organic Molecules or Complex... Ba

A Specialist Periodical Report

Elements

A Review of t h e Literature Published between

September 1972 and September 1973

The Chemical Society

ISBN : 0 85186 762 6

Printed in Northern Ireland at The Universities Press, Belfast

Preface

The framework used in Volume 1 for reporting the Chemistry of the Main-

group Elements appears to have been generally acceptable, and has been continued in Volume 2 The present volume therefore comprises eight chapters, each concerned with one of the Main Groups as defined in the

abbreviated form of the Periodic Table given in the Preface to Volume 1, and

it has now been agreed that the chemistry of zinc, cadmium, and mercury will

be included in the Specialist Periodical Reports concerned with the Transition Elements

The relative sizes of the chapters are much the same as in Volume 1 and this again reflects the amount of published research in each Group In Chapter 1,

greater coverage is given to those properties of the metals which are relevant

to their use in the generation of electrical energy from batteries, or from nuclear fission and fusion reactors, and both Chapters 1 and 2 include more

illustrative material Chapter 3 reflects a steady increase in effort throughout

the Group, but an especially large number of papers have been published on carbaborane r-complexes Chapter 4 is large, consistent with the considerable amount of research which continues to be published on each of these elements Chapter 5 now includes a short section on ‘nitrogen oxides and atmospheric chemistry,’ but the bulk of published material is again concerned with the chemistry of phosphorus; there are some 500 references to phosphorus, whereas arsenic, antimony, and bismuth together are covered by 240

references Careful selection has been necessary in Chapter 6 to avoid overlap

with other chapters or volumes Thus, this chapter contains the chemistry of sulphides of Main-group elements, but not sulphides of transition metals

Again, S-N compounds are dealt with in this chapter, whereas S-B com- pounds are in Chapter 3, and S-P and S-As compounds in Chapter 5 The

halides of the elements are treated as they arise in Chapters 1-6, and Chapter

7 is restricted to interesting recent developments in halogen chemistry, such

as the superacids Noble-gas chemistry is represented by a small number of

highly interesting papers, which are discussed in Chapter 8

We have continued the policy of referring to physical properties (and particularly spectroscopic data) of compounds only where this is essential to demonstrate some important chemical property, Similarly, we refer only to those aspects of organo-derivatives which illustrate significant features in the chemistry of the Main-group element involved On the other hand, more structures are becoming available (often highly refined) now that X-ray diffraction methods are becoming computerized; the chemistry becomes more meaningful, and is more readily explained, once the structure is known, and other physical measurements become less significant We have therefore taken every opportunity to include structures of key compounds

The whole volume is again written by members of the Department of Chemistry in the University of Nottingham, so that the maximum degree of

C C Addison

The Alkali Metals

Alloys and Intermetallic Compounds

Solvation of Alkali-metal Ions

Aqueous Solvation Non-aqueous Solvation Ions

Compounds containing Organic Molecules or Complex

Compounds containing B-0 Bonds

Compounds containing B-C Bonds Boron-containing Heterocycles Compounds containing B-S Bonds Boron Nitride and Metal Borides

Compounds containing AI-C and Al-Si Bonds 177

Compounds containing A1-0 or AI-S Bonds 183

Compounds containing Ga-0 or Ga-S Bonds 201

Compounds containing In-0, In-S, or In-Se Bonds 208

216

217

219

224

Contents vi i

By P G Harrison and P Hubberstey

260 Formaldehyde, Thioformaldehyde, Carbonyl Hal-

265

Carbonates, Thiocarbonates, and Related Anions 276

28 1

Formaldehyde and its Substituted Derivatives

Derivatives of Group VI Elements

Derivatives of Group V Elements

Hydrides of Silicon, Germanium, Tin, and Lead Halides of Silicon, Germanium, Tin, and Lead Synthesis

Reactions of Silicon, Germanium, and Tin Tetra- Physical Studies of Quadrivalent Silicon, Germa- halides and Related Compounds

nium, and Tin Halides (i) Structural studies (ii) Infrared, Raman, and microwave data (iii) N.m.r studies

(iv) Mossbauer studies

viii Contents

Silicon, Germanium, Tin, and Lead Derivatives of

Thio-germanates, -stannates, and -plumbates, and

Molecular Compounds containing M-S, -Se, and -Te (M = Si, Ge, Sn, or Pb) Bonds 370

Compounds containing Silicon-, Germanium-, Tin-,

Phosphorus and Arsenic Derivatives of Silicon,

Pseudohalide Derivatives of Silicon, Germanium, and

Derivatives containing Silicon-, Germanium-, and

Germanium(n), Tin@), and Lead(@ Halides and

Oxygen Derivatives of Silicon, Germanium, Tin, and

Transition-metal Derivatives of Silicon, Germanium, Bivalent Derivatives of Silicon, Germanium, Tin, and

Lead@) Pseudohalides Organometallic Derivatives of Bivalent Germanium, Tin, and Lead

Complexation Behaviour of Lead@) in Aqueous Catalytic Activity of Silicon- and Tin-containing Miscellaneous Physical Measurements

In termet allic Phases Binary Systems Ternary Systems

Media Systems

Chapter 5 Elements of Group V

By A Morris and D 6 Sowerby

1 Nitrogen

Elementary Nitrogen Bonds to Hydrogen

NH and NH, Compounds

NH3 and Derivatives NH; Compounds

N,H, and Derivatives Bonds to Carbon Bonds to Nitrogen Bonds to Oxygen

N2O

NO

Nitrogen(II1) Species Nitric Acid

Nitrates Miscellaneous N-0 Species Nitrogen Oxides and Atmospheric Chemistry NOz-NZO4

Bonds to Fluorine

NF,-N,F,

Miscellaneous N-F Species Bonds to Chlorine and Iodine

2 Phosphorus

Element Phosphides

X

Bonds to Boron Bonds to Carbon Phosphorus(rrr) Compounds Phosphorus(v) Compounds Bonds to Silicon, Germanium, or Tin Bonds to Halogens

Phosphorus(II1) Halides Phosphorus(v) Halides Compounds containing P-C Bonds Compounds containing P-0 Bonds

Compounds containing P-S Bonds Phosphorus(Ir1) Compounds Phosphorus(v) Compounds Pseudohalides

Compounds containing P-N-P Bonds Compounds containing P,N, Rings Phosphonitriles (Phosphazenes) Heteroatom Ring Systems Lower Oxidation States Phosphorus(v) Compounds Heteropolyacids

Monophosphates Apatites

Diphosphates Meta- and Poly-phosphates Bonds to Sulphur or Selenium

4 Antimony

General Bonds to Halogen Antimony(1Ir) Compounds Antimony(v) Compounds Bonds to Oxygen

Bonds to Sulphur or Selenium

Contents

5 Bismuth

General Bonds to Halogens Bonds to Oxygen Bonds to Sulphur or Selenium

Chapter 6 Elements of Group VI

By M G Barker

1 Oxygen

The Element Ozone Ion Species Oxygen Fluorides Water

2 Sulphur

The Element Sulphides Sulphides of Group I, 11, and I11 Metals

Group IV Metal Sulphides

Group V Metal Sulphides

Other Metal Sulphides Ternary Sulphide Phase Systems Ternary Sulphide Compounds Polysulphide Ions

Hydrogen Sulp hide Sulphur-Halogen Compounds Sulphur-Oxygen-Halogen Compounds Sulphur-Nitrogen Compounds Linear Compounds

Ring Compounds Sulphur-Nitrogen-Phosphorus Compounds Sulphur-Boron Ring Compounds

Sulphur-Oxygen Compounds Sulphur Dioxide

Sulphur Trioxide Alkali-metal Sulphates Alkaline-earth-metal Sulphates

0 ther Metal Sulphates Sulphates

Group PI1 Element Selenides

Group IV Element Selenides Group V Element-Selenium Compounds

Selenates Seleni tes Other Compounds of Selenium

4 Tellurium

The Element Tellurium-Oxygen Compounds Tellurium-Halogen Compounds Compounds with a Te-§ Bond Tellurides

Compounds with Oxygen Hydrogen Halides

2 Hydrogen

Protonic Acid Media Hydrogen-bonding Miscellaneous

in any other Single references to topics are presented systematically in the section on the appropriate metal

The elements of Groups I and I1 are so closely linked in some instances

that a section describing them jointly is presented to avoid duplication in Chapter 2 Such a case is the section on ‘Molten Salts’, which covers the chemistry of the molten salts of both Groups I and I1 but is presented only

in this chapter

2 The Alkali Metals

The hyperfine structure of the 1 sn 3P terms of singly ionized lithium -6,

-7 (Li 11) has been investigated by the beam-foil technique Zero-field quantum beats were observed in the intensity decays of transitions from the

1 sn 3P terms (n = 2, 3, or 4) in 6*7Li I1 and the magnetic hyperfine coupling constant was determined for each isotope for the 2p 3P terms Preliminary

values for the coupling constants are A (1s2p 3P,6Li 11) = 0.091 f 0.001 cm-l

(2.73 GHz), A(ls,2p 3P, Li 11) = 0.239 f 0.002 cm-l (7.17 GHz) The measured fine structures agree within a few percent with recent ca1culations.l The Auger electron spectrum of freshly filed lithium contains an emission

peak a t 51.7 eV which is attributed to the KL,L, Auger transition, and un-

identified peaks at 27.5 and 8 eV On exposure to oxygen the peaks at 51.7

and 27.5 eV disappeared but the 8 eV peak intensified The low-energy

spectrum was characterized by emissions at 13.3, 24.0, 33.0, and 40.0 eV due

to Auger transitions of lithium, oxygen, and lithium monoxide.2 A value of 3.05 eV is reported for the work function of freshly prepared lithium films.3

