Inorganic chemistry of the main group elements vol 5

Hubberstey 1 Introduction 2 The Alkali Metals as Solvent Media 3 Metallic Solutions and Intermetallic Compounds 4 Solvation of Alkali-metal Cations 5 Simple Compounds of the Alkali

A Specialist Periodical Report

Elements

Volume 5

and Septern ber 1976

All of: Department of Chemistry, University of Nottingham

The Chemical Society

British Library Cataloguing in Publication Data

Inorganic chemistry of the Main-group elements

(Chemical Society; Specialist periodical reports)

VOl 5

1 Chemistry, Inorganic 2 Chemical elements

I Addison, Cyril Clifford 11 Series

546 QD151.2 72-95098

ISBN 0-85 186-792-8

ISSN 0305-697X

Copyright @ 1978

The Chemical Society

All Rights Reserved

No part of this book may be reproduced or transmitted

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including photocopying, recording, taping or

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Filmset in Northern Ireland at The Universities Press (Belfast) Ltd, and printed at The Pitman

Press (Bath) Ltd

Preface

It has again been possible, in Volume 5 , to find authors for all chapters from amongst the inorganic chemists in the University of Nottingham, and the Senior Reporter would like to express his appreciation of the hard work to which they were prepared to commit themselves, and of the enthusiasm which they have shown Because of financial pressures, we were called upon to produce a volume

only two-thirds the length of Volume 4 The shorter the volume the more difficult becomes the task of choosing amongst the large number of worth-while research papers published during the year Readers will detect a further move in the direction of structure and reactivity as against purely physical properties; for example, Chaper 4 no longer includes cover of binary and ternary intermetallic phases, which have been included in earlier volumes All authors regret that much good work which merited mention has had to be omitted purely because of space limitation Selection has to be based on originality and novelty, but also on the need to present a readable account, and thus to include reference to all published papers on any chosen theme In this difficult task the authors have found that the opportunity to work as a team, and to maintain day to day discussion on possible overlap between chapters, has been of considerable advantage

C C ADDISON

.I

1ll

con tents

Chapter 1 Elements of Group I

By P Hubberstey

1 Introduction

2 The Alkali Metals as Solvent Media

3 Metallic Solutions and Intermetallic Compounds

4 Solvation of Alkali-metal Cations

5 Simple Compounds of the Alkali Metals

Hydrides Oxides, Hydroxides, Sulphides, etc

Halides Molten Salts Halides Nitrates

6 Compounds of the Alkali Metals containing Organic Molecules or Complex Ions

Radical-anion Salts Crown and Cryptate Complexes Lithium Derivatives

Sodium Derivatives Potassium Derivatives Rubidium and Caesium Derivatives

Chapter 2 Elements of Group I I

1 Introduction

2 Alloys and Intermetallic Compounds

Transition Metals and Rare Earths Main-Group Elements

vi

5 Compounds containing Organic or Complex Ions

Beryllium Derivatives Magnesium Derivatives Calcium Derivatives Strontium and Barium Derivatives

Chapter 3 Elements of Group 111

1 Boron

Boranes Borane Anions and Metallo-derivatives Carba- and other Non-metal Hetero-boranes Metallo- hetero boranes

Compounds containing B-C Bonds Aminoboranes and other Compounds containing

Compounds containing B-P or B-As Bonds Compounds containing B-0 Bonds

Compounds containing B-S or B-Se Bonds Boron Halides

Boron-containing Heterocycles Boron Nitride, Metal Borides, etc

2 Aluminium

General Aluminium Hydrides Compounds containing Al-C Bonds Compounds containing Al-N Bonds Compounds containing A1-0 or Al-Se Bonds Aluminium Halides

106

106

107

108

125

Hydrides of Silicon, Germanium, and Tin The Metal(w) Oxides and Related Oxide Phases

Silicates, Germanates, and Related Materials

Lead (Iv)-Ox y ge n Derivatives

1 Nitrogen

Elemental Nitrogen Reactions of N2 Complexing of N2 Nitrides

Bonds to Hydrogen Ammonia The Ammonium Ion

H ydroxylamine Bonds to Nitrogen The N2H2 Molecule

H ydrazine Azides

General Bonds to Oxygen

Nitrogen($ Species Nitric Oxide Nitrogen(xI1) Species

Nitric Acid Nitrates NO,’ Salts NOZ-NZOd

Bonds to Fluorine Bonds to Bromine and Iodine

2 Phosphorus

Phosphides Compounds containing P-P Bonds Bond to Boron

Bonds to Carbon Phosphorus(xI1) Compounds Phosp horus(v) Compounds Bonds to Silicon, Germanium, or Tin Bonds to Halogens

Phosphorus(n1) Compounds Phosphorus(v) Compounds

Phosphorus(n1) Compounds Phosphorus(v) Compounds Compounds containing P-N Rings Compounds containing Other Ring Systems

Compounds of Lower Oxidation State Phosphorus(v) Compounds

X-Ray Diffraction Studies Phase Studies

Mono-, Di-, and Poly-phosphates

4 Antimony

Antimony and Antimonides Bonds to Carbon

Bonds to Halogens Antimony(xI1) Compounds Antimony(v) Compounds

Antimony(II1) Compounds Bonds to Oxygen

Contents ix

Antimony(v) Compounds Bonds to Sulphur

The Element Sulphur-Halogen Compounds Sulphur-Oxygen-Halogen Compounds Sulphur-Nitrogen Compounds Linear Molecules

Polymeric Sulphur Nitride Cyclic Compounds Sulphur-Oxygen Compounds Oxyanions of Sulphur Sulphides

Hydrogen Sulphide Polysulphides

0 ther Sulp hides

2 Sulphur

3 Selenium

The Element Selenium-Halogen Compounds Selenium-Oxygen Compounds Metal Selenides

Other Compounds of Selenium

4 Tellurium

The Element Tellurium-Halogen Compounds Tellurium-Oxygen Compounds Tellurides

Other Compounds containing Tellurium

Chapter 7 The Halogens and Hydrogen

1 Halogens

The Elements Halides Interhalogens and Related Species Oxides, Oxide Halides, and Oxyanions Hydrogen Halides

X Contents

2 Hydrogen

Hydrogen-bonding Protonic Acids Miscellaneous

Chapter 8 The Noble Gases

1

Elements of Group

BY P HUBBERSTEY

1 Introduction

The definition of the limits of the literature search pertinent to the present Report

is complicated by the extensive role of the alkali metals as simple counter-cations

In general, papers have been abstracted which are relevant to a number of broad subject groups in which the role of the alkali metals is unique Consequently, the format of this Chapter is such that the inorganic chemistry of the alkali metals is considered collectively in sections which reflect topics presently of interest and importance

For certain topics (e.g cation solvation, molten salts, crown and cryptate complexes), the chemistry of the Group I and I1 metals is closely ipterwoven; in these cases, the data abstracted are considered once only in the relevant section in this Chapter

The extraction of alkali-metal cations from salt solutions into organic solvents has been the subject of four The ion [.rr-3-1,2-B,C2Hl,]Co- has been proposed as a nearly ideal hydrophobic anion for extraction of M' ions into

C,H,NO, uia formation of ion pairs.' Li' has been selectively extracted from

nearly neutral aqueous solutions of alkali-metal salts via the formation of the trioctylphosphine adduct of a lithium chelate of fluorinated /3 -diketones; although high separation factors were obtained from Na', K', Rb', and Cs+, selectivity

from the alkaline-earth-metal cations was found to be poor.* The extraction of

M' into PhNO, and MeNO, using hexafluoroacetylacetonate has also been

in~estigated.~'~ Dissociation constants of the alkali-metal enolates were deter- mined, the extent of association of enolate ion with enol to give a dimeric ion was deduced, and the latter's formation constant calculated

2 The Alkali Metals as Solvent Media

The role of liquid sodium as a heat-exchange medium in the fast breeder reactor, and that of liquid lithium as a prime candidate far use as the blanket medium in a deuterium-tritium-fuelled thermonuclear reactor, has maintained interest in the solution chemistry of these liquid metals

J Rais, P Selucky, and M Kyrs, J Inorg Nuclear Chem., 1976, 38, 1376

* F G Seeley and W H Baldwin, J Inorg Nuclear Chem., 1976, 38, 1049

S Tribalat and M Grall, Cornpt rend., 1976, 282, C, 457

S Tribalat and M Grall, Compt rend., 1976, 282, C , 539

1

2 Inorganic Chemistry of the Main-Group Elements

Phase equilibria for Li-Li3N dilute solutions have been investigated by two independent groups of authors.'-' Pulham et ~ 1 ' ~ ~ have determined the hypoeutectic and hypereutectic liquidi by thermal5 and by electrical resistance6 methods, respectively The freezing point of Li (453.64 K) is depressed by 0.25 K

to 453.39 K at the eutectic composition 0.068 mol YO N The depression was used

to calculate the solid solubility of Li,N in Li (0.024molYoN) at the eutectic temperature.' The solubility of Li3N in liquid Li increases smoothly from the eutectic to 2.77 mol % N at 723 K.6 Over a wide temperature range, the data can

be represented by equation (1) These latter data are corroborated by those of Veleckis et aL7 [equation (2)], who used a direct sampling technique This

agreement resolves the problem of the earlier inconsistent data' referred to in the

previous Report.' Veleckis et uL7 also measured the equilibrium nitrogen pressure over solid Li,N at temperatures between 933 and 1051 K From a thermodynamic

analysis of the solubility and decomposition data, the standard free energy of formation of solid Li3N (AGy/kJ mol-l) was estimated to be 138.9 X T/K -

163.6 For dilute solutions of Li3N in Li, the Sieverts law constant (Ks/atm-1'2=

xLi3N P-''~) is given by -13.80+ 14590 (T',K)-' The melting point of Li,N was found

to be 1086 K, in good agreement with the previously reported value of 1088 K.7

10gloXN= 1.168-2036(T/K)-' (473 s T/Ks708) (1)

