The chemistry of organic germanium, tin and lead compounds vol 1 1995 patai

The chemistry oforganic germanium, tin and lead compounds The Chemistry of Organic Germanium, Tin and Lead Compounds.. THE CHEMISTRY OF FUNCTIONAL GROUPSA series of advanced treatises un

The chemistry of

organic germanium, tin

and lead compounds

The Chemistry of Organic Germanium, Tin and Lead Compounds Volume 1

Edited by Saul PataiCopyright1995 John Wiley & Sons, Ltd

ISBN: 0-471-94207-3

THE CHEMISTRY OF FUNCTIONAL GROUPS

A series of advanced treatises under the general editorship of

Professors Saul Patai and Zvi Rappoport

The chemistry of alkenes (2 volumes) The chemistry of the carbonyl group (2 volumes) The chemistry of the ether linkage The chemistry of the amino group The chemistry of the nitro and nitroso groups (2 parts) The chemistry of carboxylic acids and esters The chemistry of the carbon nitrogen double bond

The chemistry of amides The chemistry of the cyano group The chemistry of the hydroxyl group (2 parts) The chemistry of the azido group The chemistry of acyl halides The chemistry of the carbon halogen bond (2 parts) The chemistry of the quinonoid compounds (2 volumes, 4 parts)

The chemistry of the thiol group (2 parts) The chemistry of the hydrazo, azo and azoxy groups (2 parts)

The chemistry of amidines and imidates (2 volumes) The chemistry of cyanates and their thio derivatives (2 parts)

The chemistry of diazonium and diazo groups (2 parts) The chemistry of the carbon carbon triple bond (2 parts)

The chemistry of ketenes, allenes and related compounds (2 parts)

The chemistry of the sulphonium group (2 parts) Supplement A: The chemistry of double-bonded functional groups (2 volumes, 4 parts) Supplement B: The chemistry of acid derivatives (2 volumes, 4 parts)

Supplement C: The chemistry of triple-bonded functional groups (2 volumes, 3 parts) Supplement D: The chemistry of halides, pseudo-halides and azides (2 volumes, 4 parts) Supplement E: The chemistry of ethers, crown ethers, hydroxyl groups and their sulphur analogues

(2 volumes, 3 parts) Supplement F: The chemistry of amino, nitroso and nitro compounds and their derivatives (2 parts)

The chemistry of the metal carbon bond (5 volumes)

The chemistry of peroxides The chemistry of organic selenium and tellurium compounds (2 volumes)

The chemistry of the cyclopropyl group (2 parts) The chemistry of sulphones and sulphoxides The chemistry of organic silicon compounds (2 parts) The chemistry of enones (2 parts) The chemistry of sulphinic acids, esters and their derivatives

The chemistry of sulphenic acids and their derivatives

The chemistry of enols The chemistry of organophosphorus compounds (3 volumes)

The chemistry of sulphonic acids, esters and their derivatives

The chemistry of alkanes and cycloalkanes Supplement S: The chemistry of sulphur-containing functional groups

The chemistry of organic arsenic, antimony and bismuth compounds

The chemistry of enamines (2 parts) The chemistry of organic germanium, tin and lead compounds

UPDATES The chemistry of ˛-haloketones, ˛-haloaldehydes and ˛-haloimines

Nitrones, nitronates and nitroxides Crown ethers and analogs Cyclopropane derived reactive intermediates Synthesis of carboxylic acids, esters and their derivatives

The silicon heteroatom bond Syntheses of lactones and lactams The syntheses of sulphones, sulphoxides and cyclic sulphides

Patai’s 1992 guide to the chemistry of functional groups Saul Patai

C Ge, C Sn, C Pb

Copyright  1995 by John Wiley & Sons Ltd,

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Library of Congress Cataloging-in-Publication Data

The chemistry of organic germanium, tin, and lead compounds / edited

by Saul Patai.

p cm (The chemistry of functional groups)

‘An Interscience publication.’

Includes bibliographical references (p - ) and index.

ISBN 0-471-94207-3 (alk paper)

1 Organogermanium compounds 2 Organotin compounds.

3 Organolead compounds I Patai, Saul II Series.

QD412.G5C47 1995

CIP

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0 471 94207 3

Typeset in 9/10pt Times by Laser Words, Madras, India

Printed and bound in Great Britain by Biddles Ltd, Guildford, Surrey

This book is printed on acid-free paper responsibly manufactured from sustainable forestation, for which at least two trees are planted for each one used for paper production.

Contributing authors

Harold Basch Department of Chemistry, Bar-Ilan University,

Ramat-Gan 52900, IsraelCarla Cauletti Dipartimento di Chimica, Universit`a di Roma ‘La

Sapienza’, Piazzale Aldo Moro 5, 00185 Roma, ItalyMarvin Charton Chemistry Department, School of Liberal Arts and

Sciences, Pratt Institute, Brooklyn, New York 11205,USA

Peter J Craig Department of Chemistry, School of Applied Sciences,

De Montfort University, The Gateway, Leicester,LE1 9BH, UK

J T van Elteren Department of Chemistry, School of Applied Sciences,

De Montfort University, The Gateway, Leicester, LE19BH, UK

Marcel Gielen Faculty of Applied Sciences, Free University of Brussels,

Room 8G512, Pleinlaan 2, B-1050 Brussels, BelgiumCharles M Gordon School of Chemical Sciences, Dublin City University,

