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OpenResearchOnlineTheOpenUniversity'srepositoryofresearchpublicationsandotherresearchoutputsAbinitiocalculationsofCoshieldinginmodelcomplexesJournalItemHowtocite:Moore,Elaine(2002).
AbinitiocalculationsofCoshieldinginmodelcomplexes.
InternationalJournalofMolecularSciences,3(8)pp.
873–887.
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oro.
open.
ac.
ukInt.
J.
Mol.
Sci.
2002,3,873-887InternationalJournalofMolecularSciencesISSN1422-00672002byMDPIwww.
mdpi.
org/ijms/AbInitioCalculationsofCoShieldinginModelComplexesElaineA.
MooreDepartmentofChemistry,TheOpenUniversity,MiltonKeynes,MK76AA,UKTel.
:+44(0)1908655028,Fax:+44(0)1908858327,E-mail:e.
a.
moore@open.
ac.
ukURL:http://www.
open.
ac.
uk/science/chemistryReceived:26November2001/Accepted:10May2002/Published:31August2002Abstract:RecentabinitiocalculationsofcobaltNMRshieldingshowthatDFT-GIAOcalculationsusinghybridfunctionalsarefoundtoreproduceexperimentalvalueswell.
ThismethodisusedtocalculatethevariationofthecobaltNMRshieldingtensorofsqaurepyramidalnitrosylcomplexeswithrespecttotheCoNOgeometryandtodifferingbasalligands.
TheisotropicshieldingisshowntohavealargenegativederivativewithrespecttoCoXdistancewhereXisaligatingatom.
;thederivativewithrespecttoNOdistanceissmallerbutstillsignificant.
ThezzcomponentwherezisalongtheCoN(NO)bondismoresensitivetothebasalligandsbuttheothertwoprincipalcomponentsaresensitivetotheCoNOgeometry.
Keywords:59Co,NMRshielding,DFT,abinitiocalculations,NOIntroductionThescopeofcobaltNMRspectroscopywasillustratedinarecentreview[1].
59CowasoneofthefirstnucleitobestudiedusingNMRspectroscopy.
Itisanucleuswithahighreceptivityandthelargestknownchemicalshiftrangeofaround20000ppm.
Therearealargenumberofstablelow-spinCo(III)complexeswhicharediamagneticandhencewell-suitedtoNMRstudies.
59Cochemicalshiftswerealsothesubjectofearlytheoreticalconsiderations.
Ramsey[2]derivedanapproximateformulafortheparamagnetictermintheshieldingofthecobaltatomintermsofligandfieldtheory.
()gggzgdBTAETLAr1111211113320piso8→=πσ(1)Int.
J.
Mol.
Sci.
2002,3874whereEistheaverageexcitationenergyfromthegroundstatetotheexcitedstateslinkedbytheshieldingoperator,replacedinthiscasebytheligandfieldtransition(1A1g→1T1ginthecaseofoctahedralcomplexes)toalow-lyingexcitedstate.
Thisledtoapredictionthat59Coshieldingswouldcorrelatewiththeligandfieldsplittingenergies,o,ofcobaltcomplexesandsuchacorrelationwasfoundformeasuredspectraofsimplecomplexes[3].
Inlaterwork[4-6],ther-3termandtheorbitalangularmomentumintegralwhichdeterminethecovalencyornephelauxeticeffectwerealsoshowntobeimportant.
InaseriesofCo(III)pentamminecomplexes,theangularmomentumintegralwasshowntobeofnegligibleinfluenceindeterminingthechangeinchemicalshiftandaplotofisotropicchemicalshiftgaveabettercorrelationwiththeratioofthenephelauxeticfactor,β35,totheexcitationenergythanwiththereciprocaloftheexcitationenergyalone[7].
Thenephelauxeticfactor,β,isafunctionofinterelectronrepulsionandisdefinedastheratiooftheRacahBparameter(obtainedfromopticalspectra)inthecomplexandinthegaseousmetalion.
Recently[8],ChanandAu-Yeunghaveshownthattheangularmomentumintegralisrelatedtothenuclearquadrupolecouplingconstant,QCC.
For59Cosolutionspectra,quadrupolerelaxationisthedominantmechanismandQCCcanbeobtainedfromthehalf-widthoftheresonance.
Correlationswereobtainedforcomplexes[Co(NH3)5X](3+n)+,[Co(CN)5X](2-n)-andtrans-[Co(en)2X2](3+n)+betweenthe59Cochemicalshiftand(ν1/2)1/2/Eavwhereν1/2isthesolutionlinewidthandEavistheenergyofthe1A1g→1T1gtransition.
Thissuggeststhattheangularmomentumintegralisimportantindeterminingthechemicalshift.
Thedataforeachtypeofcomplexlayontwolines,oneforcomplexeswithhardligands,X,andoneforthosewhereXisasoftligand.
ThedifferencesbetweenthehardandsoftligandsisattributedtotheincreasedcovalencyoftheCo-Xbondforsoftligandswhichcausesaquenchingoftheangularmomentum.
Fullabinitiocalculationsof59Cochemicalshieldingshaveonlyrecentlybeenfeasiblehowever.
ThelowenergyexcitationswhichgiverisetothelargechemicalshiftsobservedandtothesimplificationofthedenominatorinRamsey'sformulaposeproblemsforabinitiocalculationsandgaverisetolargeerrorsinHartree-Fockcalculations.
Formoleculescontaininglightelements,theintroductionofMP2correlationcorrections[e.
g.
9,10]andmulti-configurationalmethods[e.
g.
11]haveledtoconsiderablesuccessincalculatingchemicalshieldingtensorsincaseswheretherearelowexcitationenergies.
