Experimental and Theoretical Comparison of Actinide and Lanthanide Bonding in M[N(EPR2)2]

13 Pages·2007·0.28 MB·English

Inorg.Chem.2008, 47, 29- 41
Experimental and Theoretical Comparison of Actinide and Lanthanide
Bonding in M[N(EPR ) ] Complexes (M ) U, Pu, La, Ce; E ) S, Se, Te;
2 2 3
R ) Ph, iPr, H)
Andrew J. Gaunt,*,† Sean D. Reilly,† Alejandro E. Enriquez,† Brian L. Scott,† James A. Ibers,‡
Perumal Sekar,‡ Kieran I. M. Ingram,§ Nikolas Kaltsoyannis,*,§ and Mary P. Neu*,†
Chemistry DiVision, Plutonium Manufacturing and Technology DiVision, Materials Physics and
Applications DiVision, and Associate Directorate for Chemistry, Life, and Earth Sciences, Los
Alamos National Laboratory, Los Alamos, New Mexico 87545, Department of Chemistry,
Northwestern UniVersity, 2145 Sheridan Road, EVanston, Illinois 60208-3113, and Department of
Chemistry, UniVersity College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
ReceivedAugust14,2007
TreatmentofM[N(SiMe)] (M)U,Pu(An);La,Ce(Ln))withNH(EPPh) andNH(EPiPr) (E)S,Se),afforded
323 22 22
the neutral complexes M[N(EPR)] (R ) Ph,iPr). Tellurium donor complexes were synthesized by treatment of
223
MI(sol) (M ) U, Pu; sol ) py and M ) La, Ce; sol ) thf) with Na(tmeda)[N(TePiPr)]. The complexes have
3 4 22
been structurally and spectroscopically characterized with concomitant computational modeling through density
functional theory (DFT) calculations. The An- E bond lengths are shorter than the Ln- E bond lengths for metal
ionsofsimilarionicradii,consistentwithanincreaseincovalentinteractionsintheactinidebondingrelativetothe
lanthanide bonding. In addition, the magnitude of the differences in the bonding is slightly greater with increasing
softnessofthechalcogendonoratom.TheDFTcalculationsforthemodelsystemscorrelatewellwithexperimentally
determined metrical parameters. They indicate that the enhanced covalency in the M- E bond as group 16 is
descendedarisesmostlyfromincreasedmetald-orbitalparticipation.Conversely,anincreaseinf-orbitalparticipation
isresponsiblefortheenhancementofcovalencyinAn- EbondscomparedtoLn- Ebonds.Thefundamentaland
practical importance of such studies of the role of the valence d and f orbitals in the bonding of the f elements is
emphasized.
1. Introduction andwasteremediation.1-16Inparticular,theextenttowhich
covalentcontributionsareimportantinf-metalbondingwith
Two fundamental questions in f-element chemistry are,
(1) Roger, M.; Barros, N.; Arliguie, T.; Thue´ry, P.; Maron, L.; Ephri-
(1)towhatextentdorelativisticeffectsimpactthecoordina-
tikhine,M.J.Am.Chem.Soc.2006,128,8790.
tion chemistry of these elements, and (2) what are the (2) Miguirditchian,M.;Guillaneux,D.;Guillaumont,D.;Moisy,P.;Madic,
C.;Jensen,M.P.;Nash,K.L.Inorg.Chem.2005,44,1404.
bondingdifferencesbetween4fand5fionsofidenticalionic
(3) Roger, M.; Belkhiri, L.; Thue´ry, P.; Arliguie, T.; Fourmigue´, M.;
radii? Addressing these questions is not only a necessity to Boucekkine, A.; Ephritikhine, M. Organometallics 2005, 24, 4940.
(4) Denecke, M. A.; Rossberg, A.; Panak, P. J.; Weigl, M.; Schim-
acquire a comprehensive understanding of the fundamental
melpfennig,B.;Geist,A.Inorg.Chem.2005,44,8418.
electronic,structural,andbondingpropertiesofthefelements (5) Mehdoui, T.; Berthet, J.-C.; Thue´ry, P.; Ephritikhine, M. Chem.
butisalsohighlyrelevanttoindustriallyimportantAn(III)/ Commun.(Cambridge)2005,2860.
(6) Mehdoui, T.; Berthet, J.-C.; Thue´ry, P.; Salmon, L.; Rivie`re, E.;
Ln(III) (An ) actinide, Ln ) lanthanide) separations that Ephritikhine,M.Chem.Eur.J.2005,11,6994.
arevitaltothedevelopmentofadvancednuclearfuelcycles (7) Mehdoui,T.;Berthet,J.-C.;Thue´ry,P.;Ephritikhine,M.Eur.J.Inorg.
Chem.2004,1996.
(8) Karmazin,L.;Mazzanti,M.;Bezombes,J.-P.;Gateau,C.;Pe´caut,J.
Inorg.Chem.2004,43,5147.
*To whom correspondence should be addressed. E-mail: gaunt@ (9) Choppin,G.R.J.AlloysCompd.2002,344,55.
lanl.gov(A.J.G.),[email protected](N.K.),[email protected](M.P.N.). (10) Jensen,M.P.;Bond,A.H.Radiochim.Acta2002,90,205.
†LosAlamosNationalLaboratory. (11) Berthet, J.-C.; Miquel, Y.; Iveson, P. B.; Nierlich, M.; Thue´ry, P.;
‡NorthwesternUniversity. Madic,C.;Ephritikhine,M.J.Chem.Soc.,DaltonTrans.2002,3265.
§UniversityCollegeLondon. (12) Jensen,M.P.;Bond,A.H.J.Am.Chem.Soc.2002,124,9870.
10.1021/ic701618a CCC: $40.75 © 2008 American Chemical Society Inorganic Chemistry, Vol. 47, No. 1, 2008 29
PublishedonWeb11/20/2007
Gaunt et al.
soft donor atoms remains unresolved, as does the role of vitalforacombinedexperimentalandcomputationalinves-
the valence d and f orbitals. One approach to studying this tigation.Arelativelysmallnumberofstudieshaveobserved
topicistocrystallographicallycharacterizecomplexesof4f shorteractinide-ligandthanlanthanide-ligandbondlengths
and5fmetalions,ofsimilarionicradii,withsoft-donoratom with soft-donor atom ligands in structurally similar com-
ligands and to use increasingly precise single-crystal X-ray plexes.Forexample,inthephosphitecomplexes(MeC H ) -
5 4 3
diffractiondataandcomputationalbondingmodelstoobserve ML(M)UorCe;L)P(OCH ) CEt)theU-Pdistanceis
2 3
and provide rationale for subtle differences in M-L bond shorter than the Ce-P distance by 0.098 Å.16 In the
lengths, specifically to identify and understand differences complexes M(9-aneS )I (MeCN) (M ) U, La; 9-aneS )
3 3 2 3
in covalency. 1,4,7-trithiacyclononane)theaverageU-Sdistanceisshorter
Obviousfunctionalitiestoutilizeforstudiesofcovalency than the average La-S distance by 0.0435 Å,14 and in the
areAndLmultiplebonds.Thebondingofhigheroxidation complexes M(tpza)I3(thf) (M ) U, La; tpza ) tris[(2-
states(+VIand+V)ofsomeoftheearlyactinides(U,Np, pyrazinyl)methyl]amine)theaverageU-Npyrazinedistanceis
Pu,andAm)isdominatedbythelinearactinylcations17that shorterthantheaverageLa-Npyrazinedistanceby0.048Å.13
containthemultiplybondeddioxoOdAndOmoiety,18but The comparison of bonding in M(SMes*)3 (M ) U, La;
no high oxidation states for the lanthanides exist for SMes* is a “supermesityl” thiolate ligand) complexes
comparison with the actinyl ions. Multiple bonds in lower revealed a U-S distance that is shorter than the La-S
oxidation-state actinide ions (mostly U(IV)) occur with distance by an average value of 0.025 Å;1 this represents a
sterically bulky and inert stabilizing ligands such as Cp*- rareexampleinwhichhomoleptic4f/5fcomplexeswithsoft
(pentamethylcyclopentadienide).19 However, we are not donorshavebeencompared.Interestingly,JensenandBond
aware of any isostructural comparisons of MdL multiple conductedanEXAFSsolutionstudytolookfordifferences
bonds between 4f and 5f complexes. This is probably a inbondlengthsintrivalentAm,Cm,Nd,andSmcomplexes
reflectionofthedearthofMdLmultiplebondsreportedin withdithiophosphinicacids,whichhaveshownexceptional
f-element chemistry, particularly of An(III)dL multiple selectivityforAm(III)overEu(III)inliquid-liquidextrac-
bonds. Therefore, we need to look to other functionalities tionstudies.12However,inthatstudytherewasnoevidence
andsystemstoassesscovalencydifferencesbetweenAnand fromtheEXAFSdataofshortenedAn-Sbondsrelativeto
Ln bonding. Ln-S bonds. It may well be that the observed extraction
behavior still was the result of increased covalency in the
Coordination chemistry studies that directly compare An
An-S bonds relative to the Ln-S bonds but that the bond
andLnbondingtosoftdonoratomshavebeeninspiredtoa
length differences were too small to be observed experi-
largeextentbysolutionLn(III)/An(III)extraction,separation,
mentally. Therefore, to be able to observe bond length
and ion exchange experiments, which have demonstrated a
differences resulting from covalency, it may be necessary
preference of soft donor extractants for An(III) ions over
Ln(III) ions.10,12,15,20-23 Understanding the origin of the to use model soft-chalcogen donor complexes judiciously
chosentomaximizecovalentcharacterandthentoextrapo-
separationandextractionbehaviorswithsoftdonorsisgreatly
latethoseresultstomoreappliedsolventextractionsystems.