H G Berry, J L Subtil, E H Pinnington, H J Andrae, W Wittmann, and A

Gaupp, P h p Rev (A), 1973,7, 1609

J Boesenberg, Phys Letters (A), 1972, 41, 185

a R E Clausing, D S Easton, and G L Powell, Surface Sci., 1973, 36, 377

1

2 Inor,oanic Chemistry of the Main-group Elements

Lithium, the ‘not so rare metal’, is reviewed The discussion covers the occurrence, production, and LISGS of the irietal and its c o m p o ~ n d s ~ The metal has considerable potential in the future generation of electrical energy from the fusion reaction:

?H + :H -f :He + 17.6 MeV

The supply of tritium for this process is derived from:

Within this context, the chemical, physical, and thermal properties of lithium that are related to its use in fusion reactors have been reviewed These include natural abundance, thermodynamic and transport properties, characterization, analysis purity control, and corrosion of materials by the molten liquid5 Problems associated with tritium in the metal are also covered,,

as is the separation of tritium from lithium by crystallization or diffusion.’ The pressures of hydrogen isotopes in equilibrium with their solutions in liquid lithium have been measured The square root of the hydrogen pressure

is proportional to the hydrogen concentration in accordance with Sievert’s

Law Graphical data are presented for 2H.8 The metal is also chemically very

reactive The effect of temperature and pressure on the reaction of static molten lithium with oxygen, nitrogen, and the compounds CCl,F,, C,F,,

and SF, has been studied, The metal is hsated inductively under vacuum and a

small known volume of gas exposed to the surface Pressure and temperature changes are followed by rapid-response instr~mentation.~ The liquid metal

is a versatile solvent for both non-metals and metals Non-metals when dissolved in the metal may not have the same deleterious corrosive effect on containment materials as they do with sodium Chemical processes are affected by the different thermodynamic stability of lithium compounds This

is illustrated by the effect of oxygen on the chemical corrosion of niobium

and tantalum by static liquid lithium at 600 “C in capsules An increase in

the oxygen concentration of lithium from 100 to 2000 p.p.m has no measur- able effect, a result which is contrary to the effect of similar oxygen con-

centrations in liquid sodium or potassium The free energy of formation of lithium oxide is so great that the liquid metal getters niobium and tantalum to

an oxygen level 120p.p.m regardless of the oxygen concentration in the lithium When the transition metals contain more than a threshold level of oxygen (400 and 100 p.p.m for Nb and Ta respectively), chemical attack by lithium occurs at the grain boundaries with the formation of ternary com- pounds containing lithium, oxygen, and transition metal.1° Methods of

R Feather, Philippine Geogr J., 1973, 17, 16

H Weichselgartner, Reaktortagung, 1972, 751

T E Little, U S Nat Tech Inform Serv AD Rept, 1972, No 759378

ti V A Maroni, E J Cairns, and F A Cafasso, ANL-8001 Rept 1973

* D H J Goodall and G M McCracken, Proc Symp Fusion Technol., 7 t h , 1972, p 151

R L Klueh, ORNL-TM-4069 Rept., 1973

Elements of Group I 3

analysing the liquid are obviously important Photon activation appears applicable for the analysis of nitrogen and oxygen These elements are deter- mined by photon activation with a microtron as a pray source The 13N is separated by distillation as ammonia and collected in sulphuric acid for activity measurements Oxygen is rapidly separated by distillation as water for coincidence counting Sensitivity is 2 x

In addition to its role in the fusion reactor, liquid lithium features promin- ently in solid-state batteries,13 an area which has been reviewed.14 Lithium and another element are usually separated by a solid or liquid electrolyte perme- able to lithium ions, which migrate to form a compound with anions of the second element, thus driving electrons through the external circuit The second element has been halogen, though this may be replaced by a compound,

e.g vanadium pent0~ide.l~ Present interest is in the chalcogens, and several lithium-chalcogen systems have been investigated with this use in mind

Equilibrium phases in the Li-S system on the sulphur side of Li2S (the only

compound observed) are determined by using an unusual vapour-transport technique By this means equilibrium compositions of the melts at various temperatures can be obtained by utilizing the transport of sulphur vapour from one melt to another The Li-S phase diagram exhibits a large miscibility gap which extends from the monotectic composition, 65.5 mol % S , to

almost pure sulphur (0.035 mol % Li) at the monotectic temperature 362 f

3 "C The m.p of Li2S is 1365 f 10 "C.16 This is largely corroborated by a

second study which gives the miscibility gap from 63 to 98.8 mol % S, the

monotectic at 364.8 ' C , the m.p of Li2S as 1372 "C, and a critical temperature

for the miscibility gap of >600 "C?' An e.m.f method using cells of the type

LilLi halide eutectic mixturelLi in selenium is used to determine thermo- dynamic quantities in the lithium-selenium system From the cell data the standard free energy of formation of Li,Se at 360 "C is calculated as -94.0

kcal mol-l.ls In the Li-Te phase diagram, eutectics occur at 179.9 "C near

the lithium axis at >99.0 atom % Li, 448.5 "C at 35.7 atom % Li, and 423.1

"C at 10.5 atom % Li Two intermediate compounds are present, Li,Te and LiTe,, melting at 1204.5 and 459.9 "C, respe~tive1y.l~

The spectrum of doubly ionized sodium I11 has been studied at 2500-

1300 A and the analysis has been revised and extended as regards the 2p44s,

wt % for each element.11*12

l3 M Eisenberg, Intersoc Energy Convers Eng Conf., Con$ Proc 7 t h , 1972, 7 5

lo B Scrosati, J Appl Electrochem., 1972,2,231

Samosyuk, Radiochem Radioanalyt Letters, 1972, 11, 275

A N Dey, Ger Offen 2 155 890 (C1 H O h ) , 17 May 1973

4 Inorganic Chemistry of the Main-group Elements 3p, and 3d configurations The number of classified lines is now 177, out of

which 110 are newly observed and Classified Some of the older classifications are altered and ca 80 lines rejected as spurious The following terms and levels are new: (T)4s4P, 2 P ; (1D)4S2&,2; (lS)4s2S, (10)3p2F, 20, 2 P ;

(lS)3p2P; (3P)3d4F; (3P)3d4P, 4F5/2; and (1D)2G, 2F, 2D3/2 The 2p43s, 3p, 3d4s

configurations are now complete.20 In the range 380-18OA about 90 lines are measured, of which 50 are reported for the first time.21 The third, fourth, and fifth (i.e Na IV, N a V, and Na VI) spark spectra of sodium have been re-photographed a t 80-2400 A and the ineasurements confirm earlier analyses.22 New lines in Na IV, Na V, and Na VI are observed for the

first time and ~ l a s s i f i e d ~ ~ The K X-ray spectra of sodium excited by protons, helium, and oxygen ions of 0.8, 3.2, and 30 MeV, respectively, have been measured The strongest lines are the normal K, satellite spectra produced by multiple electron vacancies in single ion-atom collisions In the H- and He-

ion-induced spectra, Ka1,2 is the strongest transition.24 On the absorption side, the spectrum of atomic sodium between 30 and 150 eV shows lines which can

be attributed to the excitation of a 2s or 2p electron Considerably broad and asymmetric absorptions above the lP1 series limit are due to the simultaneous

excitation of a 2p and 3s electron.25

The electrical conductivity of sodium vapour has been measured in a

coaxial-cylinder, two-electrode system a t 827-1 227 "C The results support the conductivities calculated by E J Robbins et al (1967, 1968) on the basis

of a model for the vapour consisting of Na,, Na,, and Na, moieties.26 The concentration of multi-atom associates in saturated vapours at various temperatures can be semi-empirically derived In the case of unsaturated vapours, the number of associates tends to zero with increasing size The symmetry of the associates, binding energies, and mobility for sodium and potassium are given The effect of temperature is calculated on the equilib- rium between the concentration of free sodium atoms and those combined

in the cluster Agreement with experimental data is sati~factory.~' The best available thermodynamic data on liquid metals are tabulated and include m.p., entropies of fusion, heats of fusion, and heat capacities Graphical correlations are presented between heats of fusion and melting points, and between entropies of fusion and structural parameters Heat-capacity anomalies are discussed in terms of the electron configuration of the metal.2a The surface tensions of molten alkali metals from their melting temperatures

L Minnhagen and H Nietsche, Physica Scripta, 1972, 5 , 237

T Lundstrom and L Minnhagen, Physica Scripta, 1972, 5 , 243

2 2 T Goto, M S Gautam, and Y N Joshi, Physica, 1973, 66, 70

23 T Goto, M S Gautam, and Y N Joshi, Canad J Phys., 1973, 51, 1244

24 C F Moore, D K Olsen, B Hodge, and P Richard, Z Physik, 1972, 257, 288

2 6 R Morrow and J D Craggs, J Pliys (D), 1973, 6, 1274

27 V G Klyuchnikov and L A Borovinskii, Sbornik Issled Striikt Mol Krist Krist.,

Zarodyshei, 1971, 57

Elements of Group I 5

up to 1127 "C have been determined in a special high-temperature, high-

pressure apparatus The surface tensions/dyn cm-l as a function of tempera- ture (t/"C) under an atmosphere of their own vapours are given by:

7Na = 193.6 - 0.094(t - 98)

YI; = 107.1 - 0.069(t - 64)

YRb = 85.7 - 0.053(t - 38)

yCs = 68.8 - 0.045(t - 28)