Foratransitionmetalcomplex,however,verylargecomputerresourceswouldbeneededforsuchmethods.
TheadventofdensityfunctionalmethodshasmadepossibletheabinitiocalculationofNMRshieldingoftransitionmetalcomplexeswithreasonableaccuracywithlesscomputerresource.
Thefirstdensityfunctional(DFT)calculationsoncobaltcomplexes[12]wereperformedusingtheSOS-DFT-IGLOmethodofMalkinetal[13]inthedeMonsuiteofprograms[14-16].
Thecomplexesstudiedcoveredbothneutralandionicspecies-[Co(CN)6]3-[Co(NO2)6]3-,[Co(NH3)6]3+,[Co(en)3]3+,[Co(NH3)4CO3]+and[Co(acac)3].
ThebestresultswerefoundfortheBecke-Perdew[17]exchangecorrelationpotentialwiththeTZVPbasissetofMalkinetal[13-16,18,19]onthecobaltandtheInt.
J.
Mol.
Sci.
2002,3875IGLO-IIbasissetofKutzelnigg[20]onthesurroundingligands.
Althoughaconsiderableimprove-mentonprevioussemi-empiricalcalculations[21],thecalculatedvalueswereconsiderablymoreshiel-dedthantheexperimentalvaluese.
g.
-3159ppmfor[Co(CN)6]3-comparedtothecurrentlyacceptedabsoluteshieldingof-5400ppm[6].
Possiblereasonsforthediscrepancywereputforwardincludingabsenceof4ffunctionsintheCobasissetandthedescriptionoftheexcitedstateinDFTtheory.
ChanandAu-Yeung[22]comparedtheDFT-IGLOmethodusedinthisstudywiththeDFT-GIAOoptioninGaussian94[23]usingtheBecke-Perdewfunctionalon13hexacoordinatedcomplexesofCo(III)involvingtheligandsen,NH3,SCN-,N3-,H2O,NO2-,CN-,Cl-,NO,ONO-,CO32-andS2O32-.
TheyconcludedthatDFT-GIAOproducedresultsclosertoexperimentthanDFT-IGLO.
UsingtheDFT-GIAOmethodwiththehybridfunctionalB3LYPgaveresultsevenclosertoexperiment.
Asubsequentpaper[24]calculatedchemicalshiftspansandskewsforseveralcomplexesusingtheDFT-GIAO-B3LYPmethodand6-311Gbasissetswithvaryingnumbersofpolarisationfunctionsandobtainedsatisfactoryagreementwithexperiment.
Morerecentstudiesofthecomplexesstudiedinref.
12[25]usingDFT-GIAO-B3LYPinGaussian94withWachtersbasisset(62111111/3311111/3111)[26,27]oncobaltandthe6-31G*basissetontheligandatomsalsogavereasonableresults.
Theseauthorsfoundthattheadditionofffunctionstothecobaltbasissetandtheuseoflargerbasissetsgavelittleimprovement.
TheDFT-GIAOstudiesnotonlyreproducethechemicalshiftwellbutalsoyieldedaremarkablygoodvaluefortheabsoluteshieldingof[Co(CN)6]3-.
GodboutandOldfield[25]plottedthecalculatedabsolutechemicalshieldingsagainsttheexperimentalchemicalshiftsandobtainedavaluefortheabsoluteshieldingof-5162ppmastheinterceptcomparedtotheexperimentallydeterminedvalueof-5400ppm.
ThesuccessofhybridDFTmethodshasbeenanalysed[28]andattributedtomorediffusevirtualorbitals,couplingduetoHartree-FockexchangeandtheincreaseoftheHOMO-LUMOgaprelativetothatobtainedusingpureDFTmethods.
BecauseoftheiruseasmodelsforbiologicalsystemssuchasVitaminB12andtheisoelectronicFe(II)hemes,cobaltcomplexeswithmacrocyclicligandssuchasporphinshavebeenofconsiderablerecentinterest.
Arecentpaper[29]reportsacalculationofcobaltchemicalshieldingfortheporphincomplex[Co(TDCPP)(MeIm)2]+inwhichtheTDCPP(tetra(dichlorophenyl)porphyrin)groupformsaplanearoundthecobaltandtwomethylimidazolegroupsoccupypositionsaboveandbelowthisplane.
ThecalculationsusedtheDFT-GIAO-B3LYPmethodwitha6-311Gbasissetonthelighteratoms,theMaclean-Chandlerbasisset[30,31]onchlorineandtheWachters-Hayall-electronbasisset[26,32]forcobalt.
Althoughchemicalshifttensorsaremoredifficulttocalculatethantheisotropicshift,theseauthorsobtainedverycloseagreementwiththeexperimentalchemicalshifttensor.
Zhouetal[33]consideredasetofcomplexesinwhich[Co(CN)6]3-wasboundtoprotonatedpolyammoniummacrocyclics.
Theyreproducedthe59CochemicalshiftsbyalteringtheCo-CandC≡Ndistancesandthesymmetryof[Co(CN)6]3-tofitthegeometryfoundinthemacrocycles.
Int.
J.
Mol.
Sci.
2002,3876Therehavebeensomestudiesofhow59Coshieldingvarieswithchangesingeometry.
Experimentallythevariationofshieldingwithgeometryshowsupastemperaturedependenceandisotopeshifts.
Cobaltchemicalshiftshaveextremelylargetemperaturedependenceandlargeisotopeshiftsindicatingastrongdependenceongeometry.
Insimplecases,suchdatacanbeanalysedtoobtainderivativesofshieldingwithrespecttobondextensionsandangledeformations.
