Synthesis of the Pivalamidate-Bridged Pentanuclear Platinum(II,III) Linear Complexes with Pt···Pt Interactions

Pentanuclear linear chain Pt(II,III) complexes {[Pt₂(NH₃)₂X₂((CH₃)₃CCONH)₂(CH₂COCH₃)]₂[PtX‘₄]}·nCH₃COCH₃ (X = X‘ = Cl, n = 2 (1a), X = Cl, X‘ = Br, n = 1 (1b), X = Br, X‘ = Cl, n = 2 (1c), X = X‘ = Br, n = 1 (1d)) composed of a monomeric Pt(II) complex sandwiched by two amidate-bridged Pt dimers were synthesized from the reaction of the acetonyl dinuclear Pt(III) complexes having equatorial halide ligands [Pt₂(NH₃)₂X₂((CH₃)₃CCONH)₂(CH₂COCH₃)]X‘ ‘ (X = Cl (2a), Br (2b), X‘ ‘ = NO₃^-, CH₃C₆H₄SO₃^-, BF₄^-, PF₆^-, ClO₄^-), with K₂[PtX‘₄] (X‘ = Cl, Br). The X-ray structures of 1a−1d show that the complexes have metal−metal bonded linear Pt₅ structures, and the oxidation state of the metals is approximately Pt(III)−Pt(III)···Pt(II)···Pt(III)−Pt(III). The Pt···Pt interactions between the dimer units and the monomer are due to the induced Pt(II)−Pt(IV) polarization of the Pt(III) dimeric unit caused by the electron withdrawal of the equatorial halide ligands. The density functional theory calculation clearly shows that the Pt···Pt interactions between the dimers and the monomer are made by the electron transfer from the monomer to the dimers. The pentanuclear complexes have flexible Pt backbones with the Pt chain adopting either arch or sigmoid structures depending on the crystal packing.