The values correlate well with those previously p u b l i ~ h e d ~ ~

As with lithium, the majority of the literature on the commercial uses of metallic sodium is devoted to aspects of the generation of electrical energy either where the metal is used as a coolant in fast nuclear reactors or used as

an electrode in high-power batteries An indication of the extent of the nuclear use of liquid sodium is provided in a review of the principal program- mes involving fast reactors in the Technological aspects are also repre~ented?l-~* These applications steadily reveal new chemical properties

of sodium and its compounds, This is illustrated in the proceedings of a conference on the Liquid Alkali Metals which covers fundamental chemistry, physics, analytical and instrumentation techniques , sodium-water reactions , carbon and fission-product behaviour in sodium, physical processes, corro- sion, and mass transfer.35 Also, chemical reactions in liquid alkali metals are discussed, with particular emphasis on solvation aspects A comparison is

made of the nature and properties of liquid metals, representing continuous

reaction media, with other non-aqueous solvents, e g molecular liquids,

representing discontinuous media.36 Chemical aspects are generally found in the purification, analysis, and corrosion areas The non-metals oxygen , hydrogen, nitrogen, and carbon, when dissolved in the liquid metal, have a deleterious effect on transition metals, which are invariably employed as containment rnaterial~.~' Purification and analytical techniques, therefore, are primarily designed to remove38 and m o n i t ~ r ~ ~ * * ~ these elements, in many cases in sit^.^^ To prevent nitriding and embrittlement of steel submerged in

liquid sodium, ca 1 atom % calcium or magnesium can be added to the

29 A N Solov'ev and A A Kiriyanenko, Fiz Khim Poverkh Yavlenii Vys Temp

30 M Grenon, Rev Fr Energ., 1972, 23, 577

34 M E Durham, RD/B/M-2479 Rept 1972

36 C C Addison, Sci Progr (London), 1972, 60, 385

37 K Furukawa, Genshiryoku Kogyo, 1973, 19, 22

38 W Staubwasser, Ger P 1 583 891 (CI C 22b), 28 Jun 1973

1971, 108

6 Inorganic Chemistry of the Maimgroup Elements

liquid These metals, with their strong chemical affinity for nitrogen, effec- tively isolate the steel from nitrogenjl To analyse for hydrogen in liquid sodium, a nickel thimble is immersed in the liquid and evacuated to Torr on the inside The process relies on the equilibrium between dissolved and gaseous H Hydrogen leaves the liquid, diffuses through the nickel, and establishes an equilibrium pressure, the magnitude of which is dependent on its concentration in the liquid As little as 0.02 f 0.01 p.p.m

of hydrogen can be detected.42 Hydrogen may exist in a sample of sodium in

several forms, i.e dissolved sodium hydride, solid sodium hydride, or sodium hydroxide To distinguish between these requires several processes All the hydrogen is released as gas by vacuum fusion in a bath of tin at 35OoC

Amalgamation of the sample, however, releases only dissolved hydrogen

Subsequent heating to 200 "C decomposes solid sodium hydride The remain-

ing hydroxide hydrogen may be determined by difference.43 Alternatively, the remaining sodium amalgam is heated in an argon stream at 400 "C Under

these conditions sodium reacts with sodium hydroxide to give hydrogen, NaH, and Na,O Hydride decomposes to give hydrogen, which is determined

by gas ~hromatography?~ Hydrogen is also soluble in liquid potassium Over the temperature range 3 4 0 4 4 0 O C , the solubility is given by the equation:

log(C/p.p.m by wt.) = 6.8 - 2930/(T/K) The pressure of hydrogen in equilibrium with the saturated solution of

hydrogen in the metal is given by:

log(P/Torr) = 11.3 - 5860/(T/K) These pressures are the dissociation pressures of potassium hydride according

to:

KH = K + *H,

The enthalpy of formation, AH', of potassium hydride as derived from these

pressures is -13.7 kcal mol-l The equilibrium pressures of hydrogen above

unsaturated solutions of the gas in the metal are given by:

P112 = C x 104/14.2

where C is in weight % Thus Sieverts' Law is obeyed (I'll2 z C), which indicates that the species of hydrogen in the metal is m~natomic.*~ Most interest has centred on solutions of oxygen in liquid sodium since this element, more than any other, renders the liquid metal corrosive

41 A K Fischer, U.S P 3 745 068 (CI 176-38, B O l j , G21c), 10 Jul 1973

D R Vissers, J T Holmes, and P A Nelson, U.S P 3 731 523 (Cl 73/19; G Oln),

8 May 1973

4 4 M Takahashi, J Nuclear Sci Technol., 1973, 10, 54

45 M N Arnol'dov, M N Ivanovskii,V A Morozov, S S Pletenets, and V V Sitnikov,

Izvest Akad Nauk S.S.S.R., Metal., 1973, 74

Elements of Group I 7

Vanadium, niobium, and tantalum, and their alloys, have a low intrinsic soIubility in liquid sodium and suffer but slight corrosion The presence of oxygen in the liquid, however, leads to penetration by non-metals into the transition metal, internal oxidation, oxide scale formation, spallation or dissolution of oxides, and, in some cases, penetration by the sodium.4G Whether the transition-metal surface oxidizes or whether sodium extracts the oxygen contained in or on the metal depends largely on the relative free energies of formation of the transition-metal oxide and sodium oxide, respectively The situation is more complicated, however, since the energy balance is affected by the activity (or concentration) of oxygen in the sodium

or in the solid metal, i.e a dilute solution of oxygen in liquid sodium may be reducing whereas a more concentrated solution will oxidize a particular transition-metal surface Further complications arise when ternary com- pounds form which are stable in sodium Most transition metals form at least one ternary oxide with sodium These points are illustrated below Vanadium, exposed at 600 OC to static sodium solutions containing oxygen up to 4000 p.p.m , getters all oxygen from solutions which contain less than 2000 p.p.m The distribution coefficient for oxygen between vanadium and sodium is greater than lo4 at 600°C By alloying chromium or molybdenum with

vanadium, the activity coefficient of oxygen in the solid alloy is increased and hence the solubility is reduced.47 In sodium containing 2000 p.p.m oxygen at 600 O C , alloys of vanadium containing titanium or zirconium form internal precipitates of oxide during the gettering, and the concentration of oxygen dissolved in the alloy approaches that of the same alloy without titanium or zirconium.48 When titanium and zirconium are immersed in liquid sodium containing dissolved sodium oxide at 600 "C, the surfaces are covered with the ternary oxides Na,Ti04 and Na,ZrO,, respectively These

compounds were identified in situ by their X-ray diffraction patterns The

compound Na4Ti04 was detected when the sodium contained from 100 to

12 000 p.p.m oxygen At the end of long contact times the oxide T i 0 formed

below the ternary oxide, which suggests that the ternary oxide is formed first and is followed by diffusion of oxygen into the substrate metal to form TiO With zirconium, a rapid formation of the oxide ZrO, is postulated which

is followed by a slow reaction with dissolved sodium monoxide to give Na,Q, Zr0,.49 Liquid potassium, like sodium, also becomes more corrosive towards transition metals when it contains dissolved oxygen Analysis of potassium after immersion of tantalum at 600, 800, and 1000 "C shows that the amount

of tantalum finding its way into the alkali metal increases with the amount of oxygen originally dissolved in the liquid metal Again, a ternary oxide phase

is formed Oxygen held in the tantalum also promotes corrosion when the transition metal contains more than a threshold concentration of oxygen in

46 H U Borgstedt and G Frees, Rev Coatings Corrosion, 1972, 1, 43

47 R L Klueh and J H DeVan, J Less-Common Metals, 1 9 7 3 , 3 0 , 9

48 R L Klueh and J H DeVan, J Less-Common Metals, 1973,30, 25

M G Barker and D J Wood, J.C.S Dalton,

8 Inorganic Chemistry of the Main-group Elements

solid solution; potassium penetrates the solid metal intergranularly and trans-

granularly via ternary oxide formation The threshold levels of oxygen for this type of attack at 400, 800, and 1000°C are 500, 700, and lOOOp.p.m., respe~tively.~~ Distribution of radioactive corrosion products is obviously important in flowing sodium Particulate material deposits according to flow rate and geometry of circuit, size of particulate, and whether the species is soluble in the sodium or reacts preferentially with metallic parts of the circuit Initial experiments have investigated the transport and deposition character-

istics of 59Fe, 54Mn, and 6oCo The 59Fe behaviour is characterized by its

appearance as a firmly adherent layer on pipework downstream of the test

section 6oCo is similar to iron but the deposit is less strongly attached The behaviour of 54Mn is characterized by its rapid and highly preferential migration to the coldest part of the circuit.51 Adsorption of caesium, a product of the fission process, also occurs from solution in sodium at trans- ition-metal surfaces Between 100 and 200°C, caesium is adsorbed on to nickel and steel (EN-58B) surfaces but at 800 O C the adsorption is eliminated The mechanism of adsorption is not clear.52

Determinations of the solubility of oxygen in liquid sodium are numerous and the values vary From 169 individual analyses, data have been selected, therefore, to derive the mean solubility relationship:

log(S/p.p.m.) = 6.1587 - 2386.4/(T/K) from T = 387 to 828 K, using the least-squares method This equation is

recommended for fast-reactor Methods of determining these small concentrations differ widely Thus at 350-530 O C , the solubility is ca

10-850 p.p.m as determined by an e.m.f method using the cell:

where the rare-earth oxides comprise the solid electrolyte which separates the reference electrode Cu,OICu(or air]Au) from the second electrode, a mixture of sodium with sodium monoxide.54 Alternatively, a vanadium wire

is immersed in the molten sodium to allow oxygen to partition between the two metals The wire is subsequently removed and analysed for oxygen content The method relies on a knowledge of the equilibrium distribution coefficient of oxygen between sodium and vanadium These values (as

W oxygen in V) are given at 750 OC over the range 0.003-16 p.p.m oxygen in sodium.55

Carbon dissolves in liquid sodium but to a lesser extent than do hydrogen

or oxygen, and methods for determining the carbon content of liquid sodium continuously are generally less advanced than those for oxygen and hydrogen

