MULTINUCLEAR NMR-STUDY OF THE CRYSTAL-FIELD STRENGTH OF THE NITRO LIGAND AND THE EMPIRICAL ESTIMATION OF THE CO-59 NMR CHEMICAL-SHIFTS OF COBALT NITRO COMPLEXES

The variable ligand field strength of the nitro ligand has been reexamined on the basis of a steric model. An improved empirical method is proposed for the estimation of nitro ligand field strength in terms of a single correction parameter Δ (1.824 ⨯ 10-6 ppm-1) to the shift parameter SNO2(3.075 ⨯ 10-5 ppm-1) for the estimation of the 59Co NMR chemical shifts of cobalt-nitro complexes. The reversed chemical shift trend of geometrical isomers of cobalt-nitro complexes are attributed to variations in the 10Dq of the nitro ligands. The model is applied to the assignment of different isomers of cobalt-nitro compounds obtained from ligand exchange reactions of the cobaltinitrite anion with the N3- and SCN- ions. In all the ligand exchange reactions studied, it was found that mixed nitro complexes formed in the reaction predominately adopted the trans configuration. © 1990, American Chemical Society. All rights reserved.