10g10XL13N = 1.323 - 2107(T/K)-' (468 G T/Ks714) (2)

Phase equilibria of Li-LiH and Li-LiD dilute solutions have also been studied

by Pulham et a1.5T6~'0*'1 The maximum depression of the freezing point of Li by LiH5 (LiD)" is 0.08K (0.075K), corresponding to a eutectic composition of

0.016 mol%H (0.013 mol% D) These data, which indicate negligible solid solubil- ity of the salts in Li, have been used to show that both hydrogen and deuterium dissolve in liquid Li as monatomic solute species." Typically, the depression caused by small LiH concentrations (Figure 1) follows quite closely the line derived theoretically for monatomic solutes The theoretical line for a diatomic species is included in the Figure for comparison The solubilities of LiH6 and of LiD" in liquid Li have been determined by electrical resistance methods at temperatures up to 824 K (5.68 mol%H), and 729 K (2.63 mol%D), and can be

represented over a considerable part of the temperature range by equations (3)

and (4), respectively The hydrogen-deuterium isotope effect has been discussed and the experimental data have been extrapolated to predict the behaviour of tritium in liquid Li."."

loglOXH= 1.523-2308(T/K)-l ( 5 2 3 s T/KS775) (3)

10gloxD = 2.321 - 2873(T/K)-' (549 C T/K S 724) (4)

P Hubberstey, R J Pulham, and A E Thunder, J C S Faraday I, 1976, 72, 431

R M Yonco, E Veleckis, and V A Moroni, J Nuclear Materials, 1975, 57, 317

P F Adams, P Hubberstey, and R J Pulham, J Less-Common Metals, 1975, 42, 1

R J Pulham, in 'Inorganic Chemistry of the Main-Group Elements' (Specialist Periodical Reports),

ed C C Addison, The Chemical Society, London, 1976, Vol 4, Ch 1

lo P F Adams, P Hubberstey, R J Pulham, and A E Thunder, J Less-Common Metals, 1976, 46,

285

l 1 P Hubberstey, P F Adams, R J Pulham, M G Down, and A E Thunder, J Less-Common

' P F Adams, M G Down, P Hubberstey, and R J Pulham, J Less-Common Metals, 1975,42,325

Elements of Group I

r

3

'

-Diatomic soiute species

Concenhtion (mol I H) Figure 1 Depression of the freezing point of lithium by small concentrations of hydrogen,

(Reproduced by permission from J Less-Common Metals, 1976, 49, 253)

showing evidence for monatomic solute species

New solubility data for NaH in liquid Na have been determined by Whitting- ham" in a detailed study (610-677K) of the thermodynamic and kinetic properties of the liquid Na-H, system Comparison with some previous data has been effected and a composite solubility equation (5) formulated

logloxH = 1.818 - 3019(T/K)-' (435 4 T/K C 673) ( 5 )

These new solubility data for hydrogen isotopes have been collated and compared to the corresponding solubilities in NaK and K;l' surprisingly, hydro-

gen is least soluble in sodium

Solubility data have been used6'10'11 to determine solvation enthalpies, U,,

[defined as in equation (6)] for N3-, 0'-, H-, and D- in Li and for H- in Na and

K The values of U, are collected in Table 1 Those for H- and D- in Li are

lower than those for 02- and N3- by factors of ca 22 and 3', respectively,

corresponding to increasing U, with increasing charge of solute Those

for H- in Li, Na, and K are very similar, that in Li being the greatest." Solvation enthalpies have been derived13 in ab initio M.O calculations of solva-

tion clusters in Li and Na By comparison with experimental data, the best model

was deduced to be that of a tetrahedral solvation sphere of cations supplemented

by a further metal tetrahedron positioned on the three-fold axes of the first solvation sphere Other incidental results to emerge from the calculations are the effective radii for Li (0.1675 nm), Na (0.1715 nm), and H (0.0525 nm in Li and

Table 1 Solvation enthalpies for non-metal solutes in liquid alkali metals

'* A C Whittingham, J Nuclear Materials, 1976, 60, 119

4 Inorganic Chemistry of the Main- Group Elements

0.0535 nm in Na) and the effective charges on the H (-0.45 in Li and -0.25 in

of Y(H) solid solution and YH, according to reaction (8).11

(8) Li(H) + Y -+ Li + Y(H) + YH,

Enrichment of deuterium in the gaseous phase above dilute Li-LiD solutions

(x, = lop5) has been observed by Ihle and Wu14 at temperatures above 1240 K This supports the contention that deuterium can be removed from highly dilute solutions in Li by distillation The results are of importance in the context of the technology of thermonuclear reactors and have been extrapolated to Li-LiT solutions l4

Several papers pertinent to the elucidation of the corrosive properties of very dilute solutions of non-metals in liquid alkali metals have been p ~ b l i s h e d ’ ~ - ~ ~ The corrosion of V,15 Nb,15 Ta,15 Mo,16 and W16 plates suspended in dynamic liquid sodium, containing more than 5 p.p.m oxygen, has been examined at

873 K; the products were analysed through a matrix of Na by X-ray diffraction

techniques The ternary oxides Na,VO, and NaVO, were formed on V, together with a V(0) solid ~olution.~’ For Nb and Ta, only a single ternary oxide Na,MO,

corrosion of Mo was found to be independent of oxygen concentration, no ternary oxide products being observed, that of W was found to be strongly influenced by initial oxygen concentration in the Na At low oxygen levels, the cubic phase Na,WO, was identified; at very high oxygen levels in static Na, however, the orthorhombic phase Na6WO6 was observed Inclusion of labile carbon in the system containing Mo caused the formation of Mo2C.16 The closely related solid-state reaction of Na,O with Mo and W under vacuum gave the ternary phases Na,Mo05 and Na6WO6, respectively, together with unreacted refractory metal and Na vapour.16

Barker and H00per’~ have reinvestigated the products of the reaction of liquid

Na with CrO, at temperatures up to 873 K; CrO,, Cr203, and Na,CrO, were also

studied as substrates The ternary oxide NaCrO, is found in each case in which reaction took place The previously accepted reaction product, Na,Cr03, was not formed; the error has been rationalized in terms of the experimental procedure, and improved techniques have been deve10ped.l~ Gellings et ~ 1 ’ ’ have also studied

l4 H R Ihle and C H Wu, J Phys Chem., 1975, 79, 2386

l5 M G Barker and C W Morris, J Less-Common Metals, 1975, 42, 229

l6 M G Barker and C W Morris, J Less-Common Metals 1976, 44, 169

l7 M G Barker and A J Hooper, J C S Dalton, 1976, 1093

’’ H van Lith, E G van den Broek, and P J Gellings Znorg Nuclear Chem Letters, 1975, 11, 817

Elements of Group I 5

the reaction of CrO, with liquid Na, their results corroborating the identification

of NaCrO, as product The product of these reactions, NaCrO,, together with the other ternary oxides Na,CrO, and Na,CrO,, has been prepared by Barker et ul.19

by the reaction of Na,O and Cr203 or Cr, and it has been characterized by X-ray powder difTraction techniques NaCrO, decomposes reversibly to the simple oxides at cu 1068K.l’

The reaction of pure liquid Li with MO, (M=Ti, Zr, Hf, or Th) has been shown to follow thermodynamic predictions.20 TiO, and ZrO, give rise to Li,O and the appropriate transition metal; HfO, yields Hf metal, Li20, and a tet- ragonal phase, which may be the ternary oxide LiHfO,; Tho, does not react Reaction with liquid Li doped with dissolved nitrogen, however, converts all four oxides, in differing degrees, into either the mononitride or a ternary nitride Li2MN2 (M = Zr, Hf, or Th).20

Liquid K reduces NiO to Ni metal at 458 K with the concomitant formation of the ternary oxides K,NiO, and K,NiO, ; thermomagnetic analysis indicates that the reaction occurs in a single step.21 K2Ni0, was also prepared by the reaction of equimolar quantities of K,O and NiO; K,NiO, was produced by the reaction of K,O and NiO in 0, or by heating K,NiO, in a stream OP 0,

The reaction between Ba and N, in liquid Na has been investigated at

573 K.22923 Solubility studies,, showed that the reaction of a 4.40mol YO Ba

solution occurs in two stages; (i) dissolution of N2 (N, is insoluble in pure liquid

Na), and (ii) precipitation of Ba,N, the initial product of the reaction The

occurrence of these two processes is reflected in the resistivity studies2, effected

on a number of Na-Ba solutions (between 0.34 and 6.89 mol YO Ba) The extent

of the solution process was found to be a linear function [equation (9)] of the initial

Ba concentration, the solubility limit corresponding to an overall reaction com- position approximating to Ba,N This ratio, and the decrease in resistivity which invariably occurred during the solution process, leads to the concept of strong preferential solvation of the nitride ion by Ba cations, perhaps in the form of a

‘Ba,N’ solvated unit.,,

xN = 0 2 5 ~ ~ ~ (0 < xBa < 0.0689) (9)

The reaction of C,H, with liquid K has been studied in the range 5 0 3 - 6 7 1 K.,,

At low temperatures, self -hydrogenation occurs precisely according to equation (10) The surface reaction is explained by dissociative adsorption of C2H4 into H adatoms, which are subsequently employed in hydrogenation With increasing temperature, progressively less C2H6 is produced, which is attributed to the loss of