aidedbythesynthesisandcharacterizationofcrystallizable
Our approach to elucidating differences in covalency
molecular complexes containing soft-donor ligands, which
between An(III) and Ln(III) bonding, as described here, is
allowsstructuralandgeometricdatatobeobtainedthatare
toundertakeanexperimentalandtheoreticalcomparisonof
homoleptic, structurally similar An(III) and Ln(III) com-
(13) Mazzanti, M.; Wietzke, R.; Pe´caut, J.; Latour, J.-M.; Maldivi, P.;
Remy,M.Inorg.Chem.2002,41,2389. plexesinwhichtwoimportantfactorsareexplored: (1)The
(14) Karmazin,L.;Mazzanti,M.;Pe´caut,J.Chem.Commum.(Cambridge) electronegativity (or softness) of the ligand donor atom is
2002,654.
(15) Choppin,G.R.;Nash,K.L.Radiochim.Acta1995,70-1,225. varied in order to test the hypothesis that An(III) ions have
(16) Brennan, J. G.; Stults, S. D.; Andersen, R. A.; Zalkin, A. Organo- greater covalency in their bonding with soft donor ligands
metallics1988,7,1329.
than do Ln(III) ions of identical ionic radii and that the
(17) See, for example: (a) Burns, C. J.; Neu, M. P.; Boukhalfa, H.;
Gutowski, K. E.; Bridges, N. J.; Rogers, R. D. in ComprehensiVe difference in covalency is more pronounced the softer the
CoordinationChemistryII,Vol.3;McCleverty,J.A.,Meyer,T.J., donor atom. (2) The positive charge density of the 4f- and
Eds.;ElsevierPergamon: Amsterdam,2004;p189.(b)Katz,J.J.;
Seaborg,G.T.;Morss,L.R.TheChemistryoftheActinideElements, 5f-metalionsisvariedtostudytheeffectthatthelanthanide/
Vols.1and2,2nded.;ChapmanandHall: NewYork,1986. actinide contraction has upon bonding differences, in order
(18) Denning,R.G.Struct.Bonding(Berlin)1992,79,215.
totestthehypothesisthat,asthef-elementseriesistraversed,
(19) See,forexample: (a)Jantunen,K.C.;Burns,C.J.;Castro-Rodriguez,
I.;DaRe,R.E.;Golden,J.T.;Morris,D.E.;Scott,B.L.;Taw,F.L.; thepotentialforanycovalencyinthebondingdecreases.In
Kiplinger,J.L.Organometallics2004,23,4682.(b)Arney,D.S.J.;
this respect, we recently communicated the syntheses and
Schnabel,R.C.;Scott,B.L.;Burns,C.J.J.Am.Chem.Soc.1996,
118,6780.(c)Arney,D.S.J.;Burns,C.J.J.Am.Chem.Soc.1995, molecularstructuresofM[N(TePiPr2)2]3(M)U,La)24and
117,9448.(d)Cramer,R.E.;Maynard,R.B.;Paw,J.C.;Gilje,J.W. U[N(EPPh ) ] (E)S,Se)25complexesalongwithprelimi-
J.Am.Chem.Soc.1981,103,3589. 2 2 3
nary computational results on the La, U, and Pu systems26
(20) Hagstro¨m,I.;Spjuth,L.;Enarsson,Å.;Liljenzin,J.O.;Skålberg,M.;
Hudson, M. J.; Iveson, P. B.; Madic, C.; Cordier, P. Y.; Hill, C.;
Francois,N.SolVentExtr.IonExch.1999,17,221. (24) Gaunt,A.J.;Scott,B.L.;Neu,M.P.Angew.Chem.,Int.Ed.2006,
(21) Zhu,Y.Radiochim.Acta1995,68,95. 45,1638.
(22) Musikas, C.; Cuillerdier, C.; Livet, J.; Forchioni, A.; Chachaty, C. (25) Gaunt,A.J.;Scott,B.L.;Neu,M.P.Chem.Commun.(Cambridge)
Inorg.Chem.1983,22,2513. 2005,3215.
(23) Diamond, R. M.; Street, K., Jr.; Seaborg, G. T. J. Am. Chem. Soc. (26) Ingram,K.I.M.;Kaltsoyannis,N.;Gaunt,A.J.;Neu,M.P.J.Alloys
1954,76,1461. Compd.2007,444-445,369.
30 InorganicChemistry,Vol.47,No.1,2008
An(III)/Ln(III)BondingComparison
thatdemonstratedthepotentialofimidodiphosphinochalco- overseveraldays.Themotherliquorwaspipettedaway;thecrystals
genideligandsystemstofacilitateasystematicstudyofAn- werecollectedanddriedinvacuotogiveawhitepowder(0.0362
(III) vs Ln(III) covalency. Here we report a much more g,76%yield).31P{1H}NMR: (CD2Cl2): (cid:228)42.6.IR(KBr,Nujol,-
comprehensivestructuralandspectroscopiccharacterization cm-1): 1199(s), 1179(m), 1156(m), 1070(m), 1026(w), 999(w),
of M[N(EPPh ) ] (M ) U, Pu, La, Ce; E ) S, Se) and 977(w),969(w),918(w),756(w),744(m),739(m),724(s),715(m),
2 2 3
M[N(EPiPr ) ] (M)U,Pu,La,Ce;E)S,Se,Te),together 707(w), 693(s), 626(w), 619(w), 609(w), 596(s), 513(s), 493(m),
2 2 3 470(m). Anal. Calcd for C H NPSLa: C, 60.19; H, 4.35; N,
withdensityfunctionaltheorystudiesofM[N(EPH ) ] (M 79 68 3 6 6
2 2 3 2.67.Found: C,60.46;H,4.27;N,2.61.
) U, Pu, La, Ce; E ) O, S, Se, Te) models for the iPr 2.1.3.Pu[N(SPPh)](cid:226)toluene(3).Thiscompoundwasprepared
223
systems. We decided to focus our computational efforts on
as for 2 using NH(SPPh) (0.0187 g, 0.042 mmol) and Pu-
22
the six-coordinate bidentate systems, so as to remove the [N(SiMe)] (0.0100g,0.014mmol)toyieldcrystalline3,which
323
potentiallycomplicatingeffectsofM(III)-Nbondinginthe washarvestedasagreenpowderafterdrying(0.0173g,79%yield).
nine-coordinate tridentate systems. It is noteworthy that 31P{1H} NMR (CDO) (prepared in situ because of the low
4 8
undertaking a study involving nonaqueous coordination solubilityof3): (cid:228)-47.11(complex3),52.06(freeligand).UV/
chemistryofmolecularplutoniumcompoundsisparticularly vis/near-IR(solutionof3preparedinsituinTHF)((cid:236)max,nm): 247,
challengingowingtothedifficultyofhandlinghighspecific 299,351,520,566,578,612,674,787,826,920,1036,1136,1437,
1531.
activity transuranic radionuclides and the paucity of well-
2.1.4.Ce[N(SPPh)](cid:226)toluene(4).Thecompoundwasprepared
characterized precursors. Nevertheless, such studies are 223
as for 2 using NH(SPPh) (0.0672 g, 0.149 mmol) and Ce-
importantifwearetounderstandtheeffectofthef-element 22
[N(SiMe)] (0.0300g,0.048mmol)toyieldcrystalline4,which
contraction in these complexes. 323
washarvestedasapaleyellow/greenpowderafterdrying(0.0426
g,59%yield).31P{1H}NMR(CDCl): (cid:228)4.92.IR(KBr,Nujol)
2. Experimental Section 2 2
(cm-1): 1200(s), 1178(s), 1156(m), 1101(m), 1069(w), 1026(w),
2.1. Syntheses. Caution! 239Pu is a high specific-activity 999(w), 977(w), 967(w), 918(w), 894(w), 843(w), 773(w), 756-
R-particle-emittingradionuclide.Thisresearchwasconductedina (m),744(m),739(m),724(s),712(m),707(w),693(s),626(w),619-
radiological facility with appropriate analyses of hazards and (w),596(s),513(s),492(m),470(m).Anal.CalcdforC79H68N3P6S6-
implementationofcontrolsforthesafehandlingandmanipulation Ce: C,60.14;H,4.34;N,2.66.Found: C,60.86;H,4.49;N,2.54.
