Synthesis and solid state chemistry of CH₃BiI₂: A structure with an extended one-dimensional organometallic framework

Abstract

Red needle-like crystals of the title compound were grown using a reaction between Bi metal and methyl iodide under solvothermal conditions. CH3BiI2 crystallizes in the monoclinic space group C2/m with an unusual one-dimensional organic-inorganic chain-like structure. The Bi atoms have a square pyramidal local geometry, with four I atoms forming the base and one methyl group occupying an apical site. Each basal square shares trans edges with two nearest neighbors to form a one-dimensional inorganic BiI2 chain along the b-axis. All methyl groups are covalently bonded to bismuth atoms and are aligned on one side of the BiI2 basal plane. The organic-inorganic chains are held together via van der Waals interaction, forming an extended solid state structural array. Extended Huckel band structure calculations demonstrate electronic one-dimensionality for CH3BiI2. Molecular modeling suggests that the square pyramidal Bi coordination arises primarily to reduce Bi-C antibonding character in the HOMO. The resulting Bi 6s and 6p hybridization in the valence band (HOMO) leads to a stereochemically active lone pair oriented trans to each methyl group. Thermal stability and decomposition of the title compound is examined using GC mass spectroscopy and simultaneous TGA and DTA techniques. CH3BiI2 begins to decompose at 185 °C in an inert atmosphere into methyl iodide and bismuth monoiodide, providing a new pathway to the formation of the interesting low valency one-dimensional conductor, BiI.