Ligand K-edge XAS - Quantitative Applications With TDDFT

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Ligand K-edge XAS - Quantitative Applicationswith TDDFTSerena DeBeerDepartment of Chemistry and Chemical BiologyCornell UniversitySSRL SMBLow Z XAS Summer SchoolJune 23, 2010Monday, July 19, 2010

Outline Ligand K-edge XAS (a bit of history) Qualitative to more Quantitative Approaches TDDFT Calculation of Edges Applications- dithiolenes- corroles New Methods (XES)Monday, July 19, 2010

Why use Ligand K-edges?Metal K- and L-edges Oxidation state Ligand Field Geometry Spin StateLigand K-edges Probe covalency of M-L bonds Fundamental to reactivity, magnetic interactions, electrondelocalization Server as a reporter for the metal site Both metal and ligand oxidation Metal and Ligand edges together provide a more completeexperimental description of the electronic structureMonday, July 19, 2010

Ligand K- pre-edges: The Very “Qualtitative” YearsO K-edge 1s to p transitions “mightbe expected to reflect to someextent the d density of statesaround the metal atoms asmeasured by the L2,3 edges”Monday, July 19, 2010

Ligand K- pre-edges: The Qualtitative YearsRelates Cl K- pre-edge to MO pictureF K- pre-edge reflects ligand 2p- metal 3dhybridizationMonday, July 19, 2010

Ligand K-edge XAS: As a Quantitative Probe of CovalencycontinuumedgeL 4pM 3dTransitions localized on the absorbing atom pre-edge feature due to a pure ligand transition.energyL 3ppre-edgeProvides an experimental measureof ligand 3p character in the HOMO.Assign intensity to covalency (based on EPR)B. Hedman, K. O. Hodgson, E. I Solomon, J. Am. Chem. Soc., 1990, 112, 1643.Monday, July 19, 2010L 1s

Correlating Ligand K- Pre-edge Intensities to CovalencyOn a most elementary level, the intensity of the preedge position from a ligand 1s- into a metal d-basedMO is given by:I(1s ψ*) aα2where α2 is covalency and a is a proportionalityconstant – assumes the transition moment dipoleintegral is constantIs this a fair assumption?Monday, July 19, 2010

K-EdgeXAS sityMechanismFigure2.Hedman,Comparisonof K.;theSolomon,electricdipoleintensityforNeese, F.;B.; Hodgson,EI Inorg.Chem.,1999, 38,mechanisms4854-4860ligand K-edge transitions and optical charge transfer transitions.Monday, July 19, 2010a giveamounweigh1s fradialturn deffectivalueHartreand chresultsnumbemorevalueintegraconcenorbitalthe cha

Transition Dipole MomentThe transition dipole moment is the intrinsic intensity of a 1s np transition.This depends on the radial functions of the 1s and 3p orbitalsSulfurChlorinetransitiondipole integral3p radialexpectationvalueF. Neese et al., Inorg. Chem., 1999, 38, 4854.Monday, July 19, 2010

Experimentally Estimating the Transition Dipole Moment33Simproved correlationUse other spectroscopicmethodsto determine I(S)Assume Dipole Integral islinear with respect to the1s 4p Energy (eV)XPSprevious correlationR. Sarangi, S. DeBeer George, D. Jackson Rudd, R. K. Szilagyi, X. Ribas, C. Rovira, R. H. Holm, B. Hedman, K. O. Hodgson, E. I. Solomon, J.Am. Chem. Soc., 2007, 129, 2316.Monday, July 19, 2010

Experimental Observable: Oscillator StrengthThe oscillator strength of a given transition in the pre-edge region maybe factored into two contributions:1) fractional ligand character in the acceptor MO2) radial transition-dipole integral I(S) S1s r S3p 2Therefore we need to know I(S)1) Experimentally estimate2) Calculate the oscillator strength directly and apply thefactorization of I(S) and α2 after the correlation of the calculated andexperimental oscillator strengths has been establishedFocus on pre-edge region which readily relates to an MO-based pictureTD-DFT Calculations: ORCA (developed by F. Neese, Bonn)Monday, July 19, 2010