Dublin 9, IrelandSarina Grinberg Institutes for Applied Research, Ben-Gurion University

of the Negev, Beer-Sheva 84110, IsraelTova Hoz Department of Chemistry, Bar-Ilan University, Ramat-

Gan 52900, Israel

L M Ignatovich Latvian Institute of Organic Synthesis, Riga, LV 1006

LatviaJim Iley Physical Organic Chemistry Research Group, Chemistry

Department, The Open University, Milton Keynes,MK7 6AA, UK

Jill A Jablonowski Department of Chemistry and Biochemistry, University

of South Carolina, Columbia, South Carolina 29208,USA

Helen Joly Department of Chemistry, Laurentian University,

Sud-bury, Ontario P3E 2C6, CanadaThomas M Klap ¨otke Institut f¨ur Anorganische und Analytische Chemie,

Technische Universit¨at Berlin, Strasse des 17 Juni 135,D-10623 Berlin, Germany

Joel F Liebman Department of Chemistry and Biochemistry, University

of Maryland, Baltimore County, 5401 Wilkens Avenue,Baltimore, Maryland 21228-5398, USA

v

P.B 3105, Hamilton, New ZealandShigeru Maeda Department of Applied Chemistry and Chemical Engin-

eering, Faculty of Engineering, Kagoshima University,1-21-40 Korimoto, Kagoshima 890, Japan

James A Marshall Department of Chemistry and Biochemistry, University

of South Carolina, Columbia, South Carolina 29208,USA

Michael Michman Department of Organic Chemistry, The Hebrew

Univer-sity of Jerusalem, Jerusalem 91904, IsraelAxel Schulz Institut f¨ur Anorganische und Analytische Chemie,

Technische Universit¨at Berlin, Strasse des 17 Juni 135,D-10623 Berlin, Germany

Larry R Sherman Department of Chemistry, University of Scranton,

Scran-ton, Pennsylvania 18519-4626, USAJos ´e A Martinho Sim ˜oes Departamento de Qu´ımica, Faculdade de Ciˆencias,

Universidade de Lisboa, 1700 Lisboa, PortugalSuzanne W Slayden Department of Chemistry, George Mason University,

4400 University Drive, Fairfax, Virginia 22030-4444,USA

Stefano Stranges Dipartimento di Chimica, Universit`a di Roma ‘La

Sapienza’, Piazzale Aldo Moro 5, 00185 Roma, ItalyJohn M Tsangaris Department of Chemistry, University of Ioannina,

GR-45100 Ioannina, GreeceKenneth C Westaway Department of Chemistry, Laurentian University, Sud-

bury, Ontario P3E 2C6, CanadaRudolph Willem Faculty of Applied Sciences, Free University of Brussels,

Room 8G512, Pleinlaan 2, B-1050 Brussels, BelgiumJacob Zabicky Institutes for Applied Research, Ben-Gurion University

of the Negev, Beer-Sheva 84110, Israel

As was the case with the volume The chemistry of organic arsenic, antimony and

bis-muth compounds, published in 1994, it was clear that the set of five volumes describing

organometallic compounds (edited by Professor Frank R Hartley) did not deal in cient depth with organic compounds of germanium, tin and lead Hence we decided topublish the present volume, which we hope will be a useful and worthwhile addition

suffi-to the series The Chemistry of Functional Groups In this volume the authors’ literature

search extended in most cases up to the end of 1994

The following chapters unfortunately did not materialize: Mass spectra; NMR andM¨ossbauer spectroscopy; Organic Ge, Sn and Pb compounds as synthones; Ge, Sn and

Pb analogs of radicals and of carbenes; and Rearrangements Moreover, the volume doesnot contain a ‘classical’ chapter on biochemistry, although much of the relevant material isincluded in the chapter on environmental methylation of Ge, Sn and Pb and in the chapter

on the toxicity of organogermanium compounds, in the chapter on organotin toxicologyand also in the chapter on safety and environmental effects

I hope that the above shortcomings will be amended in one of the forthcoming mentary volumes of the series

supple-I will be indebted to readers who will bring to my attention mistakes or omissions inthis or in any other volume of the series

May 1995

vii

The Chemistry of Functional Groups Preface to the series

The series ‘The Chemistry of Functional Groups’ was originally planned to cover ineach volume all aspects of the chemistry of one of the important functional groups inorganic chemistry The emphasis is laid on the preparation, properties and reactions of thefunctional group treated and on the effects which it exerts both in the immediate vicinity

of the group in question and in the whole molecule

A voluntary restriction on the treatment of the various functional groups in thesevolumes is that material included in easily and generally available secondary or ter-tiary sources, such as Chemical Reviews Quarterly Reviews, Organic Reactions, various

‘Advances’ and ‘Progress’ series and in textbooks (i.e in books which are usually found

in the chemical libraries of most universities and research institutes), should not, as a rule,

be repeated in detail, unless it is necessary for the balanced treatment of the topic fore each of the authors is asked not to give an encyclopaedic coverage of his subject,but to concentrate on the most important recent developments and mainly on material thathas not been adequately covered by reviews or other secondary sources by the time ofwriting of the chapter, and to address himself to a reader who is assumed to be at a fairlyadvanced postgraduate level

