Valency and Bonding: A Natural Bond Orbital Donor-Acceptor Perspective

761 Pages·2005·10.392 MB·English

by  Frank Weinhold, Clark R. Landis

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VALENCY AND BONDING
Thisgraduate-leveltextpresentsthefirstcomprehensiveoverviewofmodernchem-
ical valency and bonding theory, written by internationally recognized experts in
thefield.TheauthorsbuildonthefoundationofLewis-andPauling-likelocalized
structural and hybridization concepts to present a book that is directly based on
currentabinitiocomputationaltechnology.
The presentation is highly visual and intuitive throughout, being based on the
recognizableandtransferablegraphicalformsofnaturalbondorbitals(NBOs)and
theirspatialoverlapsinthemolecularenvironment.Thebookshowsapplicationsto
abroadrangeofmolecularandsupramolecularspeciesoforganic,inorganic,and
bioorganicinterest.Hundredsoforbitalillustrationshelptoconveytheessenceof
modernNBOconceptsinafacilemannerforthosewithnoextensivebackground
inthemathematicalmachineryoftheSchro¨dingerequation.Thisbookwillappeal
tothosestudyingchemicalbondinginrelationtochemistry,chemicalengineering,
biochemistry,andphysics.
Frank A. Weinhold is Professor of Physical and Theoretical Chemistry at the
UniversityofWisconsin-Madison.HisacademicawardsincludetheAlfredP.Sloan
Fellowship (1970) and the Camille and Henry Dreyfus Foundation Fellowship
(1972)andhehasservedguestappointmentsatmanyprestigiousinstitutesincluding
the Quantum Chemistry Group at the University of Uppsala, Sweden, the Max-
Planck-Institutfu¨rPhysikundAstrophysikinMunich,Germany,andtheUniversity
ofColorado.Hewasthe13thAnnualCharlesA.CoulsonlecturerattheCenterfor
Computational Quantum Chemistry, University of Georgia. Professor Weinhold
has also served on the Honorary Editorial Advisory Boards of the International
JournalofQuantumChemistryandtheRussianJournalofPhysicalChemistryand
istheauthorofover150technicalpublicationsandsoftwarepackages.
Following a brief but influential career as an industrial chemist for Monsanto
Corporation, Clark Landis began his academic career at the University of Col-
orado,Boulder,movingtotheUniversityofWisconsin-Madisonin1990,wherehe
iscurrentlyaProfessorinInorganicChemistry.ProfessorLandiswasco-PIofthe
NewTraditionsSystemicReformProjectinChemicalEducationandisco-author
ofChemistryConcepTests:APathwaytoInteractiveClassroomsandacompanion
videotape.HehaslongservedasaconsultanttoDowChemicalCompanyandis
amemberofitsTechnicalAdvisoryBoard.

VALENCY AND BONDING
A Natural Bond Orbital Donor–Acceptor Perspective
FRANK WEINHOLD AND CLARK R. LANDIS
DepartmentofChemistry,UniversityofWisconsin-Madison,Wisconsin53706
  