Byanalysingisotopeshifts,Jamesonetal[34]foundfor[Co(CN)6]3-thatthefirstorderderivativeoftheshieldingwithrespecttotheCo-Cbonddistancewas–7500ppm-1,thatisthecobaltnucleusbecomesmoredeshieldedastheCo-Cdistanceincreases.
Thethermalshieldingderivativeof[Co(NO2)6]3-hasbeenmeasured[34]as-2.
85ppmK-1,overtwicethatobservedfor[Co(CN)6]3-,butthevibrationalmotionismorecomplicatedthanthatofthecyanocomplexandthereisthepossibilityofinternalrotationofthenitritogroupsothatthethermalshieldingderivativeisnoteasilylinkedtothederivativeoftheshieldingwithCo-Ndistance.
GodboutandOldfield[25]havecalculatedthevariationofcobaltshieldingwithCo-Cbonddistancein[Co(CN)6]3-andwithCo-Ndistancefor[Co(NO2)6]3-.
Theyusedageometry-optimisedstructureforthefreeionwitharangeofCo-CorCo-Ndistances.
Inbothcases,theplotswerelinearwithslopesof–4856ppm-1for[Co(CN)6]3-and–6180ppm-1for[Co(NO2)6]3-.
Theythuscorrectlypredictthattheslopesarenegative,1-2ordersofmagnitudelargerthantheshieldingderivativesoffirstrowatomsandthatthemagnitudeofthederivativeforthenitritocomplexislargerthanthatforthecyano-complex.
Wereporthereastudyof5-coordinatecobaltnitrosylcomplexeswithparticularfocusontheresponseof59CoshieldingtovariationinthegeometryoftheCoNOgrouping.
Square-pyramidalnitrosylporphincomplexeshavebeenstudiedasmodelsforNOandO2bindingtoheme-likesystems.
TheCoNOgroupcanadopttwodistinguishablegeometries,linearwithaCoNOangleof180°andbentwheretheCoNOangleisabout130°,resemblingtheFeOOarrangementinheme.
GodboutandOldfield[25]notedthattheyhaddeterminedthe59Coshieldinginanitrosylcobalttetraphenylporphinas-13530ppm.
Theyremarkedthatthiswasconsiderablymoredeshieldedthananticipated.
Howeverthisvalueyieldsachemicalshiftof8086ppmwhichisinfactveryclosetothemeasuredvalue[35]of7909ppmforcobaltnitrosyltetraphenylporphinateinsolution.
Inadditiontothedataonporphinatocomplexes,therearealsoexperimentalmeasurementsofsolutionchemicalshiftsforCoinnitrosylcomplexeswithpolydentateligandscoordinatingthroughNandOandnitrosyldithiocarbamatocomplexes.
Becauseofthelowersymmetry,square-pyramidalnitrosylcomplexeswouldbeexpectedtoshowgreaterasymmetrythanthecomplexespreviouslystudiedandthedifferentcomponentsoftheshieldingtensorcanbeshowntoresponddifferentlytogeometrychanges.
Int.
J.
Mol.
Sci.
2002,3877ComputationalmethodThestructuresofthemodelcomplexesusedwerefortheporphincomplexes,withaN-Co-Nangleof76°andaCo-N-Cangleof137°,fortheSchiffbasecomplexeswithanN-Co-Oangleof89°,aCo-N-Cangleof129.
5°,aCo-O-Cangleof136°andaC-C-Cangleof162°andforthedithiocarbamato-complexes,withaCo-S-Cangleof68°.
Allthreeligandswerekeptplanar.
Thearrangementofthebasalligandswaskeptsymmetricalasshownandfixedformostcalculations.
OptimisationgaveshorterCo-basalatomdistancesonthesidenearestthenitrosyloxygenwhenthesedistanceswereallowedtovary.
FulloptimisationoftheCoNOgroupgenerallyledtoatiltoftheCoNaxisawayfromtheperpendiculartotheplane,andtogetherwiththeshorterCo-basalatomdistanceandtheorientationofthenitrosyloxygenoverabasalligandatom,thisallowedstabilisationofthestructurethroughO-basalligandatominteraction.
Inexperimentalstructures,theCo-basalatomdistancesarekeptfixedinthesymmetricalpositionbytherestofthemoleculeasintheporphinatesand/orbythecrystalpacking,soitwasconsideredabettermodeltoretainthesymmetryofthebasalligands.
Inmostoftheresultsreportedhere,onlyoneparameter(bonddistanceorangle)wasvariedatatimekeepingallothersfixed.
Thenitrosyloxygenwaspositionedbetweenthebasalatomsforsomerunsandoveronebasalatomforothers.
Botharrangementsarefoundexperimentally.
HoweverwealsocalculatedchangesinshieldingfordithiocarbamatocomplexesallowingtheCoNOgeometrytorelaxastheCo-NdistanceandCoNOanglewerechanged.
Int.
J.
Mol.
Sci.
2002,3878OurcalculationsusedtheDFT-GIAO-B3LYPmethodinGaussian98[36]ontheDEC8400/CompaqES40cluster,Columbus,attheRutherfordAppletonLaboratory.
ThebasissetusedwasAhrlich'sVTZbasisset[37]pluspolarisationfunctionsonallatoms.
Convergencewasfoundtobeeasierusingthesamebasissetonallatoms.
Triplezetabasissets,asnotedinearlierworkdescribedintheIntroduction,givegoodresultsforCoshieldingwhenusedwithhybridfunctionals.
Theabsoluteshieldingof[Co(CN)6]3-usingtheoptimisedgeometrywithaCo-Cdistanceof191pmandC≡Ndistanceof117pmwascalculatedtobe–5882ppmandusingtheexperimentalgeometryforK3[Co(CN)6]ofCo-C190pmandC≡N113pm–5360ppmwiththismethodandbasisset.