ofradioactivematerials. 2.1.5.U[N(SePPh2)2]3(cid:226)C6D6(5).Thiscompoundwasprepared
R-phase plutonium metal pieces of weapons-grade isotopic aspreviouslydescribed.25
compositionanduraniumturnings(depletedin235U)wereobtained 2.1.6. La[N(SePPh2)2]3(cid:226)toluene (6). This compound was pre-
internallyfromLosAlamosNationalLaboratory.Allreactionswere paredasfor2usingNH(SePPh2)2(0.0540g,0.099mmol)andLa-
performedinanMBraunLabmaster130heliumatmospheredrybox. [N(SiMe3)2]3(0.0200g,0.032mmol)toyieldcrystalline6,which
Diethyl ether, toluene, hexanes, and tetrahydrofuran (THF) were washarvestedasawhitepowderafterdrying(0.0392g,69%yield).
driedwiththeuseofactivatedaluminacolumns(A2,1232,Purify). 31P{1H}NMR: (CD2Cl2): (cid:228)33.6IR(KBr,Nujol;cm-1): 1185-
Other solvents were purchased in anhydrous grade from Aldrich. (m),1165(s),1154(s),1098(m),1069(m),1024(m),998(w),977-
Allsolventswerestoredovera1:1mixtureof3and4Åmolecular (w), 967(w), 918(w), 843(w), 755(m), 743(m), 738(m), 721(s),
sieves before use. Infrared spectra were obtained as Nujol mulls 711(m), 690(s), 654(m), 618(w), 562(s), 547(m), 541(m), 507(s),
between KBr plates on a Nicolet Magna-IR 560 spectrometer 481(m), 468(w), 453(w). Anal. Calcd for C79H68N3P6Se6La: C,
equippedwithaDTGSdetector.1HNMRspectrawerereferenced 51.07;H,3.69;N,2.26.Found: C,51.60;H,3.50;N,2.22.
toresidualprotioresonances,and31PNMRspectrawerereferenced 2.1.7. Pu[N(SePPh2)2]3(cid:226)toluene (7). This compound was pre-
toexternal85%H3PO4.AllNMRspectrawereobtainedonsamples paredasfor2usingNH(SePPh2)2(0.0226g,0.042mmol)andPu-
in4mmTeflonNMRtubelinersinsertedinto5mmNMRtubes [N(SiMe3)2]3(0.0100g,0.014mmol)toyieldcrystalline7,which
inordertomultiplycontaintheradioactivesamples.NMRspectra washarvestedasagreenpowderafterdrying(0.0155g,60%yield).
were recorded at ambient temperature on a Bruker Avance 300 31P{1H}NMR(C4D8O): (cid:228)-59.18(complex7),51.97(freeligand).
MHzspectrometer.Electronicabsorptionspectrawererecordedon Peaksintegratewiththeratio7:1.UV/vis/near-IR(solutionof7in
aVarianCary6000iUVvis/near-IRspectrophotometer.Elemental THF) ((cid:236)max, nm): 245, 326, 523, 576, 611, 618, 675, 797, 811,
analyses were performed by the Micro-Mass facility at the 828, 917, 932, 1041, 1061, 1116, 1127, 1141, 1164, 1447, 1514.
UniversityofCaliforniaatBerkeley,Berkeley,CA.U[N(SiMe3)2]3 2.1.8. Ce[N(SePPh2)2]3(cid:226)toluene (8). This compound was pre-
waspreparedaccordingtotheliterature,27andPu[N(SiMe3)2]3was paredasfor2usingNH(SePPh2)2(0.0807g,0.149mmol)andCe-
preparedbyamodificationofaliteratureprocedure.27UI3(py)4and [N(SiMe3)2]3(0.0300g,0.048mmol)toyieldcrystalline8,which
PuI(py) werepreparedaccordingtotheliterature.27LaI(thf) and washarvestedasapalegreenpowderafterdrying(0.0528g,62%
3 4 3 4
CeI3(thf)4 were prepared by stirring anhydrous LaI3 and CeI3 in yield).31P{1H}NMR(CD2Cl2): (cid:228)-8.34.IR(KBr,Nujol;cm-1):
THFovernightandcollectingtheresultingpowders. 1185(w), 1167(s), 1154(s), 1098(m), 1071(w), 1025(w), 998(w),
2.1.1.U[N(SPPh )](cid:226)toluene(1).Thiscompoundwasprepared 976(w), 969(w), 936(w), 918(w), 893(w), 850(w), 772(w), 755-
223
aspreviouslydescribed.25 (w),743(w),738(m),721(s),690(m),654(m),618(w),561(m),547-
2.1.2.La[N(SPPh)](cid:226)toluene(2).NH(SPPh) (0.0448g,0.100 (m), 540(w), 530(w), 508(m), 481(w), 418(w). Anal. Calcd for
223 22
mmol)wasdissolvedinTHF(1.5mL)andfilteredthroughaglass C79H68N3P6Se6Ce: C, 51.04; H, 3.69; N, 2.26. Found: C, 51.70;
fiber filter circle. La[N(SiMe)] (0.0200 g, 0.032 mmol) was H,3.90;N,2.21.
323
dissolvedintoluene(1.5mL),filteredandcarefullylayeredontop 2.1.9.U[N(SPiPr2)2]3(9).U[N(SiMe3)2]3(0.0500g,0.070mmol)
oftheligandTHFsolution.Crystalsof2precipitatedfromsolution wasdissolvedinTHF(6mL).NH(SPiPr2)2(0.0653g,0.208mmol)
was dissolved in THF (2 mL) and added dropwise to the
U-containing solution. The resulting purple solution was stirred
(27) Avens,L.R.;Bott,S.G.;Clark,D.L.;Sattelberger,A.P.;Watkin,J.
G.;Zwick,B.D.Inorg.Chem.1994,33,2248. overnight.Thesolutionwasfiltered,andthesolventwasremoved
Inorganic Chemistry, Vol. 47, No. 1, 2008 31
Gaunt et al.
invacuotoyieldapurplepowder,whichwasdriedinvacuo(0.0642 C H NPSeU: C,29.68;H,5.81;N,2.88.Found: C,29.38;H,
36 84 3 6 6
g,79%yield).CrystalssuitableforX-raydiffractionwereobtained 5.65;N,2.74.
from a THF/hexanes solution of 9 stored at -35 (cid:176) C for several 2.1.14.La[N(SePiPr)] (14).La[N(SiMe)] (0.0300g,0.048
223 323
days. 31P{1H} NMR (C6D6): (cid:228) -525.1. IR (KBr, Nujol; cm-1): mmol)wasdissolvedinTHF(5mL).NH(SePiPr2)2(0.0591g,0.145
1266(s),1230(s),1169(m),1159(m),1096(w),1080(m),1040(w), mmol) was dissolved in THF (2 mL) and added dropwise to the
1029(m),974(m),933(m),920(w),885(m),850(m),775(m),722- La-containingsolution.Theresultingcolorlesssolutionwasstirred
(s),677(m),656(m),628(w),563(w),550(w),539(w),504(w),489- overnight,thevolumewasreducedinvacuoto1mL,andEt O(5
2
(w), 474(w). UV/vis/near-IR (solution of 9 in THF) ((cid:236)max, nm): mL)wasaddedwithshaking.Theresultantclear,colorlesssolution
302(sh),474(sh),541(sh),571,616(sh),644(sh),675(sh),710(sh), wasstoredat-35(cid:176) Cforseveraldaystogiveawhitecrystalline
779(sh),928,1097,1210,1250.Anal.CalcdforC36H84N3P6S6U: solid, which was dried in vacuo (0.0483 g, 72% yield). Single
C,36.79;H,7.20;N,3.58.Found: C,37.81;H,7.38;N,3.47. crystals suitable for X-ray diffraction were obtained from a THF
2.1.10.La[N(SPiPr2)2]3(10).La[N(SiMe3)2]3(0.0300g,0.048 solutionof14layeredwithEt2Oandstoredat-35(cid:176) Cforseveral
mmol)wasdissolvedinTHF(5mL).NH(SPiPr2)2(0.0456g,0.145 days. 31P{1H} NMR (C6D6): (cid:228) 56.78. 1H NMR (C6D6): (cid:228) 2.12
mmol) was dissolved in THF (2 mL) and added dropwise to the (m,12H;CH(CH3)2),1.29(m,72H;CH(CH3)2).IR(KBr,Nujol;
La-containingsolution.Theresultingcolorlesssolutionwasstirred cm-1): 1268(m),1231(m),1182(w),1171(m),1158(m),1098(w),
overnight, the volume was then reduced in vacuo to 1 mL, and 1080(m),1040(w),1023(m),974(m),933(m),885(m),761(m),722-
EtO(5mL)wasaddedwithshaking.Theclear,colorlesssolution (s),682(w),669(m),630(s),604(w),519(w),508(w),473(m).Anal.
