Lantern-type dinuclear CrIIIPtII and VIVPtII complexes bridged by pyridine-2-thiolate. Synthesis and characterization

Abstract

Reaction of complex [Pt(4-Hmpyt)₄]Cl₂ with Na[CrO(hmp)₂] in toluene gave the lantern-type binuclear [ClCr(4-mpyt)₄Pt] 1 (4-Hmpyt = 4-methylpyridine-2-thiol; H₂hmp = 2-hydroxy-2-methylpropionic acid). The Cl⁻ ligand of 1 was readily replaced by OH⁻ to give [(HO)Cr(4-mpyt)₄Pt] 2. [OV(L)₄Pt] type complexes (L = 4-mpyt 3a; L = pyt 3b) were obtained from the reaction of [Pt(LH)₄]Cl₂ with [VO(acac)₂] (Hpyt = pyridine-2-thiol; acac = acetylacetonato) in toluene at 160 °C in the presence of KHCO₃. Compounds 1, 2·2CH₃CN and 3a were characterized by single-crystal X-ray crystallography. These complexes have a common XM(4-mpyt)₄Pt core (M = Cr, X = Cl (1), OH (2); M = V, X = O (3a)) in which the 4-mpyt ligands bridge the Pt and M atoms to give a square-planar PtS₄ and a square-pyramidal MN₄X co-ordination sphere. The core has a crystallographically imposed 4-fold axis (2·2CH₃CN, 3a) or an approximate one (1). In the crystal structure of 1 a pair of [ClCr(4-mpyt)₄Pt] units are combined to form a dimer through two Pt⋯S interactions (2.89(1) and 3.30(1) Å) between the PtS₄ planes of the respective monomers. The M⋯Pt distances range from 2.497(2) to 2.604(7) Å. The cyclic voltammogram (CV) of 1 in CH₃CN shows a reversible wave for [ClCr(4-mpyt)₄Pt]^0/−1 with E_1/2 = −1.12 V vs. Ag/Ag⁺, whereas 2 gives an irreversible reduction peak at −1.90 V and reoxidation peaks at −1.12 V. Addition of hydrochloric acid, however, results in a dramatic change of the CV pattern to exhibit a reversible wave at E_1/2 = −1.12 V, the shape and potential are similar to those of 1 indicating the generation of [ClCr(4-mpyt)₄Pt] by replacement of OH ligand by HCl.