Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXIII Synthesis, Spectroscopy and Structural Systematics of New 1 : 1 'Cubane' Tetramers of Copper(I) and Silver(I) Halides with Triphenylarsine

Abstract

Syntheses and room-temperature single-crystal X-ray structural characterization of a number of 1 : 1 ‘cube tetramer’ adducts of copper(I) and silver(I) halides, MX, with triphenylarsine, AsPh₃, are recorded, being [XM(AsPh₃)]₄. The CuBr adduct, obtained unsolvated from toluene, orthorhombic Pbcn, a 17·844(5), b 20·778(8), c 18·430(4) Å, Z = 4 tetramers, conventional R on |F| 0·058 for N_o 1309 independent ‘observed’ reflctions (I > 3σ(I)), is isomorphous with previously recorded [ClAg(PPh₃)]₄, the tetramer having crystallographically imposed 2 symmetry. The CuI adduct, previously recorded as a monobenzene solvate, has been isolated unsolvated from toluene, monoclinic, P 2₁/n, a 19·70(5), b 27·110(7), c 13·59(2) Å, β 98·84(9)°, Z = 4 tetramers, R 0·087 for N_o 4359, isomorphous with previously recorded [ICu(PPh₃)]₄, as a 6½ benzene solvate, triclinic, P^-1 a 26·688(2), b 15·180(7), c 13·090(1) Å, α 85·41(2), β 87·580(7), γ 77·63(2)°, Z = 2 tetramers, R 0·049 for N_o 11485, and as a chloroform disolvate, triclinic, P^-1 a 22·584(9), b 13·979(2), c 13·892(2) Å, α 68 ·99(2), β 77·31(3), γ 75·65(3)°, Z = 2, R 0·041 for N_o 8701. An unsolvated AgI complex, monoclinic, P 2₁/c, a 25·26(1), b 12·506(5), c 25·228(9) Å, β 113·54(4)°, Z = 4 tetramers, R 0·054 for N_o 5520, isomorphous with previously recorded [IAg(PPh₃)]₄ (denoted ‘α’), was obtained from methanol/saturated potassium iodide solution, while a second ‘β’-form obtained from 2,4,6-trimethylpyridine, rhombohedral R3c, a 17·048(7) Å, α 61·15(5)°, Z = 2 tetramers, R 0·037 for N_o 1622, is isomorphous with previously recorded [BrAg(PPh₃)]₄, for which a redetermination is described (R 0·039 for N_o 1289); the latter has also been obtained in the common orthorhombic Pbcnarray: a 18·10(1), b 2·08(1), c 18·39(1) Å, Z = 4, R 0·041 for N_o 2877. A new ‘step’ form of [IAg(PPh₃)]₄, monoclinic, C 2/c, a 26·14(2), b 16·340(9), c 18·64(2) Å, β 114·04(8)°, R 0·058 for N_o 2107, obtained from acetonitrile and isomorphous with [BrCu(PPh₃)]₄ (step), is also recorded. In the far-infrared spectra of [(Ph₃As)₄Cu4X₄] bands which have been assigned to vibrations of the Cu₄X₄ core are: 166, 150, 135, 114 (X = Br); 136, 85 cm^-1 (X = I; 2CHCl₃ solvate). The 166, 150, 135 cm^-1 bands in the bromide are only partially resolved. These, and the 136 cm^-1 band in the iodide are assigned to the T₂ v(CuX) mode of the Cu₄X₄ core; the bands at 114 and 85 cm^-1 are assigned to the next highest frequency T₂ mode of the cluster. The splitting of the highest frequency T₂ band for the bromide is consistent with the greater degree of distortion of the Cu₄X₄core from ideal T_d symmetry in this complex relative to the iodide.