50 R L Klueh, Corrosion (Houstom), 1972, 28, 360

61 K T Claxton and J G Collier, J Brit Nuclear Energy SOC., 1973, 12, 63

5 2 H E Evans and W R Watson, RD/B/N-2094 Rept 1971

5 4 H U Borgstedt, A Marin, Z Peric, and G Wittig, Atomwirt, Atomtech., 1972, 17,

361

Elements of Group I 9

A technique, reminiscent of the electrochemical oxygen meter, is described, however, which equilibrates the carbon dissolved in liquid sodium with a membrane of a-iron at 500-700 "C This membrane forms part of an electro-

chemical cell and is separated from a reference source of carbon by a fused

electrolyte of 1 : 1 Li,CO,-Na,CO,, which is able to transfer carbon in ionic form The voltage between the membrane and reference electrode gives a measure of carbon activity in the membrane and hence in the sodium.56 Protection and security measures against accidents with liquid sodium are reviewed.57 A fire-extinguishing powder that is especially effective against alkali-metal fires consists of 45.4% NH4H,P04 (fluidized with up to 6 %

of its weight by Si02 and silicone resin), 45.4% urea, 9.1 % polystyrene micro-balls (d < 300 pm), and 0.1 % azodicarbamide; it completely extin- guishes sodium burning at >5OO0C A thick spongy carbonized coating

covers the metal, whose temperature falls very rapidly.58

High-temperature (300 "C) storage b a t t e r i e ~ ~ ~ - ~ ~ involving liquid sodium utilize the chemical reactions between sodium and liquid sulphur The Na-S system is complex, however, and contains several polysulphides with

the general formula M,S, containing S",- ions Of about 15 polysulphides of

the alkali metals described in the literature, the crystal structures have been determined for only about three, which reflects the difficulty of preparing single crystals of the polysulphides The Na,S-Na,S,-S region has been investigated mainly by high-temperature microscopy but some complementary experi- ments involve d.t.a., t.a., and quenching techniques, The components S and

Na,S melt at 118 f 1 "C and 1168 f 10 'C, respectively The intermediate

phases Na2S2, Na2S4, and Na,S5 which are formed melt at 478 f 5,294 f 2,

and 270 f 5 "C, respectively Na,S, melts incongruently The shapes of polysulphide crystals appearing just below the melting points are detected

by high-temperature m i c r o ~ c o p y ~ ~ Further d.t.a work reveals that when Na,S-Na,S, or Na4S4-S, mixtures are heated, a reaction occurs near the m.p of sulphur with formation of Na,S5 as the initial step, Unless the S:Na ratio is > 5 : 2 then further reaction between the sulphides occurs, until at

equilibrium only those species are observed corresponding to the given Na:S ratio The highest sulphide is Na,S,, and Na,S, does not exist at the m.p.; this stoicheiometry is really a 1 : 1 Na,S,-Na,S, eutecticBg The sodium poly- sulphides Na,S, and Na2S5, however, can be prepared from the reaction of

5 6 M R Hobdell and D M J Rowe, RD/B/N-2240 Rept 1972

5 7 M De la Torre Cabezas, Energ Niicl (Madrid), 1972, 16, 439

5 8 E Chahvekilian, R Peteri, and A Hennequart, Fr Demande 2 102 424 (Cl A 6 2 4 ,

5 9 J Fally, C Lasne, and Y Lazennec, Fr Demande 2 142 695 (CI H Olm), 9 Mar 1973

6 o S Gratch, J V Petrocelli, R P Tischer, R W Minck, and T J Whalen, Zntersac

61 T Nakabayashi, Ger Offen 2 240 278 (CI H Olm), 12 Apr 1973, Japan

62 J Fally and J Richez, Fr Demande 2 140 318 (C1 H Olrn), 23 Feb 1973

63 C Levine, Power Sources Symp., Proc., 1972, 25, 75

6 4 S P Mitoff, U.S P 3 672 994 (CI 136-6, H Olrn), 27 Jun 1972

12 May 1972

Energy Convers Eng Con$ Con5 Proc Ith, 1972, p 38

D G Oei, Znorg Chem., 1973, 12,435

10 Iiiorganic Chemistry of the Main-group Elements

sodium chloride with K2S, and K,S, respectively in liquid ammonia Using

KZSG, however, the only polysulphide obtained is Na,S, The physical

properties of the polysulphides are obviously important in their application

to batteries Thus the density and surface tension of liquid Na,S, and Na,S, have been determined as a function of temperature The unbranched chain structure of the polysulphide linkage is confirmed by photoelectron spectro-

~ c o p y ~ ~ Sodium tetrasulphide, Na,S,, is in fact tetragonal, with space group

142d and cell dimensions a = 9.5965, c = 11.7885 A, and 2 = 8 The struc-

ture is built up of unbranched and separated Si- ions surrounded by Na+ ions

Adjacent SZ- ions are ca 3.60 A apart Each lies on a two-fold axis and the

S-C bond distances are 2.074 (end) and 2.061 A (middle) The S-S bond

angle is 109.76' and the dihedral angle is 97.81' The co-ordination of sul-

phur around the sodium consists of two types: a distorted tetrahedral

arrangement of sulphur atoms with two pairs at 2.826 and 2.842A from a

central sodium atom; a sodium atom at the centre of a distorted octahedron with three pairs of sulphur atoms at distances 2.887, 3.043, and 3.081 A, respectively, from the sodium.G8 The monosulphide, Na2S, forms several hydrates, the stabilities of which depend on the temperature and partial pressure of water vapour above the compounds By thermally decomposing Na2S,9H20 the compound Na2S,M,0 was found to be stable over the largest

pressure and temperature range, with an enthalpy of hydration of 16.62 kcal

mol-l Heats of hydration were lower for the di- and tri-hydrate, being 6.76

and 1.96 kcal mol-l, r e s p e ~ t i v e l y ~ ~

The spectrum of doubly ionized rubidium (Rb 111) over the range 370-

3500 A has been re-analysed The existing analysis is revised and extended

Most levels of the 5s6s5p4d and 5d configurations are now known.70 A second

analysis yields most of the levels of the 4p44d, 4p55s, and 4p45p configurations The ionization energy is estimated as 39.0 f 0.3 eV.'l The vapour pressure of

liquid rubidium from 129 to 278 "C has been determined by thermogravi-

metric and mass-spectrometric techniques Calculation of the latent heat of

vaporization from the vapour-pressure data yields a value of 19.0 f 0.5

kcal (g atom)-l at 298 K The dissociation energy of the Rbz molecule is

10.0 f 0.5 kcalm01-l.~~ Both rubidium and caesium have relatively high vapour pressures which pose experimental problems in the handling of these elements The saturated vapour pressures, of R b at 683-1649OC and

0.97-101.5 atm and of Cs at 775-1600 O@ and 2.14-80.5 atm, are given by:

log(Pab/atm) = 5.25903 - 4035.65/(T/K) - 0.35387 log(T/K)

log(Pcslatm) = 5.71084 - 3904,34/(T/K) - 0.52605 log(T/K)

and

The P,, and P,, curves intersect at 1160 "C and 21.48 atm.73

67 D G Oei, Inorg Chem., 1973, 12,438

6 8 R Tegman, Acta Cryst., 1973,29B, 1463

ge R C Kerby and M R Hughson, Canad,, Mines Br., Res Rep., 1973, NO 262

7 0 J E Hansen, W Persson, and S Valind, Phys Letters ( A ) , 1972, 42, 275

71 J Reader and G L Epstein, J O p t SOC Amer., 1972, 62, 1467

72 V Piacente, G Bardi, and L Malaspina, J Chem Thermodynamics, 1973, 5 , 219

L I Cherneeva and V N Proskurin, Teplofiz Vys Temp., 1972, 10, 765

Elements of Group I 11

3 Alloys and Intermetallic Compounds

The crystal structure of Li,CdPb is f.c.c., with a = 6.837 A, d(expt) = 6.79 at

20 ' C , and d(X-ray) = 6.93 for 2 = 4 The observed and calculated X-ray

intensities are tabulated The most probable space group is T$ - F 4 3 m 7 ,

The Li-Ga phase diagram, when investigated by d.t.a., reveals four new intermetallic compounds Of these, Li,Ga, LiGa,, and LiGa, are identified by X-ray d i f f r a ~ t i o n ~ ~ The crystal structure of Li,Ge, formed in the Li-Ge system has been determined by X-ray diffraction The compound crystallizes with the orthorhombic space group Cmmm, having a = 9.24, b = 13.21,

c = 4.63 A, d(expt) = 2.25, d(ca1c) = 2.28 for 2 = 4 Li,Ge, is not iso- structural with Li,Si, but there are many similarities between the s t r u c t ~ r e s ~ ~ For a series of molten Li-Sn alloys, direct measurements of e.m.f from the electrolytic cell (-) LilLiC1, LiFILi, Sn (+), carried out at 550 'C, indicate substantial negative deviation from ideal beha~iour.~' Phase equilibria in the ternary system Wa-K-Rb have been investigated by thermal methods The ternary eutectic is at -18 "C, which is 5.7 "C lower than the Na-K binary

eutectic temperat~re.'~ The gaseous equilibria

61.4 f 3.4 kcal mol-l The experimental dissociation energy of NaAg(g)

is considerably lower than the value of 51 kcal mol-l calculated using the Pauling model of a polar bond.79 In an investigation of Na-Cd alloys from

