Synthesis and Characterization of Bis(2,2‘-bipyridyl)platinum(I): A Novel Microtubular Linear-Chain Complex

Abstract

One-electron reduction of [Pt(bpy)2]2+ (bpy = 2,2‘-bipyridyl) in aqueous solution results in the formation of black-green lustrous needles on solid electrodes. The crystalline needles grow perpendicularly from the substrate surface and reach lengths of 1−2 cm. Elemental analysis, X-ray photoelectron spectroscopy, and electrochemical measurements indicate that the new compound is a genuine PtI complex with a d9 electronic configuration and with the composition [Pt(bpy)2]NO3·2H2O. X-ray crystallographic analysis shows that the crystalline needles consist of linear chains of discrete [PtI(bpy)2] units with a Pt−Pt distance of 3.563(1) Å and with each bipyridyl ligand overlapping face-to-face (eclipsed) with its nearest neighbor. At the monomeric level, the structure of [PtI(bpy)2] units exhibits a distorted square-planar configuration with structural parameters very similar to those of the parent PtII complex, [Pt(bpy)2](NO3)2·H2O. The new linear-chain compound was prepared by chemical and electrochemical methods. The resulting crystals are relatively stable in air but oxidize slowly over a period of weeks. Scanning electron microscopy reveals that the crystals are tubular with a hollow near-hexagonal morphology. Cooperative effects influence the optical and electrical properties of the crystals. Because of extensive solid-state interactions between stacked monomeric [PtI(bpy)2] units, the crystals absorb strongly over the whole visible region and far into the near infrared. Their room temperature electrical conductivity is relatively high, 10 Ω-1 cm-1.