STRUCTURAL AND SOLID-STATE P-31 NMR-STUDIES OF TETRAMERIC 1/1 BUTYLDIPHENYLPHOSPHINE COMPLEXES OF SILVER(I) HALIDES

Tetrameric 1:1 complexes of butyldiphenylphosphine (PPh2Bu) with silver halides AgX (X = Cl, Br and I) have been synthesized, and characterized in the solid state by single-crystal X-ray diffraction studies and solid-state P-31 n.m.r. Crystals of [(PPh2Bu)AgCl]4 and [(PPh2Bu)AgBr]4 are isostructural, crystallizing in the tetragonal space group I4BAR with a 16.853(4), c 11.697(4) angstrom and R 0.060 for 999 'observed' reflections for X = Cl, and a 16.944(4), c 11.893(9) angstrom and R 0.044 for 835 'observed' reflections for X = Br. The structures consist of 'cubane' units with core distances of Ag-P 2.365(8), Ag-Cl 2.712(7), 2.682(6) and 2.569(6) angstrom for the chloride, and Ag-P 2.408(6), Ag-Br 2.819(3), 2.806(3) and 2.670(3) angstrom for the bromide. Crystals of [(PPh2Bu)AgI]4 crystallize in the same space group with similar cell dimensions, a 16.559(4) and c 12.819(3) angstrom, and R 0.053 for 638 'observed' reflections. However, the tetramers in this complex are rotated by 45-degrees around the c axis with apparent relaxation of strain at the Ag-P bond. The ligand conformation is such that the butyl groups are oriented along the c axis rather than lying in the ab plane as found for the chloride and bromide structures. The bond distances for the I3AgP core are Ag-P 2.43(1), Ag-I 2.928(4), 2.882(4) and 2.885(4) angstrom. The ligand substituents in this complex exhibit very high thermal motion although no disorder is resolved. Solid-state CPMAS P-31 n.m.r. spectra of the chloride and bromide complexes each show a simple doublet with line spacing of 640 and 595 Hz respectively assignable to 1J(Ag-107,Ag-109,P-31) scalar coupling. The spectrum of the iodide complex, however, consists of a broad single peak suggestive of a high degree of disorder in the crystal lattice, consistent with the structural results.