H from the surface by solution in the metal.,,

l9 M G Barker and A J Hooper, J C S Dalton, 1975, 2487

21 M G Barker and A P Dawson, J Less-Common Metals, 1976, 45, 323

22 C C Addison, R J Pulham, and E A Trevillion, J C S Dalton, 1975, 2082

23 C C Addison, G K Creffield, P Hubberstey, and R J Pulham, J C S Dalton, 1976, 1105

M G Barker, I Alexander, and J Bentham, J Less-Common Metals, 1975,42, 241

20

6 Inorganic Chemistry of the Main-Group Elements

3 Metallic Solutions and Intermetallic Compounds

The nature of the bonding in intermetallic phases has been and an attempt has been made to demonstrate qualitatively the dependence of both the number of phases in a binary system and their relative thermal stabilities on the electronic configurations of the component atoms Particular attention has been devoted to compounds of the alkali metals with Hg,25 Sn,26 Pb,25 Sb?' and BiZ5 The preparation of the novel compounds K2Cs and K7Cs6 by precipitation from solid K-Cs solutions at temperatures below 183 K has been reported.27 Structural analysis has shown that K2Cs (a = 0.9065, c = 1.4755 nm at 178 K) is isotypic with the hexagonal Laves phase Na2K, whereas K7Cs6 ( a = 0.9078, c = 3.2950 nm

at 178 K) forms hexagonal crystals with a novel kind of Frank-Kasper structure Although the K atoms in K7Cs, are sited in two 12-co-ordination polyhedra, the

Cs atoms occupy one of four sites with 14-fold, 15-fold (X2), and 16-fold co-ordination The K * - K, Cs - - Cs, and K - - - Cs distances vary from 0.454 to 0.461, from 0.501 to 0.546, and from 0.466 to 0 5 7 4 1 m ~ ~

The Li-In phase diagram has been exhaustively re-examined by Alexander et

~ l , ' ~ using thermal and X-ray diffraction analysis The work has confirmed the liquidus data of Grube and Wolf29 and delineated the solid-state relationships Eleven new phases (Table 2), together with the previously known LiIn phase (which extends from ca 46 to between 55 and 63 mol% Li, depending on temperature), have been observed The discovery of new phases, of which only five are stable at room temperature, has removed the apparent anomaly between the Li-In and the Li-Ga and Li-Tl systems The solid solubility of Li in In is low

(ca 1.5 mol O h Li at 432 K) and that of In in Li is very

Intermetallic phases of the Li-Pd3' and Li-Pt31 systems have been synthesized

Table 2 Intermetallic phases of the Li-In system2'

" V I Kober and I F Nichkov, Russ J Phys Chem., 1975,49, 829

26 V I Kober and I F Nichkov, Russ J Phys Chem., 1975, 49, 962

A Simon, W Bramer, B Hillenrotter, and H.-J Kullman, 2 anorg Chem., 1976, 419, 253

'* W A Alexander, L D Calvert, R H Gamble, and K Schinzel, Canad J Chem., 1976,54,1052

30 J H N van Vucht and K H J Buschow, J Less-Common Metals, 1976, 48, 345

27

Elements of Group I 7

and their structures elucidated; pertinent structural data for seven Li-Pd phases (including Li,Pd and LiPd), as determined in X-ray diffraction studies, and for Li,Pt and LiPt, as determined using neutron-diflraction techniques, are collected

{ 1.9347 0.2728 0.4186

0.4336 30 0.4280 30 0.4131 30

-

-

-

-

Thermodynamic properties of liquid Li-T132 and of liquid Na-X33 (X = Cd, Hg,

In, TI, Sn, Pb, Sb, Bi, S, Se, or Te) have been studied The unsymmetrical form

of the nature of the dependence on concentration of the thermodynamic charac- teristics of the Li-TI system, which exhibits negative deviations from Raoult's Law, is thought to be consistent with the equilibrium diagram.32 The dependence

on concentration of the entropy of mixing in the Na-X systems is S-shaped, the point of inflexion corresponding to formation of intermetallic This behaviour is attributed to a high degree of short-range order in the liquid, and of partial ionic character of the bonds in these intermetallic compounds Short-range order has also been studied in liquid Li-Pb solutions by neutron-diffraction

t e c h n i q ~ e s ~ ~ The data indicate a preference for unlike nearest neighbours; this is manifest in a reduction of distance between unlike neighbours (0.295 nm) as compared with the mean distances between the pure components (Li - - * Li = 0.300 nm; Pb - - - Pb = 0.340 nm) It has been suggested that the short-range order

is probably due to salt-like Li - - - Pb bonding No evidence for the existence of isolated LLPb clusters was obtained; indeed, in liquid Li,Pb, each Pb atom is surrounded by ca 10 Li atoms.,,

4 Solvation of Alkali-metal Cations

The majority of data published on the solvation (both aqueous and non-aqueous)

of alkali-(and alkaline-earth-)metal cations is of but peripheral interest to the inorganic chemist Consequently, the papers abstracted for this section of the Report are quite selective, dealing principally with the structural and spectros- copic properties of these solutions

3 2 S P Yatsenko and E A Saltykova, Russ J Phys Chem., 1975, 49, 292

33 A G Morachevskii, E A Maiorova, and A I Demidov, Russ J Phys Chem., 1975, 49, 1093

8 Inorganic Chemistry of the Main- Group Elements

As a starting point in a theoretical study of ionic solutions, the complex H,O- Lí-F has been ~ o n s i d e r e d ~ ~ Analysis of the stabilization energies of some 250 geometrical configurations reveals the existence of at least three possible struc- tures: (i) the Li-F-H,O structure that has C,, symmetry; (ii) a second Li-F-H,O structure with the F forming a hydrogen bond (with a hydroxy-group); and (iii) the F-Li-H20 structure that has C,,

A model for an ion immersed in a dielectric medium as a spherical charge surrounded by a region of dielectric gradient has been applied to structured solutions of strong binary electrolytệ^^ In the case of alkaline-earth-metal halides and nitrates, the results show excellent agreement with experimental data

up to concentrations of 2 or 3 mol l-1.36 Changes in cation polarizability observed

on hydration have been described by a model which attributes the changes solely

to solvent p e r t ~ r b a t i o n ~ ~ Hydration structures for alkali-metal cations have been generated from the results of a number of energy ~ a l ~ ~ l a t i o n ~ ~ ~ For Lí and Ná

a tetrahedral inner solvation sphere is the most stable configuration For K+, Rb',

and Csf, the energy differences between structures are so small that it is impossible to predict with certainty the most stable c~nfiguration.~' CND0/2 calculations have also been effected for solvation of, inter a h , Lí and Ná, by

MeOH.39 The results are compared with experimental data (only partial agree- ment is achieved) and with similar calculations for solvation by water Thermo- dynamic functions for hydration of alkali-metal cations have also been deter- mined: and the effects of solvation on the conductivity of concentrated electro- lyte solutions studied theoretically and ẽperimentallỵ~~

The structures of these ionic solutions have been studied, using X-ray difb-ac- tion,42*43 n.m.r.,4448 and ultrasonic49 techniques X-Ray diffraction measure- ments of aqueous NaI showed that the Ná ion is bonded to cụ four water molecules at a Ná - - 0 distance of cạ 0.24 nm Similar experimental data for aqueous CaBr, can be rationalized with both six- and eight-fold co-ordinate Ca2+ ions In both solutions, the halide ion is approximately octahedr- ally c o - ~ r d i n a t e d ~ ~ ' ~ ~

of aqueous LiIO, solutions containing ađed iodic acid or iodates have established that, up to concentrations of LiI03 of

3 mol l-l, the 10, ion does not substitute in the first hydration shell of the Lí ion

Studies of 7Li n.m.r relaxation

35 J W Kress, Ẹ Clementi, J J Kozak, and M Ẹ Schwartz, J Chem Phys., 1975, 63, 3907

36 L W Bahe and D Parker, J Amer Chem SOC., 1975, 97, 5664

37 H Coker, J Phys Chem., 1976, 80, 2084

38 K G Spears and S Y Kim, J Phys Chem., 1976, 80, 673

39 M Salomon, Canad J Chem., 1975, 53, 3194

40 R Jalenti and R Caramazza, J C S Faruday I, 1976, 72, 715

4 1 D Ẹ Goldsack, R Franchetto, and Ạ Franchetto, Canad J Chem., 1976, 54, 2953

42 M Maeda and H Ohtaki, Bull Chem SOC Japan, 1975, 48, 3755

43 G Licheri, G Piccaluga, and G Pinna, J Chem Phys., 1975, 63, 4412

L A Arazova, N V Bryushkova, Ẹ Ẹ Vinogradov, Ị M Karataeva, and R K Mazitov, Russ J

Inorg Chem., 1976, 21, 3

44

45 W J deWitte, R C Schoening, and Ạ Ị Popov, Inorg Nuclear Chem Letters, 1976, 12, 251

46 J W Akitt and R H Duncan, J C S Furuday I, 1976, 72, 2132

47 L Simeral and G Ẹ Maciel, J Phys Chem., 1976, 80, 552

48 M C R Symons, Spectrochim Actu, 1975, 31A, 1105

49 G Ạ Ivashina, T S Kuratova, M 0 Tereshkevich, and V G Korovina, Russ J Phys Chem.,

1975, 49, 1185

Elements of Group I 9

Cs n.m.r data4’ for caesium salts in H,O and in various non-aqueous solvents

have been interpreted in terms of the formation of contact ion-pairs, even in polar solvents of high donicity The large radius and concomitant low charge/surface ratio of Cs’ make it a poorly solvated ion, and caesium salts are more liable to form ion pairs than are Li’ or Na’