20 to 86 atom % Cd by d.t.a., single-crystal and polycrystalline forms of the compounds Na,Cd,, and NaCd, have been prepared NaCd, is cubic,

a = 8.04 A, d(expt) = 5.7 Na,Cd,, is also cubic, a = 9.322 A, d(expt) = 7.1

At 20% Cd, prismatic crystals are obtained which probably contain less Cd

than NaCd,.80 The phase diagram of Na-Hg has been re-investigated, and

changes in enthalpy, free energy, and entropy at 648 K are presented As is

75 S P Yatsenko, K A Chutonov, S I Alyamovskii, and E N Dieva, Izuest Aknd

7 6 V Hopf, W Mueller, and H Schaefer, Z Naturforsch., 1972, 27b, 1157

7 7 A 6 Morachevskii, L N Gerasimenko, A I Demidov, and 0 A Drozdova,

Elektrokhimiya, 1972, 8, 1622

B J Ott, J R Goates, and C C Hsu, J Chem Thermodynamics, 1973, 5 , 143

Nauk S.S.S.R., Metal., 1973, 185

7 9 V Piacente and K A Gingerich, High Temp Sci., 1972, 4, 312

12 Inorganic Chemistry of the Maingroup Elements

well known, the system forms a series of intermetallic compounds, amongst which the congruently melting NaHg, is the most stable.*l

The velocity of sound in liquid metals and alloys, its variation with tempera- ture, and its relation to the adiabatic and isothermal compressibility of the metals has been reviewed Experimental results are compared with theoretical considerations.*2 The velocity of sound at 7.5 MHz and the density have been

measured as functions of temperature for a number of solutions of metals in liquid sodium The results cover the whole concentration range for mercury and the range 0-5 atom % solute for Au, Cd, In, Pb, and Sn Changes in the

adiabatic compressibility and the mean molar volumes provide no convincing evidence for compound formation in the Zipid phase of Na-Hg There is,

however, a substantial volume contraction on mixing which apparently causes the compressibility, when plotted against concentration, to fall well below the straight line linking pure sodium with pure mercury The con- traction and the associated reduction in the adiabatic compressibility are not peculiar to Na-Hg since the effects for all the different solutes used are remarkably similar.83 Evidence that compound formation does occur in the liquid, however, comes from potentiometric measurements The potentials

of homogeneous liquid sodium and potassium amalgams containing 0.65-

7.19 (g atom Na)(l Hg)-l and 0.053-2.62 (g atom K)(l Hg)-l have been measured at 25 and 50 "C The experimental potentials, which are higher than

theoretical values calculated from the Turin-Nernst equation, are explained

by chemical interaction between Na (or K) with Hg The number of atoms of mercury co-ordinated with Na (or K) in liquid amalgams is calculated by the

Hildebrand equation, and, near saturation, is 5-6 and 15-16 for Na and K,

respe~tively.~~ Enthalpies of mixing sodium and gallium and the enthalpies of formation of the two compounds NaGa, and Na,Ga, have been determined calorimetrically at 723 K Referred to the pure constituents in the liquid

state, the following values are found: AH, (NaGa,) 17.5 f 1.0, AH,(Na,Ga,)

-21.5 f 1.5 kJ mol-l Using d.t.a., the latent heat of fusion of Na,Ga,

was determined as 13.5 f 0.5 kJ m01-l.~~ The density and surfxe tension of five solutions of indium containing 0.5-7.0 atom% in liquid sodium have been measured at 170-400 O C by means of the maximum-bubble-pressure technique The gram atomic volumes of these solutions, calculated from the density, indicate a substantial contraction on mixing which is about twice that for analogous Na-Cd solutions The surface tension of liquid sodium increases slightly on adding indium, indicating a lower concentration of solute in the surface than in the bulk, in contrast to the marked surface- active behaviour of cadmium.86 Two compounds are reported in the Na-Bi

a1 M A Bykova and A 6 Morachevskii, Zhur priklad Khim., 1973,46, 312

83 S P MacAlister, Phil Mag., 1972, 26, 853

a 4 L M Ruban, A I Zebreva, and V P Gladyshev, Eiektrokhimiya, 1972, 8, 1021

1 3 ~ M Gambino and J P Bros, Thermochimica Acta, 1973, 6, 129

G M B Webber, Ultrason Ind Con$ Pap., 1970, 22

H A Davies, Met Trans., 1972, 3, 2917

Elements of Group I 13

system with very high melting points: Na,Bi, m.p 775OC; NaBi (incon- gruently melting at 446 "C) These compounds are so stable that it is advan- tageous to consider them as independent components and to use for the liquid alloys of this system a quasi-ideal-solution Activities of potassium, deduced from ẹm.f data, show that concentrations below 1 atom % in liquid indium at 577 O C obey Henrýs law, with a linear dependence of the activity of K on its concentration in the alloỵ The study also reveals a limited solubility of potassium in indium.88 Thermodynamic data on liquid alloys

of potassium with thallium over the complete concentration range have been obtained from 350 to 550°C using electrochemical cells of the type K(1)I

K-glasslK, Tl(1) Partial molar enthalpies and entropies of mixing are

calculated from the results Some interesting maxima and minima are observed which indicate a region of strong chemical interaction between

potassium and thallium.sg The density of caesium vapour above solutions of caesium in liquid rubidium has been determined from 293 to 313 K and mole

fraction Cs, x = 0.13-0.77 The density of the saturated vapour increases with increasing caesium concentration For a given concentration, the density increases with increasing temperaturẹ For all values of x at 5298 K,

and for x 2 0.35 at 2 3 1 3 K, the solutions showed negative deviations from

Raoult's law If the solutions are sprayed on the vessel walls, effects due to surface adsorption are observed.g0

4 Solvation of Alkali-metal Ions

Aqueous Solration.-A review, covering the 1968-1 972 publications, deals

with physical properties, thermodynamics, and structures of non-aqueous and aqueous-non-aqueous solutions of electrolytes, and complete hydration limits.g1 Thermodynamic aspects of ionic hydration also reviewed include the thermodynamic theory of solvation; the molecular interpretation of ionic hydration; hydration of gaseous ions (AG's, AH'S, and A S S ) ; thermody-

namic properties of ions at infinite dilution in water, solvent isotope effect in hydration; reference solvents ; and ionic hydration and excess proper tiệ^^

A third review on the hydration of ions emphasizes the structure of water in the gaseous, liquid, and solid states; the size of ions; and the hydration numbers of ions and the structure of the hydrated shell from measurements

of mobility, compressibility, activity, and from n.m.r spectrạ93 Pure water

and aqueous LiCl at concentrations up to saturation have been examined by

neutron and X-ray diffraction For the neutron studies 'LiCl and D20 are employed The data are consistent with a simple model involving only

87 Ạ G Morachevskii, Elektrokhim Rafnirovanie Tyazhelykh Legkoplavkikh Metal Rasplav Solei, 1971, 37

M Ạ Bykova and Ạ G Morachevskii, Izvest V U Z., Tsuet Met., 1973, 91

J Ciurylo, Actu Phys Polon ( A ) , 1973, 43, 737

89 S Aronson and S Lemont, J Chem Thermodynamics, 1973, 5 , 155

91 K P Mishchenko, 2hur.fiz Kliim., 1972, 46, 2987

9z H L Friedman and C V Krishnan, Water: Compr Treatise 1973, 3 , 1

H Ohtaki, Kagaku (Kyoto), 1971,26, 1179

14 Inorganic Chemistry of the Main-gvoup Elements

nearest-neighbour interactions In the pure liquid and in dilute solutions the structure of the water molecule resembles that in the vapour phase Each water molecule in the liquid is tetrahedrally co-ordinated by four others This basic water structure gradually diminishes with increasing LiCl concentration and is not seen at mole ratios of ten or below The co-ordination around Li+ appears to be tetrahedral, with co-ordination through oxygen The C1- ions are octahedrally co-ordinated through H.94 A theoretical study concludes that

energetically the most favourable aquo-complexes of the ions Li+, Na+, and K+ contain six, eight, and eight water molecules, respectively The energy

E of [M(H,O),] t- complexes as a function of the distance between the metal ion and the 0 atom is calculated according to the extended Huckel method,

assuming a donor-acceptor bond between H,O molecules and alkali-metal

ions The bond energy of the aquo-complexes, AE, is obtained from AE =

E - n E ~ ~ 0 , where E H ~ O is the energy of a free water molecule The potential- interatomic distance curves show a sharp minimum (AE,) for Li+ and Na+ ions but are shallow for K+ The values of AE,/n can be used as a measure

of the respective aquo-complex stability at higher temperatures The flat potential curve for K+ suggests both a larger contribution from the second hydration shell to the total hydration shell and a greater mobility of water molecules in the hydration layer of K+ than in that for Li+ and Na+.g5 The equilibrium constant K has been determined for the Li-isotope exchange

reaction :

7Li(s) + %iCl(aq) = 6Li(s) + LiCI(aq) using an electrochemical quadruple cell without liquid junction The value of

K at 296.6 K is 1.046 f 0.13 and, when compared with values of K calculated

from statistical thermodynamic theory for various model reactions, is consistent with a tetrahedrally co-ordinated structure for the aquated lithium Hydration numbers, however, when determined by acoustic-inter- ferometer measurement of the adiabatic compressibility of the solution at infinite dilution at 35 "C, have values Lif, 3 ; Rbf, 2; Ca2+, 7, and Ba2+, 8.97

From literature data on the temperature dependence of the conductivity of

electrolytes, the radii rs of hydrated M+, M2+, and anions have been calcu-

lated using the equation Y, = O.82O/q,RO, where 7, is the viscosity/centipoise

and A, is the limiting equivalent conductance/cm2 equiv-l Selected values of r,/A at 25 O C are shown in Table 1, with crystal radii/A (Pauling)

