Di-μ-bromo-bis[(pyridine)(triphenylphosphine)copper(I)

Abstract

Cu2Br2(CsHsN)2{P(C6H5) 3}), M r = 970.0, monoclinic, C2/c, a -- 26.188 (7), b = 14.222 (3), c =11.259(4)A, fl=94.51(2) ° , V=4180(2)A 3, z =4, Dx= 1.54Mgm -3, 2(MoKct)=0.71073./k, /z= 2.90 mm -1, F(000) = 1944, T = 296 K, R = 0.047 for 1271 observed reflections. The compound is in a dimeric form; the metal atom is tetrahedrally coordi- nated to pyridine (Cu-N 2.053 (9)A), two Br atoms (Cu-Br 2.538 (2), 2.507 (2)A; Br-Cu-Br 108.50 (8) ° ) and triphenylphosphine (Cu-P 2.209 (3)A) and is slightly distorted, with a dihedral angle between the (BrCuBrl and (PCuN) planes of 90.9 (2) °. The Cu-..Cu' distance is 2.948 (2) A. Introduction. Monodentate tertiary phosphines form many complexes with Cu ~ that show a variety of stoichiometries and structures (Gill, Mayerle, Welcker, Lewis, Ucko, Barton, Stowens & Lippard, 1976). Considerable interest exists in structural studies of copper(I) derivatives, not only because of their stereochemistry but also for their importance in oxidation-reduction reactions in enzymes containing copper (Peisach, Aisen & Blumberg, 1966) and in organic synthesis (Tsuda, Fujii, Kawasaki & Saegusa, 1980). Some years ago, Jardine, Rule & Vohra (1970) reported the preparation of halogenocopper(I) com- plexes using tertiary phosphines as ligands. We synthe- sized one of them, the title compound, and pro- ceeded with its crystal structure determination because the only characterizations in the Jardine et al. (1970) paper were analytical data and molecular weight and to elucidate their hypothesis that the compound, though monomeric in solution, may be dimeric in the solid state. Experimental. Irregular colourless crystals from butanol at 277 K, max. and min. linear dimensions 0.30, 0-15 mm; Nonius CAD-4 diffractometer, graphite-monochromated Mo Ka; cell parameters by least squares on setting angles for 22 reflections, 9 < 0< 30°; w--20 scans, scan width (0.80 + 0.35 tan0) °, scan speed 6.7 ° min-~; max. range of hkl: -27 <h < 27, k< 15, l< 11, 0max=22°; standards 060, 10,~,,2 varied +2.4% of mean intensities over data collection; 2086 reflections measured, 2553 unique, Rin t = 0.014, 1271 observed above 3tr(/), Lp correc- tions; structure solved by direct methods. In final cycles of full-matrix least-squares refinement all non-hydrogen atoms anisotropic. Py H atoms included at constrained positions (C-H = 1.00 (1) A) based on those found in difference synthesis, all with fixed isotropic U= 0.06 A2; phenyl rings of triphenylphosphine as rigid bodies (C-C = 1.395, C-H = 1.08 A, all angles 120 °, H atoms with common U=0.06A2). Function minimized ~w(IFol--IFcl) 2 with w=(e2(Fo) + 0.00075Fo2)-1; max. A/e=O.O05; 135 parameters refined; excluding unobserved reflections R-----0-047, wR = 0.050; inspection of F c and Fo values indicated correction for secondary extinction required;* max. A/tr = 0.002, Ap excursions within --0.44 and 0.56 e A-3; scattering factors for non-H atom~ from Cromer & Mann (1968) with corrections for anomalous dispersion from Cromer & Liberman (1970), for H from Stewart, Davidson & Simpson (1965); programs used: MULTAN80 (Main, Fiske, Hull, Lessinger, Germain, Declercq & Woolfson, 1980); SHELX76 (Sheldrick, 1976) and ORTEP (Johnson, 1965). Most of the calculations were per- formed on a VAX 11/780 computer of the Instituto de Fisica e Quimica de S~o Carlos. Discussion. A projection of the crystallographically independent moiety is shown in Fig. 1. Positional