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

The 1:1 adducts of silver(I) halides (AgX; X = Cl, Br or I) with tricyclohexylphosphine have been prepared and their room-temperature single-crystal structures, solid-state cross polarization magic angle Spinning (CP MAS) P-31 NMR, solution P-31 NMR and far-IR spectra determined. The solid-state structures of the chloride and bromide complexes recrystallized from pyridine are unsolvated, isomorphous, centrosymmetric dihalide-bridged dimers, [{AgX[P(C6H11)(3)]}(2)], with three-co-ordinate metal centres. Crystals are triclinic, space group P (1) over bar, a approximate to 8.8, b approximate to 9.4, c approximate to 13.3 Angstrom, alpha approximate to 100, beta approximate to 92, gamma approximate to 115 degrees. Recrystallization of the iodide complex from pyridine (py) yielded a novel dimer consisting of [{AgI(py)(0.5)[P(C6H11)](3)}(2)] units in which the silver and phosphorus atoms are folded around the I ... I vector and towards a bridging pyridine ligand in a 'crevice' co-ordination mode. Recrystallization of the iodide from substituted pyridine bases did not yield further examples of such complexes but rather crystals of an unsolvated 'cubane' tetramer, [{AgI[P(C6H11)(3)]}(4)]. The far-IR spectra of the complexes exhibit bands due to nu(AgX) vibrational modes at 225, 143 cm(-1) for X = Cl, 189, 167, 135, 114 cm(-1) for X = Br, 113, 83 cm(-1) for X = I and at 115, 90 cm(-1) for [{AgI(py)(0.5)[P(C6H11)(3)]}(2)]. These spectra are interpreted in terms of idealized C-2h Ag(mu-X)(2)Ag and T-d Ag4I4 structures of the silver halide cores. The separation between the bands in the spectra of the dimeric species is a sensitive function of the extent of distortion of the cores from D-2h symmetry. The solid-state CP MAS P-31 NMR spectra of the dimers exhibit simple doublets with average (1)J(P-Ag) coupling constants of 648 Hz for [{AgCl[P(C6H11)(3)]}(2)], 612 Hz for [{AgBr[P(C6H11)(3)]}(2)] and 552 Hz for [{AgI(py)(0.5)[P(C6H11)(3)]}(2)]. Solution P-31 NMR spectra of the chloride and bromide complexes show well resolved sets of doublets due to (1)J(P-Ag-107,Ag-109) coupling at 25 and 0 degrees C respectively With average (1)J(P-Ag) coupling constants of 642 and 627 Hz. The;solution spectra of both the tetrameric and crevice iodide complexes are similar, showing broad signals at room temperature and doublets at -60 degrees C [delta 12, (1)J(P-Ag) = 544 Hz]. These structural and spectroscopic results are compared with those for other 1:1 AgX:phosphine complexes.