Table 1 Valuesof rJA andPaulingcrysta1 radii rc/A for ions in aqueous solution

Ion Li+ Na+ K+ Rb+ Cs+ NHf Mg2+ Ca2+ Ba2+ C1- Br- I-

O4 A H Narten, E Vaslow, and H A Levy, J Chem Phys., 1973, 58, 5017

O5 D A Zhogolev, Yu A Kruzlyak, B Kh Bunyatyan, and I V Matyash, Teor i

O6 G Singh and P A Rock, J Chem Plzys., 1972, 57, 5556

A V Satyavati, Current Sci., 1972, 41, 7334

eksp Khim., 1972, 8,745

with increasing temperature In structureless solvents such as nitrobenzene, phenylacetonitrile, and dimethoxyethane, values of Y, of Nas and Css ions are independent of temperature.9s The characteristic frequencies of water molecules in hydration complexes have been investigated by neutron inelastic scattering For concentrated solutions of lithium and magnesium salts and of calcium nitrate, the relaxation time of primary water of hydration increases and exceeds interaction time The self-diffusion coefficients for such complexes decrease rapidly with decreasing temperature; with increasing anion basicity; with both increasing mass of the cation and the number of water molecules in its hydration sphere; and with increasing mass of anions and their bonding

to their primary water of hydration In ternary solutions significant changes occur in the bonding and ordering or water molecules in the hydrated spheres

of the component cations, in the diffusion kinetics of the water molecules, and in the distribution of the anions relative to the cations.Qg The hydration ability of concentrated hydrochloric acid (5.8 moll-l) is stronger than that of lithium chloride From the heats of mixing of these species with 1-6 moll-1 aqueous solutions of bivalent chlorides of Mg, Ca, and Sr it appears that HCI removes more water molecules from the first co-ordination sphere of the metal cation than LiCl At lower salt concentrations the free water molecules

of the solution and not those bound to the inner co-ordination sphere of the metal transfer t o Li+ (or H+j.lo0 In the LiC10,-Ca(ClQ4j2-H,Q system at

25 "C, however, Ca2+ does not have a dehydrating effect on Lif since these ions possess similar enthalpies of hydration in saturated aqueous solutions.lo1

The nuclear magnetic relaxation rates and shifts of 'Lit and 133Cs+ in aqueous solutions containing Fe3 I- and various counter-anions are interpreted in terms

of a dipolar attraction between Lis and the unpaired electrons on the Fe3+

ion, and the formation of an ion pair between Cs+ and ferric halide complex.lo2

An increase of pressure in the range 0-1000 bar results in an enhancement

in the hydration of the ions Naf and K+ in their aqueous chloride solutions The enhancement is more pronounced at 20 than at 45 "C These conclusions

B S Krumgal'z, Zhur srrukt Khim., 1972, 13, 774

1971, No 708

Chern 3rd, 1970, 1, 99

Zhur., Khim., 1972, Abstr No 7B907.)

O 9 G I Saford and P S Leung, US Office Saline Water, Res Develop P r o p Rept.,

l o o Z G Szabo, M Palfalvi-Rozsahegyi, and K Burger, Proc Symp Co-ordination

lol S A Ivanov, Uch Zap., Yaroslav Gos Pedagog Inst., 1971, No 95, p 11 (Ref

Shporer, R Poupko, a n d Z Luz, Inorg Chem., 1972, 11,2441

16 Inorganic Chemistry of the Maingroup Elements

are drawn from an analysis of the literature data on the pressure dependence

of the adiabatic cornpre~sibility.~~~ Co-ordination of water molecules by alkali-metal ions induces a distortion which shows up in the i.r spectrum of the molecule.l@ This is more far-reaching, however, and the water structure

is destroyed by electrolytes in the order K I > K F > KBr > KCl; NaI >

NaBr > NaCl; LiI > LiBr > LiCl; LiCl > NaCl > KC1; LiBr > NaBr >

KBr; LiI > NaI > KI; KOH > NaOH > LiOH Obviously the effect of any cation on the structure of water depends greatly on its anion and vice versa.lo5 Calculations based on electrochemical data indicated that the primary hydration number of caesium iodide is zero Thus, the standard free energies

of transfer of Cs+ and I- from water to aqueous organic solvents should be very low.lo6 This is compatible with the order of extraction of alkali-metal halides from aqueous solution byp-alkylphenols Cs, Rb, and K are extracted from chloride solutions at p H 9.5-13.8 by 0.5-4 mol 1-1 solutions of alkylphenols (ROH; R = C, or C,) in kerosine by formation of ROM,-

nROH in the organic phase, n being 1.2, 1.2, and 2.2 for Cs, Rb, and K,

respectively The distribution ratios between the organic and aqueous phases from the aqueous solutions containing <0.15 mol 1-1 chlorides are D,, >

D,, > DK On extraction, however, from solutions containing >0.15

mol 1-1 chlorides the sequence is reversed The extraction from low metal concentrations is governed mainly by the dehydration energy (low for caesium) of the cations In concentrated solutions, the dehydration energy of the ions is levelled off to some extent, and the formation energy of the phenol- ate becomes the prominent factor influencing the extraction.lo7

As the dielectric constant of the solvent in which the alkali-metal ion is dissolved decreases, then the degree of pairing with its counter-ion increases Thus the equivalent conductance of 2 x 10-4-1.5 x 10-2mol 1-1 lithium chloride solutions in water-sulpholane mixtures (0-100 % water corre- sponding to a dielectric constant D from 43 to 75) at 35 OC, steadily decreases

as sulpholane is added, with noticeable ion-pair association for mixtures with

D < 62.1°s Similarly with caesium bromide solutions.10g The diffusion coefficients of the ions Cs+ and Br- in water-dioxan mixtures decrease with increasing salt concentration When interpreted on a model based on ap- plicable ionic interaction theory, this is evidence for progressive ion-pair formation The vapour pressures above salt solutions (50.05 moll-l) in water-tetrahydrofuran mixtures are used to obtain the rate of change of the standard chemical potential of the electrolytes, 3c0/ ax,, with the solvent composition and to obtain solvation numbers The compounds NaNO,,

lo3 0 Ya Samoilov, A L Seifer, and N A Nevolina, Zltur strukt Khim., 1973, 14, 360

lo* L I Gudim, Dopooidi Akad Nauk Ukrain R.S.R., Ser A , 1972, 34, 904

l o 5 A A Ennan andV A Lapshin, Zhur strukt Khim., 1973,14,21

Io6 T Mussini and P Longhi, Chimica e Industria, 1972, 54, 1093

lo' Z Abisheva, L I Pokrovskaya, A M Reznik, and V E Plyushchev, Izuest Akad

lo* G Petrella, M Castagnolo, A Sacco, and L Lasalandra, Z Naturforsch., 1972, 27a,

H Latrous, P Turq, and M Chemla, J Chim phys., 1972, 69, 1644

Nauk Kazakh S.S.R., Ser khim., 1972, 22, 2 8

1349

mole fraction water) for dioxan solvation of the ions decrease in the order BPh, > AsPhz >> Na+ > CI- > OH-, where Na+ is approximately equally solvated by water and dioxan molecules With decreasing xl, the differences between the d,uo/dx, values decrease markeclly.l12 The limiting electrical conductivities of 10-4-2 x 1W2 niol 1-1 LiCl solutions in 0-100 % water- DMF mixtures show minima near 25 % and 4 % DMF These could be attributed to either an exchange of the smaller water molecules for larger DMF molecules in the solvent sheath of the ions, or a change in the solvent structure, i.e due to the appearance of DMF,3H,0.113 Sodium ion pref- erentially forms long-lived complexes with DMSO and DMF in mixtures of

either of these solvents with ethanenitrile or propanone This is deduced from the quadrupolar broadening of the 23Na n.m.r in these solutions In mixtures

of water or methanol with ethanenitrile or propanone, however, no long- lived complexes are 0 b ~ e r v e d l ~ ~

Some aqueous systems that have been investigated are listed in Table 2.115-160

Non-aqueous Solvation.-The absorption spectra of solutions of lithium and

of potassium in liquid ammonia at -7OOC have been measured using a spectrophotometric cell incorporating sapphire windows The envelope of strongly overlapping bands in the 3200cm-l region of the pure solvent is resolved into components which are assigned to 2v4, vl, and v, in increasing energy The N-H stretching frequency of the solvent shifts to lower energy with increasing concentration of both lithium and potassium metal Solvating molecules have stretching vibrations of lower energy than bulk solvent molecules The solvated molecules, therefore, give an additional band displaced from that for the solvent The shift is independent of the nature of the metal over the concentration range 5 x 10-,-5 x 10-2moll-1 This

C Treiner, J F Bocquet, and M Chemla, J Chim phys., 1973, 70, 472

112 S Villermaux, V Baudot, and J J Delpuech, Bull SOC chim France, 1972, 1781

113 Z Kozlowski, Acta Chim Acad Sci Hung., 1972, 17,49

R D Green and J S Martin, Canad J Chem., 1972, 50, 3935

Li,S0,,K2S04 ; Li2S04,Rb2S0, ; 3Li,SQ4 ,Rb2S04,2H20 ; SLi2SO4,Rb2SO4,4H20 ; 5LizS04 ; K2S04 ,Rb2SO4 ,2H20

-

-

- 7NaHC03,Na3As04

4Na2S0, ,3 CdSO, ,3Hz0

V G Skvortsov, Zhur neorg Khim., 1973, 18, 243

R Turgunbekova, K Nogoev, and K Sulaimankulov, Zhur neorg Khim.,

K.-Abykeev, A G Bergman, and K Sulaimankulov, Zhur neorg Khim., 1973,18,246

I N Lepeshkov and I M Karataeva, Zhur neorg Khim., 1972, 17, 3341

R Vilcu and F Irinei, Bull SOC chim belges, 1972, 81, 479

neorg Khim., 1973,18, 239

A Akbaev, Zhur priklad Khim., 1973, 46, 648

M G Manvelyan, V D Galstyan, E A Sayamyan, and A G Alakhanyan, Armyan

khim Zhur., 1972,25,840

Ya S Shenkin, S A Ruchnova, and N A Rodionova, Zhur neorg Khim., 1973,

18, 235

N P Andronova, Uch Zap., Yaroslau Gos Pedagog Inst., 1971, No 95, p 142

(Ref Zhur., Khim., 1972, Abstr No 7B905.)

