Crystal structures and spectroscopic studies of the mononuclear complex [AgBr(PPh3)2] and binuclear [Ag2X2(PPh3)4]·2CHCl3(X = Cl or Br)

Abstract

The structure of the silver(I) complexes [AgBr(PPh3)2] and [Ag2X2(PPh3)4]·2CHCl3(X = Cl or Br) have been determined by single-crystal X-ray diffraction. The complex [AgBr(PPh3)2] crystallizes in the monoclinic space group C2/c and contains discrete monomeric [AgBr(PPh3)2] units with essentially trigonal-planar AgBrP2 co-ordination, and a crystallographic two-fold axis of symmetry coincident with the Ag–Br bond. The geometric parameters for the silver atom environment are: Ag–Br 2.568(1), Ag–P 2.458(2)A, P–M–P 124.14(5), P–M–Br 117.93(3)°. The complexes [Ag2X2(PPh3)4]·2CHCl3(X = Cl or Br) are isomorphous, monoclinic, space group C2/c, and contain [Ag2X2(PPh3)4] dimers. Each of the two silver atoms in the structure is four-co-ordinated by forming bonds with the P atoms of the two phosphine ligands and the two doubly bridging halide atoms. The Ag and X atoms lie in a plane, and each of the molecules in the unit cell has a C2 axis which passes through the two X atoms. A chloroform molecule is hydrogen bonded to each X atom. The far-IR spectra of these complexes show bands which are assigned to ν(AgX) modes, and the spectra of these and the unsolvated dimer [Ag2Cl2(PPh3)4] are analysed to yield information about the Ag–X bonding. The Raman spectrum of [AgBr(PPh3)2] shows a band which is assigned to a ν(AgP) mode, an assignement which is confirmed by the observation of similar bands in the Raman spectra of the isostructural gold(I) complexes [AuX(PPh3)2](X = Cl, Br or I). The solid-state cross-polarization magic-angle spinning (CP MAS)31P NMR spectra of the silver complexes show multiplets die to 1J(AgP) coupling. The spectra of the dimers show separate chemical shifts for the crystallographically inequivalent phosphorus atoms, and 2J(PP) coupling between these atoms. The splitting patterns are interpreted in terms of the silver co-ordination environment.