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NMR Spin-Spin Coupling Constants for Heavy Atom Systems

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. Heavy Atom Compounds.

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NMR Spin-Spin Coupling Constants for Heavy Atom Systems

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  1. 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

  2. Heavy Atom Compounds • Relativistic theoretical treatment • Estimated absolute relativistic effects of >100% for 6th 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

  3. Methodology Spin-spin coupling constants Indirect interactionK(A,B) Electrons with orbital- and spin- magnetic moments Direct interaction Nucleus B Spin magnetic moment creates magnetic field Nucleus A Spin magnetic moment creates magnetic field 3

  4. we need to know including relativity Reduced coupling tensor Reduced coupling constant Coupling constants in Hz from the NMR spectrum 4

  5. Variationally stable two-com- ponent relativistic Hamiltonian The ZORA one-electron Hamiltonian Molecular effective Kohn-Sham potential if used in DFT Tnrel + relativistic corrections of T and V + spin-orbit effects Magnetic field due tonuclear magnetic moments Replacement to account for magnetic fields 5

  6. The ZORA Hyperfine Terms Requires solution of 1st-order pertur- bation equations Nuclei A and B, directions j and k of magnetic moments 6

  7. 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 0th order Kohn-Sham orbitals • Solution of the coupled 1st 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 dependencein V, Xa approximation for 1st order exchange potential 7

  8. 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

  9. Tungsten compounds Lead compounds ** * W(CO)6 W(CO)5PF3W(CO)5PCl3W(CO)5WI3cp-W(CO)3HWF6 PbH4 * Pb(CH3)2H2 Pb(CH3)3H Pb(CH3)4 PbCl4 ** * exp. extrapolated from Pb(CH3)xHy ** not directly measured 9

  10. Platinum compounds Mercury compounds Pt(PF3)4 Hg(CN)2 [Hg(CN)4]2- (CH3)Hg-X PtX2(P(CH3)2) Hg(CH3)2 cis-PtCl2(P(CH3)3)2trans-PtCl2(P(CH3)3)2cis-PtH2(P(CH3)3)2 trans-PtH2(P(CH3)3)2 Pt(P(CH3)3)4 Pt(PF3)4 Hg(CH3)2 CH3HgCl CH3HgBr CH3HgI Hg(CN)2 [Hg(CN)4]2- 10

  11. Results II : spin-orbit coupling 2 contributions: a) spin-orbit coupling for 0th order orbitals b) ZORA spin-dipole (SD) operator *) VWN functional, Hg-C and Pt-P coupling constants, SO = spin-orbit 11

  12. Results III : solvent effects • Experimentalcouplings • obtained in solution • Coordinationof the heavyatom by solvent moleculesimportant ? 12

  13. *) Hg-C coupling, VWN functional, scalar ZORA (numbers in brackets: ZORA spin-orbit) 13

  14. cis-PtH2(PMe3)2 trans-PtH2(PMe3)2 *)K / 1020 kg/m2C2Pt-P coupling, VWN functional. scalar ZORA (in brackets: ZORA spin-orbit) 14

  15. 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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