DOMOsSOMOsvirtual continuumA Simple TD-DFT Protocol for K-Edge XAS Localize 1s-orbitals of symmetry equivalent S,Cl Include only 1s Virtual excitations in the TD-DFTequations Calculate dipole and quadrupole contributions to thetransition moments Use large basis sets on the XAS absorber atom Treat scalar relativistic effects through ZORA Compensate negative total charges through COSMOTD-DFT: lengthΨ 0 µED ΨI (X jbI YjbI ) ψj r ψbjb velocityIIΨ 0 µED ΨI i (X jb Yjb ) ψj ψbjb(dipole velocity preferred on theoretical ground but in practice dipolelength is more stable; for exact wavefunctions both forms would beS. DeBeer George, T. Petrenko, F. Neese, ICA, 2007 identical)1sMonday, July 19, 2010

The Quadrupole IntensityProblem: Straightforward application of the ED and MD operators: 1 21µEQ,ab (ri,ari,b 3 ri δab )µMD,a 2 (li 2si )aiiLeads to results that depend (a LOT) on the choice of the coordinate origin which isunphysical!Solution: (Taras Petrenko) Choose the origin that leads to the fastest convergence of themultipole expansion of the light/matter interaction. First shift the origin by R:!and then requireLeading to:!!!!Solving this linear system for R gives the best possible origin. It usually nearly coincideswith the X-ray absorber atomMonday, July 19, 2010!

Cl K- pre-edge: Method CalibrationexperimentalBP86CP(PPP): metalTZVP: ClCOSMOGround state DFTsymmetry equivalent chlorine 1s orbitalslocalizedcalculatedTD-DFT - allowing only for excitations fromthe localized chlorine 1s orbitals.Relative Intensities well-reproducedConstant energy shift 85.5 ( /- 0.3 eV)S. E. Shadle et al., J. Am. Chem. Soc., 1995, 117, 2259.S. DeBeer George, P. Brant, E. I. Solomon, J. Am. Chem. Soc.,2005, 127, 667.S. DeBeer George, T. Petrenko, F. Neese, ICA, 2007Monday, July 19, 2010

Effect of functional, basis set, solvation & relativistics For all [MCl4]n complexesFor [MCl4]2- complexes onlyPeturbationAvg EnergyShiftError in Norm.IntensityAvg Energy ShiftError in Norm.IntensityOpt method85.3 (0.6)0.0685.5 (0.3)0.06B3LYP64.0 (0.6)0.1164.1 (0.6)0.10LB9440.3 (0.8)0.2040.8 (0.5)0.18IGLO-III86.4 (0.7)0.0986.8 (0.2)0.08TZVP85.7 (0.9)0.2685.9 (0.63)0.32Inf DE85.4 (0.6)0.0785.7 (0.2)0.05No solv84.9 (0.6)0.0685.2 (0.3)0.06ZORA61.1 (0.6)0.0661.0 (0.7)0.06DKH277.3 (1.2)0.0677.8 (1.9)0.06S. DeBeer George, T. Petrenko, F. Neese, ICA, 2007.Monday, July 19, 2010

Monday, July 19, 2010

Generic ORCA Input FileMonday, July 19, 2010

Metal K-EdgescontinuumedgeAbsorption IntensityvirtualMetal-d- basedSOMOs VirtualsDOMOsEXAFS1s 4p1s 3dLigand-1sPhoton Energy (eV)Metal-1spre-edge edgefeature feature EXAFSMonday, July 19, 2010

TD-DFT with Inclusion of QuadrupoleexperimentcalculationEnergies and intensities are well-reproducedDeBeer George, S.; Petrenko, T.; Neese, F.J. Phys. Chem. A, 2008, 112, 12936.Monday, July 19, 2010

