Lantern type heterobimetallic complexes. Tetra-µ-4-methylpyridine-2-thiolato bridged platinum(II)cobalt(II) and oxidation complexes†

Abstract

A lantern type bimetallic complex [(CH₃CN)Co(4-mpyt)₄Pt] 1 (4-Hmpyt = 4-methylpyridine-2-thiol) was obtained by the reaction of [Pt(4-Hmpyt)₄]Cl₂ with CoCl₂ in the presence of base and recrystallization from acetonitrile. The complex was characterized by single-crystal X-ray crystallography and is paramagnetic. It has a tetragonal Co(4-mpyt)₄Pt core in which 4-mpyt ligands bridge Pt and Co atoms. The Pt atom has a square-planar co-ordination by four S atoms, whereas the Co atom has a square-pyramidal co-ordination by five N atoms, the N atom of acetonitrile being located at the axial position of Co. The Co· · ·Pt distance is 2.573(2) Å. Oxidation of 1 yielded diamagnetic [Co^II(4-mpyt)₄Pt^IIIX] type complexes (X = Cl 2a, Br 2b, N₃ 2c or NCS 2d): 2a and 2b were obtained by the reaction of 1 with iodobenzene dichloride or Ce^IV in the presence of Br^– respectively, while the reaction with pseudo-halides in air gave 2c and 2d. They have been characterized by variable-temperature ¹H NMR and X-ray photoelectron spectroscopies. Complexes 2a–2d exist as the oligomer [{Co(4-mpyt)₄PtX}_n] where up to four tetragonal [Co(4-mpyt)₄PtX] units are linked by Pt–X–Co bridges. Cyclic voltammetry (CV) of 1 in acetonitrile displayed a one-electron oxidation peak at –0.05 V and two rereduction peaks at –0.17 and –0.40 V vs. an Ag–Ag⁺ electrode at 25 °C. The CVs of 1 and 2a show similar temperature dependences which can be interpreted on the basis of the dissociation–association equilibrium of the Co^IIPt^III species in the co-ordinating solvent.