Table Of ContentNobleGasChemistry
Noble Gas Chemistry
Structure,Bonding,andGas-PhaseChemistry
FeliceGrandinetti
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Contents
Preface ix
PartI AnOverviewofNobleGasChemistry 1
1 AHistoricalIntroduction 3
1.1 TheDiscoveryoftheElements 3
1.2 TheEmergingofDifferentChemistries 7
1.2.1 Bulk-PhaseCompounds 8
1.2.2 MoleculesinColdMatrices 11
1.2.3 MoleculesinLiquidandSupercriticalNobleGases 12
1.2.4 ChemistryUnderHighPressures 13
1.2.5 GaseousNeutralComplexes 14
1.2.6 Gas-PhaseIonChemistry 16
1.3 TheDevelopmentoftheDiverseFields 18
2 TypicalCompoundsandBondingMotifs 23
2.1 GeneralConsiderations 23
2.2 ClustersofNobleGasAtoms 26
2.3 MonocoordinatedCompounds 29
2.4 Dicoordinated(‘Inserted’)Compounds 30
2.5 PolycoordinatedCompounds 41
2.6 Cage,Inclusion,andAdsorptionCompounds 47
2.7 TheEffectsofthePressure 51
3 ChemistryinSilico 55
3.1 TheRoleofCalculationsinNobleGasChemistry 55
3.2 MethodsofBondingAnalysis 56
3.2.1 TheAIMTheory 56
3.2.2 TheAnalysisoftheELF 57
3.2.3 TheAnalysisoftheH(r) 58
3.2.4 TheNBOAnalysis 62
3.2.5 TheEDA-NOCVAnalysis 64
3.2.6 TheAnalysisoftheCDFunction 66
vi Contents
3.3 AboutthePerformanceoftheTheoreticalMethods 66
3.4 IllustrativeExamples 70
3.4.1 ProbingtheBondingCharacter 70
3.4.2 StructureandStabilityoftheXeF (n=1−6) 84
n
3.4.3 Open-shellCompounds 88
3.4.4 ExploringthePES 91
3.4.5 NeutralCompoundsofHeliumandNeon 99
3.4.6 NovelCompoundsofArgon,Krypton,andXenon 123
3.4.7 RadonCompounds 133
3.4.8 TheAerogenBond 138
PartII Gas-PhaseChemistryoftheNobleGases 147
4 NeutralSpecies 149
4.1 ComplexeswithAtomsandDiatomicMolecules 149
4.1.1 TheInteractionEnergy 149
4.1.2 TheCorrelationFormulas 150
4.1.3 TheNg andNgNg′ 154
2
4.1.4 AboutthevanderWaalsRadiioftheNobleGases 157
4.1.5 TheEfimovStateofHe 159
3
4.1.6 ComplexeswithH ,N ,andO 160
2 2 2
4.1.7 ComplexeswithC ,CO,andCS 162
2
4.1.8 ComplexeswiththeDihalogens 166
4.1.9 ComplexeswiththeHydrogenHalides 173
4.1.10 ComplexeswithDiatomicMetalHalides 178
4.2 ComplexeswithPolyatomicMolecules 183
4.2.1 ComplexeswithCO ,CS ,andCOS 183
2 2
4.2.2 ComplexeswithH OandNH 186
2 3
4.2.3 ComplexeswithHydrocarbons 191
4.2.4 ComplexeswithHalocarbons 194
4.2.5 ComplexeswithOtherOrganicMolecules 197
4.3 DicoordinatedCovalentCompounds 200
5 IonicSpecies 203
5.1 NobleGasesasLigandsofIonicSpecies 205
5.1.1 ComplexeswithMetalCations 205
5.1.2 ComplexeswithNon-MetalCations 220
5.1.3 ComplexeswithAnions 227
5.2 ProtonatedNobleGasesandOtherRelatedSpecies 229
5.2.1 ArH+asaNaturallyOccurringSpecies 229
5.2.2 TheNgH+andNg H + 231
m n
5.2.3 ComplexesoftheNgH+withSimpleLigands 241
5.2.4 OtherNobleGasIonsofPotentialInterstellarInterest 244
5.3 NobleGasIonicReactions 249
5.3.1 ReactionsInvolvingSingly-chargedCations 249
5.3.2 ReactionsInvolvingDoubly-chargedCations 253
Contents vii
A ChemicalCompositionofAir 259
B AbInitioandDFTElectronicStructureMethods 261
C AtomicChargesofDiatomicMolecules 269
D BondDistancesandPolarisabilitiesofDiatomic
Molecules 271
References 273
Index 337
ix
Preface
Theelementsofgroup18(thenoblegases)are,generally,perceivedasonlyless
reactive.Onlykryptonandxenonform,infact,isolablecompounds(theradioac-
tiveandshort-livedradonishardlyinvestigated),andthesynthesisofcompounds
containinghelium,neon,andargonstillremainsanopenchallenge.Chemistryis,
however,alsoamatterofenvironmentandconditions,and,particularlyfornoble
gaschemistry,aproperchoiceofthesefactorsmayopendoorsthatwouldremain,
otherwise,definitelylocked.TheHArFdetectedsofarincoldmatrices,andthe
Na Herecentlyobtainedatthehighestpressures(uniquecompoundsofargon
2
