Lewis-base adducts of Group 11 metal(I) compounds .73. Synthesis, spectroscopy and structural systematics of new 1:1 'cubane' tetramers of copper(I) and silver(I) halides with triphenylarsine

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) Angstrom, Z = 4 tetramers, conventional R on \F\ 0.058 for N-0 1309 independent 'observed' reflections (I > 3 sigma(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 2(1)/n, a 19.70(5), b 27.110(7), c 13.59(2) Angstrom, beta 98.84(9)degrees, Z = 4 tetramers, R 0.087 for N-0 4359, isomorphous with previously recorded [ICu(PPh3)](4), as a 61/2 benzene solvate, triclinic, <P(1)over bar> a 26.688(2), b 15.180(7), c 13.090(1) Angstrom, alpha 85.41(2), beta 87.580(7), gamma 77.63(2)degrees, Z = 2 tetramers, R 0.049 for N-0 11485, and as a chloroform disolvate, triclinic, <P(1)over bar> a 22.584(9), b 13.979(2), c 13.892(2) Angstrom, a 68.99(2)) beta 77.31(3), gamma 75.65(3)degrees, Z = 2, R 0.041 for N-0 8701. An unsolvated AgI complex, monoclinic, P 2(1)/c, a 25.26(1), b 12.506(5), c 25.228(9) Angstrom, beta 113.54(4)degrees, Z = 4 tetramers, R 0.054 for N-0 5520, isomorphous with previously recorded [IAg(PPh3)](4) (denoted 'alpha'), was obtained from methanol/saturated potassium iodide solution, while a second 'beta'-form obtained from 2,4,6-trimethylpyridine, rhombohedral R3c, a 17.048(1) Angstrom, alpha 61.15(5)degrees Z = 2 tetramers, R 0.037 for N-0 1622, is isomorphous with previously recorded [BrAg(PPh3)](4), for which a redetermination is described (R 0.039 for N-0 1289); the latter has also been obtained in the common orthorhombic Pbcn array: a 18.10(1), b 21.08(1), c 18.39 (1) Angstrom, Z = 4, R 0.041 for N-0 2877. A new 'step' form of [1Ag(PPh3)](4), monoclinic, C 2/c, a 26.14(2), b 16.340(9), c 18.64(2) Angstrom, beta 114.04(8)degrees, R 0.058 for N-0 2107, obtained from acetonitrile and isomorphous with [BrCu(PPh3)](4) (step), is also recorded. In the far-infrared spectra of [(Ph3As)(4)Cu4X4] bands which have been assigned to vibrations of the Cu4X4 core are: 166, 150, 135, 114 (X = Br); 136, 85 cm(-1) (X = I; 2CHCl(3) 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 T-2 v(CuX) mode of the Cu4X4 core; the bands at 114 and 85 cm(-1) are assigned to the next highest frequency Ta mode of the cluster. The splitting of the highest frequency Ta band for the bromide is consistent with the greater degree of distortion of the Cu4X4 core from ideal T-d symmetry in this complex relative to the iodide.