Thesevaluesareveryclosetotheexperimentallydeterminedoneandgiveusconfidenceinourmethod.
ResultsThecalculatedshieldingtensorsforourmodelcomplexesareshowninTable1alongwiththeMullikenchargesonCo.
isthespanandκtheskew.
Intermsoftheprincipalcomponentsofthetensor,σ11,σ22andσ33whereσ11≤σ22≤σ33,=σ33-σ11andκ=3*(σiso-σ22)/.
WedefinemolecularaxessothattheCoN(NO)bondformsthezaxisandtheyaxisisbetweenthebasalligands.
ForthemajorityoftheporphinandthiocarbamatocomplexeswheretheCoNOgroupisinthexzplaneandtheCoNOangleisintherange115-140°,oneprincipalcomponent,usuallyσ33butinsomecasesσ22,isσyy.
The1axisisrotatedbyanangleof5-15°fromthexaxistowardsthezaxisinthexzplaneforthedithiocarbamatocomplexes.
Fortheporphincomplexesthe1axisisrotatedbyaslightlylargerangle(12-20°)fromthezaxistowardsthexaxis.
TheSchiffbasecomplexesandthosewheretheCoNOgroupisnotinthexzplanearelesssymmetricalandnoneoftheprincipalaxescoincideswithx,yorz.
TheprincipalaxesoftheSchiffbasecomplexesarehoweverclosetothoseoftheporphincomplexes.
ForlargeCoNOangles,σxxandσyybecomemorenearlyequalasthecomplexapproachesC2vsymmetry.
Ananalysisofthedenergylevelsinsquare-pyramidalnitrosylcomplexesofiridiumwasobtainedbyMingos[38]usingtheWolfsberg-Helmholtzmethod.
Usingtheorientationjustdescribed,theHOMOwasthea'orbitalincludingcontributionsfromdz2,dxzandtheπ*andσorbitalsonNOandtheLUMOana"orbitalwithcontributionsfromdyzandtheπ*onNO.
Thesewouldbeexpectedtoprovidealargecontributiontotheparamagneticshielding,particularlyσxx,forCofromdz2todyzwhichwillbedependentontheCo-NObond.
Howeverthereisanothercontribution,primarilytoσzz,fromdxytodx2-y2whichdoesnotinvolveNOorbitalsandwillbehighlydependentontheCo-basalligandinteraction[39].
ThusifthislattercontributionpredominatesweshouldexpectlittledependenceoftheshieldingontheCoNOgeometry.
OurcalculationsonthedithiocarbamatocomplexesindicatethattheHOMOisthedz2/NObondinga'orbitalandtheLUMOthedyz/NOπa"orbital.
BothorbitalsbecomelowerinenergyastheCoNbonddistanceincreasesortheCoNOangledecreasesbuttheInt.
J.
Mol.
Sci.
2002,3879Table1.
CalculatedCoshieldingtensorsformodelsquarepyramidalnitrosylcomplexes.
r(Co-basalatom)/pmr(Co-N(NO))/pmr(NO)/pm∠CoNO/°σiso/ppmσ11/ppmσ22/ppmσ33/ppm/ppmκMullikenchargePorphincomplexes197.
6173.
8101120-15542-21851-15902-8871129000.
080.
243""112"-16057-21373-16990-9807115660.
240.
259"""130-16528-21809-17688-10086107230.
320.
253"""140-17460-22853-18628-10898119550.
290.
244""114120-16157-21348-17153-9969113790.
260.
261""116"-16257-21345-17300-10126112190.
280.
263"183.
3112"-17576-22245-18695-11789104560.
020.
297Schiffbasecomplexes195.
0/183.
3173.
0101125-13142-18634-13220-7571110630.
220.
327"173.
8112120-13760-18432-14374-847499580.
180.
348""116120-13993-18478-14759-8441100370.
230.
352""112130-14128-18889-14762-8734101550.
190.
342""116129-14337-19002-15021-8988100740.
200.
347""112140-14864-19872-15224-9496103760.
100.
335"180.
6112127-14888-19207-15695-976294450.
260.
372"183.
3101130-14398-19196-14936-9062101340.
160.
367"193101125-15230-19466-15928-1029691700.
230.
403""110140-17685-22727-17220-1310921408-0.
070.
417""116120-17274-23250-16977-1159511655-0.
080.
432Dithiocarbamatocomplexes200172.
8110120-5713-9074-5388-26776397-0.
15-0.
241210172.
8101115-6922-9798-6025-49444854-0.
55-0.
142"177"120-7443-11338-5963-50286310-0.
70-0.
129"172.
8110*120-7761-11836-5871-55766266-0.
90-0.
1357848-12553-5794-51987355-0.
84-0.
146"""130-8074-13072-5694-54567616-0.
94-0.
143"""140-8711-14238-6407-54888750-0.
79-0.
142"""150-10036-16659-8360-508711272-0.
43-0.
143"""160-12904-22024-12393-429617728-0.
09-0.
147"""170-19965-33982-22636-3279307030.
26-0.
152210172.
8112120-8023-12959-5777-53337626-0.
88-0.
145"173.
8""-8085-12301-6136-58186483-0.
90-0.
127"175117*135-9422-15016-7733-55189498-0.
53-0.
124"177110120-8380-13515-5845-57797736-0.
98-0.
124210183101120-8053-12367-6054-57376630-0.
90-0.
09"110"-9191-14995-6684-58949101-0.
83-0.
093Int.
J.
Mol.
Sci.
2002,3880Table1.