2
wasstoredat-35(cid:176) Cforseveraldaystogiveawhitecrystalline Calcd for C36H84N3P6Se6La: C, 31.85; H, 6.24; N, 3.01. Found:
solid, which was dried in vacuo (0.0350 g, 67% yield). Crystals C,31.93;H,6.27;N,3.06.
suitableforX-raydiffractionwereobtainedfromaTHFsolution 2.1.15. Pu[N(SePiPr)] (15). Pu[N(SiMe)] (0.0108, 0.015
223 323
of10layeredwithEt2Oandstoredat-35(cid:176) Cforseveraldays.1H mmol) was dissolved in THF (5 mL), and NH(SePiPr2)2 (0.0183
NMR (C6D6): (cid:228) 2.25 (m, 12H; CH(CH3)2), 1.38, 1.23 (m, 72H; g,0.045mmol)wasadded.Thesolutionwasstirredovernightand
CH(CH3)2). Less intense peaks were also observed for the minor was filtered to give a green filtrate, and then the solvent was
freeligandcomponent.31P{1H}NMR(CD): (cid:228)64.31(complex removedinvacuo.Thegreenpowderwasdissolvedintoluene(1.5
6 6
10),86.76(freeligand).Peaksintegratedwiththeratio12.9:1.IR mL),filtered,thenlayeredwithhexanes,andstoredat-35(cid:176) Cfor
(KBr, Nujol; cm-1): 1268(s), 1232(s), 1162(m), 1096(w), 1080- several days to give green crystals, which were dried in vacuo
(m), 1040(w), 1026(m), 974(m), 931(m), 884(s), 773(s), 722(s), (0.0078 g, 36% yield). 1H NMR (CD): (cid:228) 2.23 (m, 12H;
6 6
677(m),656(s),630(w),563(w),551(w),540(w),506(w),489(m), CH(CH)), 1.30 (s, 72H; CH(CH)). 31P{1H} NMR (CD): (cid:228)
32 32 6 6
475(w), 419(m), 413(m). Anal. Calcd for C H NPSLa: C, -20.06. UV/vis/near-IR (solution of 15 in benzene) ((cid:236) , nm):
36 84 3 6 6 max
40.18;H,7.87;N,3.90.Found: C,40.53;H,7.97;N,3.91. 298,330,414,529,556,577,608,618,683,802,826,914,1053,
2.1.11.Pu[N(SPiPr)] (11).Pu[N(SiMe)] (0.0246g,0.034 1086,1149,1452.
223 323
mmol)wasdissolvedinTHF(5mL),andNH(SPiPr) (0.0321g, 2.1.16.U[N(TePiPr)] (16).Thiscompoundwaspreparedas
22 223
0.102 mmol) was added. The solution was stirred overnight and previouslydescribed.24
thenwasfilteredtogiveagreenfiltrate.Et2O(1mL)wasadded 2.1.17.La[N(TePiPr2)2]3(17).Thiscompoundwaspreparedas
with shaking, and the mixture was stored at -35 (cid:176) C for several previouslydescribed.24
daystogivegreencrystals,whichweredriedinvacuo(0.0162g,
2.1.18.Pu[N(TePiPr)] (18).PuI(py) (0.0148g,0.016mmol)
223 3 4
40% yield). 1H NMR (CD): (cid:228) 2.20 (s, 12H; CH(CH)), 1.32,
6 6 32 wassuspendedinEtO(5mL),andNa(tmeda)[N(TePiPr)]inEtO
1.22 (s, 72H; CH(CH3)2). 31P{1H} NMR (C6D6): (cid:228) -1.40. UV/ (0.0307g,0.047mm2ol)(2.5mL)wasadded(tmeda)te2tr2amethy2l-
vis/near-IR(solutionof11inbenzene)((cid:236) ,nm): 286,299(sh),
max ethylenediamine).Anorange/redsuspensionformedimmediately.
321(sh),345(sh),392,526,578,608,619,680,801,823,915,1051,
The suspension was stirred for 20 min and then stored overnight
1130,1139,1149,1450. at-35(cid:176) Ctoallowthesolidtosettletothebottomofthevial.The
2.1.12.Ce[N(SPiPr2)2]3(12).Ce[N(SiMe3)2]3(0.0150g,0.024 motherliquorwaspipettedaway,andthesolidwasdriedinvacuo.
mmol)wasdissolvedinTHF(5mL),andNH(SPiPr2)2(0.0227g, Toluene(5mL)wasaddedtothesolid,thesolutionfiltered,and
0.072 mmol) was added and the solution stirred overnight. The EtO(10mL)wasaddedtothefiltratewithshaking.Theresultant
2
resultant green solution was filtered, and then Et2O (1 mL) was solution was stored at -35 (cid:176) C for several days to give a red
addedwithshaking.Themixturewasstoredat-35(cid:176) Cforseveral microcrystalline solid, which was dried in vacuo (0.0119 g, 43%
days to give a few green crystals, which were suitable for X-ray yield).SinglecrystalssuitableforX-raydiffractionwereobtained
diffraction. fromaTHF/EtOsolutionof18storedat-35(cid:176) Cforseveraldays.
2
2.1.13. U[N(SePiPr2)2]3 (13). U[N(SiMe3)2]3 (0.0500 g, 0.070 1HNMR(C7D8): (cid:228)1.97(m,12H;CH(CH3)2),1.19(s,72H;CH-
mmol)wasdissolvedinTHF(6mL).NH(SePiPr2)2(0.0850g,0.209 (CH3)2).31P{1H}NMR(C7D8): (cid:228)-62.22.UV/vis/near-IR(solution
mmol) was dissolved in THF (2 mL) and added dropwise to the of 18 in toluene) ((cid:236)max, nm): 467(sh), 579, 620, 685, 804, 829,
U-containing solution. The resultant purple solution was stirred 916,1057,1087(sh),1148,1465.
overnight.Thesolutionwasfiltered,andthesolventwasremoved 2.1.19. Ce[N(TePiPr)] (19). CeI(THF) (0.0300 g, 0.037
223 3 4
invacuotoyieldapurplepowder,whichwasdriedinvacuo(0.0771 mmol) was suspended in Et O (5 mL). Na(tmeda)[N(TePiPr ) ]
2 2 2
g,76%yield).CrystalssuitableforX-raydiffractionwereobtained (0.0720g,0.111mmol)wasdissolvedinEt O(2.5mL)andadded
2
from a THF/hexanes solution of 13 stored at -35 (cid:176) C for several dropwise to the Ce-containing solution to afford a salmon-pink
days. 31P{1H} NMR (CD): (cid:228) -573.9. IR (KBr, Nujol; cm-1): coloredsuspension,thatwasstirredfor20minandthenstoredat
6 6
1262(m),1256(m),1230(s),1162(w),1097(w),1081(w),1040(w), -35(cid:176) Ctoallowthesolidtosettletothebottomofthevial.The
1028(m),973(w),933(m),905(w),885(m),850(m),764(w),722- motherliquorwaspipettedaway,andthesolidwasdriedinvacuo.
(m),682(w),671(m),632(s),604(w),519(w),509(w),474(w),418- Toluene(3mL)wasaddedtothesolid,thesolutionfiltered,and
(w).UV/vis/near-IR(solutionof13inTHF)((cid:236) ,nm): 482(sh), EtO (10 mL) added to the filtrate with shaking. The resultant
max 2
538,579,658(sh),783(sh),832,935,1073,1235.Anal.Calcdfor solutionwasstoredat-35(cid:176) Cforseveraldaystogiveapink-red
32 InorganicChemistry,Vol.47,No.1,2008
An(III)/Ln(III)BondingComparison
attachedto.Allnon-hydrogenatomswererefinedanisotropically.
Structuresolution,refinement,graphics,andcreationofpublication
materialswereperformedusingSHELXTL.31Furtherdetailsmay
befoundintheSupportingInformation.
2.3. Computational Details. All calculations were carried out
usinggradient-correcteddensityfunctionaltheory,asimplemented
intheGaussian(G03)32andAmsterdamDensityFunctional(ADF)33
quantum chemical codes. Spin-unrestricted calculations were
performedonallLnandAncomplexestoaccountfortheformal
fnconfigurationsofeachLn(III)andAn(III)ionwiththeexception
oftheformallyf0La(III)ion,onwhichspin-restrictedcalculations
wereperformed.
2.3.1.G03.TheGGAfunctionalPBE34,35wasusedforallG03
calculations. (14s 13p 10d 8f)/[10s 9p 5d 4f] segmented valence
basissetswithStuttgart-Bonnvariety36relativisticeffectivecore
potentials (RECPs) were used for the actinides, and a (14s 13p
10d8f)/[10s8p5d4f]segmentedvalencebasissetwithaStuttgart-
Figure 1. Thermal ellipsoid plot (at the 50% probability level) of the BonnRECP36wasusedforeachlanthanide.6-31G*basissetswere
structure of Pu[N(SePPh2)2]3 (7), with the H atoms and lattice toluene usedfortheO,S,Se,N,andPatoms,andthesmaller6-31Gset
molecule omitted for clarity. The complexes 1-6 and 8 have identical wasusedforH.Tewasdescribedwitha(4s5p)/[2s3p]Stuttgart
connectivity.