’H n.m.r data for aqueous solutions of Be(NO,), and BeCl, have been

interpreted46 as arising from rapid proton exchange between bulk H 2 0 and H,O

in three ionic environments: (i) the cationic complex Be(H,O):’, (ii) a second hydration sphere oriented by the electric field of the cation, and (iii) H,O near the anions It has been suggested that the fact that a known tetrahydrated cation, Be(H,O):+, gives results which are consistent with a primary co-ordination number of 4 is a key result, and that it gives strong support to the contention, based on similar results for M’ ions, that these are also t e t r a h ~ d r a t e d ~ ~ Unfortu- nately, in a related 2sMg F.T n.m.r study47 of aqueous solutions of magnesium salts, it was found to be impossible to predict, a priori, the relative importance of the solution structures considered The effect of temperature and of added aprotic solvents (e.g MeCN) on the ‘H n.m.r spectra of H,O and MeOH solutions containing Mg” (and A13’) have been a ~ c e r t a i n e d ~ ~ The data are thought to be indicative of strong secondary solvation, effected principally via hydrogen bonding, but with a small contribution from the electrostatic effect

An ultrasonic study of aqueous solutions of alkaline-earth-metal salts has been

~ n d e r t a k e n ~ ~ The observations suggest that the stability of the solvated structures depends on the capacity of the ions for hydration and complex formation, their dimension, and their shape

Ionic solvation in H,O+cosolvent mixtures has been the subject of a num- ber of recent ~ ~ m m u n i ~ a t i o n ~ ’ ~ - ~ ~ Cosolvents have included acetone,” form- amide,’* NN-dirnethylf~rmamide,’~ NN-dimethyla~etamide,’~ t-butyl alcoh01,’~ and dioxan.” Interpretation of ‘H n.m.r data (173-303 K) for solutions of Be(N03), in aqueous acetone solutionsso has shown that Be2+ is present mainly in the form of tetra-aquo complexes, coexisting with (probably) polymerized hydroxo(oxo)diaquo complexes The existence of the tetra-aquo complex has been confirmed by analyses of ”0 n.m.r spectra of aqueous Be(NO,), The formation of solvated cationic species in H20 i- formamide (Na+)’l and H 2 0 +

DMF (Li+, Na+, K+)52 mixtures has also been investigated in a study of the

viscosities of these solutions The interaction of lithium salts with dilute H,O+ DMA mixtures has been studied, using 13C n.m.r technique^;'^ the results have been interpreted in terms of the transient species Li’(H,O),DMA and Li+(H20)5DMA Thermodynamic parameters for the transfer of alkali-metal salts from H 2 0 into HzO + t-butyl alcohol (MCl; M = Li, Na, K, Rb, or C S ) ’ ~ and into H,O + dioxan (LiC1, NaCl, CsI)’’ mixtures have been ascertained Similar ther- modynamic data for the transfer of, inter a h , BaZ+ from H,O into methanol,

133

5 0 V A Shcherbakov and 0 G Golubovskaya, Russ J Inorg Chem., 1976, 21, 28

5 1 J M McDowall, N Martinos, and C A Vincent, J C S Faraday I, 1976, 72, 654

53 M J Adams, C B Baddiel, G E Ellis, R G Jones, and A J Matheson, J C S Faraday 11, 1975,

71, 1823

54 C F Wells, J C S Faraday I, 1976, 72, 601

10 Inorganic Chemistry of the Main-Group Elements

generally a methyl group

Figure 2 Solvation shells about M2+ in (a) water and (b) dipolar aprotic solvents; R is

(Reproduced by permission from J Amer Chem SOC., 1975, 97, 3888)

hexamethylphosphoramide, acetonitrile, DMF, and DMSO have been deter- mined.56 It has been noted that divalent cations have more than one layer of solvent molecules in their solvation shells, for most of the solvents studied Whereas hydrogen bonding is thought to be the mechanism whereby hydration shells are built up, extension to secondary shells in the case of dipolar aprotic solvents is possible only through alternative and weaker mechanisms, such as enhancement of the induced dipoles in the first solvation shell A pictorial

representation of these two schemes for solvation of M2+ ions is shown in Figure

The ‘effective’ solvation numbers (i.e total number of moles of solvent solvated

to one mole of solute) of NaI, KI, LiN03, LiClO,, L X (X=Cl, Br, or I), and CaCl, and of LiC1, LiBr, LiN03, and LiC104 in MeOH have been deduced from

‘H n.m.r studiess7 and conductivity experiment^,^^ respectively The solvation numbers are quite similar to hydration numbers; this observation is accepted as evidence that both solvents bind primarily through the oxygen atom of the solvent and not the hydroxyl proton Furthermore, it is thought that the positive ion is more highly solvated than the negative ion, and that M2+ ions are more effectively

solvated than M’ ions.57

The conductivities of MClO, (M=Na, K, Rb, or Cs) in ethylene glycol have been determined and the temperature coefficients of their mobilities estimated;” the analysis of the data shows that the M’ ions are strongly solvated Observa- tions noted in studies of the viscosities of solutions of MI (M = Li, Na, K, Rb, or Cs) in DMSO also indicate that solvation of M’ is important in this

2.56

56 G R Hedwig, D A Owensby, and A J Parker, J Amer Chem Soc., 1975, 97, 3888

57 F J Vogrin and E R Malinowski, J Amer Chem SOC., 1975, 97, 4876

” P A Skabichevskii, Russ J Phys Chem., 1975, 49, 100

59 R Fernandez-Prini and G Urrutia, J C S Faraday I, 1976, 72, 637

Elements of Group I 11

The effect of triethanolamine (TEA) on the conductances of solutions of alkali-metal 2,4-dinitrophenolates in THF has been ascertained;6' the observed increase in conductivity in the presence of the TEA has been interpreted as due to formation of cation-ligand and ion pair-ligand complexes The structures of the M'-TEA complexes (1) are assumed to be similar to that found in the Na' solid-state complex; the three hydroxyethyl groups of the TEA are envisioned to

form a pocket of Lewis-base cations which can accept and surround the M' ions.61

0-f

(1)

1.r and 'H n.m.r spectra of HDO and of MeOH, at low concentration in MeCN, propylene carbonate, 1,1,3,3-tetramethylurea, and NN-dimethyl- formamide containing various salts [LiClO,, LiBr, Sr(C104)2, Ca(SCN),], have been determined at 308 f 2 K.62 The results suggest the presence of solvent- bonded, cation-bonded, anion-bonded, and solvent-shared or solvent-separated ion complexes.62

5 Simple Compounds of the Alkali Metals

This section deals principally with binary derivatives of the alkali metals; ternary compounds are omitted since they are considered, as appropriate, either elsewhere in this Report or in that covering the inorganic chemistry of the transition metals.63 Included here are subdivisions relating to hydrides, oxides and related species, and halides Compounds of Group IV and V non-metals are not discussed because of the paucity of data A separate section, entitled 'Molten Salts', dealing with the chemistry of molten halides (and nitrates) as solvents, is also included

Hydrides.-Several papers describing theoretical analyses of alkali-metal hydride molecules have been The applicability of potential-energy func- tions for these molecules has been examined? and the mixing of ionic and covalent configurations for NaH, KH (and MgH') Possible low- energy paths for the formation of the Li - - - H bond have been

and the spectroscopic properties of, inter alia, LiH calculated.68

The preparation of NaH has been the subject of two communications.69~70 The

H B Flora and W R Gilkerson, J Phys Chem., 1976,80,679

62 I D Kuntz and C J Cheng, J Amer Chem Soc., 1975, 97,4852

63 'Inorganic Chemistry of the Transition Elements', (Specialist Periodical Reports), ed B F G

64 M M Pate1 and V B Gohel, Spectrochim Acra, 1975, 3% 855

65 R W Numrich and D G Truhlar, J Phys Chem., 1975, 79, 2745

67 R Datta, Indian J Chem., 1976, 1 4 4 269

6a A M Semkow and J W Linnett, J C S Faraday Ll, 1976, 72, 1503

69 J Subrt, P Kriz, J Skrivanek, and V Prochazka, Coll Czech Chem Comm., 1975, 40, 3766

Johnson, The Chemical Society, London

W B England, N H Sabelli, and A C Wahl, J Chem Phys., 1975, 63,4596

12 Inorganic Chemistry of the Main-Group Elements

product of the simplest synthetic route (direct reaction of the elements at increased pressure and temperature in a rotating autoclave) is a sintered substance

of low reactivity, contaminated with Na, and being of stoicheiometry NaH,.,.69 In

the presence of catalysts (e.g R,CHCHO, R,CHCR,OH, R,CHCHROH, and

K,CHCO,H), however, a product of stoicheiometry NaH and of large specific

area is ~ b t a i n e d ~ * The kinetics of the uncatalysed reaction (conditions: 5-

40 atm, 543-613 K) have been elucidated, and an apparent activation energy of 54.27 kJ mol-' has been determined.69

Oxides, Hydroxides, Sulphides, etc-The chemistry of rubidium and caesium suboxides has been studied by Simon and c o - w ~ r k e r s ~ ~ - ~ ~ The preparation and crystal growth of Rb6O;l Rbg02,71 cs70,72 and C S , O ~ ~ has been described The exact formula, [Rb902]Rb3, and structure of Rb60 have been derived from

single-crystal data, the crystals being grown at temperatures below 265 K in a

Weissenberg camera.71 The characteristic [Rb902] units (Figure 3a), in which the oxygen atoms are octahedrally co-ordinated, occur as in Rb902 itself, alternating with layers of metallic Rb Similar structural chemistry is observed in the caesium suboxides, in which the [Csl1O3] unit (Figure 3b) is a recurrent moiety; thus, low-temperature (103,253 K, 243 K, C S ~ O ~ ~ ) single-crystal X-ray diffrac- tion studies show that the structures of C s 7 0 and @s,O correspond to the formulae [CsllO,]Csl, and [Cs,,O,]Cs, respectively In Cs,O, the [Csl103] clus-

ters, in which the oxygens are again octahedrally co-ordinated (Figure 3b), form a

n

Figure 3 Schematic representations of (a) the Rb,O, moiety in Rb,O, and (b) the Cs,,O,

