Crystal structures and vibrational spectroscopy of [NBu4][Cu(CN)X] (X = Br, I) and [NBu4[Cu3(CN)4]•CH3CN

The new compounds [NBu4][Cu(CN)X] (X = Br (1), I (2)) and [NBu4][Cu-3(CN)(4)]. CH3CN (3) have been prepared by reaction of [NBu4]X with CuCN in acetone (1, 2) or acetonitrile (3), and have been characterized by X-ray crystallography and vibrational spectroscopy. Compounds 1 (C34H72Br2Cu2N4, a = 17.4956(11) Angstrom, b = 12.1741(8) Angstrom, c = 19.2434(12) Angstrom, orthorhombic, Pna2(l), Z = 4) and 2 (C34H72Cu2I2N4, a = 21.683(2) Angstrom, b = 12.233(2) Angstrom, c = 17.632(3) Angstrom, beta = 111.710(10)degrees, monoclinic, P2(l)/c, Z = 4) contain infinite one-dimensional (zigzag) -Cu-I-CN-Cu-I-CN- chains which run parallel to the crystallographic a (X = Br) or c (X = I) axis. Each Cu-I center within these chains is additionally bound to an X = Br or I atom, and the whole network is planar, with successive planar units stacked in the b direction. Bands in the IR and Raman spectra are assigned to nu(CN), nu(CuC/N), delta(CuCN), and delta(NCuC) modes of the CuCN chains. The IR spectra of the products of the reversible reaction of CuCN with aqueous KX (X = Br, I) show v(CN) and delta(NCuC) as well as bands due to coordinated water, suggesting that these CuCN/KX/H2O compounds are mixed halogeno(cyano)cuprates with hydrated K+ counterions whose structures are similar to those observed in [NBu4][Cu(CN)X]. The structure of 3 (C12H39Cu3N6, a = 16.8572(4) Angstrom, b = 14.1180(3) Angstrom, c = 13.39100(10) Angstrom, beta = 113.30(3)degrees, monoclinic, C2, Z = 4) consists of two-dimensional polymeric sheets of composition [Cu-3(CN)(4)(-)](infinity) in the ac plane, which are made up of infinite one-dimensional (zigzag) -Cu-I-CN-Cu-I-CN- chains parallel to the a axis, with each CUT center within these chains being additionally bound to a linear [CN-Cu-CN-] group which links adjacent chains, so that the structure contains both two-coordinate and three-coordinate copper atoms. Successive planar sheets are stacked in the b direction, with the [NBu4](+) cations and noncoordinating acetonitrile molecules lying within rings of composition (CuCN)(8).