Redox Interconversion between Cobalt(III) Thiolate and Cobalt(II) Disulfide Compounds.
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ABSTRACT: 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 L1SSL1 (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide) result in the formation of either the high-spin cobalt(II) disulfide compound [CoII2(L1SSL1)Cl4] or a low-spin, octahedral cobalt(III) thiolate compound, such as [CoIII(L1S)(MeCN)2](BF4)2. Addition of thiocyanate anions to a solution containing the latter compound yielded crystals of [CoIII(L1S)(NCS)2]. The addition of chloride ions to a solution of [CoIII(L1S)(MeCN)2](BF4)2 in acetonitrile results in conversion of the cobalt(III) thiolate compound to the cobalt(II) disulfide compound [CoII2(L1SSL1)Cl4], as monitored with UV-vis spectroscopy; subsequent addition of AgBF4 regenerates the Co(III) compound. Computational studies show that exchange by a chloride anion of the coordinated acetonitrile molecule or thiocyanate anion in compounds [CoIII(L1S)(MeCN)2]2+ and [CoIII(L1S)(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 [FeII2(L1SSL1)Cl4] is different from that of cobalt(II) compound [CoII2(L1SSL1)Cl4]. In contrast to cobalt, reaction of ligand L1SSL1 with [Fe(MeCN)6](BF4)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.
SUBMITTER: Jiang F
PROVIDER: S-EPMC6150680 | biostudies-literature | 2018 Aug
REPOSITORIES: biostudies-literature
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