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

Abstract

A series of mononuclear complexes [Ag{As(C₆H₁₁)₃}₂X] (X = Cl, Br, I, CN, NCO, OClO₃, O₂NO or O₂CCF₃) have been synthesized and characterised by room temperature single crystal X-ray determinations and low-frequency vibrational spectroscopy. For X = Cl, Br, I or OClO₃ the crystal structures are isomorphous with a number of their previously recorded P(C₆H₁₁)₃ counterparts, crystallising in the familiar monoclinic C2/c array with the Ag–X bond lying on a crystallographic 2 axis (the perchlorate is disordered) which also relates the pair of As(C₆H₁₁)₃ ligands. The silver environment in all is planar three-co-ordinate XAgAs₂. For X = CN, NCO or O₂NO the derivative lower-symmetry triclinic P array, also common among the P(C₆H₁₁)₃ analogues is found. The trifluoroacetate, resembling the nitrate in that the anion behaves as a small ‘bite’ bidentate ligand, [Ag{As(C₆H₁₁)₃}₂(O₂CCF₃)], is monoclinic space group P2₁/n. The thiocyanate by contrast, utilising the ambidentate capacity of the SCN ligand, remarkably, is a linear polymer, · · ·{As(C₆H₁₁)₃}₂Ag(SCN)Ag(SCN)· · ·, triclinic, space group P1, in which the silver atom environment is four-co-ordinate, NSAgAs₂. Far-IR spectra of the halide and pseudo-halide complexes in the series exhibit single bands due to ν(AgX) vibrational modes at 230, 165, 139, 262 and 311 cm^–1 for X = Cl, Br, I, NCO and CN respectively. These are all higher than the values for the corresponding P(C₆H₁₁)₃ complexes, suggesting that the Ag–X bonding is stronger in the As(C₆H₁₁)₃ complexes, this being the result of weakened Ag–L bonding in going from L = P(C₆H₁₁)₃ to As(C₆H₁₁)₃.