and helium, respectively), are two major illustrative examples. But the binding
capabilitiesofthenoblegasesaregreatlyenhancedalsoundertheisolatedcon-
ditionsofthegasphase.Inthisenvironment,alltheelements,includinghelium
and neon, really ‘forget’ to be inert, and form an exceptionally large family of
molecularspecies,rangingfromfragilevanderWaalsadductstostronglybound
covalentspecies.Avarietythatis,probably,uniqueintheperiodictable!Inter-
estingly, this richness is, in essence, the daughter of the inertness. Thus, while
resistant(especiallyHe,Ne,andAr)todefinitelybreaktheirelectroniccloudsto
formtrueionicorcovalentbonds,thenoblegasatomsarestillsensitivetothe
polarisation effects exerted by neutral and ionic binding partners. The stabilis-
inginteractionsthusrangefromdispersionforcestoelectrostaticandinductive
interactions,withincasecontributionofchargetransfer.Andthespectrumofthe
bondingmotifsfurtherenlargesunderphotodissociatingorionisingconditions
thatfavouralsotheformationoftruecovalentbonds.ThesimplestHeH+ was,
indeed,firstdetectedin1925,nearly40yearsbeforethebreakthroughadvances
inxenonchemistrythatofficiallydestroyedthemythofnoblegasinertness!And
ArH+ was quite recently detected in the galactic and extragalactic regions as
the first naturally occurring species containing a noble gas atom: a connection
between Nature and laboratory that, certainly, rejuvenates the interest for the
gas-phase chemistry of the noble gases. This is, indeed, the main topic of this
book,withemphasisonbothneutralandionicspecies.Thematteris,certainly,of
experimentalinterest,butitenjoysalsothemajorcontributionofthecalculations
that are extensively employed not only to aid the interpretation of the experi-
mentsbutalsotoindependentlyexplorestillunreportedmoleculesandions.The
subtitleofthebook‘Structure,Bonding,andGas-PhaseChemistry’wishesalso
toemphasisethestrictrelationshipinthisfieldbetweenexperimentsandtheory.
x Preface
Thebookisdividedintwoparts.Thefirstone(Chapters1–3)isintendedasan
introductoryoverviewofnoblegaschemistry,alsofunctionaltothesecondpart,
morespecificallyconcernedwithgaseousneutral(Chapter4)andionicspecies
(Chapter 5). Chapter 1 is, in particular, a historical introduction to noble gas
chemistry, aimed at emphasising the salient facts that marked the discovery of
theelements,theemergingoftheirreactivityunderdifferentexperimentalcondi-
tions,andthesubsequentevolutionofthesefields.Chapter2illustratesaclassifi-
cationofnoblegascompounds,groupedhereinfivecategories(clustersofnoble
gas atoms, monocoordinated-, dicoordinated-, polycoordinated compounds,
and cage, inclusion, and adsorption compounds) that appeared best suited for
gaseous species. Alternative classifications could be, certainly, generally taken,
andIcouldsaythesamefortheselectedillustrativeexamples.Chapter3iscon-
cernedwiththeapplicationsofthecalculations,withemphasisonissuesofmajor
interestin noble gas chemistry,particularlygas-phase chemistry: the structure
andstabilityofnoblegascompounds,theirbondingcharacter,andthekinetics
oftheirformationanddecompositionprocesses.Themethodsmostextensively
employed to perform the bonding analysis of noble gas compounds are also
shortlyrecognisedhere.Themethodsmostcommonlyemployedforelectronic
structurecalculationswere,instead,brieflyrecalledinAppendixB.Chapter4is,
mainly,concernedwiththestructure,bonding,andstabilityofgaseousneutral
species. The first discussed systems are monocoordinated adducts of diverse
compositionandcomplexity,examinedintermsofapreliminarilyoutlinedinter-
pretativemodel.Gaseousdicoordinatedcovalentcompoundsarealsoaccounted.