There-It is realized that no plan can be devised for a volume that would give a complete erage of the field with no overlap between chapters, while at the same time preserving thereadability of the text The Editors set themselves the goal of attaining reasonable coveragewith moderate overlap, with a minimum of cross-references between the chapters In thismanner, sufficient freedom is given to the authors to produce readable quasi-monographicchapters

cov-The general plan of each volume includes the following main sections:

(a) An introductory chapter deals with the general and theoretical aspects of the group.(b) Chapters discuss the characterization and characteristics of the functional groups,i.e qualitative and quantitative methods of determination including chemical and physicalmethods, MS, UV, IR, NMR, ESR and PES as well as activating and directive effectsexerted by the group, and its basicity, acidity and complex-forming ability

(c) One or more chapters deal with the formation of the functional group in question,either from other groups already present in the molecule or by introducing the new groupdirectly or indirectly This is usually followed by a description of the synthetic uses ofthe group, including its reactions, transformations and rearrangements

(d) Additional chapters deal with special topics such as electrochemistry, istry, radiation chemistry, thermochemistry, syntheses and uses of isotopically labelledcompounds, as well as with biochemistry, pharmacology and toxicology Whenever appli-cable, unique chapters relevant only to single functional groups are also included (e.g

photochem-‘Polyethers’, ‘Tetraaminoethylenes’ or ‘Siloxanes’)

ix

x Preface to the series

This plan entails that the breadth, depth and thought-provoking nature of each chapterwill differ with the views and inclinations of the authors and the presentation will neces-sarily be somewhat uneven Moreover, a serious problem is caused by authors who delivertheir manuscript late or not at all In order to overcome this problem at least to someextent, some volumes may be published without giving consideration to the originallyplanned logical order of the chapters

Since the beginning of the Series in 1964, two main developments have occurred.The first of these is the publication of supplementary volumes which contain materialrelating to several kindred functional groups (Supplements A, B, C, D, E, F and S) Thesecond ramification is the publication of a series of ‘Updates’, which contain in eachvolume selected and related chapters, reprinted in the original form in which they werepublished, together with an extensive updating of the subjects, if possible, by the authors

of the original chapters A complete list of all above mentioned volumes published todate will be found on the page opposite the inner title page of this book Unfortunately,the publication of the ‘Updates’ has been discontinued for economic reasons

Advice or criticism regarding the plan and execution of this series will be welcomed

by the Editors

The publication of this series would never have been started, let alone continued,without the support of many persons in Israel and overseas, including colleagues, friendsand family The efficient and patient co-operation of staff-members of the publisher alsorendered us invaluable aid Our sincere thanks are due to all of them

Harold Basch and Tova Hoz

2 Structural aspects of compounds containing C
E (E D Ge, Sn,

Kenneth M Mackay

3 Stereochemistry and conformation of organogermanium, organotin

James A Marshall and Jill A Jablonowski

4 Thermochemistry of organometallic compounds of germanium, tin

6 Photoelectron spectroscopy (PES) of organometallic compounds

Carla Cauletti and Stefano Stranges

7 Analytical aspects of organogermanium compounds 339

Jacob Zabicky and Sarina Grinberg

Jacob Zabicky and Sarina Grinberg

Jacob Zabicky and Sarina Grinberg

10 Synthesis of M(IV) organometallic compounds where M D Ge,

John M Tsangaris, Rudolph Willem and Marcel Gielen

11 Acidity, complexing, basicity and H-bonding of organic germanium,

tin and lead compounds: experimental and computational results 537

Axel Schulz and Thomas A Klap¨otke

xi

14 The photochemistry of organometallic compounds of germanium,

Charles M Gordon and Conor Long

15 Syntheses and uses of isotopically labelled organic derivatives of

Kenneth C Westaway and Helen Joly

16 The environmental methylation of germanium, tin and lead 843

P J Craig and J T van Elteren

E Lukevics and L M Ignatovich

List of abbreviations used

xiv List of abbreviations used

HOMO highest occupied molecular orbital

HPLC high performance liquid chromatography

Ip ionization potential

ICR ion cyclotron resonance

LAH lithium aluminium hydride

LCAO linear combination of atomic orbitals

LDA lithium diisopropylamide

LUMO lowest unoccupied molecular orbital

List of abbreviations used xv

SET single electron transfer

SOMO singly occupied molecular orbital

TLC thin layer chromatography

TMEDA tetramethylethylene diamine

In addition, entries in the ‘List of Radical Names’ in IUPAC Nomenclature of Organic

Chemistry, 1979 Edition Pergamon Press, Oxford, 1979, p 305 322, will also be used

in their unabbreviated forms, both in the text and in formulae instead of explicitly drawnstructures

CHAPTER 1

The nature of the C
M bond

(M = Ge, Sn, Pb)