[Reproduced by permission from (a) Reu Chim minerale, 1976, 13, 98, and (b) 2 anorg

moiety in Cs,O

Chem., 1976, 423, 2031

7 1 A Simon and H.-J Deiseroth, Rev Chim minerale, 1976, 13, 98

7 3 A Simon, H.4 Deiseroth, E Westerbeck, and B Hillenkotter, 2 anorg Chem., 1976, 423, 203

Elements of Group I 13 hcp arrangement, the single Cs atoms occupying the quasi-octahedral sites of this arrangement, as in the case of NiAs7,

UPS [He (I)] data for the suboxides Cs1103, [ C S ~ ~ O ~ ] C S ~ ~ , and [Cs1103]Rb7 have been determined at 98*5 K.74 Extremely narrow oxygen 2p levels are observed (Table 4) as well as significant differences in the binding energies of the

5p levels of chemically different Cs atoms The results are rationalized in terms of the structurally derived bonding models discussed above.74

Table 4 Binding energieslev in alkali-metal s ~ b o x i d e s ~ ~

13.2 14.0 13.1

The standard enthalpy of formation of Li,O, AHf)(Li,O,c,298.15 K) has been

calculated to be (-597.9 f 0.3) kJ mol-’ in a determination of the enthalpy of

reaction of Li,O with H,0.7s

An abortive attempted synthesis of Li(0,) [and of Ca(O,),], involving the oxidation of LiOH [Ca(OH)2] in a low-pressure discharge, sustained in oxygen, has been reported;76 the sole products of the reaction were Li,O, (CaO,)

of the melting temperatures of K,O (1013 K), KO, (778 K), and K 2 0 2 (818K), as well as the crystalline transition (dimorphous /3- tetragonale P-NaC1 type cubic) temperature of KO2 (425 K), has been under-

taken, using fritted CaO crucibles The crystal symmetries of the two KO,

modifications, of K 2 0 (cubic anti-CaF,), and of K 2 0 2 (orthorhombic) were

confirmed by X-ray diffraction techniques.77 The melting temperature of KO2 has also been determined in a study of the KO2-KNO, phase diagram.78 The

experimentally determined value for commercial KO, (773 f 1 K) was corrected for assumed KOH impurities (xKOH=0.045) to give an a posteriori value of (784f2) K The KO,-KNO, phase diagram is a simple eutectic system, with eutectic temperature and composition 495 f 1 K and 34 mol % KO,, respectively Spectroscopic studies of Li(OH),H,O (i.r.),79 Li(OD),D,O (i.r.?’ ,H n.m.r.80), and M(OH),nH,O (M = Rb or Cs; n = or 1) (i.r.)79 have been effected Interpre- tation of the i.r data for Li(OH),H,O is said to confirm the presence of co-ordinated H 2 0 and OH- ion The H,O and OH- ions in Li(OH),H20 form discrete, planar, hydrogen-bonded [(OH-),(H,O),] anionic units, rather than the extended chains observed in other alkali-metal hydroxide hydrates The ,H n.m.r study (82K) of Li(OD),D,O has shown that the crystal is ordered The OD- points along the c-axis of the crystal and the plane of the D 2 0 molecule is

A d.t.a

7 5 G K Johnson, R T Grow, and W N Hubbard, J Chem Thermodynamics, 1975, 7 , 781

76 P Sadhukan and A T Bell, J Inorg Nuclear Chem., 1976, 38, 1570

77 A deKozak, J.-C Bardin, and A Erb., Reu Chim minerale, 1976, 13, 190

7 8 J M deJong and G H J Broers, J Chem Thermodynamics, 1976, 8, 367

79 I Gennick and K M Harmon, Inorg Chem., 1975, 14, 2214

Faraday II, 1975, 71, 1352

14 Inorganic Chemistry of the Main- Group Elements

perpendicular to the same direction, giving rise to strong but markedly non-linear hydrogen bonds between the two species.*o

The phase relationships between MOH (M=Li, Na, or K) and Ba(OH), have been elucidated.*l Although Ba2’ ions cannot be inserted in the LiOH lattice, their penetration into those of NaOH and KOH is facile, the probability of insertion being greater with KOH Conversely, the probability of insertion of alkali-metal cations into Ba(OH), is low In all three systems, an intermediary, non-stoicheiometric phase with composition close to MOH,2Ba(OH), (M = Li,

Na, or K) is formed.81

Alkali-metal polysulphides have been the subject of a number of recent publications.82-86 The central theme of most of these papers is the polysulphide anion; hence the data will not be considered in detail in this Chapter

Halides.-Theoretical calculations have been performed on both alkali-metal halide m 0 1 e c u l e s ~ ~ ~ ~ ~ and cry~tals.~’-’~ In an analysis87 of the dipole moments of alkali-metal halide molecules, the extent of effective charge transfer was found to vary from 0.76 (LiI) to 0.99 (CsF), in an order that is predictable from the Periodic Table

Expressions for the force constant, i.r absorption frequency, Debye tempera- ture, cohesive energy, and atomization energy of alkali-metal halide crystals have been ~btained.~’”~ Gaussian and modified Gaussian interatomic functions were used as a basis; the potential parameters were evaluated, using molecular force constants and interatomic distances A linear dependence between spectroscopi- cally determined values of crystal ionicity and crystal parameters (e.g interatomic

distances, atomic vibrations) has been observed.” Such a correlation permits quantitative prediction of coefficients of thermal expansion and amplitude of thermal vibrations of the atoms The temperature dependence (295-773 K) of the atomic vibrations for NaF, NaCl, KC1, and KBr has been determined,92 and molecular dynamics calculations have been performed on LiI and NaC1.93 Empiri- cal values for free ion polarizabilities of alkali-metal, alkaline-earth-metal, and halide ions have been obtained from static crystal polarizabilities;94 the results for the cations are in agreement with recent experimental and theoretical work The adsorption of H,O on a variety of alkali-metal halide crystals has been

studied by i.r and far4.r spectro~copy.’~ For the majority of halides (typically

81 M Michaud, G Ado, and G Papin, Bull Soc chim France, 1975, 1479

82 J.-M Letoffe, J.-M Blanchard and J Bousquet, Bull SOC chim France, 1976, 395

83 H H Eysel, G Wieghardt, H Kleinschmager, and G Weddigen, Z Naturforsch., 1976,31b, 415

84 G J Janz, J W Coutts, J R Downey, and E Roduner, Inorg Chem., 1976, 15, 1755

G J Janz, J R Downey, E Roduner, G J Wasilczyk, J W Coutts, and A Eluard, Inorg Chem.,

1976,15, 1759

8 5

86 B Kelly and P Woodward, J C S Dalton, 1976, 1314

g7 R L Matcha and S C King, J Amer Chem Soc., 1976, 98, 3420

89 K P Thakur and L Thakur, Indian J Chem., 1976,14A, 97

90 K P Thakur, J Inorg Nuclear Chem., 1976, 38, 1433

91 S Deganello, Z Krist., 1975, 142, 186

92 S DeganeUo, Z Krist., 1975, 142, 45

93 J Michielsen, P Woerlee, F van den Graaf, and J A A Ketalaar, J C S Faraday II, 1975, 71,

94 H Coker, J Phys Chem., 1976, 80, 2078

K B Hathaway and J A Krumhansl, J Chem Phys, 1975, 63, 4313

1731

Elements of Group I 15 NaCl), two surface H 2 0 species are inferred: (2) involves hydrogen bonding of both hydroxyl bonds to halide ions whereas (3), which occurs at higher coverages,

involves hydrogen bonding of one hydroxy-group only to halide ions Lithium salts exhibit only (2) at all coverages up to mon01ayer.~~ The adsorption potential

of H, and of N, on the [loo] plane of a distorted NaCl lattice has also been investigated .96

CsBr, has been prepared in high purity; its enthalpy of formation, AH, (CsBr,,c), has been determined by solution calorimetry to be -433.8 f 2.0 kJ r n ~ l - ~ ~ ' Using ionic models, the energies (and entropies) of a number of configurations of M& (M = Li or Na) ions have been ~ a l c u l a t e d ~ ~ The most stable configuration is that with a linear arrangement of atoms (Dmh); the calculated entropy for this configufation agrees with the experimental value

Molten Salts.-Interest in the solution chemistry of molten salts (of both alkali- metal and alkaline-earth-metal cations) has been maintained during the period of this Report; as in previous Reports, the majority of the abstracted data describes aspects of the chemistry of halide and nitrate melts

Halides In a study of emulsions in molten salts, the concentration and particle size distribution of dispersed Li in molten LiCl have been examined;"' the influence

of Li20 and of Li,N has also been considered The solubility of I2 in fused MI (M = Li, Na, K, or Cs) has been determined."' Analysis of the results shows that M+ cations, I2 molecules, and I- and 13 anions are present, the proportion of 1; increasing in the sequence KI < RbI < CsI The solubility of MgO in fused MC1 (M=Na, K, Rb, or Cs),lo2 of TiO, in fused MCl, (M=Mg, Ca, or Sr),lo3 and of MOCl (M = Y, La, or Nd) in MC12 (M = M g , Ca, Sr, or Ba)lo4 has been measured The hypothesis that the dissolution mechanism for the MgO-MCI solutions

96 A Ben Ephraim and M Folman, J C S Furuday 11, 1976,72,671

97 A K Shukla, J C Ahluwalia, and C N R Rao, J C S Furaduy I, 1976,72,1288

98 L R Morss, J Chem Thermodynamics, 1975, 7 , 709

* A V Gusarov, Russ J Phys Chem., 1975, 49, 1576

loo T Nakajima, K Nakanishi, and N Watanabe, Bull Chern SOC Japan, 1976, 49, 994

lo' L E Ivanovskii, W N Nekrasov, V S Mironov, and V A Biryukov, Russ J Phys Chern., 1975,

