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Crystal Structures and Vibrational Spectroscopy of [NBu4][Cu(CN)X] (X = Br, I) and [NBu4][Cu3(CN)4]·CH3CN

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posted on 14.09.2000, 00:00 by Graham A. Bowmaker, Hans Hartl, Victoria Urban
The new compounds [NBu4][Cu(CN)X] (X = Br (1), I (2)) and [NBu4][Cu3(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) Å, b = 12.1741(8) Å, c = 19.2434(12) Å, orthorhombic, Pna21, Z = 4) and 2 (C34H72Cu2I2N4, a = 21.683(2) Å, b = 12.233(2) Å, c = 17.632(3) Å, β = 111.710(10)°, monoclinic, P21/c, Z = 4) contain infinite one-dimensional (zigzag) −CuI−CN−CuI−CN− chains which run parallel to the crystallographic a (X = Br) or c (X = I) axis. Each CuI 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 ν(CN), ν(CuC/N), δ(CuCN), and δ(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 ν(CN) and δ(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 (C22H39Cu3N6, a = 16.8572(4) Å, b = 14.1180(3) Å, c = 13.39100(10) Å, β = 113.30(3)°, monoclinic, C2, Z = 4) consists of two-dimensional polymeric sheets of composition [Cu3(CN)4-] in the ac plane, which are made up of infinite one-dimensional (zigzag) −CuI−CN−CuI−CN− chains parallel to the a axis, with each CuI 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.