basisset37augmentedto(4s5p7d)/[2s3p3d]withSTO-3G*38,39
microcrystalline solid, which was dried in vacuo (0.0221 g, 36% polarizationfunctions(forconsistency,as6-31G*includespolariza-
yield).SinglecrystalssuitableforX-raydiffractionwereobtained tion functions on O, S, and Se); a Stuttgart RECP was also used
fromaTHF/EtOsolutionof19storedat-35(cid:176) Cforseveraldays. forTe.37ThevalidityofthisaugmentedTebasissetwaschecked
2
1H NMR (CD): (cid:228) 0.18 (s, 12H; CH(CH)), -0.06, -0.81 (d, byconstructingananalogousSebasissetsaStuttgart(4s5p)/[2s
7 8 32
72H;CH(CH)).31P{1H}NMR(CD): (cid:228)-9.98.IR(KBr,Nujol; 3p] augmented to (4s 5p 4d)/[2s 3p 2d]sand performing test
32 7 8
cm-1): 1275(m),1227(m),1202(m),1181(w),1171(w),1157(m), geometryoptimizationson[M(N(SePH2)2)3]forM)La,U;similar
1097(w), 1077(m), 1033(w), 1018(m), 974(m), 932(m), 881(m), geometrieswerefoundwithbothmethods.Thedefaultvaluesfor
772(w), 723(s), 694(m), 659(m), 635(m), 609(m), 597(m), 510- theintegrationgrid(“fine”)andtheconvergencecriteriawereused
(m),471(m).Anal.CalcdforC H NPTeCe: C,26.20;H,5.13; forallLa,Ce,andUgeometryoptimizations(maximumforce)
36 84 3 6 6
N,2.55.Found: C,26.55;H,5.06;N,2.48. 4.5(cid:2)10-4auÅ-1;SCF)10-8).ThePucalculationsweremore
2.2.CrystallographicDataCollectionandRefinement.Each problematic, and the following convergence criteria were
Pu-containing crystal was coated with Paratone-N and then achieved: [Pu(N(OPH2)2)3](maximumforce)7(cid:2)10-4auÅ-1;
mounted inside a 0.5 mm capillary. The capillaries were sealed SCF ) 10-7), [Pu(N(SPH2)2)3] (maximum force ) 8 (cid:2) 10-4 au
withwax,andtheirexternalsurfaceswerecoatedwithathinfilm Å-1;SCF)10-5),[Pu(N(SePH2)2)3](maximumforce)5(cid:2)10-4
ofacrylicdissolvedinethylacetate(HardasNailsnailpolish)to auÅ-1;SCF)10-8),and[Pu(N(TePH2)2)3](maximumforce)8
provide appropriate containment of the radioactive material. (cid:2) 10-4 au Å-1; SCF ) 10-5). A natural charge and population
Otherwise, non-Pu-containing crystals were mounted in Nylon analysis40-46wascarriedoutonallG03optimizedstructures.Little
cryoloopsfromParatone-Noilunderanargon-gasflow.Thedata spincontaminationwasfoundforthequadrupletU(III)complexes,
for525and12werecollectedonaBrukerP4/CCDdiffractometer asevidencedbythefactthatthevaluesofÆS2æ werecloseto3.75
at 203 K with the use of a Bruker LT-2 temperature device. The
(31) SHELXTL5.10;BrukerAXS: Madison,WI,1997.
instrumentwasequippedwithasealed,graphite-monochromatized
(32) Frisch,M.J.;etal.Gaussian03,revisionD.01;Gaussian: Wallingford,
MoKRX-raysource((cid:236))0.71073Å).Ahemisphereofdatawas CT,2004.
collectedusing(cid:246)scans,with30sframeexposuresand0.3(cid:176) frame (33) (a)ADF,SCM,TheoreticalChemistry,VrijeUniversiteit,Amsterdam,
The Netherlands (http://www.scm.com). (b) Fonseca Guerra, C.;
widthsat203(2)K.Thedataforalltheothercrystalswerecollected
Snijders,J.G.;teVelde,G.;Baerends,E.J.Theor.Chem.Acc.1998,
on a Bruker SMART APEX II CCD X-ray diffractometer with a 99,391.(c)teVelde,G.;Bickelhaupt,F.M.;Baerends,E.J.;Fonseca
KRYO-FLEX liquid nitrogen vapor cooling device at 141(2) K. Guerra, C.; van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T., J.
Theinstrumentwasequippedwithagraphite-monochromatizedMo Comput.Chem.2001,22,931.
KRX-raysource((cid:236))0.71073Å),withMonoCapX-raysource (34) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1996, 77,
3865.
optics.Ahemisphereofdatawascollectedusing(cid:246)scans,with5 (35) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1997, 78,
sframeexposuresat0.3(cid:176) framewidths.Datacollectionandinitial 1396.
(36) Cao,X.;Dolg,M.J.Mol.Struct.(THEOCHEM)2004,673,203.
indexingandcellrefinementwerehandledwithAPEXII28software.
(37) Bergner,A.;Dolg,M.;Ku¨chle,W.;Stoll,H.;Preu(cid:226),H.Mol.Phys.
Frameintegration,includingLorentz-polarizationcorrectionsand 1993,80,1431.
finalcellparametercalculations,werecarriedoutusingSAINT+29 (38) Hehre,W.J.;Stewart,R.F.;Pople,J.A.J.Chem.Phys.1969,51,
software. The data were corrected for absorption with the SAD- 2657.
(39) Collins,J.B.;Schleyer,P.v.R.;Binkley,J.S.;Pople,J.A.J.Chem.
ABS30 program. Decay of reflection intensity was monitored via
Phys.1976,64,5142.
analysisofredundantframes.Eachstructurewassolvedusingdirect (40) Carpenter,J.E.;Weinhold,F.J.Mol.Struct.(THEOCHEM)1988,
methods and difference Fourier techniques. All hydrogen-atom 169,41.
(41) Carpenter,J.E.Ph.D.Thesis,UniversityofWisconsin: Madison,WI,
positionswereidealizedandrodeontheatomstowhichtheywere
1987.
(42) Foster,J.P.;Weinhold,F.J.Am.Chem.Soc.1980,102,7211.
(28) APEXII1.08;BrukerAXS: Madison,WI,2004. (43) Reed,A.E.;Weinhold,F.J.Chem.Phys.1983,78,4066.
(29) SAINT+7.06;BrukerAXS: Madison,WI,2003. (44) Reed,A.E.;Weinstock,R.B.;Weinhold,F.J.Chem.Phys.1985,
(30) Sheldrick, G. SADABS 2.03; University of Go¨ttingen: Go¨ttingen, 83,735.
Germany,2001. (45) Reed,A.E.;Curtiss,L.A.;Weinhold,F.Chem.ReV.1988,88,899.
Inorganic Chemistry, Vol. 47, No. 1, 2008 33
Gaunt et al.
e6
T
compd8 CHCeNPSe79683661859.15hR3c15.1571(3)15.1571(3)57.057(3)90.0090.00120.0011352.0(6)60.02320.0480 compd19 CeHCeNP63684361650.60P2/c122.235(2)13.8343(14)20.843(2)90.00113.5540(10)90.005877.1(11)40.03950.0568 K.
compd7 CSeHNPPuSe679683661958.03hR3c15.1505(4)15.1505(4)56.984(3)90.0090.00120.0011327.6(7)60.02060.0536 24compd17compd18 CCHLaNPTeHNPPuT36843663684361649.391749.53P2/cP2/c1122.456(6)22.348(2)13.866(4)13.7485(15)20.828(5)20.723(2)90.0090.00113.295(3)113.6330(10)90.0090.005957(3)5833.0(11)440.05440.04840.12850.0882 )exceptfor12whereT203(2)
compd6 CHLaNP7968361857.93hR3c15.1824(5)15.1824(5)57.129(4)90.0090.00120.0011404.2(10)60.02570.0497 24compd16 CHNPTeU36843661748.51P2/c122.3600(18)13.7678(11)20.6919(17)90.00113.405(2)90.005845.8(8)40.03830.0643 orallcompounds
f
e6 K
(cid:226)abTable1.SelectedCrystallographicDataforM[N(EPPh)]solvateandM[N(EPiPr)]Complexes223223 (a)M[N(EPPh)]Complexes223 2525compd1compd2compd3compd4compd5 empiricalformulaCCCCHNPSUCHLaNPSHNPPuSHCeNPSHDNPSeU796836679683667968366796836678606366fw1675.631576.571676.661577.781948.99hhhhhspacegroupR3cR3cR3cR3cR3ca(Å)15.0066(9)15.0368(7)15.0053(4)15.0131(3)15.1699(10)b(Å)15.0066(9)15.0368(7)15.0053(4)15.0131(3)15.1699(10)c(Å)56.107(4)56.186(5)56.133(4)56.130(2)56.846(7)R(deg)90.0090.0090.0090.0090.00(deg)90.0090.0090.0090.0090.00(cid:226)(deg)120.00120.00120.00120.00120.00(cid:231)3V(Å)109424(12)11002.0(12)10945.5(8)10956.4(5)11329.1(18)Z66666R10.02340.03050.02550.03380.0270wR20.05640.06790.06180.10390.0678 (b)M[N(EPiPr)]Complexes223 compd9compd10compd11compd12compd13compd14compd15 empiricalformulaCCCCCHNPSUCHLaNPSHNPPuSHCeNPSHNPSeUCHLaNPSeHNPPuS368436636843663684366368436636843663684366368436fw1175.271076.151176.321077.361456.671357.551457.69hhhhspacegroupP1P1P1P1C2/cP2/cC2/c1a(Å)12.974(3)13.0101(11)12.941(4)13.042(3)23.649(2)22.156(4)23.531(8)b(Å)13.333(3)12.3384(11)13.320(4)13.340(3)13.1855(12)13.517(2)13.118(5)c(Å)18.787(4)18.7969(15)18.779(5)18.965(4)19.6924(18)20.325(4)19.625(7)R(deg)91.189(4)91.1880(10)90.930(4)90.672(3)90.0090.0090.00(deg)108.914(4)108.7370(10)109.056(3)109.289(3)115.2850(10)114.051(3)115.520(6)(cid:226)(deg)117.146(4)117.2740(10)117.154(3)117.232(2)90.0090.0090.00(cid:231)3V(Å)2680.5(11)2690.4(4)2669.3(13)2716.6(9)5552.3(9)5558.4(17)5467(3)Z2222444R10.06090.04120.04130.03830.03180.04570.0868wR20.14470.09240.07310.06840.08410.09320.1558 ))))abSolvatetolueneexceptfor5whereitisCD.T141(2)Kforallcompoundsexceptfor5whereT203(2)K.T141(2)66
34 InorganicChemistry,Vol.47,No.1,2008
An(III)/Ln(III)BondingComparison
Table2. SelectedBondDistances(Å)forM[N(EPPh2)2]3Complexes
compd bond distance bond distance differencea
U[N(SPPh2)2]3(1) U-N 2.632(2) U-S 2.9956(5)
La[N(SPPh2)2]3(2) La-N 2.652(4) La-S 3.0214(11) 0.026(1)
Pu[N(SPPh2)2]3(3) Pu-N 2.612(3) Pu-S 2.9782(6)
Ce[N(SPPh2)2]3(4) Ce-N 2.637(3) Ce-S 3.0052(6) 0.0270(8)
U[N(SePPh2)2]3(5) U-N 2.701(3) U-Se 3.0869(4)
La[N(SePPh2)2]3(6) La-N 2.706(3) La-Se 3.1229(3) 0.0360(5)
Pu[N(SePPh2)2]3(7) Pu-N 2.668(2) Pu-Se 3.0710(2)
Ce[N(SePPh2)2]3(8) Ce-N 2.691(3) Ce-Se 3.1013(3) 0.0303(4)
aDifferenceisbetweenAn-EandLn-Ebondlengths.
