Hydrothermal Syntheses, Structures, and Properties of [Cu₃Cl₂CN(pyrazine)] and Copper(I) Halide Pyrazine Polymers

Crystals of copper halide and pseudohalide compounds with pyrazine are synthesized under hydrothermal conditions. The title compound, [Cu3Cl2CNPz] (1) (Pz = pyrazine), is a new copper compound exhibiting an unusual -(Cu3Cl2)- polymeric stair structural motif and three-coordinate cyanide. Compound 1 crystallizes in the monoclinic space group P2(1)/m, with a = 3.6530(7) A, b = 17.160(3) A, c = 6.9800(14) A, beta = 90.58(3) degrees, and Z = 2. In addition, the series of complexes [Cu2X2Pz] for X = Cl (2), Br (3), and I (4) are also crystallized under hydrothermal conditions. The inorganic polymer [Cu2Br2Pz] (3) belongs to the triclinic space group P1, with a = 6.9671(14) A, b = 7.849(2) A, c = 8.099(2) A, alpha = 71.69(3) degrees, beta = 70.71(3) degrees, gamma = 85.43(3) degrees, and Z = 2. The structure of 3, is similar to the recently reported structure for [Cu2Cl2Pz] (2) (Kawata, S.; Kitagawa, S.; Kumagai, H.; Iwabuchi, S.; Katada, M. Inorg. Chim. Acta 1998, 267, 143). The third member of the series, [Cu2I2Pz], is found to be isostructural on the basis of X-ray powder diffraction results. The lattice parameters are refined from indexed reflections to a = 7.115(10) A, b = 8.321(19) A, c = 8.378(17) A, alpha = 71.1(3) degrees, beta = 67.3(1) degrees, and gamma = 83.0(2) degrees. Electronic spectra show that compounds 1-4 have optical band gaps in the range 2.2-2.4 eV. The infrared and Raman spectra as well as the thermal properties of all compounds are presented.