Density Functional Study of Cobalt-59 Nuclear Magnetic Resonance Chemical Shifts and Shielding Tensor Elements in Co(III) Complexes

Abstract

A density functional method has been used to successfully predict the isotropic 59Co nuclear magnetic resonance (NMR) chemical shifts of the following anionic, cationic and neutral Co(III) complexes: [Co(CN)6]3-, [Co(NH3)6]3+, [Co(NO2)6]3-, [Co(NH3)4CO3]+, Co(acac)3, and [Co(en)3]3+. Isotropic chemical shifts are well-reproduced by using Wachters' cobalt basis set and uniform 6-31G* basis sets on the light atoms, together with the use of the B3LYP hybrid functional. In addition, the principal elements of the 59Co shielding tensor (σ11, σ22, and σ33), the absolute shieldings of Co(CN)63- and Co(acac)3, and the Co−C bond length shielding derivative for Co(CN)63- are also in good agreement with previous experimental estimates. There are no obvious distinctions between the predicted shifts (or shielding tensor elements) of anionic and cationic complexes. The ability to successfully predict both shift trends, absolute shieldings, shielding tensor elements, and a vibrational shielding derivative for d6 transition metal complexes opens up new possibilities for probing metal ions in biological systems by using NMR spectroscopy.