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 No 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 No 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 No 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 No 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 No 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 No 1622, is isomorphous with previously recorded [BrAg(PPh3)]4, for which a redetermination is described (R 0·039 for No 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 No 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 No 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 Td symmetry in this complex relative to the iodide.