HAROLD BASCH and TOVA HOZ

Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel

Fax: +(972)-3-535-1250; e-mail: HBASCH@MANGO.CC.BIU.AC.IL

I INTRODUCTION 2

II ATOMIC PROPERTIES 3

III CALCULATIONAL METHODS 5

IV STRUCTURES 49

A XH4 49

B XH3A 50

C XH3AH 51

D XH3AH2 52

E XH3AH3 54

F XH3AB 55

G XH3ABH 58

H XH3ABH3 60

I XH3ABH5 63

J XH3ABC 65

K XH3ABCH 71

L XH3ABCH2 72

M XH3ABCH3 73

N XH3ABCD 75

O XH3ABCDH 78

P XH3ABCDH3 79

V BOND DISSOCIATION ENERGIES 81

A XH4 85

B XH3A 85

C XH3AH 86

D XH3AH2 86

E XH3AH3 86

F XH3AB 87

G XH3ABH 88

H XH3ABH3 88

I XH3ABH5 89

1

The Chemistry of Organic Germanium, Tin and Lead Compounds Volume 1

Edited by Saul Patai Copyright1995 John Wiley & Sons, Ltd

ISBN: 0-471-94207-3

2 Harold Basch and Tova Hoz

J XH3ABC 89

K XH3ABCH 89

L XH3ABCH2 90

M XH3ABCH3 90

N XH3ABCD 90

O XH3ABCDH3 90

VI REFERENCES 91

I INTRODUCTION

The nature of the carbon M bond as a function of the metal (M) atoms Ge, Sn and Pb has been traditionally described using differences in the atomic properties of these atoms

to explain trends in molecular bonding characteristics such as bond distances, angles and energy properties Emphasis has been on a comparison of properties contrasting behavior relative to carbon and silicon bonding to C, and among the metals themselves The importance of relativistic effects in determining the properties of the heavier metal ligand bonds has also been extensively addressed

The ability of the lightest of the Group 14 atoms, the carbon atom, to bind in so many ways with carbon and with other atoms in the Periodic Table attracts extensive comparison with the analogous compounds of Si, Ge, Sn and Pb, both real and hypothetical The wider the comparison, the greater the opportunity to gain insight into the secrets of chemical binding involving the Group 14 atoms, and to detect the nuances that differentiate their properties Some of the causes of the differences are large, obvious and consistent Other causes are more subtle and difficult to identify A combination of contrary trends can effectively mask their individual characters when the individual effects are small The most obvious property to examine for trends and their causes is geometric struc-ture Historically, bond lengths and bond angles in molecules were used to elucidate electronic structure trends and construct descriptions of chemical bonding1 The major obstacle hindering this approach is the general lack of a sufficiently large number and variety of experimentally known molecular structures Happily, recent developments in

ab initio electronic structure theory have provided chemists with the tools for accurately

calculating geometric structures for ever-increasing sizes of molecules2 At the same time, developments in relativistic effective core potentials (RCEP)3 have allowed the incorpo-ration of both direct and indirect radial scaling effects due to relativistic properties of the core electrons in the heavier atoms into the electronic structure description of their valence electrons As has been known for some time already, certain differences in chemical prop-erties in going down a column in the Periodic Table can be attributed to relativistic effects

in the heavier atoms4

Therefore, the common approach to building a bonding description of these type com-pounds is to combine the few experimentally known geometric structures with a larger number of theoretically calculated geometries to infer bonding properties and trends in simple Group 14 compounds It is, however, first necessary to identify those atomic properties which distinguish the various Group 14 atoms and which can contribute to differences in the properties of their corresponding compounds Of course, the same properties which can be used to explain trends in geometric structure could also be used for energy properties, such as bond dissociation energies However, energy properties typically involve both an initial state and a final state, where the energetics of the process depend on the difference in properties between the two states, both involving the same Group 14 atom Trends in energy properties as a function of atom then involve another differencing step This can be more subtle and difficult than treating just geometry, which involves only one state In addition, theoretical methods for calculating geometry are more developed and reliable than for energy difference properties

1 The nature of the C
M bond (M D Ge, Sn, Pb) 3

In this review we will first discuss the atomic properties that are expected to be vant to trends in molecular structure and bonding for compounds of the Group 14 atoms5.Reference will be made mainly to atomic radii6and atomic orbital energies6 9 The resul-tant conclusions will contribute to interpreting trends in the geometric structures of smallmolecules having the generic formula XH3
Y, where X D C, Si, Ge, Sn and Pb, and

rele-Y is one of the 53 substituents ranging from rele-Y D H to rele-Y D C(O)OCH3 The lated XH3
Y bond energies will also be presented and analyzed The generated data willallow other derivative thermodynamic quantities for simple generic-type chemical reac-tions involving the Group 14 atom compounds to be calculated The XH3
Y moleculesare restricted to those having a formal single bond between the Group 14 atom X and thedirect bonding atom of the Y group

calcu-II ATOMIC PROPERTIES

The atomic properties of most relevance to determining the structure and energies ofmolecular compounds have been identified and discussed4,5 The values of these propertiesare collected in Table 16 16 The ground-state electronic configuration of the Group 14

atoms is [core]ns2np2, with n D 2,3,4,5 and 6 for C, Si Ge, Sn and Pb, respectively.