(continued)r(Co-basalatom)/pmr(Co-N(NO))/pmr(NO)/pm∠CoNO/°σiso/ppmσ11/ppmσ22/ppmσ33/ppm/ppmκMullikencharge""116"-9928-16694-7291-579810896-0.
73-0.
099"193110"-10685-17718-8411-592811790-0.
58-0.
046"""130-11096-18580-8880-582912751-0.
52-0.
040"""140-12264-21000-10216-557515425-0.
40-0.
036226.
5172.
8110120-11632-16300-11881-671595850.
080.
046175111*130-12536-16297-11985-93256972-0.
240.
057"175116.
6#129.
5#-12757-18754-11704-781410940-0.
290.
058"183116.
25#127.
3#-14240-21366-12180-917412192-0.
510.
091"193115.
86#124.
8#-16284-25185-12588-1107714108-0.
790.
129"187.
85#116.
23#120-14936-22490-12502-981712673-0.
580.
11"183.
57#116.
12#130-14535-21980-12143-948112499-0.
570.
093"180.
8#115.
89#140-14907-22965-11683-1007212893-0.
750.
078"191.
0#101127.
7#-13822-18922-13503-90409882-1.
100.
108"186.
04#112127.
1#-14359-21167-12569-934211825-0.
450.
100"185.
34#114126.
9#-14455-21545-12417-940212143-0.
500.
099240.
0173.
8101*120-16943-23093-14668-1306710026-0.
680.
237*Oofnitrosyloverbasalligandatom#partiallyoptimisedgeometrydecreaseintheHOMOenergyisgreatersothattheenergygapalsodecreases.
TheMullikenpopulationonCoincreasesslightlywithCoNdistanceandNOdistanceanddecreaseswithCoNOangle,butismainlydeterminedbythebasalligands,increasingastheCo-basalliganddistanceincreasesreflectingaloweringofcovalency.
Figure1showsthevariationoftheisotropicshieldingandtheprincipalcomponentswithCo-N(NO)distanceforbothfixedNOdistanceandCoNOangleandwhentheCoNOgeometryisallowedtorelax.
TheNOdistancefortheseriesofrunsinwhichtheCoNOgeometryisoptimisediscloseto1.
16andsowehaveusedaseriesofrunswithanNOdistanceof1.
16forthefixedgeometrycomparison.
σ11andσ33bothdecreasewithincreasingCo-Ndistanceforthetwosetsofdatashown.
σ22showstheleastvariationwithCo-Ndistanceasisexpectedforacomponentthatismainlyσzz.
RelaxingtheCoNOgeometryhaslittleeffectonthepatternofchange.
Thenotabledifferenceinσ22stemsfromthedifferenceinthebasalligands.
ThederivativeoftheisotropicshieldingwithrespecttotheCo-Ndistanceisabout–19000ppm-1forthecomplexesinfigure1.
ReferencetothedatainTable1showsasmallerderivativeforcomplexeswithshorterNOdistances.
Int.
J.
Mol.
Sci.
2002,3881-30000-25000-20000-15000-10000-5000170175180185190195Co-Ndistance/pmShielding/ppmFigure1.
VariationofshieldingwithchangeinCo-NdistanceforasetofdithiocarbamatocomplexesforwhichtheCoNOgeometryisrelaxed(solidlines)andforSchiffbasecomplexeswithCoNO120°andanNOdistanceof1.
16(dottedlines)isotropicshielding,σ11,σ22andσ33.
Theisotropicshieldingisalsomarkedlydependentonthebasalligands.
Adjustingthecobaltdistancetothebasalligandsinthedithiocarbamatocomplexfrom2.
0to2.
1to2.
65ledtoanincreaseinshieldingequivalenttoaderivativegreaterthan–20000ppm-1duetoincreasesinσxxandσzzarisingfromdecreasedoverlapofdz2anddx2-y2withbasalligandorbitals,asshowninfigure2.
Inthisfigureσyyandσzzrefertowhicheverofσ22andσ33areclosesttothesecomponents,asthedirectionofthe2and3axeschangeacrosstheseries.
σzzisparticularlysensitivetochangesinCo-Sdistanceasexpected.
WewouldexpectsomeeffectfromalteringtheNOdistancebecausethenitrogenorbitalsareusedinbondingtoOandCoandastheNObondisweakened,theCoNbondisstrengthened.
ThecalculatedshieldingshowsadecreasewithincreasingNOdistance,figure3,forallcomponentsexceptσ11.
Fortheporphinmodelshowntheplotsaremuchclosertolinearwithderivativesof–4747ppm-1thanthosewithrespecttoCo-liganddistance,althoughlargerderivativesarefoundforsomeofthedithiocarbamatocomplexes.
CoNOgroupshavethepotentialtowag(varyingtheangle)andswing(varyingthepositionofthenitrosyloxygenwithrespecttothebaseligands).
Varyingtheanglefrom120°to140°,therangeofInt.
J.
Mol.
Sci.
2002,3882-18000-16000-14000-12000-10000-8000-6000-4000-2000195200205210215220225230Co-Sdistance/pmshielding/ppmFigure2.
CalculatedvariationofCoshieldingwithCo-Sdistancefordithiocarbamatocomplexeswithr(co-N)=1.
728,r(NO)=1.
10andaCoNOangleof120°.
isotropicshielding,σ11,σyyandσzz.
Figure3.
VariationofcalculatedCoshieldingwithNOdistanceforamodelporphincomplexwithr(CoN)=1.
74isotropicshielding,σ11,σ22andσ33-25000-23000-21000-19000-17000-15000-13000-11000-9000-7000100105110115120NOdistance/pmshielding/ppmInt.
J.
Mol.
Sci.
2002,3883Figure4.