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo
Cambridge University Press
The Edinburgh Building, Cambridge  ,UK
Published in the United States of America by Cambridge University Press, New York
www.cambridge.org
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© Cambridge University Press 2005
This book is in copyright. Subject to statutory exception and to the provision of
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without the written permission of Cambridge University Press.
First published in print format 2005
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Contents
Preface pagevii
1 Introductionandtheoreticalbackground 1
1.1 TheSchro¨dingerequationandmodelsofchemistry 1
1.2 Hydrogen-atomorbitals 8
1.3 Many-electronsystems:Hartree–Fockandcorrelatedtreatments 13
1.4 PerturbationtheoryfororbitalsintheHartree–Fock
framework:thedonor–acceptorparadigm 16
1.5 Densitymatrices,naturallocalizedanddelocalizedorbitals,
andtheLewis-structurepicture 21
1.6 Naturalresonancestructuresandweightings 32
1.7 Pauli-exchangeantisymmetryandstericrepulsions 36
1.8 Summary 40
NotesforChapter1 41
2 Electrostaticandionicbonding 45
2.1 Introduction 45
2.2 Atomicandionicorbitals 47
2.3 Chargetransferandhybridizationinionicbonding 49
2.4 Donor–acceptortheoryofhybridizationinionicbonding 55
2.5 Ionic–covalenttransitions 60
2.6 Ion–dipoleanddipole–dipolebonding 64
2.7 Bentioniccompoundsofheavyalkalineearths 73
2.8 Ionicbondingind-blockelements 76
2.9 Summary 86
NotesforChapter2 87
v
vi Contents
3 Molecularbondingins/p-blockelements 89
3.1 Introduction 89
3.2 Covalentandpolarcovalentbonding 90
3.3 Conjugationandaromaticity 182
3.4 Hyperconjugation 215
3.5 Hypervalency:3c/4e“ωbonds” 275
3.6 Hypovalency:3c/2ebridgebonds 306
3.7 Summary 351
NotesforChapter3 353
4 Molecularbondinginthed-blockelements 363
4.1 Introduction 363
4.2 Lewis-likestructuresforthed-blockelements 365
4.3 Hybridizationandmolecularshape 372
4.4 Covalentandpolar-covalentbonding 387
4.5 Coordinativemetal–ligandbonding 434
4.6 Beyondsigmabonding:transition-metalhyperbonding
andpiback/frontbonding 447
4.7 Hypovalency,agosticinteractions,andrelatedaspects
ofcatalyticactivationatmetalcenters 479
4.8 Hyperconjugativeeffects 519
4.9 Multielectroncoordination 522
4.10 Verticaltrendsintransition-metalbonding 545
4.11 Localizedversusdelocalizeddescriptions
oftransition-metalbondingandhyperbonding 563
4.12 Summary 573
NotesforChapter4 575
5 Supramolecularbonding 579
5.1 Anintroductoryoverviewofintermolecularforces 579
5.2 Hydrogenbonding 593
5.3 Charge-transfercomplexes 661
5.4 Transition-statespecies 678
5.5 Couplingofintramolecularandintermolecularinteractions 693
5.6 Summary 702
NotesforChapter5 704
AppendixA.Methodsandbasissets 710
AppendixB.Chemicalperiodicity 715
AppendixC.Units 723
Chemical-speciesindex 727
Authorindex 732
Subjectindex 740
Preface
Twodauntingquestionsfacetheauthorsofprospectivetextbooks.(1)Forwhomis
thebookintended?(2)Whatmakesitdifferentfromotherbooksintendedforthe
sameaudience?Wefirstaddressthesequestions.
Onemightthinkfromcountingthemathematicalequationsthatthebookisin-
tended for a theoretical physicist. This is partially true, for indeed we hope the
subject is presented in a way that will satisfy a rigorously inclined mathemati-
cal physicist that “valency and bonding” is not just murky chemical voodoo, but
authenticsciencegroundedinthedeepesttenetsoftheoreticalphysics.
Beyond Chapter 1 the reader may be relieved to find few if any equations that
would challenge even a moderately gifted high-school student. The emphasis on
orbitaldiagramsand“doingquantummechanicswithpictures”mightthensuggest
thatthebookisintendedforundergraduatechemistrystudents.Thisisalsopartially
true.Forexample,webelievethatourtreatmentofhomonucleardiatomicmolecules
(Section 3.2.9) should be accessible to undergraduates who commonly encounter
