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

Dark blue PPh₄]Co^III(²L)] (2), where (²L)²⁻ represents the closed-shell dianion of 4,6-di-tert-butyl-2-(pentafluorophenyl)amino]benzenethiol, has been synthesized from the reaction of H₂(²L) 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(²L)₂I]⁰ (3), where (²L)¹⁻ represents the one-electron oxidized π radical anion of (²L)²⁻. Crystalline Co^III(⁴L)] (4), where (⁴L)³⁻ is the π radical monoanion of bis-2,2′-(1,2-diphenylethylenediimine)-benzenethiolate, was precipitated from a toluene reflux of Co^II(³L)₂], where (³L)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(⁴L)] (5). The reaction of Zn(CH₃CO₂)₂ with 2-phenylbenzothiazoline in methanol resulted in the formation of Zn^II(³L)₂]⁰ (6). The two monoanions 2, and 5, along with N(n-Bu)₄]Co(abt)₂] (1) (abt²⁻ = 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 d⁶ Co(III) or d⁷ Co(II) cannot be unambiguously assigned for these neutral and monoanionic species.