Variationofcalculated59CoshieldingwithCoNOangleformodelnitrosylcomplexes:dithiocarbamatocomplexwithoptimisedCoNOgeometry(solidline),modelSchiffbasecomplexwithr(CoN)=1.
738andr(NO)=1.
12(dottedline)isotropicshielding,σ11,σ22andσ33anglesfoundinmostbentCo(III)nitrosylcomplexes,producedadecreaseinshieldingofabout1000–2000ppmabout10%oftheabsoluteshielding.
Thisisexemplifiedinfigure4wheretheisotropicshieldingisplottedagainstCoNOangleforamodelSchiffbasemodelcomplex.
SimilarchangeswithchangeinanglewereobtainedforaporphinmodelcomplexandfordithiocarbamatoandSchiffbasecomplexeswithdifferentCoNandNOdistances.
Inthiscase,thepartiallyoptimisedstructuredisplaysadifferentpatterntotheserieswithfixedCoNOgeometrywiththeshieldinggoingthroughamaximum.
InthesestructuretheCo-Ndistancedecreaseswithincreasingangleandasshowninfigure1thiswillleadtoanincreaseinshielding,offsettingthedecreaseduetoincreaseinangle.
Theeffectofligandswingingwasinvestigatedbycalculatingtheshieldingwiththenitrosyloxygenintwopositions,betweentwobasalligatingatomsandoveronebasalatom.
Thechangesinthetensorforatypicaldithiocarbamatocomplexcanbeseenbycomparingthestarredentrieswithnon-starredentriesforthedithiocarbamatocomplexwithCo-N=1.
728,N-O=1.
1andCoNOangleof120°inTable1.
Thesedifferencesarenotlargebutarenoticeable.
Averagingoverthesetwopositionswouldgiveareducedspanbecausethetensorprincipalcomponentswillnotbeexactlyalignedforthetwopositions.
-25000-23000-21000-19000-17000-15000-13000-11000-9000115120125130135140NOdistance/pmshielding/ppmInt.
J.
Mol.
Sci.
2002,3884ForthecomplexwiththeObetweentheligands,thenoneprincipalaxisisalongtheyaxiswiththeothertworotatedby12°fromthexandzaxes,whereasallthreeaxesarerotatedfortheothercomplexleadingtooneaxislyingalmostoverCo-SdirectionwhereSistheatomoverwhichthenitrosyloxygenlies.
DiscussionandConclusionsDensityfunctionalcalculationsofcobaltshieldinginCo(III)complexesusingDFT/GIAOmethodswithmoderately-sizedbasissetsandhybriddensityfunctionalshavebeenfoundbyseveralgroupstogivegoodagreementwithexperimentalshieldingvalues.
Agreementisgoodnotonlyforsimpleoctahedralcomplexesbutalsoforlargersystemssuchasporphinatocomplexes.
Wehavefoundthatsuchcalculationsalsogivegoodresultsforsquare-pyramidalnitrosylcomplexesofcobalt.
Analysisoftheshieldingtensorsshowsthatthelargestcomponentarisesfromthedz2todyztransition.
Theparamagneticpartofthiscomponentincreasesrapidlywithincreasingcobalt-liganddistance.
Theprincipalcomponentclosesttozz,wherethezaxisisalongtheCo-N(NO)bond,showsamarkeddependenceoncobalt-basalligatingatomdistanceandthenatureoftheligandaswouldbeexpectedforacomponentarisingprimarilyfromorbitalsinthebasalplane.
ThethirdprincipalcomponentbycontrastismoresensitivetoCo-N(NO)distancethantothebasalligands.
TheisotropicshieldingdisplayslargechangeswithCo-NandCo-basalligatingatomdistance.
Thelargechangesintheshieldingoftheorderof-103-104ppm/withvariationincobaltligatingatomdistanceagreewithexperimentalobservationsoftemperaturevariationandisotopeshiftswhichindicatethatcobaltshieldingisverysensitivetochangesingeometry.
TheisotropicshieldingdecreaseswithNOdistancebutthederivativeissmallerthanthatwithrespecttoCo-ligatingatomdistancesandthemostnegativecomponentoftheshieldingtensorcandecreasewithincreasingNOdistance.
ChangesintheshieldingtensorwithCoNOanglearemuchsmaller.
Forcomplexeswiththebasalligandsarrangedattheexperimentaldistancesfromthecobalt,thentheshieldingincreasesNArecentstudyonB12modelsystems[40]showsthatincreaseinaxialCo-CbonddistanceduetosubstitutionofdifferentalkylgroupsleadstoanincreasedHOMO-LUMOgapviadecreaseoftheHOMOenergy.
OurstudiesshowthatincreaseoftheCo-N(NO)distanceleadstoaloweringinenergyofbothHOMO(Codz2/NOσ/π)andLUMO(Codyz/NOπ)withagreaterloweringoftheLUMOleadingtoadecreaseinHOMO-LUMOenergygap.
Ideally,forcomparisonwithexperimentalchemicalshiftscalculationsshouldbecorrectedfortemperatureeffects,althoughthisisdifficultexceptforsimplecasessuchas[Co(CN)6]3-wheremostoftheeffectcomesfromthevariationinonedistance(CoC).
Int.
J.
Mol.
Sci.
2002,3885AcknowledgementIshouldliketothanktheUKcomputationalchemistryworkingpartyforagrantoftimeontheEngineeringandPhysicalScienceResearchCouncil(EPSRC)'ssuperscalarfacilityattheRutherfordAppletonLaboratory.
References1.
Chan,C.
C.
;Au-Yeung,S.
C.
F.
InAnnualReportsonNMRSpectroscopy;Webb,G.
A.
,Ed.
