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

Abstract

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)³¹P NMR, solution ³¹P 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, a≈8.8, b≈9.4, c≈13.3 Å, α≈100, β≈92, γ≈115°. 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 v(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(µ-X)₂Ag 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 ³¹P NMR spectra of the dimers exhibit simple doublets with average ¹J(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 ³¹P NMR spectra of the chloride and bromide complexes show well resolved sets of doublets due to ¹J(P–^107,109Ag) coupling at 25 and 0 °C respectively with average ¹J(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 °C [δ 12, ¹J(P–Ag)= 544 Hz]. These structural and spectroscopic results are compared with those for other 1 : 1 AgX : phosphine complexes.