[Cu₄I₇ ³⁻]_n: A novel 1-D iodocuprate aggregate

A new cationic ligand, 1-methyl-3-(methylthio)pyrazin-1-ium iodide (MMTPI), has been designed and synthesized by regioselective alkylation of 2-methylthiopyrazine with MeI. Reaction of this ligand with CuI in a 3:4 molar ratio under mild conditions (MeCN, r.t.) produces new iodocuprate, [Cu₄I₇(MMTP)₃]_n, containing one-dimensional inorganic chains [Cu₄I₇ ³⁻]_n. The latter are constructed from the basket-shaped {[Cu₃(μ₃-I)](I)₃(μ₂-I)₃} building blocks, which are linked by tetrahedral Cu atoms through bridging iodine atoms. The UV–Vis diffuse reflectance measurements reveal that the title iodocuprate possesses semiconductor behaviour with the band gap of 1.80 eV. The thermal stability and electronic structure of the iodocuprate are also discussed.