The molecular and electronic structures of monomeric cobalt complexes containing redox noninnocent o-aminobenzenethiolate ligands

Dark blue [PPh4][Co-III(L-2)] (2), where (L-2)(2) represents the closed-shell dianion of 4,6-di-tert-butyl-2-[(pentafluorophenyl)amino]benzenethiol, has been synthesized from the reaction of H-2(L-2) and CoCl2 (2:1) in acetonitrile with excess NEt3, brief exposure of the solution to air, and addition of [PPh4]Br. The oxidation of 2 with one equivalent of iodine produces the neutral species [Co-III(L-2 center dot)(2)I](0) (3), where (L-2 center dot)(1) represents the one-electron oxidized p radical anion of (L-2)(2). Crystalline [Co-III(L-4 center dot)] (4), where (L-4 center dot)(3) is the p radical monoanion of bis-2,2'-(1,2-diphenylethylenediimine)-benzenethiolate, was precipitated from a toluene reflux of [Co-II(L-3)(2)], where (L-3)(2) is the closed-shell monoanion of 2-(phenylmethylamino)benzenethiol. The reduction of 4 with CoCp2 under anaerobic conditions yielded dark violet crystals of [CoCp2][Co-III(L-4)] (5). The reaction of Zn(CH3CO2)(2) with 2-phenylbenzothiazoline in methanol resulted in the formation of [Zn-II(L-3)(2)](0) (6). The two monoanions 2, and 5, along with [N(n-Bu)(4)][Co(abt)(2)] (1) (abt(2) = o-aminobenzenethiolate), and neutral 4 have all been shown by X-ray crystallography to be square planar. A tetrahedral geometry was adopted by 6. From temperature dependent (3-300 K) magnetic susceptibility measurements, it was established the monoanions have a triplet ground state characterized by a large zero field splitting. EPR measurements of 4, and electrochemically oxidized 1 and 2 reveal distinctly different spin Hamiltonian parameters that are interpreted with the aid of density function theoretical (DFT) calculations. It is shown that oxidation states describing a d(6) Co(III) or d(7) Co(II) cannot be unambiguously assigned for these neutral and monoanionic species. (C) 2010 Elsevier B.V. All rights reserved.