;AcademicPress,London,SanDiego,2000;vol.
41,pp1-54.
2.
Ramsey,N.
F.
MagneticShieldingofNucleiinMolecules.
Phys.
Rev.
1950,78,699-703.
3.
Freeman,R.
;Murray,G.
R.
;Richards,R.
E.
Cobaltnuclearresonancespectra.
Proc.
Roy.
Soc.
A1957,242,455-466.
4.
Jurani,N.
Inorg.
Chem.
1980,19,1093.
5.
Jurani,N.
Nephelauxeticeffectinparamagneticshieldingoftransition-metalnucleiinoctahedrald6complexes.
J.
Am.
Chem.
Soc.
1988,110,8341.
6.
Bramley,R.
;Brorson,M.
;Sargenson,A.
M.
;Schffer,C.
F.
;J.
Am.
Chem.
Soc.
1985,107,2780.
7.
Mason,J.
PatternsofNuclearMagneticShieldingofTransition-MetalNuclei.
Chem.
Rev.
1987,87,1299-1312.
8.
Chan,J.
C.
C.
;Au-Yeung,C.
F.
Interpretationof59CoNMRshieldingusingthehardandsoftacid-baseconcept.
J.
Chem.
Soc.
FaradayTrans.
1996,92,1121-1128.
9.
Gauss,J.
J.
Chem.
Phys.
1993,99,3629.
10.
Bouman,T.
D.
;Hansen,Aa.
E.
NMRshieldingcalculationsbeyondcoupledHartree-Fock:secondordercorrelationeffectsinlocalised-orbital/local-origincalculationsofmoleculescontainingphosphorus.
Chem.
Phys.
Lett.
1990,175,292-298.
11.
VanWüllen,C.
;Kutzelnigg,W.
CalculationofnuclearmagneticresonanceshieldingsandmagneticsusceptibilitiesusingmulticonfigurationHartree-Fockwavefunctionsandlocalgaugeorigins.
J.
Chem.
Phys.
1996,104,2330-2337.
12.
Chan,J.
C.
C.
;Au-Yeung,S.
C.
F.
;Wilson,P.
J.
;Webb,G.
A.
SOS-DFPT-IGLOcalculationsof59CoNMRshieldingparametersofhexacoordinateddiamagneticCo(III)complexes.
J.
Mol.
Struct.
(THEOCHEM)1996,365,125-130.
13.
Malkin,V.
G.
;Zhidomorov,G.
M.
Zh.
Strukt.
Khim.
1988,29,32.
14.
Malkin,V.
G.
;Malkina,O.
L.
;Salahub,D.
R.
Chem.
Phys.
Lett.
1993,204,80.
15.
Malkin,V.
G.
;Malkina,O.
L.
;Salahub,D.
R.
Chem.
Phys.
Lett.
1993,204,87.
16.
Malkin,V.
G.
;Malkina,O.
L.
;Casida,M.
E.
;Salahub,D.
R.
J.
Am.
Chem.
Soc.
1994,116,5898.
17.
Perdew,J.
P.
,Phys.
Rev.
B1986,33,8822.
18.
Schfer,A.
J.
Chem.
Phys.
1992,97,2571.
19.
Wachters,A.
J.
H.
,J.
Chem.
Phys.
1970,52,1033.
20.
Kutzelnigg,W.
;Fleischer,U.
;Schindler,M.
;NMR:BasicPrinciplesandProgress1990,23,165.
21.
Lamphun,B.
N.
;Webb,G.
A.
J.
Mol.
Struct.
(THEOCHEM)1983,104,191.
Int.
J.
Mol.
Sci.
2002,388622.
Chan,J.
C.
C.
;Au-Yeung,S.
C.
F.
Acomparativestudyofthecalculationof59CoNMRshieldingconstantsofhexacoordinateddiamagneticCo(III)complexesusingDFT-IGLOandDFT-GIAOmethods.
J.
Mol.
Struct.
(THEOCHEM)1997,393,93-96.
23.
Gaussian94,M.
J.
Frisch,G.
W.
Trucks,H.
B.
Schlegel,P.
M.
W.
Gill,B.
G.
Johnson,M.
A.
Robb,J.
R.
Cheeseman,T.
Keith,G.
A.
Petersson,J.
A.
Montgomery,K.
Raghavachari,M.
A.
Al-Laham,V.
G.
Zakrewski,J.
V.
Ortiz,J.
B.
Foresman,J.
Ciolowski,B.
B.
Stefanov,A.
Nanayakkara,M.
Challacombe,C.
Y.
Peng,P.
Y.
Ayala,W.
Chen,M.
W.
Womg,J.
L.
Andres,E.
S.
Replogle,R.
Gomperts,R.
L.
Martin,D.
J.
Fox,J.
S.
Binkley,D.
J.
Defrees,J.
Baker,J.
P.
Stewart,M.
Head-Gordon,C.
GonzalezandJ.
A.
Pople,Gaussian,Inc.
,PittsburghPA,1995.
24.
Chan,J.
C.
;Au-Yeung,S.
C.
F.
DensityFunctionalStudyof59CoChemicalShieldingTensorsUsingGauge-IncludingAtomicOrbitals.
J.
Phys.
Chem.
A,1997,101,3637-3640.
25.
Godbout,N.
;Oldfield,E.
DensityFunctionalStudyofCobalt-59NuclearMagneticresonanceChemicalShiftsandShieldingTensorElementsinCo(III)Complexes.
J.
Am.
Chem.
Soc.
1997,119,8065-8069.
26.
Wachters,A.
J.
H.
J.
Chem.
Phys.
1970,52,1033.
27.
Wachters,A.
J.
H.
IBMTech.
Rept.
