15N NMR shielding tensors in bent nitrosyl complexes of cobalt

Moore, Elaine A. and Mason, Joan (2002). 15N NMR shielding tensors in bent nitrosyl complexes of cobalt. Journal of Molecular Structure, 602 - 603 pp. 347–356.

DOI: https://doi.org/10.1016/S0022-2860(01)00775-X


An ibitio calculations of nitrogen NMR chemical shielding tensors are presented for square-pyramidal cobalt model complexes with an apical nitrosyl ligand as a function of the geometry of the CoNO grouping. It is shown that the isotropic nitrogen shielding decreases with increasing N-O distance (in the range 101 - 116 pm) and with increasing CoN distance (in the range 173 - 193 pm). With increasing CoNO angle, in the models studied, the isotropic shielding initially decreases up to about 140 degrees and then increases. For complexes with the same CoNO geometry and S-, N- or O-ligating ligands, the shielding increases in the order S < N, O. The variation of the shielding with the CoNO geometry is mainly due to variations in the shielding tensor component parallel to the NO bond which mixes n(N) and pi*(N=O) orbitals. The calculations give no evidence for differing CoNO geometries producing similar isotropic shieldings but very different spans and skews of the shielding tensor as given by the experiments in some series of compounds. It is likely that there is CoNO motional averaging (libration or spinning) in the solid state, as described for [Co(NO)(TPP)], in complexes for which anomalously small spans are observed.

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