Structural and spectroscopic studies of halogenocuprate(I) complexes

Abstract

Reaction of tetraalkylammonium halides, PPh3 and copper(I) halides in a 1 : 1 : 1 mole ratio in dichloromethane yields complexes [NR4][Cu(PPh3)X2](R = Et, X = Cl or Br; R = Pr, X = Br, I; R = Bu, X = Br) and [NEt4]2[Cu2(PPh3)2I4]. These have been characterized by infrared and cross polarization magic angle spinning (CP MAS)31P NMR spectroscopy, and the structures of most have been determined by single-crystal X-ray diffraction. The compounds [NR4][Cu(PPh3)X2] in the first group above contain mononuclear anions [Cu(PPh3)X2]– with essentially trigonal planar PCuX2 co-ordination. The P–Cu–X and X–Cu–X angles are all within 5 ° of the ideal trigonal angle of 120 °. The compound [NEt4]2[Cu2(PPh3)2I4] contains the centrosymmetric binuclear anion [Cu2(PPh3)2I4]2–{a dimer of [Cu(PPh3)I2]–} in which the two copper atoms are bridged by two iodine atoms, and each copper atom is also bound to a terminal iodine atom and PPh3 molecule. The FIR spectra of the mononuclear complexes [Cu(PPh3)X2]– show strong bands at 264, 195 and 175 cm–1 for X = Cl, Br and I respectively, which are assigned to the asymmetric v(CuX) stretching mode of the bent X–Cu–X units, and weak bands at 194, 150 and 128 cm–1 due to the symmetric v(CuX) mode. In addition, the X = Cl complex shows a strong band at 126 cm–1 which is assigned as the δ(CuCl2) bending mode. The dimer [Cu2(PPh3)2I4]2– shows a remarkably simple spectrum in the v(CuI) region: a partially resolved doublet at 113 and 126 cm–1. The above vibrational frequencies are compared with those of the species [CuX2]– and [Cu2I4]2–, from which the present species can be considered to be derived by addition of one PPh3 molecule per copper atom. The solid state CP MAS 31P NMR spectra generally consist of asymmetric quartets due to coupling of the 31P nucleus to the quadrupolar copper nucleus, and the splitting patterns are interpreted in terms of the copper co-ordination environment.