TD-DFT with ORCA: Theory vs ExperimentHigh-SpinLow-SpinDeBeer George, S.; Petrenko, T.; Neese, F.J. Phys. Chem. A, 2008, 112, 12936.Monday, July 19, 2010

Dithiolene 2M Fe,Co,Ni,Cu,Pd,Pt,AuMonday, July 19, 2010 Classical coordination complexes (Holm, Maki,Gray, Stiefel, Schrauzer, Wieghart ) Candidate materials for nonlinearoptic devices and catalysis Biological impact (Molybdopterines) Controversial electronic sturcture

Dithiolene 2M Fe,Co,Ni,Cu,Pd,Pt,AuMonday, July 19, 2010 Classical coordination complexes (Holm, Maki,Gray, Stiefel, Schrauzer, Wieghart ) Candidate materials for nonlinearoptic devices and catalysis Biological impact (Molybdopterines) Controversial electronic sturcture

Do dithiolene ligands contain radicals?2.0[AuIII(LS,S)2]1[AuIII(LS,S)(LS,S )]Normalized AbsorptionNormalized Absorption1.21.0Sulfur K-EdgeMetal III(LS,S)2]1[AuIII(LS,S)(LS,S )]0.011900 11905 11910 11915 11920 11925 11930 11935Energy (eV)No Effect on Metal-Edge: Ligand Centered Oxidation0.0246824722476Energy (eV)New Pre-Edge Peak: Ligand Centered OxidationK. Ray, S. DeBeer George, E. I. Solomon, K. Wieghardt, F. Neese, Chem. Eur. J., 2007, 13, 2783.Monday, July 19, 20102480

Do dithiolene ligands contain radicals?2.0[AuIII(LS,S)2]1[AuIII(LS,S)(LS,S )]Normalized AbsorptionNormalized Absorption1.21.0Sulfur K-EdgeMetal III(LS,S)2]1[AuIII(LS,S)(LS,S )]0.011900 11905 11910 11915 11920 11925 11930 11935Energy (eV)No Effect on Metal-Edge: Ligand Centered Oxidation0.0246824722476Energy (eV)New Pre-Edge Peak: Ligand Centered OxidationYES! . But what determines when and how it happens?K. Ray, S. DeBeer George, E. I. Solomon, K. Wieghardt, F. Neese, Chem. Eur. J., 2007, 13, 2783.Monday, July 19, 20102480

Electronic Structure of Square Planar [M(LSS)2]1b1g(dxy)2b2g1b1u2b3g2ag(dz2)1b2g (dxz)2b3g (dyz)1ag(dx2-y2)Monday, July 19, 20101auMonoanions:Ni, Pd, Pt,(S 1/2)Cu, Au (S 0)Co(S 1)Dianions:Fe(S 1)

Insights from XAS on Dithiolenesb1gb2gb1u1sI IIRadical character along the series:[Fe(LS,S)2]2- [Cu(LS,S)2]- [Co(LS,S)2]- [Ni(LS,S)2]- [Pd(LS,S)2]- [Pt(LS,S)2]- [Au(LS,S)2]“Innocent” ligandsAmbiguousK. Ray, S. DeBeer George, E. I. Solomon, K. Wieghardt, F. Neese, Chem. Eur. J., 2007, 13, 2783.Monday, July 19, 2010Ligand Radicals

Chromium TrisdithiolenesΘ 39.1 Θ 45.6 avg. C–S 1.740 Åavg. C–C 1.396 Åavg. C–S 1.751 Åavg. C–C 1.409 ÅNBu4[Cr(LBu)3] (S 1/2)H2LBu,NEt3[NBu4]2[Cr(LCl)3] (S 1)CrCl3(thf)3Two other structures, both octahedral:[Cr(mnt)3]2- (S 1) and [Cr(mnt)3]3- (S 3/2)Monday, July 19, 2010H2LCl, NEt3Kapre, Wieghardt et al. Inorg. Chem. 2007, 46, 7827Lewis & Dance Dalton Trans. 2000, 3176

Chromium K-edge XAS5990.05990.35990.1Cr 1s 3dMonday, July 19, 2010Pre-edge energy within 0.3 eVAll CrIII!!

