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

A lantern type bimetallic complex [(CH3CN)Co(4-mpyt)(4)Pt] 1 (4-Hmpyt = 4-methylpyridine-2-thiol) was obtained by the reaction of [Pt(4-Hmpyt)(4)]Cl-2 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)(4)Pt 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) Angstrom. Oxidation of 1 yielded diamagnetic [Co-II(4-mpyt)(4)(PtX)-X-III] type complexes (X = Cl 2a, Br 2b, N-3 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 H-1 NMR and X-ray photoelectron spectroscopies. Complexes 2a-2d exist as the oligomer [{Co(4-mpyt)(4)PtX}(n)] where up to four tetragonal [Co(4-mpyt)(4)PtX] 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 degrees 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 (CoPtIII)-Pt-II species in the co-ordinating solvent.