(M ) U, Pu, La, or Ce) with 3 equiv of NH(EPPh ) (E )
2 2
S, Se) in THF/toluene results in ligand deprotonation and
coordination to the metal ion, to afford the neutral
M[N(EPPh ) ] (1-8) complexes (eq 1).
2 2 3
Figure 2. Thermal ellipsoid plot (at the 50% probability level) of the
structureofPu[N(TePiPr2)2]3(18),withtheHatomsomittedforclarity.
Thecomplexes9-17and19haveidenticalconnectivity.
in all cases, with 3.770 for [U(N(TePH))] being the largest
223
deviation from the ideal. Similar results were found for the Ce
systems,with0.757beingthelargestdeviationfromtheideal0.75 The molecular structures of 1-8 (Figure 1, Table 1a)
(fortheTecomplex).SpincontaminationinthePucomplexesis consistofnine-coordinatemetalcentersandanionsthatare
more significant than in the U and Ce complexes; however the
tridentate through both chalcogen atoms and the nitrogen
largest ÆS2æ calculated was 8.865 for [Pu(N(TePH ))], not a
223 atom.Thegeometryaboutthemetalcenterisbestdescribed
significantdeviationfromtheideal8.75.
asdistortedtricappedtrigonalprismatic.Althoughionicradii
2.3.2ADF.Single-pointcalculationsonoptimizedG03structures
are available for nine-coordinate La(III) and Ce(III), none
were carried out in ADF. As with G03 the PBE functional was
areavailablefornine-coordinateU(III)orPu(III).49Theionic
used.TZPzero-orderregularapproximation(ZORA)basissetswere
used for each of the f elements together with DZP ZORA basis radiiforsix-coordinateU(III)andLa(III)are1.025and1.032
sets for O, S, Se, P, and N; DZ was used for H. ADF does not Å,respectively,whereasthoseforsix-coordinatePu(III)and
have a DZP basis set for Te, so TZP polarization functions were Ce(III)are1.00and1.01Å,respectively.Becausewewish
added to the DZ basis. The frozen-core approximation was used. to compare bond distances involving 5f and 4f trivalent
A5dcorewasusedforeachactinide;4dforthelanthanidesand cations of similar size, we chose the U(III)/La(III) and Pu-
Te, 3d for Se, 2p for S, P, and 1s for O, N. Mulliken overlap (III)/Ce(III) pairs (Table 2). Judging from the limited data
populationanalyses47,48werecarriedout.
available,49 we believe that the difference in radii for nine
2.3.3.LigandModelsandPointGroupSymmetry.Asnoted
coordinationwithinthesepairsremainsessentiallythesame
in the Introduction, we have thus far focused the computational
asitisforsixcoordination.Asanexample,theionicradius
studiesontheexperimentallycharacterizedM[N(EPiPr)] systems.
223
ofCe(IV)increasesby0.27Åongoingfromsixcoordination
HowevertheuseoftheiPrgroupsinthecalculationsisextremely
to twelve coordination; the corresponding increase in the
time-consuming, so, to cut computational cost, we tested two
approximationsbysubstitutingiPrforHorMe.Sincewesought radius of U(IV) is 0.28 Å. The salient bond distances for
to model the R ) iPr complexes, only six-coordinate complexes comparison are summarized in Table 2. The U-S distance
withlocalenergyminimawereconsidered,andwedidnotexamine is2.9956(5)Åin1andisshorterthantheLa-Sdistanceof
thepossibilitythataglobalenergyminimumcouldresultinanine- 3.0214(11) in 2 by 0.026(1) Å, a significantly larger
coordinatecomplexwithbothEandNcoordinationtothemetal. difference than the difference in ionic radii between U(III)
Extensivetests(datanotshownhere)ontheenergies,bondlengths, andLa(III)of0.007Å.Thecorrespondingdifferenceinbond
andchargesofthesecomplexesrevealedthatthechoiceofRgroup lengthsis0.0360(5)ÅbetweenaU-Sedistanceof3.0869-
does not affect the metal-chalcogen bond lengths or charges to (4) Å in 5 and a La-Se distance of 3.1229(3) Å in 6.
anysignificantextent.Wealsotestedthevalidityofidealizingthe
Whereas5isadeuterobenzenesolvate,6isatoluenesolvate.
geometries to the D symmetry group (with its favorable conse-
3
Weassumethatthedifferenceinbondlengthsisnotaffected
quencesforelectronicstructureanalysis),andagainconcludedthat
by the difference in solvents.
thishaslittleimpactuponthequalityoftheresults.Thusthepresent
paperfocusesonstudiesintheD pointgroup. ThecomparisonofbondlengthsbetweenthePu(III)and
3
Ce(III)complexesalsorevealssignificantlyshorteractinide-
3. Results chalcogen bonds relative to lanthanide-chalcogen bonds.
3.1. Syntheses, Structure, and Characterization of The Pu-S bond length in 3 is 2.9782(6) Å compared to
M[N(EPPh ) ] Complexes. Treatment of M[N(SiMe ) ] 3.0052(6) Å for Ce-S in 4, a difference of 0.0270(8) Å.
2 2 3 3 2 3
This difference is 0.0303(4) Å in the Se analogue, with a
(46) Weinhold,F.;Carpenter,J.E.InTheStructureofSmallMolecules Pu-Se distance in 7 of 3.0710(2) Å and a Ce-Se distance
and Ions; Naaman, R., Vager, Z., Eds.; Plenum Press: New York, in8of3.1013(3)Å.TheSe-M-Seanglesareslightlylarger
1988;p227.
(47) Politzer,P.;Mulliken,R.S.J.Chem.Phys.1971,55,5135.
(48) Grier,D.L.;Streitwieser,A.,Jr.J.Am.Chem.Soc.1982,104,3556. (49) Shannon,R.D.ActaCrystallogr.1976,A32,751.
Inorganic Chemistry, Vol. 47, No. 1, 2008 35
Gaunt et al.
