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NMR Spin-Spin Coupling Constants for Heavy Atom Systems A ZORA Density Functional Approach Jochen Autschbach & Tom Ziegler, The University of Calgary, Dept. of Chemistry University Drive 2500, Calgary, Canada, T2N-1N4 Email: jochen@cobalt78.chem.ucalgary.ca 1
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Heavy Atom Compounds Relativistic theoretical treatment Estimated absolute relativistic effects of >100% for 6 th row elements for NMR spin- spin coupling constants Bonding changes qualitatively due to relativity scaling of nonrelativistic orbital coupling contributions might be misleading Therefore a full relativistic treatment for the spin-spin coupling constants is needed 2
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Spin-spin coupling constants Nucleus A Spin magnetic moment creates magnetic field Direct interactionNucleus B Spin magnetic moment creates magnetic field Electrons with orbital- and spin- magnetic moments Indirect interaction Indirect interaction K (A,B) Methodology 3
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we need to know including relativity including relativity Reduced coupling tensor Coupling constants in Hz from the NMR spectrum Reduced coupling constant 4
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The ZORA one-electron Hamiltonian Replacement to account for magnetic fields T nrel + relativistic corrections of T and V + spin-orbit effects Magnetic field due to nuclear magnetic moments Molecular effective Kohn-Sham potential if used in DFT Variationally stable two-com- ponent relativistic Hamiltonian 5
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Nuclei A and B, directions j and k of magnetic moments The ZORA Hyperfine Terms Requires solution of 1 st -order pertur- bation equations 6
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Description of the program Auxiliary program for ADF (Amsterdam Density Functional V. 99 and 2.3, see www.scm.com) Based on nonrelativistic, ZORA scalar or ZORA spinorbit 0 th order Kohn-Sham orbitals Solution of the coupled 1 st order Kohn- Sham equations due to FC-, SD-, and PSO term (instead of finite perturbation) Accelerated convergence for scalar relativistic calculations (< 10 iterations) Spin-dipole term available Currently no current-density dependence in V, X approximation for 1 st order exchange potential 7
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Results I : scalar ZORA One-bond metal ligand couplings Hg-C Pt-P W-C, W-H, W-P, W-F Pb-H,Pb-C, Pb-Cl FC + PSO + DSO terms included J.A., T. Ziegler, JCP 113 (2000), in press 8
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Tungsten compounds W(CO) 6 W(CO) 5 PF 3 W(CO) 5 PCl 3 W(CO) 5 WI 3 cp-W(CO) 3 H WF 6 Lead compounds PbH 4 * Pb(CH 3 ) 2 H 2 Pb(CH 3 ) 3 H Pb(CH 3 ) 4 PbCl 4 ** * exp. extrapolated from Pb(CH 3 ) x H y ** not directly measured * ** 9
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Platinum compounds Pt(PF 3 ) 4 PtX 2 (P(CH 3 ) 2 ) cis-PtCl 2 (P(CH 3 ) 3 ) 2 trans-PtCl 2 (P(CH 3 ) 3 ) 2 cis-PtH 2 (P(CH 3 ) 3 ) 2 trans-PtH 2 (P(CH 3 ) 3 ) 2 Pt(P(CH 3 ) 3 ) 4 Pt(PF 3 ) 4 Hg(CH 3 ) 2 CH 3 HgCl CH 3 HgBr CH 3 HgI Hg(CN) 2 [Hg(CN) 4 ] 2- Hg(CH 3 ) 2 (CH 3 )Hg-X [Hg(CN) 4 ] 2- Hg(CN) 2 Mercury compounds 10
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Results II : spin-orbit coupling 2 contributions: a)spin-orbit coupling for 0 th order orbitals b) ZORA spin-dipole (SD) operator System *) K / 10 20 kg/m -2 C -2 nrelscalarSOExpt. Hg(CN) 2 227443455578 HgMeBr129189203256 cis-PtH 2 (PMe 3 ) 2 91102114179 *) VWN functional, Hg-C and Pt-P coupling constants, SO = spin-orbit 11
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Results III : solvent effects Experimental couplings obtained in solution Coordination of the heavy atom by solvent molecules important ? 12
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K / 10 20 kg/m -2 C -2 *) Hg(CN) 2 +2MeOH+4MeOHExpt.+4THFExpt. 443 (450) 542 (549) 574 (585) 578582558 HgMeCl+3CHCl 3 +4CHCl 3 Expt.+3DMSOExpt. 203234278263295308 HgMeBr+2CHCl 3 +3CHCl 3 Expt.+3DMSOExpt. 127224234263295308 HgMeI+2CHCl 3 +3CHCl 3 Expt.+3DMSOExpt. 125193241239295283 HgMe 2 +2CHCl 3 +3CHCl 3 Expt.+3DMSOExpt. 75108122127131133 *) Hg-C coupling, VWN functional, scalar ZORA (numbers in brackets: ZORA spin-orbit) 13
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*) K / 10 20 kg/m 2 C 2 Pt-P coupling, VWN functional. scalar ZORA (in brackets: ZORA spin-orbit) cis- PtH 2 (PMe 3 ) 2 trans- PtH 2 (PMe 3 ) 2 no solvent *) 102 (114)170 +1 acetone154155 +2 acetone169 (184)277 Expt.179247 14
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Summary NMR shieldings and spin-spin couplings with ADF now available for light and heavy atom systems Based on the variationally stable two- component ZORA method Relativistic effects on spin-spin couplings are substantial and recovered by ZORA Spin-orbit effects are rather small for the investigated cases Coordination by solvent molecules has to be explicitly taken into account for coordinatively unsaturated systems 15
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