,1969RJ584.
BasissetswereobtainedfromtheExtensibleComputationalChemistryEnvironmentBasisSetDatabase,Version1.
0,asdevelopedanddistributedbytheMolecularScienceComputingFacility,EnvironmentalandMolecularSciencesLaboratorywhichispartofthePacificNorthwestLaboratory,P.
O.
Box999,Richland,Washington99352,USA,andfundedbytheU.
S.
DepartmentofEnergy.
ThePacificNorthwestLaboratoryisamulti-programlaboratoryoperatedbyBattelleMemorialInstituefortheU.
S.
DepartmentofEnergyundercontractDE-AC0676RLO1830.
ContactDavidFellerorKarenSchuchardtforfurtherinformation.
28.
Schrechenbach,G.
,J.
Chem.
Phys.
1990,110,11936.
29.
Xu,X-P.
;Au-Yeung,S.
C.
F.
ADFTand59CoSolid-StateNMRStudyoftheChemicalShieldingPropertyandElectronicInteractionintheMetalloporphyrinSystem.
J.
Am.
Chem.
Soc.
2000,122,6468-6475.
30.
Maclean,A.
D.
;Chandler,G.
S.
J.
J.
Chem.
Phys.
1993,98,5648.
31.
Krishnan,R.
;Binkley,J.
S.
;Seeger,R.
;Pople,J.
A.
J.
Chem.
Phys.
1980,72,650.
32.
Hay,P.
J.
J.
Chem.
Phys.
1977,66,4377.
33.
Zhou,P.
;Au-Yeung,S.
C.
F.
;Xu,X-P.
,ADFTand59CoSolid-StateNMRstudyoftheSecond-SphereInteractioninPolyammoniumMacrocyclesCobaltCyanideSupercomplexes.
J.
Am.
Chem.
Soc.
1999,121,1030.
34.
Jameson,C.
J.
;Rehder,D.
;Hoch,M.
J.
Am.
Chem.
Soc.
1987,109,2589-259435.
Groombridge,C.
J.
;Larkworthy,L.
F.
;Marécaux,A.
;Povey,D.
C.
;Smith,G.
W.
;Mason,J.
Synthesisand15NNuclearMagneticResonanceShiftTensorsofBentNitrosylComplexeswithN-SubstitutedSalicylideneiminateColigands;theShifttensorasaCriterionofMNOBondAngle.
J.
Chem.
Soc.
DaltonTrans.
1992,3125-3131.
36.
Gaussian98,RevisionA.
7,M.
J.
Frisch,G.
W.
Trucks,H.
B.
Schlegel,G.
E.
Scuseria,M.
A.
Robb,J.
R.
Cheeseman,V.
G.
Zakrzewski,J.
A.
Montgomery,Jr.
,R.
E.
Stratmann,J.
C.
Burant,S.
Int.
J.
Mol.
Sci.
2002,3887Dapprich,J.
M.
Millam,A.
D.
Daniels,K.
N.
Kudin,M.
C.
Strain,O.
Farkas,J.
Tomasi,V.
Barone,M.
Cossi,R.
Cammi,B.
Mennucci,C.
Pomelli,C.
Adamo,S.
Clifford,J.
Ochterski,G.
A.
Petersson,P.
Y.
Ayala,Q.
Cui,K.
Morokuma,D.
K.
Malick,A.
D.
Rabuck,K.
Raghavachari,J.
B.
Foresman,J.
Cioslowski,J.
V.
Ortiz,A.
G.
Baboul,B.
B.
Stefanov,G.
Liu,A.
Liashenko,P.
Piskorz,I.
Komaromi,R.
Gomperts,R.
L.
Martin,D.
J.
Fox,T.
Keith,M.
A.
Al-Laham,C.
Y.
Peng,A.
Nanayakkara,C.
Gonzalez,M.
Challacombe,P.
M.
W.
Gill,B.
Johnson,W.
Chen,M.
W.
Wong,J.
L.
Andres,C.
Gonzalez,M.
Head-Gordon,E.
S.
Replogle,andJ.
A.
Pople,Gaussian,Inc.
,PittsburghPA,1998.
37.
A.
Schafer,H.
HornandR.
Ahlrichs,J.
Chem.
Phys.
1992,972571.
BasissetswereobtainedfromtheExtensibleComputationalChemistryEnvironmentBasisSetDatabase,Version9/11/00,asdevelopedanddistributedbytheMolecularScienceComputingFacility,EnvironmentalandMolecularSciencesLaboratorywhichispartofthePacificNorthwestLaboratory,P.
O.
Box999,Richland,Washington99352,USA,andfundedbytheU.
S.
DepartmentofEnergy.
ThePacificNorthwestLaboratoryisamulti-programlaboratoryoperatedbyBattelleMemorialInstituefortheU.
S.
DepartmentofEnergyundercontractDE-AC0676RLO1830.
ContactDavidFellerorKarenSchuchardtforfurtherinformation.
38.
Mingos,D.
M.
P.
,Inorg.
Chem.
1973,12,1209.
39.
Duffin,P.
A.
;Larkworthy,L.
F.
;Mason,J.
;Stephens,A.
N.
;Thompson,R.
M.
LigandFieldEffectsintheNuclearMagneticShieldingofNitrogen-15andCobalt-59inBentNitrosylComplexesofCobalt(III).
Inorg.
Chem.
1987,26,2034-2040.
40.
Jensen,K.
P.
;Sauer,S.
P.
A.
;Liljefors,T.
;Norrby,P-O.
TheoreticalInvestigationofStericandElectronicEffectsinCoenzymeB12Models.
Organometallics2001,20,550.
2002byMDPI(http://www.
mdpi.
org).