NMR SpinSpin Coupling Constants for Heavy Atom Systems

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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_at_cobalt78.chem.ucalgary.ca
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Heavy Atom Compounds

• Relativistic theoretical treatment
• Estimated absolute relativistic effects of gt100
  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
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Methodology

• Spin-spin coupling constants

Indirect interaction K(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
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Reduced coupling tensor
Reduced coupling constant
Coupling constants in Hz from the NMR spectrum
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• The ZORA one-electron Hamiltonian

Variationally stable two-com- ponent relativistic
Hamiltonian
Tnrel relativistic corrections of T and V
spin-orbit effects
Molecular effective Kohn-Sham potential if used
in DFT
Magnetic field due tonuclear magnetic moments
Replacement to account for magnetic fields
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The ZORA Hyperfine Terms
Requires solution of 1st-order pertur- bation
equations
Nuclei A and B, directions j and k of magnetic
moments
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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 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 (lt 10 iterations)
• Spin-dipole term available
• Currently no current-density dependencein V, Xa
  approximation for 1st order exchange potential

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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
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Tungsten compounds
Lead compounds


W(CO)6 W(CO)5PF3W(CO)5PCl3W(CO)5WI3cp-W(CO)3HW
F6
PbH4 Pb(CH3)2H2 Pb(CH3)3H Pb(CH3)4 PbCl4
exp. extrapolated from Pb(CH3)xHy not
directly measured
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Platinum compounds
Mercury compounds
Pt(PF3)4
Hg(CN)2
Hg(CN)42-
(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(PF
3)4
Hg(CH3)2 CH3HgCl CH3HgBr CH3HgI Hg(CN)2 Hg(CN)42
-
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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
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Results III solvent effects

• Experimentalcouplings
• obtained in solution
• Coordinationof the heavyatom by solvent
  moleculesimportant ?

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

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