Abstract
Recent ab initio calculations of cobalt NMR shielding show that DFT-GIAO calculations using hybrid functionals are found to reproduce experimental values well. This method is used to calculate the variation of the cobalt NMR shielding tensor of sqaure pyramidal nitrosyl complexes with respect to the CoNO geometry and to differing basal ligands. The isotropic shielding is shown to have a large negative derivative with respect to CoX distance where X is a ligating atom.; the derivative with respect to NO distance is smaller but still significant. The zz component where z is along the CoN(NO) bond is more sensitive to the basal ligands but the other two principal components are sensitive to the CoNO geometry.
Highlights
The scope of cobalt NMR spectroscopy was illustrated in a recent review [1]. 59Co was one of the first nuclei to be studied using NMR spectroscopy
Density functional calculations of cobalt shielding in Co(III) complexes using DFT/GIAO methods with moderately-sized basis sets and hybrid density functionals have been found by several groups to give good agreement with experimental shielding values
We have found that such calculations give good results for square-pyramidal nitrosyl complexes of cobalt
Summary
The scope of cobalt NMR spectroscopy was illustrated in a recent review [1]. 59Co was one of the first nuclei to be studied using NMR spectroscopy. Because of the lower symmetry, square-pyramidal nitrosyl complexes would be expected to show greater asymmetry than the complexes previously studied and the different components of the shielding tensor can be shown to respond differently to geometry changes.
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