Synthesis and characterization of copper(I) halide/pseudohalide adducts of 2-benzoylpyridine and x-ray crystal structure of [di-μ-iodo-bis(N,O-2-benzoylpyridine)dicopper(I)]

Dark-brown copper(I) complexes of the type CuXL, for X = Cl, Br, I, SCN and N₃, and orange-yellow complexes of the type (CuX)₂L, for X = Cl or Br, where L = 2-benzoylpyridine, have been prepared and characterized. All complexes exhibit strong CT bands in the visible region and gave non-conducting solutions in acetone and nitrobenzene. The IR spectral data suggest that 2-benzoylpyridine acts as a monodentate ligand in the orange-yellow complexes and as a bidentate chelating ligand in the brown complexes, whereas bridging halides and pseudohalides exist in both types. The structure of the 1 : 1 black iodide complex, as determined by X-ray crystallography, features a discrete, centrosymmetric [CuI(2-benzoylpyridine)]₂ molecule with a short Cu⋯Cu distance of 2.587(1) Å. Each copper atom in the dimeric molecule is tetrahedrally coordinated by two μ-iodine atoms and the carbonyl oxygen and nitrogen atoms of the chelating 2-benzoylpyridine ligand. The orange-yellow complexes display visible emission when excited in the UV region, whereas the brown complexes do not.