2-(Diphenylphosphino)pyridine (dppy) as monodentate or bridging ligand in silver(I) complexes. Crystal structures of [Ag(eta1-dppy)4][ClO4] and [Ag2(eta1-dppy)(mu-dppy)2][ClO4]2

The silver(I) homoleptic complexes [Ag-2(dppy)(n)](ClO4)(2) (n=2 for 1 or 3 for 2) and [Ag(dppy)(n)]ClO4 (n=3 for 3 or 4 for 4) [ dppy = 2-( diphenylphosphino) pyridine ] have been isolated in the solid state and characterised in solution by means of variable-temperature P-31 NMR spectroscopy. Both dinuclear species 1 and 2 possess an 8-membered annular core structure with two ligands bridging head-to-tail the metal ions, while in the mononuclear derivatives all dppy ligands act as P-bound monodentate. Treatment of 1 with increasing amounts of dppy revealed (by P-31 NMR spectroscopy) that complexes 2, 3 and 4 are formed in a stepwise manner. Surprisingly, no stable single complex is formed when the ddpy/Ag(I) ratio is 2. A mixture of complexes 2, 3 and 4, along with unidentified products, is conversely present in solution. The solid state structures of complexes 2 and 4 have been determined by single-crystal X-ray diffraction. In 2 the Ag(I) centres possess different environments, one metal ion being two-coordinated (NP donor set) and the other being three-coordinated (NP2 donor set). The cations of 4 present the metal bound to four dppy ligands in a slightly distorted tetrahedral environment. Of the two crystallographically independent cations, one shows the axial Ag-P bond length shorter (2.566(8) Angstrom) than the value for the off-axis Ag-P bonds (2.624(5) Angstrom).