Spectroscopic and structural studies on 1∶1 adducts of silver(I) salts with tricyclohexylarsine

Abstract

Adducts of a number of silver(I) salts, AgX, with tricyclohexylarsine, of 1∶1 AgX∶As(C₆H₁₁)₃ stoichiometry have been synthesized for X = Cl, Br, I, NO₃, NCO or CN and subjected to room temperature single crystal X-ray determinations and studies of their low frequency vibrational spectra. The chloride is binuclear [{(C₆H₁₁)₃As}Ag(µ-Cl)₂Ag{As(C₆H₁₁)₃}], isomorphous with its previously recorded P(C₆H₁₁)₃, X = Cl, Br counterparts, the silver environment being quasi-planar, trigonal AsAg(µ-Cl)₂; the nitrate is isomorphous, with a central planar Ag(µ-O)₂Ag array, a pair of oxygen atoms, one from each of a pair of symmetry-related nitrate groups, bridging the two silver atoms. The present bromide, unlike its P(C₆H₁₁)₃ counterpart, is not a dimer, but, like the iodide, a ‘cubane’ tetramer; the iodide is isomorphous with its P(C₆H₁₁)₃ analogue, a crystallographic 2 axis passing through a pair of opposed faces of the tetramer, but the bromide is of a new type, rhombohedral space group R. Remarkably, the cyanate is also of the cubane form, the first recorded (other than an organometallic) incorporating a first-row atom, obtained unsolvated and bis(pyridine) solvated. The cyanide is a linear polymer . . . {(C₆H₁₁)₃As}₂AgNCAgCN{As(C₆H₁₁)₃}₂AgNC . . . (‘α’ phase, from 2-methylpyridine); a second ‘β’ phase was obtained from 2,4,6-trimethylpyridine, of similar form, while from pyridine, a solvate of 3∶4∶2 AgCN∶As(C₆H₁₁)₃∶py stoichiometry [{Ag[As(C₆H₁₁)₃]₂(py)}₂(CN)][Ag(CN)₂] was obtained. The structure of the E = Px = CN unsolvated 1∶1 analogue was also determined, also being a linear polymeric array like its E = As counterpart. The far-IR spectra of the halide complexes exhibit bands due to ν(AgX) vibrational modes at 229, 148 cm^–1 (X = Cl), 167, 151, 125, 109 cm^–1 (X = Br) and at 111, 86 cm^–1 (X = I). These spectra were interpreted in terms of idealised C_2h Ag₂Cl₂ and T_d Ag₄X₄ structures of the silver halide cores.