16 Inorganic Chemistry of the Main-Group Elements

involves physical introduction of MgO into the free space in the melt structure has been advanced.", The extent of solubility in Ti02-MC12 solutions is found to be almost an order of magnitude greater than in the corresponding alkali-metal halides (with the exception of LiC1).lo3

Calorimetric data have been obtained for a number of fused salt systems.'0s-108 The enthalpies of mixing of LiF-NaF, NaF-KF, LiF-KF (all at 1360K), and of LiF-KF (at 1176 K) mixtures have been redetermined by Kleppa et aZ.los by a direct mixing technique The results are in reasonable agreement with values previously reported by Kleppa et aLio9 and by Gilbert,'" but differ considerably

from the recent data of MacLeod and Cleland."' Enthalpies of formation of NaCl-MgCl,, KC1-MgCl,, and NaC1-KC1-MgCl, mixtures have been determined calorimetrically;lo6 standard enthalpies of formation of the compounds KCl,MgCl, (-9.04k 0.46 kJ mol-') and 2NaC1,MgC12 (5.44 f 0.88 kJ mol-l) have been derived A physicochemical study (1193-1650 K)ll2 of KC1-MgC12 melts has shown that vapour-pressure isotherms are of limited use in establishing the complexes present in the liquid phase

A semi-quantitative model, based on the assumption of dissociated complex species in the melt, has been developed to aid interpretation of experimental enthalpies of mixing of molten sa1ts.'O7 Comparison of estimated equilibrium constants and enthalpies of formation of the complex species (typically LaClg- and GdCg-) present in the solutions (KC1-LaCl,, CsCl-GdCl,) with experimental data for the corresponding solid-state compounds (K,LaCl,, Cs,GdCk) shows satisfactory agreement Data for the enthalpy of mixing of LiF-ZnF, (1273 K), NaF-ZnF, (1279 K), and KF-ZnF, (1232,1325 K) liquid mixtures indicate that

the principal anionic complex in these systems is Z n K or possibly a polymer of this composition.108 Evidence has also been put forward for the presence of FeCl,, Fe2C1;, and Fe,C16 in a potentiometric and spectrophotometric study (573 K) of KCl-FeC1, melts.'13 Certain identification of the complexes in the LiC1-ThCl, system was not possible in a study (963-1203 K) of the vapour phase

in equilibrium with the melt.'',

The reaction of MS, (M =Ti or Nb) with H2S in alkali-metal halide melts in a

flow reactor system (1073-1273 K) yielded layered ternary sulphides, A,,sMS2

(A = Li,Na,K,Rb, or Cs; M =Ti or Nb)."' ZrP,07 and MZr,(PO,), (M = Na or K) are formed on reaction of Zr(PO,), with MCl (M=Na or K) rnelts.'l6 The influence of pretreatment conditions and of cover gas (air, Ar, or Cl,) is consi- dered; whereas ZrP,O, is converted into MZr,(PO,), in the presence of air, such a change is not observed in the presence of Ar or C1,.'16

lo5 K C Hong and 0 J Kleppa, J Chem Thermodynamics, 1976, 8, 31

'06 G Yu Sandler, I L Reznikov, and E I Yaskelyainen, Russ J Phys Chem., 1975, 49, 462

lo' F Dienstbath and R Blachnik, Z anorg Chern., 1975, 417, 100

log J L Holm and 0 J Kleppa, J Chem Phys., 1968, 49, 2425

'lo R A Gilbert, J Phys Chem., 1963, 67, 1143

'11 A C Macleod and J Cleland, J Chem Thermodynamics, 1975, 7 , 103

'12 B P Burylev and V L Mironov, Russ J Phys Chem., 1975, 49, 937

H A Andreasen and N J Bjerrum, Inorg Chem., 1975, 14, 1807

'14 M V Smirnov, V N Khudolozhkin, and V Ya Kudyakov, Russ J Phys Chem., 1975, 49, 822

'15 R Schollhorn and A Lerf, J Less-Common Metals, 1975, 42, 89

'16 A I Kryukova, N V Vorob'eva, I A Korshunov, G N Kazantsev, and 0 V Skiba, Russ J Inorg

0 J Kleppa and M Wakihara, J Inorg Nuclear Chem., 1976, 38, 715

1-13

Chem., 1976, 21, 228

Elements of Group I 17

The stoicheiometry and mechanism of the cathodic reduction of HCl dissolved

in LiCI-KCl eutectic mixture have been elucidated.' l7 Complete dissociation into H' and C1- ions occurs, followed by a two-step cathodic evolution of H, [equation (1 l)]; the charge-transfer step is reversible and faster than the combination

reaction Interaction of Sn2+ ions with F-, Br-, I-, and CN- ions has been studied

in an equimolar NaC1-KC1 melt and the data have been compared with those of the similar Pb2' system.'" Sn2' is capable of forming complexes with halide ions

by a single co-ordination step; under the same conditions, Pb2' does not show the ability to form complexes with Br-, but is capable of co-ordinating up to three CN- ions The stability constants of the complexes formed [MF', SnBr', MI',

MCN', Pb(CN),, and Pb(CN), (M=Sn or Pb)] have been determined Four solvated Se species of low oxidation state (possibly Sei+, Sei', Set;, Se:;) have been detected in a spectrophotometric study"' of the reduction (by Se) of dilute solutions of SeCl, in NaCI-AlCI, eutectic mixture

Several studies of the behaviour of the lanthanides and actinides in molten halides have been undertaken recently '20-'25 E.m.f measurements have estab- lished that Nd3+ ions are in equilibrium with the metal in LiCI-KC1 eutectic melt containing 2 wt O/O NdC1, (700-912 K),12' and that Th4' ions exist in solutions of

ThCI, in LiC1-KCI eutectic melts (573-1373 K).12' This latter observation con- tradicts an earlier report of thorium of low oxidation state [namely (II)] in these melts; the erroneous data are explained on the basis of contamination by Tho, and on misinterpretation of the e.m.f -composition plots.121 Reactions of Th and ThCl, with UO, and (Th,U)02 in fused LiC1-KCl and NaC1-MgCl, eutectic melts

have also been studied (773-973 K),12, the equilibrium (12) being considered in

some detail By sparging gaseous mixtures (containing H20, HCl, Cl,, N,) of

known composition through the melts, a study of the redox behaviour of Np [equations (13) and (14)] in solution in the fused LiC1-KCl eutectic mixture has

NpOZ+ + C1- -+ N p O l + iC1, (13)

N p O l + 4HC1 + Np4+ + 2H,O + iC1, + 3C1- (14)

been effe~ted.',~ The investigation was rendered quantitative by following the variation in concentration of the Np species, using visible and near-i.r absorption spectroscopy Thermodynamic properties of dilute solutions of actinide chlorides

in LiCl-KC1 (UCl,, UCl,, NpCl,, NpCl,, and PuC1,) and LiC1-NaC1 (UCl, and

UCl,) eutectics have also been investigated (673-823 K).124 The heterogeneous

'18 Yu K Delimarskii, L I Zarubitskaya, and V F Grischenko, Russ J Inorg Chem., 1976,21,221

'" R Fehrmann, N J Bjernun, and H A Andreasen, Inorg Chem., 1975,14, 2259

120 A P Bayanov, E N Ganchenko, and Yu A Afanas'ev, Rum J Phys Chem., 1975, 49, 1442 12' P Chiotti and C H Dock, J Less-Common Metals, 1975, 41, 225

lZ2 P Chiotti, M C Jha, and M J Tschetter, J Less-Common Metals, 1975, 42, 141

123 R Lysy and G Duyckaerts, Inorg Nuclear Chem Letters, 1976, 12, 205

N Q Minh and B J Welch, Austral J Chem., 1975, 28, 2579

18 Inorganic Chemistry of the Main- Group Elements

catalytic reduction of Uv to UIV by H, [equation (15)] has been studied at 328 K,

in molten LiF-BeF,-ThF, (72-16-12 mol %), which is the composition of the fuel carrier salt for the molten-salt breeder ~ e a c t 0 r l ~ ~ The hydrogen reduction is rate-determining; the application of Pt catalysts to achieve a 10- to 100-fold increase in reaction rate has been r e ~ 0 r t e d l ~ ~

Nitrates Thermodynamic parameters ( A H = 114 kJ mol-'; A P = 62 J rno1-l K-')

for reaction (16) in NaN0,-KNO, eutectic melt have been determined (500-

700 K),126 Corresponding data ( A H = 95 kT mol-'; AS*= 84 J mol-' K-l) for reac- tion (17) have also been calculated Physicochemical analyses have been carried out on NaN03-KN0,,127 Ca(N0,),-Sr(N0,),,128 Sr(N03)2-Ba(N03)2128 binary

systems (generally as part of a quaternary reciprocal system), and LiN03-

R~NO,-CSNO,~~' and LiN03-KN03-Sr(N03)2130 ternary systems

CrOz-, MnO,, Fe203, and Cr,O,, respectively In all cases, S2- was oxidized to SO:- and the nitrate melt was reduced to nitrite and nitrogen 0 ~ i d e s l ~ '

The electrochemical behaviour of H,O in molten LiN0,-KNO, eutectic has

been e 1 ~ c i d a t e d l ~ ~ Contrary to previous reports, electroreduction of H,O is

coupled with nitrite reduction, probably involving an autocatalytic mechanism and

an adsorbed intermediate

The kinetics of reaction (18) have been ascertained by allowing Na4P,0, to react with nitrate melts in the temperature range 610-625 K.13, The reaction only occurs in the presence of Li' ions; this observation is rationalized by a reaction mechanism in which P204- experiences a change in its average co- ordination with increasing Li' concentration, resulting in the P-0-P bridge being made more susceptible to rupture by NO, at higher Li' 1 e ~ e l s l ~ ~

