Relativistic Approximations to Paramagnetic NMR Chemical Shift and Shielding Anisotropy in Transition Metal Systems

Abstract

We apply approximate relativistic methods to calculate the magnetic property tensors, i.e., the g-tensor, zero-field splitting (ZFS) tensor (D), and hyperfine coupling (HFC) tensors, for the purpose of constructing paramagnetic nuclear magnetic resonance (pNMR) shielding tensors. The chemical shift and shielding anisotropy are calculated by applying a modern implementation of the classic Kurland-McGarvey theory ( J. Magn. Reson. 1970 , 2 , 286 ), which formulates the shielding tensor in terms of the g- and HFC tensors obtained for the ground multiplet, in the case of higher than doublet multiplicity defined by the ZFS interaction. The g- and ZFS tensors are calculated by ab initio complete active space self-consistent field and N-electron valence-state perturbation theory methods with spin-orbit (SO) effects treated via quasidegenerate perturbation theory. Results obtained with the scalar relativistic (SR) Douglas-Kroll-Hess Hamiltonian used for the g- and ZFS tensor calculations are compared with nonrelativistically based computations. The HFC tensors computed using the fully relativistic four-component matrix Dirac-Kohn-Sham approach are contrasted against perturbationally SO-corrected nonrelativistic results in the density functional theory framework. These approximations are applied on paramagnetic metallocenes (MCp) (M = Ni, Cr, V, Mn, Co, Rh, Ir), a Co(II) pyrazolylborate complex, and a Cr(III) complex. SR effects are found to be small for g and D in these systems. The HFCs are found to be more influenced by relativistic effects for the 3d systems. However, for some of the 3d complexes, nonrelativistic calculations give a reasonable agreement with the experimental chemical shift and shielding anisotropy. The influence of scalar relativity is strong for the 5d IrCp system. This mixed ab initio/DFT technique, with a fully relativistic method used for the critical HFC tensor, should be useful for the treatment of both electron correlation and relativistic effects at a reasonable computational cost to compute the pNMR shielding tensors in transition metal systems.

Ab initio paramagnetic NMR shifts via point-dipole approximation in a large magnetic-anisotropy Co(ii) complex

“…The related def2-TZVP-DKH basis has been found to represent a good compromise between the computational cost and accuracy in previous pNMR computations. 11,15,20 In accordance with our previous experience, 9,20 there is a significant impact on the g-and ZFS tensors of dynamical electron correlation accounted for via the NEVPT2 method, as compared to the CASSCF results ( Table 2). Both the D -parameter of the ZFS tensor and the anisotropy of the g-tensor decrease upon adopting the NEVPT2 correction.…”

“…All the 10 quartet roots as well as 15 doublets possible within this active space were included. It has been shown 9,15,38,39 that this methodology gives good results for the EPR parameters including the critical ZFS tensor, for systems with two or more unpaired electrons. a Optimised bond lengths, see illustration of the structure in Fig.…”

“…electron paramagnetic resonance (EPR) parameters can be calculated quite reliably using molecular quantum-chemical (QC) codes. pNMR modeling of 3d transition metal clusters has been by now well-probed 10,11,[14][15][16] and chemical shifts in such systems can be calculated by first-principles methods with a predictive accuracy. We retained only one of the two aliphatic 16-carbon chains of the complex.…”

Coordination‐Induced Interlinked Covalent‐ and Metal–Organic‐Framework Hybrids for Enhanced Lithium Storage

“…Furthermore, the 13 C NMR spectra of COF/Mn‐MOF are largely identical to pristine COF and pristine Mn‐MOF (Figure S2d, Supporting Information). However, the chemical shift variation of two C atoms next to N atom in COF structure and C atoms of Mn‐MOF should be ascribed to the coordination interaction between N atoms of COF and the paramagnetic Mn centers from MOF 5d,7…”

Probing the Local Magnetic Structure of the [FeIII(Tp)(CN)3]− Building Block Via Solid‐State NMR Spectroscopy, Polarized Neutron Diffraction, and First‐Principle Calculations

“…[89][90][91][92][93][94][95][96][97][98][99] To assemble the Zeeman g-tensors, the hyperfine coupling matrices, and the orbital shielding, we have used the pNMRShift program developed by the Autschbach's group. Such acomputational strategy has already been applied successfully to al arge panel of transition-metal complexes.…”