In L
S coupling the electronic ground state has the term symbol3P Relativistic effects

are very large for the heaviest atom, lead, with a spin orbit coupling in the thousands

of cm
117 The splitting of the valence np1/2 and np3/2 spinors can affect molecularbinding through their different spatial and energetic interactions with other atoms, even inclosed-shell electronic states18 For simplicity, spin orbit averaged values for calculatedproperties are shown in Table 1 for discussing trends and making comparisons

The trend in orbital energy values for the valence ns and np atomic orbitals going

down the Group 14 column is shown in Table 1 The orbital energies are taken from thenumerical atomic Dirac Fock compilation of Desclaux6 and these open-shell systems

do not rigorously obey Koopmans’ Theorem19 As such, besides the other approximationsinherent to Koopmans’ Theorem, these orbital energies can only give a rough measure ofvalues and trends in the atomic orbital ionization energies In any event, these numbersshow an interesting behavior which must reflect fundamental underlying effects The

(absolute value) np orbital energy is seen to decrease steadily, if not uniformly, with

increasing atom size There is a relatively very large energy gap between the carbon andsilicon atoms, small gaps among the Si
Ge and Sn
Pb pairs, and a somewhat larger

energy gap between the Ge and Sn orbital energies The valence ns atomic orbital energy,

on the other hand, is seen to have a sawtooth, alternating behavior in going down theGroup 14 column20 As with the np atomic orbital, there is a very large energy decrease

between carbon and silicon, but from Si the orbital energies alternately increase anddecrease Again, the differences between Si and Ge and between Sn and Pb are small,while the gap between Ge and Sn is larger

The experimental ionization energies7 9 in Table 1 show similar trends; ns ionization alternates, while np ionization decreases until Pb, where it increases slightly Again, there

is a large energy gap between carbon and silicon The calculated atomic radii (hr i) for

the Desclaux orbitals6in Table 1 mirror the general behavior of the orbital and ionization

energies: sawtooth for ns and uniformly increasing for np, where the np values for Sn

and Pb are almost equal

Although it is not completely clear which definition of each property is most priate for discussing molecular bonding (i.e with or without spin orbit averaging, radialmaxima or expectation values, choice of final state for ionization energy, etc.) the gen-eral trends seem to be roughly independent of definition The size and energies of thetwo valence atomic orbitals, which properties should be very important for the atom’s

appro-4 Harold Basch and Tova Hoz

TABLE 1 Properties of the Group 14 atoms

cIn eV; from References 7 9.

d For the process, ns2np2(3P ) ! ns1np2(4P ).

e For the process, ns2np2 ( 3P ) ! ns2np1 ( 2P ).

fIn eV; from References 10 and 11.

gIn 10
24cm3; from References 12 and 13; dipole polarizability.

hRelative to hydrogen D 2.20.

i Average of np atomic ionization energy and electron affinity Data from appropriate lines in this Table See

Reference 14.

jPauling scale (Reference 1) as calculated in Reference 15.

k Weighted average of ns and np ionization energies from the appropriate lines in this Table See Reference 16.

lhr i in au; from Reference 6.

chemical behavior, generally show different trends for ns and np The ns energy nates with increasing atom size while the np energy generally decreases steadily, at least until Pb The result is a nonuniform trend in energy gap between the ns and np atomic orbitals which can affect the degree of ns np hybridization in chemical bonds involving

alter-the Group 14 atoms, and, alter-thereby, alter-the chemical behavior of alter-their molecular compounds

On the other hand, the ns np atomic radius (hr i) difference increases steadily with atomic

number, with a particularly large change between carbon and silicon This difference can

also affect the degree of ns np hybridization through the (radial) overlap which controls

the bonding effectiveness of resultant hybrid valence orbitals We can therefore anticipate

a somewhat complex, somewhat alternating chemical behavior going down the Group 14column of the Periodic Table1,4,16,20

Another property which anticipates these trends is the electronegativity, also shown forseveral definitions in Table 1 Pauling’s empirical electronegativity scale based on bondenergies, as updated by Allerd15, shows a sawtooth behavior, with predictable chemi-cal consequences Electronegativity is used to correlate a vast number of chemical andphysical properties Allen’s revised definition of electronegativity16as the average config-

uration energy of the valence ns and np electrons also shows the alternating behavior with

atomic number in the Group 14 column, as expected from the above discussion of orbitaland ionization energies The Mulliken definition14, based on just the np atomic orbital

ionization energy and the corresponding electron affinity, does not show the sawtooth

1 The nature of the C
M bond (M D Ge, Sn, Pb) 5

behavior, and must be considered deficient for neglecting the effect of the ns atomic

orbital on chemical behavior The Mulliken scale also defines a higher electronegativityfor hydrogen relative to carbon15

The source of the differential behavior between the ns and np atomic orbitals in going

down the Group 14 column of the Periodic Table can be attributed to a combination

of screening and relativistic effects, both of which preferentially stabilize the ns atomic

orbital4,16 Filling the first transition series affects germanium this way through incompletescreening of its 4s atomic orbital which gives it a higher effective nuclear charge Fillingthe first lanthanide series analogously stabilizes the Pb 6s atomic orbital through incom-plete screening, which is further enhanced by relativistic effects4,20 Although incomplete

screening and relativistic terms also affect the np atomic orbital, the stabilization is stronger for the ns atomic orbital because of its nonzero charge density at the nucleus.

The dipole polarizability term for the atoms (in Table 1) shows the usual gap betweencarbon and silicon, increasing values for Si ! Sn and a decrease at lead This is anotherreason to expect somewhat unusual behavior for lead compounds compared to the lightermetals

The role of d-type orbitals is not addressed in Table 1 This subject has been addressedfor second-row atoms in previous reviews21,22 which contain many references to thissubject It is very difficult to define the energy and radius of the outer-sphere d-type

orbitals (nd) in isolated atoms since they are not occupied in the ground state Rather

than make use of some excited state definition, we prefer to postpone a discussion of thissubject until after an inspection of the calculated results on the molecular compounds

III CALCULATIONAL METHODS

Using atomic properties alone for predictive capabilities with regard to the geometric andelectronic structure of molecules is often insufficient Except for weakly bound systems,the chemical bond is more than just a perturbation of the electronic structure of atoms.Molecular properties determined experimentally have been used to infer the electronicstructure description of simple systems, from which predictions are made for more com-plicated molecules using group property and additivity concepts This empirical approachhas been used very extensively in identifying and defining the determining factors in thegeometric and electronic structure of molecules These latter are then used in a predictive

mode for unknown systems The opposite approach is to use ab initio quantum chemical

calculations to determine everything The disadvantages in the latter methodology is that

no intuitive understanding is derived from the purely mechanical calculational process

which can be used for chemical systems that are too large for the ab initio machinery.