Sulfur K-edge XAS2469.82469.72469.9Characteristic ligand π-radicalpre-edge feature* 15% oxidized impurityMonday, July 19, 2010

IIICl Cl2[Cr (L )(L )2]DFT Broken Symmetry, BS(3,1)Θcalc 45.3 Θexp 45.3 Monday, July 19, 2010(S 1)

Electronic Structure[CrIII(LCl )2(LCl)]1-[CrIII(LCl)3]3-S 1/2S 1S 3/2Θcalc 49.2 Θcalc 45.3 Θcalc 48.3 Θexp 39.1 Θexp 45.3 Θexp 51.5 [Cr(LBu)3]1-Monday, July 19, 2010[CrIII(LCl )(LCl)2]2-[Cr(mnt)3]3-

Time Dependent Cr(LCl)3]3monoanion: 1edianion: 2e-LCltrianion: 3e-Calculated: 55 eV shiftCr SOMOsLCl SOMOsIIIsulfur 1sIMonday, July 19, 2010IIDeBeer George, Petrenko, Neese Inorg. Chim. Acta 2008, 361, 965

Neutral ComplexBroken symmetry DFT calculation of [Cr(LBu)3], S 0 – predicts octahedral geometryΘ 47.9 BS(3,3) S 020 kcal mol-1 lower than UKSMonday, July 19, 2010

Anticipated S K-edge[Cr(LBu)3]0αCalculated: 55 eV shifteg[Cr(LBu)3]1-empty for neutral[Cr(LBu)3]3-[Cr(LBu)3]2-LBuCr SOMOsIsulfur 1sIMonday, July 19, 2010

From biological to chemical catalysis.Alkane hydroxylation:Fe(tpfp)ClAlkene epoxidation:P450, CPORH ½O2 ROHFeIV OP (Compound I)FeIV-O/OH (Compound II)Fe(tpfc)ClMonday, July 19, 2010High-valent species areinvoked in catalyticmechanism

Corroles: Metal- or Ligand-based Oxidation?Fe(IV)S 1Fe-N(cor) 1.88-1.92 ÅFe-Cl 2.24 ÅDisp. from Fe-N4 plane 0.42 ÅcorroleORFe(III)corroleS 1 3/2 Fe(III) – 1/2 cor Mӧssbauer Fe(tpfc)Clδ 0.19 mm/s EQ 2.93 mm/sNMR – upshifted meso-H resonances suggestinglarge negative spin densities on carbons.Zakharieva et al, JACS, 2002, 124, 6636.Monday, July 19, 2010

Corroles: Metal- or Ligand-based Oxidation?Fe(IV)S 1Fe-N(cor) 1.88-1.92 ÅFe-C(Ph) 1.98 ÅDisp. from Fe-N4 plane 0.27 ÅcorroleORFe(III)corroleS 1 3/2 Fe(III) – 1/2 cor Mӧssbauer Fe(Et8C)Clδ -0.10 mm/s EQ 2.99 mm/sNMR – upshifted meso-H resonaces ( 1/4 of theCl-Corr)Zakharieva et al, JACS, 2002, 124, 6636.Monday, July 19, 2010

Porphyrin and Corrole ModelsFe(tpfp)ClS 5/2Fe(III)Fe K-edgeCl K-edgeN K-edgeMonday, July 19, 2010Fe(tpfc)ClS 1Fe(IV) OR Fe(III) cor*Fe(Et8-Cor)PhS 1Fe(IV)Fe K-edgeCl K-edgeN K-edgeFe K-edgeN K-edge

