Synthesis, characterization, and DFT studies of thione and selone Cu(I) complexes with variable coordination geometries

Coordination of Cu(I) halides with N,N'-dimethylimidazole selone (dmise) and thione (dmit) ligands was examined by treating CuX (X = Cl, Br, I) with one or two equivalents of dmise or dmit. The reaction of CuI and CuBr with one molar equivalent of dmise results in unusual selenium-bridged tetrameric Cu(4)(μ-dmise)(4)(μ-X)(2)X(2) copper complexes with average Cu-Se bond lengths of 2.42 ? and a Cu(2)(μ-X)(2) core (X = I (1) or Br (6)) that's in a rhomboidal structure. The reaction of CuX (X = Cl, Br, and I) with two equivalents of dmit or dmise results in trigonal planar Cu(I) complexes of two different conformations with the formula Cu(dmit)(2)X (3a, 3b, 4, and 7) or Cu(dmise)(2)X (2, 5, and 8) with average Cu-S and Cu-Se bond lengths of 2.23 ? and 2.34 ?, respectively. The coordination geometry around the copper center in complexes 1 to 8 is determined by the type of halide and chalcogenone ligand used, intramolecular π-π interactions, and short contact interactions between X-H (X = I, Br, Cl, Se or S). The theoretical DFT calculations are in good agreement with experimental X-ray structural data and indicate that dmise ligands are required for formation of the tetrameric complexes 1 and 6. Electrochemical studies show that the trigonal copper selone complexes have more negative potentials relative to analogous copper thione complexes by an average of 108 mV.