In this review we will try to combine the best of both approaches On the one hand,there are very little experimental data for the Group 14 compounds for the atoms below

Si For simple molecular compounds of Ge, Sn and Pb, ab initio methods can be used

to generate an ‘experimental’ database from which the electronic structure properties ofsuch compounds can be inferred Hopefully, the principles learned from this referenceset of molecules can then be applied to larger systems Although not the subject ofthis chapter, the corresponding carbon and silicon21 systems are also examined to helpelucidate trends in properties going down the complete Group 14 column of the PeriodicTable and for general comparison purposes More experimental information is available forthe corresponding carbon and silicon compounds so that these can also be used to evaluatethe accuracy of the calculated properties of the germanium, tin and lead database set

The ab initio methods and approach used here are similar to that reported in previous

studies22 24 The geometries of a generic set of XH3Y molecules were determinedcalculationally X is any one of the Group 14 atoms (carbon, silicon, germanium, tinand lead) and Y is any of the substituent groups, F, AlH , BH, SH, Br, H, CCH, PH ,

6 Harold Basch and Tova Hoz

NH2, SCH3, Cl, NO, ON, C(O)H, SeCN, NCSe, C(O)F, C(O)NH2, ONO2, NCS, SCN,

CH2CH3, C(O)OH, NO2, ONO, PC, CP, NCO, OCN, CN, NC, OCH3, CHDCH2, NNN,

OH, CH3, SiH3, GeH3, SnH3, PbH3, CF3, C(O)OCH3, OC(O)CH3, PO, OP, C(O)Cl,

OF, OSiH3, C(O)CH3, PO2, OPO, OPO2 and OS(O)OH The Y substituents are writtenwhere attachment to X is through the leftmost atom Attachment to X alternately bydifferent atoms of the Y group gives rise to the possibility of linkage isomerism for the

Y group The plethora of bonding possibilities with respect to type of atom, attachmentsite, substitution and conformation should combine to give a balanced and comprehensivepicture of the chemical bonding situation in these systems

The geometries of the XH3Y molecules were optimized at the MP2 (Moeller Plesset

to second order) level2 using compact effective potentials (CEP) for the atoms in thefirst two rows of the Periodic Table (B
F and Al
Cl)25 and their relativistic analogs(RCEP) for the main group atoms below the second row26 The RCEP are generated fromDirac Fock all-electron relativistic atomic orbitals6,27and therefore implicitly include theindirect relativistic effects of the core electrons on the radial distribution of the valenceelectrons18 This could be particularly important for the lead atom The effective potentials

or pseudopotentials replace the chemically inactive core electrons

The valence electron Gaussian basis sets were taken from the respective CEP25 andRCEP26 tabulations The published basis sets show a valence atomic orbital splitting

that can be denoted as (R)CEP-N1G, where N D 3 for first- and second-row atoms, and N D 4 for the heavier main group elements This type basis set is generically called

double-zeta (DZ) for historical reasons connected to Slater orbital (exponential-type) basissets In these calculations the valence DZ distributions were converted to triple-zeta (TZ)

by splitting off the smallest exponent Gaussian member of the contracted (N ) set, to give the (R)CEP-K 11 valence atomic orbital distribution (K D 2 for first- and second-row atoms and K D 3 for beyond) The valence TZ Gaussian basis set for each atom was

augmented by a double (D) set of d-type polarization (DP) functions (all 6 components)taken from the GAMESS tabulation28,29as follows The reported29single Gaussian d-typepolarization function was converted to DP form by scaling the single Gaussian exponent(˛) by 1.4˛ and 0.4˛ to form two distinct d-type polarization functions Both the singleand double set of single Gaussians exponents are displayed in Table 2 The valence TZhydrogen atom basis set was taken from the GAUSSIAN9230code as the 311G group, andaugmented by a single Gaussian p-type polarization function with exponent 0.9 Overall,this basis set is denoted TZDP All geometry optimizations were carried out in this basisset at the MP2 level (denoted MP2/TZDP or MP2/CEP-TZDP) using the GAUSSIAN9230set of computer programs

The extended basis sets are necessary to describe the adaptation of the atom to themolecular environment Experience has shown31that the major effect on the radial extent

of each atom in a molecule is in the bonding region A frozen atomic orbital basis set isunable to provide the differential flexibility required in the short, intermediate and long-range radial distances from the nucleus to accurately describe the electron density changes

in the molecule The valence TZ basis set has that flexibility Analogously, Magnusson32has recently discussed the effect of angular polarization functions on the inner and outerparts of the valence atomic orbitals of the main group elements The different polarizationneeds in the different regions of space about each atom in the molecule leads to the use

of a double set of d-type basis function

The MP2 level calculation is the first step beyond the Hartree Fock (HF) level33,34,and is thereby defined as a post-Hartree Fock method Theory predicts35 and actual cal-culations have shown2 that HF level calculated geometries generally give bond distancesthat are too short compared to experiment for normal covalent bonds For these cases,MP2 level optimized geometries give better agreement with experiment36 The same is

