Effect of geometrical isomerism on metal nuclear magnetic resonance chemical shifts in octahedral d6 transition-metal complexes

Abstract

Experimental observation that metal n.m.r. chemical shifts for geometrical isomers in octahedral d⁶ transition-metal complexes exhibit two, mutually opposite, trends in relation to their geometrical configuration has been rationalized in terms of a theoretical model for calculation of the shifts. Over 100 shifts, of more than 50 pairs of geometrical isomers, of vanadium(-I), ruthenium(II), cobalt(III), rhodium(III), and platinum(IV) complexes of the type MA_{6 –n}B_n were considered. It is shown that complexes whose metal shifts are mainly governed by the spectrochemical properties of the ligands generally exhibit negative deviations from the additivity of ligand contributions to the chemical shifts, and higher chemical shifts for trans than for cis isomers. Complexes whose metal shifts are mainly governed by the nephelauxetic properties of the ligands generally exhibit positive deviations from additivity and lower chemical shifts for trans than for cis isomers.