P,O;- + 2N0; -+ 2PO:- + 2N0, (g) + i02 (8) (18) The reactions of a number of titanium-(m) and-(Iv) compounds (K2TiFs, TiCl,, TiO,, TiC14)134 and of iron-(II), -(I~I), and -(w) compounds [K2Fe04, FeCl,,

A D Kelmer and M R Bennett, Inorg Nuclear Chem Letters, 1976, 12, 333

lZ6 F Paniccia and P G Zambonin, J C S Faraday I, 1976, 72, 1512

lZ7 H Aghai-Khafri, J P Bros, and M Game-Escard, J Chem Thermodynamics, 1976, 8, 331

P I Protsenko and L M Kuvakina, Russ J Inorg Chem., 1975, 20, 924

Yu G Litvinov, I I Il'yasov, and V I Sawa, Russ J Inorg Chem 1975, 20, 1418

A I Kryukova and I A Korshunov, Rwss.J Znorg Chem., 1975,20,809

1 2 8

1 2 9

13' B J Meehan and S A Tariq, Austral J Chern., 1975, 28, 2073

1 D G Lovering, R M Oblath, and A K Turner, J C S G e m Comm., 1976, 673

133 J L Copeland, A S Metcalf, and B R Hubble, J Phys Chem., 1976, 80, 236

Elements of Group I 19

FeO(NO,), FeS04,2H20, FeC1,,4H20, FeC0,]135 have been studied in molten LiNO,-KNO, eutectic In the Ti study, which was also effected in basic nitrate melt solutions containing Na202, Na20, or NaOH, TiO, (as anatase) and titanates

of varying basicity were produced, depending on base concentrations and temper- ature; when C1- was present, (NO),[Ticl,] sublimed from the melts.134 For the Fe systems, Fe203 was invariably the final product, although there was evidence for the intermediate formation of higher oxides from K2Fe04 and of ferrate(II1) from FeO(N0,); C1- ions stabilized Fe3' cations in the melt solution, but not Fe2' cations

The kinetics of oxidation of formate in molten equimolar NaNO,-KNO, have been determined (538-585 Although the reactions could not be rep- resented by a simple stoicheiometry, the kinetic analysis indicates that nitrite has

a role as an oxidant and as a catalyst, as well as being a product of the oxidation

A series of reactions, which include acid-base-dependent and -independent processes, possibly involving as intermediates NO; and NO' cations and nitrogen oxides, respectively, have been proposed to account for the observed kinetic data 136

6 Compounds of the Alkali Metals containing Organic Molecules or

To simplify the text in this Section, radical anion salts and crown compounds and cryptates are considered collectively in special subdivisions The majority of the data, however, are discussed in subdivisions devoted to derivatives of the indi- vidual alkali metals For those data pertinent to several alkali metals, they are

described once only, in the subdivision of the lightest metal considered

Radical-anion Salts.-Radical-anion salts of the alkali metals have been prepared

in neat solvents under high-vacuum conditions, by bringing a solution of a crown compound in benzene, toluene, or mesitylene into contact with an alkali-metal

Two complexes containing a dilithiated stilbene fragment have been prepared and isolated from the reactions of 1,2-diphenylethane with N-chelated butyl- lithium The molecular and crystal structures of these compounds,

stilbene bis(1ithium tetramethylethylenediamine) (Figure 4a) and stilbene bis(1ithium pentamethyldiethylenetriamine) (Figure 4b), have been determined by

X-ray diffraction techniques Each structure contains two amine-solvated Li

atoms located above and below the olefinic bond of a stilbene molecule The stilbene molecule is planar in both structures, and is in a trans configuration about the C(7)-C(7') bond, which is ca 0.01 nm longer than that in tr~ns-stilbene.'~~

The optical and 13C n.m.r spectra of THF solutions of the related dilithium and

disodium salts of tetraphenylethylene dianion, as well as the spectra of their mixtures, have been examined.139 The data can be rationalized in terms of the

Complex Ions

reaction begins quickly, and is complete after a few hours at 253K

1 D H Kerridge and A Y Khudhan, J Inorg Nudear Chem., 1975, 37, 1893

13' D H Kerridge and J D Bourke, J Inorg Nuclear Chrn., 1976, 38, 1307

1 G V Nelson and A von Zelewsky, J Amer Chem SOC., 1975, 97, 6279

1 M Walczak and G Stucky, J Amer Chem SOC., 1976, 98, 5531

20 Inorganic Chemistry of the Main-Group Elements

AC2'

ACl

c4 C4/

Figure 4 The molecular structures of (a) stilbene bis(1ithium tetramethylethylenediamine) and

(Reproduced by permission from J Amer Chem SOC., 1976, 98, 5531)

(b) stilbene bisflithium pentamethyldiethylenetriarnine)

Figure 5 Environment of the Rb+ ion in biphenylrubidium bis(tetrag1yme)

(Reproduced by permission from J Arner Chem SOC., 1976, 98, 680)

tentative salt structure Li+,Ph2CxPh2,Li+, in which the two CPh, groups are lying in two mutually perpendicular planes One Li' ion is located close to the negative carbon framework and the other is fully solvated by THF molecules some distance away

The molecular and magnetic structures of biphenylrubidium bis(tetraglyme) have been e1~cidated.l~' Single-crystal X-ray diffraction data show each Rb' ion

to be spherically surrounded by 10 oxygen atoms of the solvent molecules (Figure

5 ) , leading to a solvent-separated ion-pair structure E.s.r and n.m.r data are consistent with the observed dimeric structure of the biphenyl anions.14o The disproportionation [reaction (19)] of lithium salts of radical anions of naphthalene, anthracene, tetracene, perylene, and pyrene in Et2Ol4I and of sodium tetracenide in C6&142 has been investigated The magnitudes of the disproportionation constants of the lithium salts are astonishingly great; neverthe- less, an interesting correlation between these values and the cation-anion Coulomb energy has been 0 b ~ e r v e d l ~ ~

Crown and Cryptate Complexes.-Interest in crown, cryptate, and related com- plexes of alkali-metal (and alkaline-earth-metal) ions has been maintained during the period of this Report A new class of ether-ester ligands (4) and (5) has been deve10ped.I~~ Whereas (4) forms complexes with Mg", Ca2', Sr2+, and Ba2+, (5) forms complexes with Ca", Sr*', and Ba2' only The complex between (4) and Mg2' is the first reported Mg2+ crown compound; although the Mg2+ is probably bound within the cavity, it is possible that it may be bound to the externally directed 1,3-dicarboxy-gro~p.l~~

140 J J Mooij, A A K Klaasen, E de Boer, H M L Degens, Th E M van den Hark, and J H

14' G Levin, B E Holloway, and M Szwarc, J Amer Chem SOC., 1976, 98, 5706

1 J Pola, G Levin, and M Szwarc, J Phys Chem., 1976, 80, 1690

143 J S Bradshaw, L D Hansen, S F Nielsen, M F Thompson, R A Reeder, R M Izatt, and J J

Noordik, J Arner Chem Soc., 1976, 98, 680

22 Inorganic Chemistry of the Main- Group Elements

(8) R1 = R2 =But (9) R1 = H; R2 = C,,H,,

A number of crystalline complexes of DB12C4 (6), of DB18C6 (7) and its derivatives (8) and (9), and of DB24C8 (10) with some M' and M2" perchlorates and picrates have been synthesized 144 Identification and characterization was effected by elemental analysis, i.r., u.v., 'H n.m.r spectroscopy, conductivity, and

X-ray diffraction analysis With complexes of (8) and (9), it was not possible to isolate all complexes in the crystalline form; indeed, the steric hindrance afforded

by the alkyl substituents affects the stability of the complexes and hinders the possibility of is01ation.l~~

The crystal and molecular structures of the complex formed between DB24C8

(10) and two molecules of sodium o - n i t r ~ p h e n o l a t e ~ ~ ~ and of the solvated (MeOH

144 Lj Tusek, M Meider-Gorican, and P R Danesi, Z Nuturforsch., 1976, 31b, 330

Elements of Group I 23

Figure 6 Projections of (a) the crown ligand (DB24C8) and Na+ ions on the mean plane of

the 8 ether oxygen atoms, and (b) the o-nitrophenolate ion on the mean plane of the 6 ring carbon atoms, in the crystal formed between DB24C8 and two molecules of sodium o-nitrophenolate The atomic numbering scheme, bond lengths, and Na - * 0 distancesIA are shown

(Reproduced from J C S Dalton, 1975, 2374)

or H20) complex formed between B15C5 (12) and Ca(NCS),146 have been

determined In the Na' complex, the polyether ring folds around the pair of Na' ions (Figure 6a) Each cation interacts with three oxygen atoms of the ligand; each

of the fourth pair of oxygen atoms is 0.2965nm from a cation; not directed towards the cation, and not involved in co-ordination An o-nitrophenolate anion

on each side of the crown ring completes the six-fold co-ordination of the cations; each anion chelates one cation, and the phenolate oxygen (carrying most of the anionic charge) bridges the pair of cations (Figure 6b).145 The molecular structures

of the Ca2' complexes show a new irregular conformation of the crown ether (consistent with i.r spectra) and eight-fold co-ordination of Ca2', comprising five

ether oxygen atoms, two isothiocyanate nitrogen atoms, and one oxygen atom

from the solvent (Figure 7).146

J D Owen and N Wingfield, C S Chem Comm., 1976, 318

24 Inorganic Chemistry of the Main- Group Elements

Figure 7 Co-ordination polyhedra of the Ca2+ ion in BISCS-Ca(NCS),-MeOH

(Reproduced from J C S Chern Cornm., 1976, 318)

Two s t u d i e ~ l ~ ' , ~ ~ ~ of the solution structures of these complexes have been undertaken, using n.m.r spectroscopic techniques The interactions of Na+, K', Cs', and Ba2' with DB18C6 (7), B18C6 (14), and DB30C10 ( l l ) , in H 2 0 , H20-acetone mixtures, and CHCl,, have been studied by 'H- and 13C-n.m.r spectroscopy as a function of concentration and of the anion (I-, SCN-, and C10T).147 Complexes of (7) and (14) have the same structures in solution