1 The nature of the C
M bond (M D Ge, Sn, Pb) 7TABLE 2 Polarization and diffuse Gaussian exponentsa

aExcept for H, the polarization functions are d-type and the diffuse functions

are sp-type For the hydrogen atom polarization is p-type and diffuse is s-type.

b˛1D 1.4˛; ˛2D 0.4˛; values of ˛ are from Ref 29.

true for vibrational frequencies37 The reason for the improved description of the normalcovalent bond at the post-HF level is the improved description of the incipient homolyticbond dissociation process (i.e reduced ionicity) at the MP2 level compared to HF in theneighborhood of the equilibrium bond distances The resultant geometry optimized bondlengths are listed in Tables 3 8

TABLE 3 Bond distances (in ˚ A) not involving Group 14 atomsa

Bond type

8 Harold Basch and Tova Hoz

TABLE 3. (continued )

Bond type

1 The nature of the C
M bond (M D Ge, Sn, Pb) 9TABLE 3. (continued )

Bond type

10 Harold Basch and Tova Hoz

TABLE 4 Bond distances (in ˚ A) involving carbona

1 The nature of the C
M bond (M D Ge, Sn, Pb) 11TABLE 4. (continued )

12 Harold Basch and Tova Hoz

1 The nature of the C
M bond (M D Ge, Sn, Pb) 13TABLE 4. (continued )

aMP2 optimized geometries in the TZDP basis set.

bAverage bond lengths.

cDouble or triple bond.

14 Harold Basch and Tova Hoz

TABLE 5. (continued )

Bond type

aMP2 optimized geometries in the TZDP basis set.

bAverage bond lengths.

c

1 The nature of the C
M bond (M D Ge, Sn, Pb) 15TABLE 6 Bond distances (in ˚ A) involving germaniuma

Bond type

16 Harold Basch and Tova Hoz

TABLE 6. (continued )

Bond type

aMP2 optimized geometries in the CEP-TZDP basis set.

bAverage bond lengths.

TABLE 7 Bond distances (in ˚ A) involving tina

1 The nature of the C
M bond (M D Ge, Sn, Pb) 17TABLE 7. (continued )

aMP2 optimized geometries in the TZDP basis set.

bAverage bond lengths.

TABLE 8 Bond distances (in ˚ A) involving leada

18 Harold Basch and Tova Hoz

aMP2 optimized geometries in the TZDP basis set.

bAverage bond lengths.

The MP2/TZDP optimized structures were then used to calculate the stationary stategeometry force constants and harmonic vibrational frequencies, also at the MP2 level.These results serve several purposes Firstly, they test that the calculated geometry isreally an energy minimum by showing all real frequencies in the normal coordinateanalysis Secondly, they provide values of the zero-point energy (ZPE) that can be used

1 The nature of the C
M bond (M D Ge, Sn, Pb) 19

to convert the total electronic energy differences to thermodynamic enthalpies that takeinto account zero-point vibrational energy differences in chemical reactions Thirdly, theyprovide values of vibrational frequencies in the XH3Y series that can be compared for atomand substituent effects This information contributes another dimension to the analysis ofthe electronic structure description of the bonding in these systems

Another property obtained at the MP2 level using the relaxed MP2 densities calculated

as energy derivatives38,39 are the Mulliken populations and atomic charges A hensive discussion of the whole topic of population analyses has recently been given40.The specific deficiencies of the Mulliken partitioning of the basis function space in thewave function charge distribution is well known41 Clearly, great care must be taken ininterpreting trends in structure properties based on derived atomic charges alone Theindividual MP2 atomic charges were summed to calculate group charges for all the XH3and Y substituents These are shown in Table 9 The individual s, p and (five compo-nent) d contributions to the atomic populations at the MP2 level for the X atoms in allthe XH3Y molecules are found in Table 10 The individual atomic charges for all theatoms in XH3Y are tabulated in Tables 11 15 The MP2/TZDP level dipole moments aretabulated in Table 16

compre-TABLE 9 Mulliken charges on the H and XH 3 groups in RYa

20 Harold Basch and Tova Hoz

CH 3 1.18 3.06 0.06 1.14 2.11 0.26 1.25 2.16 0.17 1.19 2.06 0.16 1.32 1.98 0.08 SiH 3 1.22 3.36 0.06 1.18 2.38 0.22 1.27 2.38 0.15 1.21 2.27 0.15 1.36 2.15 0.08 GeH 3 1.22 3.37 0.07 1.22 2.42 0.22 1.31 2.42 0.15 1.23 2.32 0.16 1.40 2.17 0.08 SnH 3 1.25 3.43 0.06 1.22 2.50 0.22 1.30 2.52 0.14 1.23 2.41 0.15 1.42 2.26 0.08 PbH 3 1.27 3.42 0.06 1.24 2.51 0.22 1.30 2.55 0.15 1.23 2.44 0.15 1.41 2.30 0.08

