Redox Interconversion between Cobalt(III) Thiolate and Cobalt(II) Disulfide Compounds

[Image: see text] The redox interconversion between Co(III) thiolate and Co(II) disulfide compounds has been investigated experimentally and computationally. Reactions of cobalt(II) salts with disulfide ligand L(1)SSL(1) (L(1)SSL(1) = di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide) result in the formation of either the high-spin cobalt(II) disulfide compound [Co(II)(2)(L(1)SSL(1))Cl(4)] or a low-spin, octahedral cobalt(III) thiolate compound, such as [Co(III)(L(1)S)(MeCN)(2)](BF(4))(2). Addition of thiocyanate anions to a solution containing the latter compound yielded crystals of [Co(III)(L(1)S)(NCS)(2)]. The addition of chloride ions to a solution of [Co(III)(L(1)S)(MeCN)(2)](BF(4))(2) in acetonitrile results in conversion of the cobalt(III) thiolate compound to the cobalt(II) disulfide compound [Co(II)(2)(L(1)SSL(1))Cl(4)], as monitored with UV–vis spectroscopy; subsequent addition of AgBF(4) regenerates the Co(III) compound. Computational studies show that exchange by a chloride anion of the coordinated acetonitrile molecule or thiocyanate anion in compounds [Co(III)(L(1)S)(MeCN)(2)](2+) and [Co(III)(L(1)S)(NCS)(2)] induces a change in the character of the highest occupied molecular orbitals, showing a decrease of the contribution of the p orbital on sulfur and an increase of the d orbital on cobalt. As a comparison, the synthesis of iron compounds was undertaken. X-ray crystallography revealed that structure of the dinuclear iron(II) disulfide compound [Fe(II)(2)(L(1)SSL(1))Cl(4)] is different from that of cobalt(II) compound [Co(II)(2)(L(1)SSL(1))Cl(4)]. In contrast to cobalt, reaction of ligand L(1)SSL(1) with [Fe(MeCN)(6)](BF(4))(2) did not yield the expected Fe(III) thiolate compound. This work is an unprecedented example of redox interconversion between a high-spin Co(II) disulfide compound and a low-spin Co(III) thiolate compound triggered by the nature of the anion.