Lewis-base adducts of Group 11 metal(I) compounds .71. Synthesis, spectroscopy and structural systematics of some 1:2 binuclear adducts of silver(I) compounds with triphenylarsine, [(Ph3As)(2)Ag(mu-X)(2)Ag(AsPh3)(2)], X = Cl, Br, I, SCN

The syntheses and room-temperature single-crystal X-ray structural characterization of binuclear 1:2 adducts formed between silver(I) (pseudo-)halides, AgX, and triphenylarsine, AsPh3, for X = Cl, Br, I, SCN (1)-(4), are described. The chloride (1), obtained from 2-methylpyridine, is triclinic, <P(1)over bar>, a 10.410(2), b 12.716(2), c 14.196(6) Angstrom, alpha 113.38(2), beta 109.41(2), gamma 75.08(1)degrees, Z = 1 (dimer); conventional R on \F\ was 0.037 for N-0 3979 independent 'observed' (I > 3 sigma(I)) reflections. The bromide (2a), obtained from 2,6-dimethylpyridine, and iodide (3), obtained from a mixture of AgI/saturated KI in MeOH solutions, are isomorphous, monoclinic, P 2(1)/c, a approximate to 24.2, b approximate to 13.9, c approximate to 20.2 Angstrom, beta approximate to 109.5 degrees, Z = 4 dimers; R was 0.046 and 0.044 for N-0 5670 and 6039 respectively. The thiocyanate (4) has a similar cell, a 24.12(1), b 12.558(8), c 23.244(4) Angstrom, beta 110.11(3)degrees, Z = 4 dimers, R being 0.044 for N-0 7956; one of the thiocyanate ligands (which bridge in Ag-SCN-Ag mode) is disordered. A second polymorph of the bromide (2b) (from a mixture of AgBr/saturated KBr in H2O) is also monoclinic, P 2(1)/c, a 14.121(8), b 25.577(3), c 21.968(2) Angstrom, beta 125.54(3)degrees, Z = 4 dimers (R was 0.047 for N-0 5715). Ag-As range between 2.568(1) and 2.633(1) Angstrom throughout the series; in the isomorphous bromide and iodide, values increase slightly: 2.578(1)-2.611(1), cf. 2.601(2)-2.633(1) Angstrom respectively. Ag-X are 2.568(2)-2.670(2) (Cl); 2.688(2)-2.715(2) (Br); 2.828(2)-2.856(1) Angstrom (I); Ag-S, N for the ordered SCN group are 2.646(3), 2.255(6) Angstrom. A redetermination of improved precision (R 0.035, N-0 6030) is reported for the triphenylphosphine/thiocyanate analogue. The far-infrared spectra of [(Ph3As)(2)Ag(mu-X)(2)Ag(AsPh3)(2)] show v(AgX) bands at 185, 145 (X = Cl), 145, 130, 106 (X = Br) and 121 cm(-1) (X = I). The splittings and band widths reflect a decrease in the degree of distortion of the Ag(mu-X)(2)Ag units from a symmetrically bridged structure from X = Cl to I.