Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXI Synthesis, Spectroscopy and Structural Systematics of Some 1 : 2 Binuclear Adducts of Silver(I) Compounds with Triphenylarsine, [(Ph3As)2Ag(µ-X)2Ag(AsPh3)2], X = Cl, Br, I, SCN

Abstract

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, a 10·410(2), b 12·716(2), c 14·196(6) Å, α 113·38(2), β 109·41(2), γ 75·08(1)°, Z = 1 (dimer); conventional R on F was 0·037 for N_o 3979 independent ‘observed’ (I > 3σ(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 2₁/c a≈ 24·2, b ≈ 13·9, c ≈ 20·2 Å, β ≈ 109·5°, Z = 4 dimers; R was 0·046 and 0·044 for N_o 5670 and 6039 respectively. The thiocyanate (4) has a similar cell, a 24·12(1), b 12·558(8), c 23·244(4) Å, β 110·11(3)°, Z = 4 dimers, R being 0·044 for N_o 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 2₁/c, a 14·121(8), b 25·577(3), c 21·968(2) Å, β 125·54(3)°, Z = 4 dimers (R was 0·047 for N_o 5715). Ag–As range between 2·568(1) and 2·633(1) Å 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) Å respectively. Ag–X are 2·568(2)-2·670(2) (Cl); 2·688(2)–2·715(2) (Br); 2·828(2)–2·856(1) Å (I); Ag-S, N for the ordered SCN group are 2·646(3), 2·255(6) Å. A redetermination of improved precision (R 0·035, N_o 6030) is reported for the triphenylphosphine/thiocyanate analogue. The far-infrared spectra of [(Ph₃As)₂Ag(µ-X)₂Ag (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(µ-X)₂Ag units from a symmetrically bridged structure from X = Cl to I.