Synthesis and structure of ionic Ccopper(I) pi-complexes with propargylammonium chloride and bromide [HC equivalent to CCH2NH3]CuX2

The crystals of [HC drop CCH2NH3]CuX2 (X = Cl (I), Br (II)) were prepared b y alternating-current electrosynthesis and characterized by X-ray crystallo graphy and IR spectroscopy. Complex I crystallizes in space group Pcab, a = 19.010(6) Angstrom, b = 7.404(5) Angstrom, c = 8.690(3) Angstrom, V = 1223 . 1 (10) Angstrom (3), Z = 8. The structure of II is described by space gro up P2(1)/b, a = 10.047(l) Angstrom, b = 7.673(l) Angstrom, c = 8.971(l) Ang strom, gamma = 103.04(2)degrees, V = 673.75(13) Angstrom (3), Z = 4. The st ructure of I consists of discrete units of the above-indicated composition, the copper atom forming a planar trigonal environment. In II, similar stru ctural units are combined through the elongated Cu-Br distance (2.910(l) An gstrom) to give chains along the [010] direction. The complexes differ in t he efficiency of pi -bonding; the Cu-(midpoint of the C dropC bond) distanc e and the C-C bond length are 1.923(9), 1.23(l) Angstrom and 1.960(6), 1.19 2(8) Angstrom for I and II, respectively. The v(C dropC) frequencies in I a nd II are 157 and 137 cm(-1) lower than the corresponding values for the fr ee ligand. The decrease in the v(C-sp-H) values by 92 and 84 cm(-1) attests to the activation of the dropC-H bond.