Table3. 31PNMRShifts(ppm)forM[N(EPR2)2]3Complexes
compd 31PNMRshift(ppm) compd 31PNMRshift(ppm)
U[N(SePPh2)2]3(5) -722.6 Ce[N(TePiPr2)2]3(19) -10.0
U[N(TePiPr2)2]3(16) -696.7 Ce[N(SePPh2)2]3(8) -8.3
U[N(SPPh2)2]3(1) -680.6 Pu[N(SPiPr2)2]3(11) -1.4
U[N(SePiPr2)2]3(13) -573.9 Ce[N(SPPh2)2]3(4) 4.9
U[N(SPiPr2)2]3(9) -525.1 La[N(TePiPr2)2]3(17) 29.5
Pu[N(TePiPr2)2]3(18) -62.2 La[N(SePPh2)2]3(6) 33.6
Pu[N(SePPh2)2]3(7) -59.2 La[N(SPPh2)2]3(2) 42.6
Pu[N(SPPh2)2]3(3) -47.1 La[N(SePiPr2)2]3(14) 56.8
Pu[N(SePiPr2)2]3(15) -20.1 La[N(SPiPr2)2]3(10) 64.3
than the S-M-S angles, presumably owing to the larger Table4. SelectedBondDistances(Å)forM[N(EPiPr2)2]3Complexesa
size of Se compared to S. The [EPNPE] linkage has minor compd bond avdistance difference
deviations from planarity with the angle between the PE2 U[N(SPiPr2)2]3(9) U-S 2.854(7)
andAlMthEou2gphlanneostrathnegindgirfercotmfo5c.2ustoo6f.0th(cid:176)i.s study, in the PLua[[NN((SSPPiiPPrr22))22]]33((1101)) LPua--SS 22..889129((13)) 0.038(7)
M[N(EPPh2)2]3complexes1-8,MiscoordinatedtobothE UCe[N[N(S(SePPiiPPrr22))22]]33((1123)) UCe--SSe 22..986644((72)) 0.045(4)
andtoN.Nitrogenisasofterdonoratomthanoxygen,and La[N(SePiPr2)2]3(14) La-Se 3.019(3) 0.055(8)
it is of interest to also compare the An-N distances to the Pu[N(SePiPr2)2]3(15) Pu-Se 2.917(4)
Ln-Ndistances.TheM-Ndistancesin1-8arestatistically LUa[[NN((TTeePPiPiPrr22)2)2]3]3(1(167)) ULa--TTee 33..126244((23)) 0.060(4)
differentinthreeofthefourcomparisons.TheU-Ndistance Pu[N(TePiPr2)2]3(18) Pu-Te 3.123(3)
in 1 is shorter than the La-N distance in 2 by 0.020(4) Å, Ce[N(TePiPr2)2]3(19) Ce-Te 3.182(1) 0.059(3)
Pu-Nin3shorterthanCe-Nin4by0.025(4)Å,U-Nin aEsd’s associated with the average distances were determined by
5 shorter than La-N in 6 by 0.005(4) Å, and Pu-N in 7 summingthesquaresoftheesdassociatedwitheachofthesixindependent
M-Ebondsandtakingthesquarerootofthatvalue.
shorter than Ce-N in 8 by 0.023(4) Å.
center is best described as distorted trigonal prismatic.
La(III)isdiamagnetic(4f0),andcomplexes2and6display
SelectedcrystallographicdataareprovidedinTable1b,and
resonances at 42.6 and 33.6 ppm, respectively, in the 31P
the salient bond distances are summarized in Table 4. For
NMRspectra(Table3).Theothercomplexes(1,3-5,7,8)
comparativepurposeswehavechosentouseaverageM-E
alldisplayparamagenticallyshiftedresonances(Ce(III),4f1;
bond distances to identify differences in bonding. In this
U(III),5f3;Pu(III),5f5),withtheU(III)complexesdisplaying
respect,thefollowingcaveatsarenoted.Compounds9-12
the largest downfield chemical shifts, with a resonance at
crystallize in the space group P1h, and compounds 14 and
-722.6ppmforU[N(SePPh ) ] (5).Theresonancesforthe
2 2 3 16-19 crystallize in the space group P2 /c. All of these
Pu(III) and Ce(III) complexes are shifted to a much lesser 1
complexeshavethreelongandthreeshortM-Ebonds(one
extent. The UV/vis/near-IR spectra of the Pu and U
longandoneshortbondperligand).Compounds13and15
complexeshaveabsorbancesresultingfromLaporteforbid-
both crystallize in the space group C2/c, and because of
den 5f-5f transitions and allowed 5f-6d transitions, with
symmetry one of the ligands in these complexes has two
multipleabsorptionbandsinthe500-1300nmregion.There
identicalM-Elengths,whereastheothertwoligandseach
are also intense charge-transfer bands below 500 nm.
have one short and one long M-E bond. All of the U/La
We were unable to isolate the analogous Te donor
andPu/Cecomparisonsarebetweenisostructuralcompounds
complexes. Treatment of UI (THF) with [Na(tmeda)-
3 4 with the exception of 13 (U[N(SePiPr ) ] in space group
{N(TePPh ) }] resulted in TeII[N(TePPh ) ] as the only 2 2 3
2 2 2 2 2 C2/c) and 14 (La[N(SePiPr ) ] in space group P2 /c). In
tractableproductandagraypowder,whichwasmostlikely 2 2 3 1
comparing the bond distances between 13 and 14 the fact
elemental Te. However, as we describe in the next section,
that they are not in the same space group is ignored.
replacement of the phenyl rings on the ligands with iPr
Compound15(Pu[N(SePiPr ) ] )doesnothavealanthanide
groups allows access to the Te donor complexes. 2 2 3
counterpart for comparison because we were unable to
3.2. Syntheses, Structure, and Characterization of
crystallize Ce[N(SePiPr ) ] .
M[N(EPiPr ) ] Complexes. Treatment of M[N(SiMe ) ] 2 2 3
2 2 3 3 2 3
(M ) U, Pu, La, or Ce) with 3 equiv of NH(EPiPr ) (E )
2 2
S, Se) in THF or treatment of MI (py) (sol ) py, M ) U,
3 4
Pu; sol ) THF, M ) La, Ce) with 3 equiv of [Na(tmeda)-
{N(TePiPr)}]inEtOyieldstheneutralM[N(EPiPr)] (9-
2 2 2 2 2 3
19)complexes(eqs2and3).Wewereunabletoisolatethe
Ce[N(SePiPr ) ] complex. We could not isolate a bulk
2 2 3
quantity of Ce[N(SPiPr ) ] to allow spectroscopic charac-
2 2 3
terization,soonlythecrystalstructurewasdetermined.The
molecular crystal structures of 9-19 (Figure 2, Table 1b) IntheR)iPrseriesofcompoundsthecrystallographically
consist of six-coordinate metal centers and anions that are independent M-E distances frequently differ significantly.
bidentate through both chalcogen atoms. The N atoms of We have chosen to average M-E distances for a given
theligandsdonotcoordinate.Thegeometryaboutthemetal compound. The resultant differences among average U-E
36 InorganicChemistry,Vol.47,No.1,2008
An(III)/Ln(III)BondingComparison
Table5. SelectedBondDistances(Å)fortheModel(Calculated)
M[N(EPH2)2]3Complexes
compd bond avdistance difference
U[N(OPH2)2]3 U-O 2.393
La[N(OPH2)2]3 La-O 2.417 0.024
Pu[N(OPH2)2]3 Pu-O 2.364
Ce[N(OPH2)2]3 Ce-O 2.390 0.026
U[N(SPH2)2]3 U-S 2.849
La[N(SPH2)2]3 La-S 2.916 0.067
Pu[N(SPH2)2]3 Pu-S 2.830
Ce[N(SPH2)2]3 Ce-S 2.890 0.060
U[N(SePH2)2]3 U-Se 2.955
La[N(SePH2)2]3 La-Se 3.027 0.072
Pu[N(SePH2)2]3 Pu-Se 2.932
Ce[N(SePH2)2]3 Ce-Se 2.996 0.064
U[N(TePH2)2]3 U-Te 3.126
La[N(TePH2)2]3 La-Te 3.232 0.106
FPuig,uCree;E3.)ROe,laSti,vSeec,aTlceu)laattetdhero(Mpt-imEiz)efdorgeMom[Ne(tEriPesH.2r)(2M]3-(MO))haLsab,eUen, CPue[[NN((TTeePPHH22))22]]33 PCue--TTee 33..123052 0.067
settozeroforeachmetal.
of the diamagnetic La(III) complexes 10 and 14, which
vsLa-EandPu-EvsCe-Edistancesarenecessarilyless displayresonancesforthefreeligandinadditiontothemetal
accurate than for the R ) Ph series of compounds (which complexes. The UV/vis/near-IR spectra of the Pu and U
containonlyoneindependentM-Edistance).Nevertheless, complexeshaveabsorbancesresultingfromLaporteforbid-
theresultantdifferencesfortheR)iPrseriesofcompounds den 5f-5f transitions and allowed 5f-6d transitions, with
(Table4)showthesametrendsasdothosefortheR )Ph multipleabsorptionbandsinthe500-1300nmregion.There
seriesofcompounds(Table2).Specifically,theaverageU-S are also intense charge-transfer bands below 500 nm.
distance is 2.854(7) Å in 9 and is shorter than the average 3.3. Density Functional Theory Calculations. 3.3.1.