1 The nature of the C
M bond (M D Ge, Sn, Pb) 21TABLE 10. (continued )

CCH 1.24 3.06 0.09 1.21 2.10 0.27 1.32 2.15 0.18 1.26 2.03 0.16 1.35 1.93 0.08 C(O)H 1.15 3.11 0.07 1.20 2.17 0.24 1.31 2.23 0.17 1.24 2.12 0.16 1.37 2.04 0.09 CHCH 2 1.19 3.09 0.08 1.18 2.13 0.26 1.28 2.20 0.18 1.21 2.10 0.17 1.33 2.01 0.09 OCH 3 1.25 2.85 0.12 1.08 1.89 0.33 1.21 1.93 0.22 1.16 1.82 0.19 1.33 1.78 0.10 SCH 3 1.21 3.12 0.10 1.17 2.11 0.30 1.29 2.17 0.21 1.23 2.08 0.21 1.37 1.98 0.11 OSiH 3 1.26 2.86 0.12 1.09 1.90 0.34 1.20 1.94 0.23 1.15 1.82 0.19 1.33 1.79 0.11

CH 2 CH 3 1.19 3.09 0.09 1.14 2.12 0.26 1.25 2.18 0.17 1.19 2.09 0.16 1.33 2.00 0.08 OCN 1.27 2.84 0.11 1.12 1.88 0.29 1.25 1.91 0.19 1.21 1.82 0.16 1.37 1.77 0.09 NCO 1.28 2.92 0.10 1.13 1.96 0.30 1.22 1.99 0.20 1.17 1.85 0.17 1.33 1.82 0.09 SCN 1.22 3.10 0.09 1.19 2.09 0.29 1.30 2.15 0.20 1.25 2.05 0.20 1.39 1.95 0.11 NCS 1.31 2.91 0.10 1.15 1.96 0.30 1.23 1.98 0.19 1.17 1.84 0.15 1.34 1.83 0.09 SeCN 1.24 3.22 0.10 1.23 2.20 0.29 1.32 2.20 0.20 1.25 2.10 0.18 1.39 1.98 0.09 NCSE 1.31 2.91 0.10 1.13 1.97 0.29 1.21 1.97 0.17 1.16 1.86 0.13 1.31 1.82 0.07 NNN 1.25 2.94 0.10 1.14 1.99 0.31 1.25 2.03 0.21 1.20 1.92 0.19 1.36 1.86 0.11 ONO 1.25 2.89 0.11 1.12 1.92 0.30 1.25 1.99 0.20 1.21 1.91 0.18 1.35 1.84 0.11

NO 2 1.29 2.97 0.08 1.17 2.02 0.27 1.27 2.06 0.20 1.22 1.95 0.18 1.36 1.88 0.12 OPO 1.26 2.86 0.11 1.10 1.91 0.30 1.23 1.96 0.21 1.19 1.87 0.20 1.36 1.78 0.13

PO 2 1.22 3.26 0.07 1.21 2.26 0.24 1.33 2.30 0.17 1.27 2.20 0.18 1.39 2.11 0.11 C(O)F 1.18 3.12 0.07 1.19 2.16 0.24 1.29 2.23 0.18 1.23 2.12 0.17 1.35 2.04 0.10 C(O)Cl 1.18 3.10 0.07 1.20 2.14 0.25 1.30 2.19 0.18 1.24 2.08 0.18 1.36 2.00 0.10 C(O)OH 1.19 2.12 0.07 1.19 2.16 0.24 1.29 2.21 0.17 1.23 2.11 0.17 1.35 2.03 0.10 C(O)NH 2 1.20 3.14 0.06 1.20 2.18 0.24 1.30 2.24 0.18 1.24 2.15 0.18 1.36 2.07 0.11 C(O)CH 3 1.17 3.14 0.07 1.20 2.19 0.24 1.32 2.25 0.17 1.26 2.17 0.17 1.38 2.09 0.09

CF 3 1.20 3.12 0.07 1.20 2.18 0.25 1.30 2.26 0.18 1.24 2.16 0.18 1.36 2.10 0.11 ONO 2 1.26 2.86 0.11 1.11 1.89 0.30 1.24 1.93 0.21 1.20 1.84 0.19 1.35 1.76 0.12 OPO 2 1.26 2.84 0.11 1.11 1.88 0.30 1.23 1.92 0.20 1.20 1.84 0.19 1.36 1.74 0.12 C(O)OCH 3 1.20 3.11 0.07 1.20 2.15 0.24 1.30 2.21 0.17 1.24 2.11 0.17 1.35 1.96 0.09 OC(O)CH 3 1.26 2.87 0.11 1.10 1.90 0.30 1.23 1.94 0.21 1.19 1.86 0.20 1.34 1.78 0.12 OS(O)OH 1.26 2.89 0.11 1.09 1.91 0.31 1.23 1.95 0.22 1.19 1.86 0.20 1.34 1.77 0.13

aGeometry optimized at the MP2/TZDP level, 5 d-type distribution Connectivity is to the leftmost atom in Y.

TABLE 11 Mulliken atomic charges calculated at the MP2 level for carbon compoundsa

22 Harold Basch and Tova Hoz

1 The nature of the C
M bond (M D Ge, Sn, Pb) 23TABLE 11. (continued )

24 Harold Basch and Tova Hoz

1 The nature of the C
M bond (M D Ge, Sn, Pb) 25TABLE 12. (continued )

26 Harold Basch and Tova Hoz