Chapter 5 is concerned with gas-phase ion chemistry, and illustrates issues of
current interest such as the behaviour of the noble gases as ligands of ionic
species,thechemistryofprotonatednoblegasesandotherrelatedspecies,and
thepropertiesofotherionsofpotentialinterstellarinterest.Illustrativeexamples
ofgaseousionicreactionsinvolvingnoblegasatomsarealsoaccounted.
Thebookis,mostly,builtonoriginalresearcharticlespublishedinjournals.The
variousauthorsandgroupsarementionedinthecitedreferences,andIwishto
thankthecolleagueswhokindlyprovidedreprintsorpreprintsoftheirwork.The
choiceofthecoveredissuesandillustrativeexamplesis,certainly,notexhaustive,
andmirrors,tosomeextent,myownexperienceinthisfield.Iapologisehereto
anyonewhosecontributionmayhavebeenmissed.Arelevantpartofthecited
articleswereaccessedthroughtheonlinelibraryoftheItalianNationalCouncilof
Research,andIamreallyindebtedtothisinstitutionforthisinvaluablesupport.
I greatly appreciated stimulating discussions with the colleagues in Perugia L.
Belpassi, F. Pirani, and F. Tarantelli, and I am also grateful to my coworkers in
ViterboS.Borocci,N.Bronzolino,andM.Giordani,whosharedwithme,over
theyears,theinterestfornoblegaschemistry.Finally,thisbookis,certainly,also
theresultofthelove,patience,andunderstandingofmyfamily:mywifeFranci,
andmychildrenSilviaandSimone.Tothem,mydeepestgratitude.Thebookis
alsodedicatedtomyparents,andtothememoryofmyuncle.
Viterbo,September2017 FeliceGrandinetti
1
PartI
AnOverviewofNobleGasChemistry
3
1
AHistoricalIntroduction
1.1 TheDiscoveryoftheElements
The discovery of the noble gases is one of the most fascinating episodes in the
historyofscience.Ittellsaboutcreativenessandintuition,aswellasrigourand
perseverance.Itisalsoarealshowcaseoffundamentalandappliedsciencework-
inginconcert.
Allthenoblegases(butradon)arenaturalconstituentsofair,withpercentages
involumewhichrangefromc.0.9%(Ar)tolessthan9×10−6%(Xe)(seeAppendix
A).However,whileapparentlysoaccessible,theseelementsremainedunknown
untiltheendofthenineteenthcentury,whenphysicalmethods,particularlyspec-
tralanalysisandliquefactionofgases,becamesufficientlywelldeveloped.Itwas
not that chemists and physicists had not previously encountered them. In par-
ticular,in1785,whenreportingabouthis‘Experimentsonair’,Cavendish(1785,
p.382)wrote:
Havingbythesemeans[exhaustiveelectricsparking]condensedasmuch
asIcouldofthephlogisticatedair[N ],Iletupsomesolutionofliverof
2
sulphur to absorb the dephlogisticated air [O ]; after which only a small
2
bubble of air remained unabsorbed, which certainly was not more than
1/120 of the bulk of the phlogisticated air let up into the tube; so that if
there is any part of the phlogisticated air of our atmosphere which dif-
fers from the rest, and cannot be reduced to nitrous acid, we may safely
conclude,thatitisnotmorethan1/120partofthewhole.
He had actually isolated argon (and, probably, also other noble gases), but he
did not recognise this residue as a new element. The official discovery had to
waitmorethanonecentury,anditsannouncementwastheepilogueofareally
intriguingstory.In1892,LordRayleigh(bornJohnWilliamStrutt)hadobserved
thatthenitrogenobtainedfromthereactionofammoniawithoxygenwaslighter
thanthenitrogenrecoveredfromcommonair.Thedifferencewassmall(nearly
onepartin1000),but,asRayleighwroteinalettertoNatureofSeptember29
(Rayleigh, 1892, p. 512), it was ‘entirely outside the errors of experiment’. He
declaredtobe‘muchpuzzled’bythesefindings,‘obligedifanyofyourchemical
readers can offer suggestions as to the cause’. No proposals came at that time,
and Rayleigh continued to work on this anomaly. He could thus confirm that,
NobleGasChemistry:Structure,Bonding,andGas-PhaseChemistry,FirstEdition.FeliceGrandinetti.
©2018Wiley-VCHVerlagGmbH&Co.KGaA.Published2018byWiley-VCHVerlagGmbH&Co.KGaA.