La-S distance of 2.892(1) Å in 10 by 0.038(7) Å. The StructuralData.ThecalculatedM-Ebonddistances,r(M-
average U-Se distance of 2.964(7) Å in 13 is shorter than E), for M[N(EPH ) ] (M ) La, U, Pu, Ce; E ) O, S, Se,
2 2 3
theaverageLa-Seof3.019(3)Åin14by0.055(8)Å.The Te)aregiveninTable5.Thecalculatedr(M-E)agreevery
average U-Te distance is 3.164(2) Å in 16 and is shorter wellwithexperimentinallcasesforwhichdataareavailable;
thantheaverageLa-Teof3.224(3)Åin17by0.060(4)Å. the maximum discrepancy between theory and experiment
Moving along the f-element series, we observe significant is ca. 0.04 Å, and the mean absolute difference is less than
bond length differences between the Pu(III) and Ce(III) 0.02Åinallcases.AsthechalcogenischangedfromOto
complexes.TheaveragePu-Sdistanceof2.819(3)Åin11 Te,r(M-E)lengthenssignificantly,theincreasebeinglargest
isshorterthantheaverageCe-Sdistanceof2.864(2)in12 between O and S, followed by a smaller increase from S
by 0.045(4) Å. The average Pu-Te distance of 3.123(3) Å throughSetoTe.r(M-O)issimilarforallfourmetals,and
in 18 is shorter than the average Ce-Te distance of 3.182- the difference between analogous r(Ln-E) and r(An-E)
(1) Å in 19 by 0.059(3) Å. pairs increases down group 16. Figure 3 emphasizes this
The E-M-E bite angles are smaller than the angles in pointbynormalizingr(M-O)tozeroforeachofthemetals.
thetridentateR-Phcomplexes,reflectingtheabsenceofN Itcanclearlybeseenthatwhereasr(U-E)increasesasthe
coordination. As was observed in the R ) Ph complexes, chalcogenbecomesheavier,r(Pu-E)increasesslightlymore
theE-M-Ebiteanglesincreaseasthechalcogengroupis steeply and r(Ln-E) increases considerably more steeply.
descendedfromStoSetoTeandthesizeofthedonoratom Thus, while r(La-O) is ca. 0.02 Å longer than r(U-O),
increases.TheligandsintheR)iPrcomplexes,9-19,are r(La-Te) is ca. 0.11 Å longer than r(U-Te). A similar,
twisted to a greater extent than are those in the R ) Ph though less dramatic, pattern is observed for Ce and Pu;
complexes. This is likely a result of the greater steric r(Ce-O) is ca. 0.03 Å longer thanr(Pu-O) and r(Ce-Te)
hindranceoftheiPrgroupsrelativetothephenylrings,which is ca. 0.07 Å longer than r(Pu-Te). These calculated
results in the inability of the N atoms to coordinate to the structuraldatasuggestthatU-EandPu-Ebondingforthe
metal. The angles between the ME and MP planes range heavier chalcogens is indeed somewhat different from that
2 2
from21.5to24.5(cid:176) ,comparedtoonly5.2to6.0(cid:176) intheR) intheanalogousLncomplexes.Wealsonotethatwhilethe
Ph tridentate complexes. generaltrendofdifferencesbetweenAn-EandLn-Ebond
In the 31P NMR spectra (Table 3), the diamagnetic La- lengthsfromthestructuraldataarereplicatedcomputation-
(III) (4f0) complexes 10, 14, and 17 display resonances at ally, the calculated differences are slightly larger than the
64.3, 56.8, and 29.5 ppm, respectively. The U(III), Pu(III) experimentally observed differences. In addition the DFT
andCe(III)complexesalldisplayparamagneticshifts,with studiespredictasmallerdifferencebetweenPu-EandCe-E
thelargestdownfieldshiftobservedforU[N(TePiPr ) ] (16) bondlengthscomparedtothosebetweenU-EandLa-E,a
2 2 3
at-696.7ppm.The31PNMRspectraalsohaveresonances phenomenon, which within experimental errors, was not
of small intensity at values for the free ligand suggesting observed from the single-crystal X-ray structural data.
thatinsolutionthereissomedissociationordecomposition 3.3.2. Natural Charges and Populations. The natural
ofthecomplexes.Thisissupportedbythe1HNMRspectra charges for selected atoms are presented in the Supporting
Inorganic Chemistry, Vol. 47, No. 1, 2008 37
Gaunt et al.
Information. It is immediately apparent that the charges on the E,
N, and P atoms are rather similar for all four metals for a
given chalcogen. The principal difference between the
complexes comes in the metal charges, which for all E
decrease in the orderq >q >q >q . It is noticeable
La Ce Pu U
that the difference in q for analogous Ln/An pairs is
M
significantlysmallerforCe/PuthanforLa/U.Forthelatter,
q is ca. 13% larger than q in the O system, a difference
La U
whichincreasesto25%forSandSebeforereducingtoca.
20% for Te. By contrast, the difference in the Ce/Pu
compoundsisca.6%forO,risingtoca.10%fortheheavier
chalcogens. This suggests that while the metal-chalcogen
bond in both the La and Ce compounds is more polar than
in their actinide equivalents, this difference in ionicity is
larger for the La/U pair than for the Ce/Pu pair. Further
evidence for this comes from examination of the charge Figure4. MolecularorbitalenergyleveldiagramsforM[N(EPH2)2]3(M
)La(a)andU(b);E)O,S,Se,Te),calculatedintheD3pointgroup.
differences between M and E as a function of both metal TheenergyofthelowestunoccupiedorbitalofeachoftheLacomplexes
and chalcogen. For La, there is a ca. 36% reduction in q (number53,shownindarkblue)hasbeensettoanenergyof0eV,ashas
La
- q as E is altered from O to Te. For the other metals, theenergyofthemoststableofthehighestoccupied(5f-based)orbitalsof
E(La) theUcomplexes(alsoshownindarkblue).ThemeanenergiesoftheR-
the corresponding values are ca. 38% for Ce, ca. 40% for and (cid:226)-spin components of each spatial MO are presented for the U
Pu,andca.41%forU.Thus,thedecreaseinionicitydown compounds.Fororbitals35-52,redindicatesa1symmetryMOs,turquoise
group 16 is largest for the U compounds and smallest for a2MOs,andblackeMOs.
the La compounds, and hence the natural charges reinforce anddorbitals,theactinidecomplexesaremorecovalentthan
the conclusions from the calculated and experimental ge- their lanthanide counterparts on account of the greater
ometriesthatthebondingintheactinidesystems,particularly involvement of the 5f orbitals over the 4f orbitals.
the U complexes, is somewhat different from that in the 3.3.3. Mulliken Overlap Populations. Calculated Mul-
lanthanides. liken overlap populations for the target complexes are
The natural atomic orbital populations for the metals are presented in the Supporting Information. Two sets of data
presented in the Supporting Information. The values given are provided for each metal. The first set is the overlap
have been obtained by subtracting the formal values from population between the metal atom and an individual
the calculated ones; i.e., they show the enhancement of the chalcogen, while the second set is for the interaction of an
populationsabovetheformal.Ineachcasethelatteris2for M3+ center with the trianionic ligand set. Mulliken overlap
the s orbitals, 6 for the p, and 0 for the d. The formal f populations can be considered as the number of electrons
populationsare0forLa(III),1forCe(III),3forU(III),and covalentlybondingbetweentwoatomsorgroupsofatoms.
5 for Pu(III). It is immediately apparent that the (n - 1)p Both sets of data suggest enhanced covalency in the
populationsareessentiallyunalteredfromtheirformalvalues compoundsoftheheavierchalcogensforallfourmetals,in
in all cases. By contrast, there are increases of the other agreementwiththeconclusionsfromthenaturalchargeand
orbital populations above their formal values, which may population analyses. Both the Ln-E and Ln3+-L 3- data
3
betakenasevidenceoftheinvolvementoftheseorbitalsin forthetwofamiliesoflanthanidecompoundsareverysimilar
covalentbondingwiththeligands.Forallfourmetals,thes tooneanother.ComparisonofLaandCewithU,however,
populationincreasesasgroup16isdescended,andtheextent revealssignificantlylargeroverlappopulationsintheactinide
of this increase is broadly similar in all cases. The d systems, at least for E ) S, Se, and Te, suggesting greater
populationsalsoincreasedowngroup16byanamountthat covalency in the U compounds. The Pu data generally lie
is generally slightly more significant than for the s. By betweentheLnandUvalues,indicatingthatthebondingin
contrast,thefpopulationsdonotchangeverymuchasgroup thePucomplexesisintermediateincovalencybetweenthat
16isdescended.ThereisaslightreductionfromOtoTein in the compounds of the early 4f elements and U.
the La and Ce f populations, while those for Pu are very 3.3.4. Molecular Orbital Structure. To test further the
similar in all four complexes. For U, there is greater conclusionsdrawnfromthenaturalandMullikenanalyses,
variability, with no clear pattern down group 16. we have probed the molecular orbital structure of the La
We conclude that the natural populations support the andUcomplexes.MOenergyleveldiagramsforM[N(EPH )]
2 2 3
chargesinfindinggreatercovalencyasgroup16isdescended (E)O,S,Se,Te)aregiveninFigure4for(a)M)Laand
for all four metals. This increase in covalency arises from (b) M ) U. To allow the electronic structures to be better
increases in metal d and, to a slightly lesser extent, s compared,thediagramshavebeenconstructedbyarbitrarily
populations from O to Te. By contrast, there is no such setting the energy of the lowest unoccupied orbital of each
increaseinmetalfpopulationdowngroup16,althoughitis of the La complexes to an energy of 0 eV. This orbital
noticeablethatthefpopulationsfortheactinidesarelarger (number53)ispredominantly(>95%)4fincharacterinall
than for the lanthanides. This suggests that while increases fourcases.FortheUsystems,thehighestoccupiedorbitals
in covalency down group 16 are a function of the metal s containtheanticipatedthree5felectrons,andtheenergyof
38 InorganicChemistry,Vol.47,No.1,2008