1 D Live and S I Chan, J Amer Chem Soc., 1976, 98, 3769

E Mei, J L and Popov, J Chem k.,

148

Elements of Group I 25

as complexes of (7) in the crystalline Although K', Cs', and BaZ+ derivatives of (11) in solution were found to have the same configuration as that

reported for the crystalline K+ complex,'5o the Na+ complex has an alternative struc-

ture.14' Evidence has been presented for complete removal of the solvation sphere

of the cation on complexation to (ll), but this is not the situation for (7) and (14) The existence of a previously postulated 'sandwiched' complex with a Cs' ion between two molecules of (7) in solution has also been demonstrated 133Cs n.m.r studies of Cs' complexes of (16) and (17), in propylene carbonate (PC), pyridine

(PY), acetone, DMF, DMSO, and acetonitrile (AN), have shown that the solvent plays an important role in the complexation process.148 In PC, PY, and acetone, the data for the crown complex indicate a two-step reaction with increasing ligand concentration: (i) the formation of a stable 1 : 1 complex, and (ii) the addition of a second molecule to form a 2 : 1 'sandwich' complex (see above147) In DMSO and

AN, 'sandwich' complexes are not The cryptate complex is less stable than the crown complex Furthermore, the Cs' ion is either not fully enclosed by the ligand or the solvent can interact with it through the cryptate openings.148 Several papers defining the thermodynamic properties (stabilities) of crown and cryptate complexes of M' and M2' ions have been published r e ~ e n t l y ; l ~ l - ' ~ ~ the origins of the stability sequences are generally discussed in terms of cation size and ligand structural features (topology, binding sites, etc.) Stability constants, at infinite dilution, for complex formation of DB18C6 (7) with, inter alia, Nat, K+,

Rb', Cs', Sr", and Ba2' have been determined spectrophotometrically in aque- ous The monodissociated ion pairs (SrCl)' and (BaCl)' complex more

strongly with (7) than the free ions Sr2' and Ba2' The behaviour of (7) with M2'

ions is much more sensitive to their ionic size than in the case of M' ions.151 Similar data for complex formation of (7) with M' ions have been determined in

DMSO, DMF, and PC.152 The results show that the selectivity of (7) towards M'

is dependent on ionic diameter, cavity size, and the donor number of the solvent The effect of substituents on the stability of Na' and K complexes of B15C5 (13)

149 D Bright and M R Truter, J Chem Soc (B), 1970, 1544

M A Bush and M R Truter, J C S Perkin U, 1972, 345

lS1 E Shchori, N Nae, and J Jagur-Grodzinski, J C S Dalron, 1975, 2381

lS2 N Matsuura, K Umemoto, Y Takeda, and A Sasaki, BuII Chem SOC Japan, 1976, 49, 1246 lS3 R Ungaro, B EIHaj, and J Smid, J Amer Chem Soc., 1976, 98, 5198

26 Inorganic Chemistry of the Main- Group Elements and B18C6 (15), in acetone, has been e~tab1ished.l~~ Although the effect is pronounced for Na' complexes of (13), it is much smaller for Na' complexes of (15), being almost non-existent for electron-withdrawing substituents Substituent effects were somewhat larger for K' complexes of (15) Although formation constants could not be determined for K' complexes of (13), substituent effects on complexation were noticeable 153 Concurrent conductivity studies have shown that

1 : 1 and 2 : 1 crown : cation complexes can exist simultaneously in mixtures of K'

with (13).153 Conductivity studies on the association of complexes of (7) with Na' and K' ions and SCN- ions, in nitrobenzene-toluene mixtures, have also been undertaken 155

The stability constants of complexes formed by cryptates (18)-(23) with M'

stability display much higher stability than any previously known complexes The selectivity of the complexes is remarkable The optimum fit of M' into the ligand cavity agrees well with the selectivity of the ligands (18), (19), and (20) for Li', Na', and K', respectively Whereas these smaller ligands display peak selectivity, the larger ones display plateau selectivity, with only small differences in stability for K+, Rb', and Cs' Unusual selectivities are observed for complexes of M2'

ions; for example, the high Ca2'/Mg2', Ca2'/Sr2', and Ba2'/Ca2' ratios for ligands

(18), (19), and (20), respectively Furthermore, M2'/M+ selectivities are of consid- erable interest, particularly the unique selectivity of ligand (18) for Li' over Mg2' and Ca" A marked increase in cryptate complex stability and selectivity is observed in changing solvent from H 2 0 to MeOH.154 The kinetics of complexing

of Ca2' by ligands (18)-(20) have also been e~tablished."~

u b e (18) 1 0 0 (19) 1 1 0 (20) 1 1 1 (21) 2 1 1 (22) 2 2 1 (23) 2 2 2 The crystal structures of Na', K', and Rb' tetranactin complexes have been

The data have been considered in detail in a previous

as a result of abstraction from a preliminary communication.159 published in

lS5 P R Danesi, R Chiarizia, C Fabiani, and C Domenichini, J Inorg Nuclear Chern., 1976,38,1226

R J Pulham, in 'Inorganic Chemistry of the Main-Group Elements' (Specialist Periodical Reports),

ed C C Addison, The Chemical Society, London, 1974, Vol 2, p 28

Elements of Group I 27

Figme 8 Co-ordination of the Li+ ions in lithium tetrakis(dimethylphenylsilyl)rnercurate(xr): only the carbon atoms fotming the cages around the Li' ions are included; the C(2) and C(2') carbons are methyl carbons, while all other carbons are phenyl carbons

(Reproduced by permission from J Amer Chem SOC., 1975, 97, 6261)

Lithium Derivatives.-The crystal and molecular structures of lithium tetrakis(di-

methylphenylsilyl)mercurate(Ir) have been determined.la The Li' ion (Figure 8)

is novelly encompassed in a cage composed of five carbon, three silicon, and one mercury atom The Li + - C distances (0.24-4.26 nm) are slightly longer than those in alkyl-lithium derivatives, but similar to those in lithium-hydrocarbon ion pairs The Li - * Si distances (0.29-0.30 nm) are longer than those observed in silyl-lithium derivatives; the Li * Hg distance is 0.258 nm

In a single-crystal neutron and X-ray diifraction investigation of Li - - - H - - C interactions in LiB(CH,),, the Li atoms are shown to be bridged by the B(CH,),

groups, through linear B - - - CH, - Li and multi-centre fragments (Figure 9).16'

The structural features in the linear B - 9 - CH, - - Li moiety are similar to those found in the intermolecular interaction between tetrameric units in CH,Li, with a trihydrogen-bridged group The other methyl bridging arrangement is similar to that in [(CH,),Al],, with a dihydrogen-bridged linkage Mass spectrometric studies show that LiB(CH,), is also associated in the gas phase.16'

Alkali-metal dimethylformamidyls, MCONMe, (M = Li-Cs), have been pre- pared by direct reaction between the metal and DMF;I6' characterization of the

products was based on elemental analysis, i.r spectroscopy, and t.g.a data Direct

"" M J Albright, T F Schaaf, W M Butler, A K Hovland, M D Glick, and J P Oliver, J Amer

"' W E Rhine, G Stucky, and S W Peterson, J Amer G e m Soc., 1975, 97, 6401

Chem Soc., 1975,97,6261

28 Inorganic Chemistry of the Main- Group Elements

Figure 9 Partial molecular stmcture of LiB(CH,),, showing the bridging and linear methyl

(Reproduced by permission from J Arner Chem SOC., 1975, 97, 6401)

geometry

reaction of Li vapour with alkenes (e g isobutene, butadiene) yields polylithiated alkanes and alkenes, via both Li substitution for H and Li addition to the ethylenic The products were reactive, red-black solids, which, although metallic in appearance, were very brittle.'63

Vibrational spectra of a number of moieties (complex amides, crown complexes, oxide glasses, oxyanions) have been assigned, assuming a basic four-co-ordinate

Li - - - 0 polyhedron [v(asym) = ca 400 cm-1].164 Similar but more limited data were obtained for compounds of Na+, K and Mg2+

Five-fold co-ordinate Li, in the form of a distorted trigonal bipyramid with

Li - - * 0 distances varying from 0.2031 to 0.2122 nm, has been observed in the molecular structure of lithium hydrogen oxydiacetate.165 The bipyramids form pairs by sharing an edge, with a shortest Li * Li distance of 0.3156 nm The interaction of Li', Na+, and Kf with cis- and trans-l-benzyl-2,3-

dibenzoylaziridine in MeCN has been studied by means of 'H n.m.r and i.r

spectroscopy.166 For all cations, association with the cis-isomer is preferred, presumably via chelation at the carbonyl oxygens; the order of association was Li' > Na' > K' At a LiBr : cis-isomer ratio above 0.4, a white crystalline product, which analysed to a 2 : 1 adduct of LiBr, could be isolated.'66 Finally, e.s.r spectra

of the ion pairs formed by the 4-nitropyridine anion radical with Li', Na', and K

in dimethoxyethane and THF have been determined as a function of tempera- ture.16'

J A Morrison, C Chung, and R A Lagow, J Amer Chem SOC., 1975, 97, 5015

C N R Rao, H S Randhawa, N V R Reddy, and D Chakravorty, Specrrochirn Actu, 1 9 7 5 , 3 1 4

1283

H Herbertsson, Actu Cryst., 1976, B32, 2381

A B Norman, G R Smith, and H P Hopkins, J Phys Chem., 1976, 80, 25

P Cremaschi, A Gamba, G Morosi, C Oliva, and M Simonetta, J C S Faraduy 11, 1975, 71,

1829