P F Rza-Zade and M A Abbasov, Zssled 061 Neorg Fiz Khim., 1971, 143 (Ref Zhur., Khim., 1972, Abstr N o 22B813.)

A S Karnaukhov, T P Fedorenko, and V G Shevchuk, Uch Zap., Yaroslau Gos

Pedagog Znst., 1971, No 95, p 123 (Ref Zhur., Khim., 1972, Abstr No 9B865.)

A V Krizhanovskii, E S Nenno, and R M Skripnichenko, Zhur neorg Khim.,

1972,17,2526

M A Durymanova and A E Telepneva, Zhur priklad Khim., 1972,45, 1610

V I Mikheeva S M Arkhipov, and A E Pruntsev, Izuest Akad Nauk S.S.R., Ser

khim., 1973, 1181

M Motoyama, M Kadota, and S Oka, Nippon Kaisui Gakkai-Shi, 1972,26, 16

G I< Loseva, Tr Nouocherkassk, Politekh Inst., 1972, No 266, p 78 (Ref Zhur.,

V G Skvortsov, Zhur priklad Khim., 1972, 45, 2735

A M Babenko, Zhur neorg Khim., 1972,17, 3059

A G Bergman and L F Shulyak, Zhur neorg Khim., 1973, 18, 1379

Table 2 Aqueous systems that have been investigated

138 V A Tatarinov, Uch Zap., Yaroslav Gos Pedagog Inst., 1971, No 95, p 52 (Ref

Zhur., Khim., 1972, Abstr No 7B926)

140 Ya S Shenkin, S A Ruchnova, and N A Rodionova, Zhur neorg Khim., 1972,17,

3368

A P Solov’ev, Uch Zap., Mord Univ., 1971, No 81, p 39 (Ref Zhur., Khim., 1972

Abstr No 12B799.)

142 A K Molodkin and 0 V Geroleva, Zhur neorg Khim., 1972,17, 3379

143 N N Runov, Uch Zap., Yaroslav Gos Pedagog Inst., 1971, N o 95, p 72 (Ref Zhur., Khim., 1972, Abstr N o 7B939.)

144 V N Pilipchenko, L Zharnovskaya, P I Trendovatskii, and V M Shpikula, Zhur

neorg Khim., 1972, 17, 3361

lP6 V K Filippov, V M Makarevskii, and M A Yakimov, Zhur neorg Khim., 1973,

18, 1682

(Alma-Afa), 1971, No 12, p 203 (Ref Zhur., Khim., 1972, Abstr No 18B766.)

14’ J Balej Coll Czech Chem Comm., 1972, 37, 3855

148 A K Sengupta and B B Bhaumik, Indian J Chem., 1972, 10, 752

149 K G Myakishev and A P Kostin, Zhur neorg Khim., 1973, 18, 271

160 Yu M Timoshenko, Zhur neorg Khim., 1973, 18, 854

151 T V Mozharova, V A Borovaya, and E N Pavlyuchenko, Zhur priklad Khim.,

1972,45, 1872

lSz V I Vereshchagina, V N Derkacheva, L F Shulyak, and L V Zolotareva, Zhur

163 M Nagatani and R Kubo, Kagoshima Daigaku Kogakubu Kenkyu Hokoku, 1972,79

L V Savel’eva, S B Stepina, V E Plyushchev, and A P Rysev, Izoest V U Z.,

Khim i khim Tekhnol., 1972,15, 1605

155 N Nishimura, T Higashiyama, S Yamamoto, and S Hasegawa, Nippon Kagaku

Kaishi, 1973, 1059

15’ G Gode and L Klavina, Zhur neorg Khim., 1972, 17, 2851

15* G N Zavorueva, Uch Zap., Yaroslav Gos Pedagog Inst., 1971, No 95, p 64

159 Yu V Ushakov, Zhur neorg Khim., 1973, 18, 273

160 Yu G Vlasov, B L Seleznev, and E A Elchin, Zhur neorg Khim., 1972, 17, 3069 (Ref Zhur., Khim., 1972, Abstr No 7B927.)

20 Inorganic Chemistry of the Main-group Elements

contrasts with the cation dependence of this band in solutions of salts in ammonia, where the absorption is attributed to Mf - - - NH, dipole inter- actions Also the magnitude of the v3 shift as a function of concentration is greater for M than for Mf (400 times greater for K than for KI) These

results are attributed to the formation, with increasing metal concentration,

of a ncw solvated species of cation which incorporates the solvated electron,

i.e a form of solvated cation-electron pair.161 The magnetic susceptibility of

solutions of alkali metals in liquid ammonia has been measured over the concentration range where the solutions show a progressive transition towards the metallic state The general transport properties of metal-NH, solutions have been analysed and a model is proposed for the mechanism of the transi-

tion to the metallic state.162 This transition occurs at ca 1-9 mole per cent

metal Over this region metal-ammonia solutions exhibit rapid variations with concentration of their static and transport properties Concentrated

( > 10 mole per mole) metal-ammonia solutions are more like liquid metals

and show electronic transport It is proposed that the intermediate 1-9

mol (mol)-l region is microscopically inhomogeneous, so that the solution consists of a mixture of metallic clusters of a mean concentration >9 mol (mol)-l together with small cation-electron diamagnetic c0mp1exes.l~~

Photoelectron emission by potassium (0.002-3 moll-l) and sodium (0.01 3- 0.21 and 7.2mol1-l) in liquid ammonia at -6OOC has been investigated

from 1.55 to 5.4 eV The spectrum is composed of the previously reported

band at ca 3.2 eV and a new band peaking at ca 4.6 eV The highly asym-

metric low-energy band, 3.2 eV, is assigned to photoelectron emission by

solvated electrons The 4.6 eV symmetrical photoelectron emission band results from bound-bound transitions followed by a u t o i ~ n i z a t i o n ~ ~ ~ Alkali metals dissolved in liquid ammonia react with zirconium disulphide ZrSz in

sealed tubes at 20°C to form several phases The alkali metals partially or

wholly occupy the layers of empty sites in the host structure to form NaZrS,

or KZrSz when the ammonia solutions contain high concentrations of alkali metal At lower concentrations, only one layer out of two is occupied

No reduction of ZrS,, occurs At very high concentrations, sodium occupies

octahedral sites whereas potassium occupies either octahedral or prismatic sites A comparison of the X-ray diffraction data of NaZrS, with those of ZrS, indicates an increase in the lattice parameter c but little change in a upon incorporation of sodium.165 These compounds resemble those of TiS, with the alkali metals The compounds h4,TiS (M = Na or K) have been reported

previously For M = Li, x = 0-1; M = Rb, x = 0.42-1, 0.12-0.32, and 0.04-0.06; M = Rb, x = 0.56-1, 0.08-0.10, and 0.03-0.04 The lattice

parameters of these compounds are compared with those of the sodium and

P F Rusch and J J Lagowski, J Phys Chern., 1973,77,210

J P Lelieur, Report 1972, CEA-R-4333

163 J Jortner and M H Cohen, J Chem Phys., 1973, 58, 5170

1 G 4 H Aulich, B Baron, P Delahay, and R Lugo, U.S Nat Tech Inform Service, AD

J Cousseau, L Trichet, and J Rouxel, Bull SOC chim France, 1973, 872

Rept 1972, No 750277

Elements of Group I 21

potassium phases, With increasing values of x in Li,TiS2, a and c increase monotonically as the Li atoms progressively fill the octahedral sites of the TiS2 host lattice The structures of the different types of phases are classified

on the basis of the co-ordination number of the intercalated alkali-metal atom, the periodicity of the occupation of the available sites between successive (STiS) layers of the host structure, and the mode of succession of the sulphide layers.166 Single crystals of MoS, can also be intercalated with alkali metals (Li, Na, K, Rb, and Cs) by the liquid ammonia technique X-Ray results show considerable expansion of the c-axis after intercalation

(Ac; 6.745, 2.704, 4.286, 4.899, and 7.312 A for Li,.,MoS,, Na,.,MoS,,

KO, ,MoS,, Rb,, ,MoS,, and Cs, ,MoS2, respectively) All intercalated crys taIs

are superconducting, which is attributed to electron transfer from the alkali metal to an empty band of M 0 S p 7 Potassium naphthalenide solutions also

react with MS, (M = Ti,Mo, or W) to give K,MS2 (x = 0.49-0.76) With sodium naphthalenide, the first step in the reaction gives Na,MS,, but lithium naphthalenide and subsequently sodium naphthalenide reduce the sulphides to the respective metals.16*

The absorption spectra of solutions of alkali metals in various amines display up to two bands; one at 1400 nm, which is independent of the metal

and which is attributed to a solvated electron, and a second band which peaks

between 660 and 1OOOnm which is independent of the metal and which is attributed to a metal-containing species Evidence has been accumulating which suggests that this is a metal anion, M-, (J P h p Chem., 1971, 75,

