Additive and non-additive ligand effects in mixed halide–carbonyl–nitrile osmium complexes

Abstract

In the series [OsX₆]^3–, [OsX₅(CO)]^2–, trans-[OsX₄(CO)₂]^1–(X = Br) and the series trans-[OsX₄(MeCN)₂]^1–, trans-[OsX₄(MeCN)(CO)]^1–, trans-[OsX₄(CO)₂]^1–, osmium IV/III and III/II redox couples shift two to three times further for the first introduction of CO than for the second, contrary to recent predictions; the corresponding halide to Os^III charge-transfer spectra (X = Cl and Br) confirm the strongly non-linear accumulation of ligand electronic effects, in accord with preliminary X-ray data and near-IR crystal-field spectra.