73138-17-7Relevant academic research and scientific papers
New insights concerning the trans influence based upon the linkage isomeric ratios of thiocyanate in cobaloxime complexes
Kargol, Joseph A.,Lavin, Karen D.,Crecely, Roger W.,Burmeister, John L.
, p. 1515 - 1522 (1980)
The linkage isomeric ratios for thiocyanate trans to various donors have been determined for a series of cobaloxime complexes[trans-bis(dimethylglyoximato)(ligand)(thiocyanato)cobalt(III)] by utilizing proton NMR measurements. The chemical shift of the methyl protons of the dimethylglyoximate group is sensitive to the nature of the axial ligands, the τ values of the S-bound isomers being ca. 0.1 ppm less than those of the N-bound isomers in an aromatic solvent such as nitrobenzene. It was found that the presence of a small amount of Co(II) is necessary in order to facilitate isomerizatiori and the attainment of equilibrium. The ratio of sulfur- to nitrogen-bound species, K(S/N), is related to the trans influence and the basicity of the trans ligands. The observed order of decreasing trans influence is roughly the following: alkyls ? phosphites ≈ pyridines > anilines > phosphines > thioureas, K(S/N) decreasing in the reverse order. Within the pyridine, aniline, and phosphine series, K(S/N) decreases as the pKa of the trans ligand increases. Greater through-space P-H coupling is present for phosphorus donors trans to S-bound thiocyanates than to N-bound thiocyanates. The bridging ability in inner-sphere electron-transfer reactions for the three ions studied decreases in the order NCS- > CN- > NO2-. The influence of solvent upon K(S/N) and the clarification of some discrepancies concerning previously reported cobaloximes are also discussed.
