STRUCTURAL AND SPECTROSCOPIC STUDIES OF HALOGENOCUPRATE(I) COMPLEXES

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) P-31 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-degrees of the ideal trigonal angle of 120-degrees. 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 nu(CuX) stretching mode of the bent X-Cu-X units, and weak bands at 194, 150 and 128 cm-1 due to the symmetric nu(CuX) mode. In addition, the X = Cl complex shows a strong band at 126 cm-1 which is assigned as the delta(CuCl2) bending mode. The dimer [Cu2(PPh3)2I4]2- shows a remarkably simple spectrum in the nu(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 P-31 NMR spectra generally consist of asymmetric quartets due to coupling of the P-31 nucleus to the quadrupolar copper nucleus, and the splitting patterns are interpreted in terms of the copper co-ordination environment.