Spectroscopic and structural studies on 1 : 2 adducts of silver(I) salts with tricyclohexylphosphine

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 C2h Ag2Cl2 and Td Ag4X4 structures of the silver halide cores.