thetopicinintroductorychemistrycourses.
Our principal goal has been to translate the deepest truths of the Schro¨dinger
equationintoavisualizable,intuitiveformthat“makessense”evenforbeginning
students,andcanhelpchemistryteacherstopresentbondingandvalencyconceptsin
amannermoreconsistentwithmodernchemicalresearch.Chemistryteacherswill
findherearatherwideselectionofelementarytopicsdiscussedfromahigh-level
viewpoint. The book includes a considerable amount of previously unpublished
material that we believe to be of broad pedagogical interest, such as the novel
Lewis-likepictureoftransition-metalbondingpresentedinChapter4.
Because we are both computational chemistry researchers, we have naturally
directed the book also to specialists in this field, particularly those wishing to in-
corporatenaturalbondorbital(NBO)andnaturalresonancetheory(NRT)analysis
into their methodological and conceptual toolbox. Researchers will find here a
vii
viii Preface
ratherbroadsamplingofNBO/NRTapplicationstorepresentativechemicalprob-
lems throughout the periodic table, touching on many areas of modern chemical,
biochemical,andmaterialsresearch.
But,weexpectthatthemajorityofreaderswillbethosewithonlyarudimentary
commandofquantumchemistryandchemicalbondingtheory(e.g.,atthelevelof
junior-yearphysicalchemistrycourse)whowishtolearnmoreabouttheemerging
abinitioanddensity-functionalviewofmolecularandsupramolecularinteractions.
Whilethisisnota“textbookinquantumchemistry”perse,webelievethatthebook
canserveasasupplementbothinupper-levelundergraduatecoursesandingraduate
coursesonmoderncomputationalchemistryandbondingtheory.
Inidentifyingthefeaturesthatdistinguishthisbookfrommanypredecessors,we
donotattempttoconcealtheenormousdebtofinspirationowedtosuchclassicsas
Pauling’s Nature of the Chemical Bond and Coulson’s Valence. We aspire neither
to supplant these classics nor to alter substantially the concepts they expounded.
Rather,ourgoalistotakeasimilarlyglobalview,butdevelopamorecurrentand
quantitative perspective on valency and bonding concepts such as hybridization,
electronegativity, and resonance, capitalizing on the many advances in wavefunc-
tioncalculationandanalysisthathavesubsequentlyoccurred.Wehopetherebyto
sharpen,revitalize,andenhancetheusefulnessofqualitativebondingconceptsby
presentinga“twenty-first-centuryview”ofthenatureofchemicalbonding.
Readerswhoareaccustomedtoseeingchemicaltheorizingbuttressedbycompar-
isonswithexperimentsmaybesurprisedtofindlittleofthelatterhere.Throughout
thisbook,computersolutionsofSchro¨dinger’sequation(ratherthanexperiments)
are regarded as the primary “oracle” of chemical information. We specifically as-
sume that high-level calculations (e.g., at the hybrid density-functional B3LYP/
6-311++G∗∗ level) can be relied upon to describe molecular electronic distribu-
tions, geometries, and energetics to a sufficient degree of chemical accuracy for
ourpurposes.(Infact,theaccuracyisoftencomparabletothatofthebestavailable
experimentaldata,morethanadequateforqualitativepedagogicalpurposes.)The
viewpointofthisbookisthatmodernabinitiotheorynolongerrequiresextensive
experimentalcomparisonsinorderforittobeconsideredseriously,andindeed,the-
orycanbeexpectedtosupplanttraditionalexperimentalmethodsinanincreasing
numberofchemicalinvestigations.Inthedeepestsense,thisisa“theorybook.”
Dual authorship naturally brings a distinctive blend of perspectives. The book
reflectstheinfluenceofa“donor–acceptor”perspectivebasedonNBO/NRTwave-
function analysis methods developed in the research group of F. W. (a physical
chemist).WhileNBOanalysesarenowrathercommoninthechemicalliterature,
thepresentworkprovidesthefirstbroadoverviewoforganicandinorganicchemi-
calphenomenafromthisgeneralviewpoint.Thebookalsoincorporateskeyinsights
gainedfromconstructingvalence-bond-based(VALBOND)molecular-mechanics