3092) The 660-1000 nm band obeys the criterion for a charge-transfer-to- solvent transition that the position of the peak, Y , be a linear function of the temperature coefficient, dv/dT Thus the existence of the anion, M-, is proposed in solutions of the alkali metals in MeNH, and EtNH,169 and again

in solutions of Na and K in EtNH,, Et,NH, Pr,NH, propane-l,2-diamine,

(Me,N),PO, Et,O, PrizO, THF, MeOCH,CH,OMe, and diglyme, in which

the solubility of the metal has been enhanced by employing cyclic polyethers

of the crown and cryptate classes to complex the alkali-metal cations.170 For a spherically symmetrical Na species with J = 1 a magnetic moment of 1.0 B.M is to be expected Experimentally, values ranging from 0.5 to 1.3 B.M are found for Na- in EtNH,.171

Modern advances in solvation theory are reviewed.17, A second critical

review of the thermodynamic functions and crystallographic data of some solid solvates (e.g NaI,3MeOH; LiC1,py; and CoC1,,6NH3) shows that the relative acid-base properties of the constituent cation, anion, and solvate molecule can well be described by the HSAB (hard and soft acids and bases) concept.173

lG6 J Bichon, M Danot, and J Rouxel, Compt rend., 1973, 276, C, 1283

l G 7 R B Somoano, V Hadek, and A Rembaum, J Chem Phys., 1973, 58, 697

l G 8 E Bayer and W Ruedorff, Z Naturforsch, 1972, 27b, 1336

l G S K Bar-Eli and G Gabor, J Phys Chem., 1973, 77, 323

C Duboc, Ann Chim (France) 1973, 8 , 81

22 Inorganic Chemistry of the Main-group Elements

The enthalpies of ammoniation of gaseous cations relative to that of Na+, and

of gaseous anions and the electron relative to that of I-, have been determined

from an analysis of enthalpies of solution of salts and metals in liquid ammonia Selected experimental enthalpies of formation, AH,/kcal m o F , of

ion pairs in liquid ammonia at -33 "C are shown in Table 3 The AHf of a

Table 3 Experimental values of AH,/kcal mol-l for ion pairs in liquid ammonia

0

0

0

- 19.7 -20.7 -19.0

certain ion pair, e.g Na+ C1-, is found by combining the standard enthalpy of

formation of NaCl (-98.2 kcal mol-l) with its heat of solution in liquid ammonia (-1.5 kcal mol-l) AH, of an ion-electron pair is merely the heat

of solution of the metal in liquid ammonia Values in parenthesis are extrap- olated It is demonstrated that the relative ammoniation enthalpies of the

individual ions can be obtained from the Born equation if an effective radius

which is 0.61 13 greater than the crystalline radius is assumed for each ion In addition, the absolute ammoniation enthalpies for the gaseous ions are

evaluated at -33OC and compared with those deduced from the Born

equation Values of AH/kcal mol-l for selected ions are shown in Table 4.174

Table 4 Experimental and calculated ammoniation enthalpies of some ions

N M Senozan, J Inorg Nuclear Chem., 1973, 35, 727

Elements of Group I 23

solvent-separated and contact ion pairs involving Li+ and NO; ions.175 The

enthalpies of solution at 25 OC for the salts LiCl, LiNO,, NaBr, Nal, NaNO,,

KBr, KI, KNO,, RbNO,, and CaNO, in DMF have been measured calori-

metrically and the enthalpies of solvation of the component ions calc~1ated.l~~ Conductance measurements have been made at 25 "C for solutions of the salts NaClO,, KClO,, LiNO,, NaNO,, KNO,, NaSCN, KSCN, NaBr, potassium picrate, and Pr,NBr in hexamethylphosphortriamide (HMPT)

Potassium salts are more conducting than the corresponding sodium salts and the ions migrate independently in HMPT Alkali-metal cations are sol- vated by ca 2HMPT molecules whereas the anions can be considered as naked All of the salts, except KNO, and Pr,NBr, are completely dissociated in this s01vent.l~~ In solutions of perchlorates in hexamethylphosphoramide (HMPA),

the ionic equivalent conductivities of cations obtained on the assumption that the conductivity of the perchlorate ion is 15.5 are Li+ 5.2, Na+ 5.8,

K+6.1, Rb+6.1, (36.4, Ca2+8.6, Sr2+8.6, Ba2+8.4, Me,N+7.9, Et,N+9.3, Pr,N+ 6.8, Bu,N+ 5.9, and Hex,N+ 4.5 cm2 e q u i r l L2-l The Stokes' Law radius of a univalent cation is smallest for Et,N+ The solvation number obtained from the effective ionic radius of Robinson and Stokes (1965) is

1 to 2 for alkali-metal ions and ca 3 for alkaline-earth ions.178 The association

of the ions Lif, Na+, and Mg2+ with perchlorate in methyl cyanide has been

studied spectroscopically On increasing the salt concentration, additional bands appear in the i.r spectrum of the C 1 0 ~ ions owing to the formation of

M+ Clog ion pairs: for solutions of Na+ these are at 11 19, for Li+ at 1070 and 1132, and for Mg2+ at 1040 and 1154 cm-1.179 The enthalpies of solution

of the salts LiClO, and LiNO, in isoamyl alcohol decrease with increasing concentration, especially 50.1 moll-l At 25 "C, the values at infinite dilution are -9.90 kcal mol-l for LiClO, and -2.75 kcal mol-l for LiNO, The enthalpies of solution of the salts in the alcohol are more exothermic than those in water,ls0 A quantitative study of n.m.r chemical-shift variation

as a function of salt (LiCl, LiBr, LiI, NaI, and KI), molality, and temperature

gives values for effective solvation numbers of 4 for lithium salts and 6 for sodium and potassium iodides.lS1 Conductivity data for solutions of sodium iodide in acetone from -50 to +50 OC provide ionic association constants,

which with increasing temperature show a rise that is explained by the endothermic effect of ion de-solvation Positive values of entropy change indicate that disorder increases during the ionic association of sodium iodide.182 The solvation numbers of Na+, K+, and I- ions at 25 "C, calculated

V A Zverev and G A Krestov, Teor Rastuorov, 1971, 148 (Ref Zhur., Khim., 1972,

P Bruno, M R Della Monica, and E Righetti, J Phys Chem., 1973, 77, 1258

179 I S Perelygin and M A Klimchuk, Ural Konf Spektrosk., 7th, 1971, No 2, p 125

(Ref Zhur., Khim., 1972, Abstr No 12B1185.)

180 P A Skabichevskii and I I Klement'eva, Zhur.fiz Khim., 1973, 47, 692

lE1 A Lindheimer and B Brun J chim Phys., 1972, 69, 1454

24 Inorganic Chemistry of the Main-group Elements

from conductance data for solutions of NaI, KI, and KSCN in acetone,

when compared with solvation numbers for the same ions in ethanol and water, illustrate that the intrinsic structure of the solvent plays a major role

in the solvation process.ls3 The i.r spectra of solutions of Li, Na, K, Rb, and Cs salts in sulpholane show absorptions which are independent of the anion Solvation appears to take place in a manner similar to that observed

for DMSO solutions but sulpholane, a dipolar solvent with a high (44)

dielectric constant, is a far weaker donor It is proposed that solvent-separated ion pairs are formed in sulpholane solutions.1s4 The electrical conductivities

of solutions of the Li, Na, K, and Rb salts of 2,4-dinitrophenol in THF at

25 O C have been measured with and without added triphenylphosphine oxide Ion-pair dissociation constants of the salts are derived from variation of the conductivities with salt concentration These constants increase with increas- ing cation size, as expected for contact ion pairs Cation-ligand association constants, KL, are derived from the increases in the conductivities due to added Ph,PO Values for KL are for Li 3500, Na 250, K 87, and Rb 53 I mol-l This is just the order of association expected from the cationic radii An ion- dipole model, modified to take into account the influence of surrounding polarizable solvent, is able to explain the r e ~ u 1 t s l ~ ~ Ion-solvent interactions are detected in cyclohexane solutions of NaAlBu, by means of differential vapour pressure analysis The observed departure from ideality is attributed

to an aggregation process The apparent degree of aggregation varies from pairs of ions at ca 0.0025 niol 1-1 to an aggregation number of 6 at ca

2 moll-l Addition of THF to the salt solutions lowers the apparent molecular weight of the solute The magnitude of this effect increases with both an increase in the ratio of THF:NaAlBu, and with an increase in NaAlBu, concentration This is attributed to a loss of aggregate stability in both instances.ls6 Thermochemical measurements on solutions of sodium iodide

and caesium iodide in DMSO at 25 "C provide integral enthalpies of solution

With solutions of NaI, an increase in salt concentration causes an increase in the exothermic effect attributed to the ability of NaI to form solvates with Me,SQ The energetics of solvation of Na+ ions are appreciably greater than

those for Cs+ ions.lS7 In anhydrous acetic acid solutions containing 0.001-

0.032 mol 1-1 metal acetate at 25 O C , the dissociation constants ( K B ) for

M+OAc- = M+ + OAc-, determined by a potentiometric method, are PKB = 6.13 & 0.04, 5.93 f 0.10, and 5.84 f 0.10 for M = K, Rb, and Cs, respectively For M = Li, Na, K, Rb, and Cs the linear plot of pKB us log a3

has a slope of +1, where a is the radius of M+.ls8 The optical absorption spectra have been measured for solutions of triphenylene reduced with alkali

lS3 Yu I Gerzhberg, B S Krumgal'z, and D G Traber, Teor Rastvoroo, 1971, 115

lE4 T L Buxton and J A Caruso, J Phys Chem., 1973, 77, 1882

lS5 H B Flora and W R Gilkerson, J Phys Chem., 1973, 77, 1421

lS6 J H Muller and M C Day, J Phys Chem., 1972, 7 6 , 3472

lS7 0 I Kyabchenko, M L Klyueva, K P Mishchenko, and N P Novoselov, Zhur

(Ref Zhur., Khim., 1972, Abstr No 5B1485.)

ohshchei Khim., 1973, 4 3 , 467