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

Abstract

A series of monomeric [AgX{P(C₆H₁₁)₃}₂] complexes have been prepared for X = CN, I, Br, Cl, SCN, NCO, NO₃ or ClO₄ and characterized by single-crystal X-ray determinations, solid-state cross polarization magic angle spinning (CP MAS)³¹P NMR, solution ³¹P NMR and far-infrared spectroscopy. For X = CN, I, Br, Cl or SCN the crystal structures are isomorphous, crystallizing in a monoclinic C2/c cell with a≈17, b≈9.3, c≈25 Å, β≈110°, Z= 4; the SCN complex exhibits anion disorder/space group ambiguity. For X = NCO or NO₃(redetermined) the structures are isomorphous with the previously studied perchlorate, crystallizing in a triclinic P cell derivative of the C2/c array with a≈9.3, b≈9.8, c≈23 Å, α≈95, β≈96, γ≈116°. The Ag–P bond lengths correlate inversely with the P–Ag–P angles and depend on the donor properties of the anion X, with, however, a reverse trend noted for the halide complexes. The solid-state CP MAS ³¹P NMR spectra show splitting due to ¹J(P–Ag) coupling which progressively increases from 322 Hz for X = CN to 505 Hz for X = ClO₄. For the triclinic species further splitting is observed and assigned to ²J(P–P) coupling between the crystallographically inequivalent phosphorus atoms. These NMR results are consistent with the structural results except for the chloride and perchlorate systems where experiments suggest that both triclinic and monoclinic phases co-crystallize in proportions which depend on the recrystallization procedures. Solution ³¹P NMR spectra show doublets assignable to 1 : 2 species. For X = Br, Cl, NCO or SCN signals assignable to 1 : 1 species are also observed. Comparison with solid-state data show differences in ¹J(P–Ag) that are ascribed to differences in θ(P–Ag–P) in the solution and solid states. Far-IR spectra of the halide and pseudo-halide complexes in the series exhibit single bands due to v(AgX) vibrational modes at 207, 149, 121 for X = Cl, Br or I and at 288, 241 and 174 cm^–1 for X = CN, NCO or SCN, these latter results providing rare data for the vibrational frequencies of terminal Ag–C, Ag–N and Ag–S bonds.