Fe K-edge XASPre-edge 1 eV lower inFe(corrole) Cl vs. heme(dominantly 4pz mixing)Consistent with weaker axialligandMonday, July 19, 2010

Fe K-edge XASMonday, July 19, 2010

Fe K-edge XASFe(corrole)Ph rising edge and preedge to highest energyPre-edge increased in intensity,despite (less distortion)Mediated by shorter Fe-C bondand a second dz2 hole?Monday, July 19, 2010

Cl K-edge XASSimilar Fe-Cl covalency(Cl contributes to dxz, dyz, dz2)Similar effective charge on ClSimilar d-manifold energySupports an S 3/2 Fe(III)assignment for the Fe(corrole)ClMonday, July 19, 2010

N K-edge XASN K-edge suggests a moreoxidized ligand in Fe(corrole)ClLow energy pre-edge featurepresent only in Fe(corrole)ClSuggests a corrole π* radicalin Fe(corrole)ClMonday, July 19, 2010

N K-edge XASN K-edge suggests a moreoxidized ligand in Fe(corrole)ClLow energy pre-edge featurepresent only in Fe(corrole)ClSuggests a corrole π* radicalin Fe(corrole)ClLow energy pre-edge feature isabsent in Fe(corrole)PhPh(Corrole) edge indicates amore reduced ligandMonday, July 19, 2010

Ground State DFT – Fe(corrole)Cldz2corrolespin coupled pairInteraction between Fe-dz2 andcorrole π-orbitaldxz, yzFe(III) S 3/2 CorrradicalConsistent w/ previousDFT studies (Ghosh,Walker/Trautwein, andNeese)dxyMonday, July 19, 2010

DFT: Fe(corrole)Cl – Unoccupied Orbitalsαββ dx2-y2α dx2-y2β dz2dxz, yzα corroleπ*Monday, July 19, 2010XAS probes theunoccupied orbitals

Ground State DFT – Fe(corrole)Phdz2No Broken SymmetrySolutioncorroledxz, yzFe(IV) S 1dxyMonday, July 19, 2010Consistent w/ previousDFT studies (Walker/Trautwein,)

DFT: Fe(corrole)Ph – Unoccupied Orbitalsαββ dx2-y2α dx2-y2β dz2α dz2dxz, yzXAS probes theunoccupied orbitalsMonday, July 19, 2010

TD-DFT: Fe K-edgesexperimenttheoryFe K-edge energies and intensities are well-reproducedMonday, July 19, 2010

TD-DFT: Cl K-edgesexperimenttheoryCl K-edge energies and intensities are well-reproducedMonday, July 19, 2010

DFT: N K-edgesFe(corrole)ClFe(corrole)Phα corroleπ*Ground-state DFT N 2p character show reasonable agreementMonday, July 19, 2010

SummaryPre-edges of ligand and metal edges are accessible using a relatively simple TDDFTapproach Ligand and metal K-edge applications to dithiolenes have helped resolve electronicstructure controversies Similar applications to corroles have been demonstratedMonday, July 19, 2010

AcknowledgmentsGroup MembersMartha BeckwithP. ChandrasekaranNicole LeeJennie LinChristopher PollockChantal StieberCollaboratorsFrank Neese (Bonn)Taras Petrenko (Bonn)Karl Wieghardt (MPI)Stephen Sproules (MPI)Ed Solomon (Stanford)Ann Walker (Arizona)Uwe Bergmann (Stanford)Ken Finkelstein (Cornell) Cornell University ACS PRFBeam time: SSRL, CHESSMonday, July 19, 2010

Transition Dipole Moment The transition dipole moment is the intrinsic intensity of a 1s np transition. This depends on the radial functions of the 1s and 3p orbitals Sulfur Chlorine F. Neese et al., Inorg. Chem., 1999, 38, 4854. transition dipole integral 3p radial expectation value Monday, July 19, 2010

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