Structural and Solid-State ³¹P N.M.R. Studies of Tetrameric 1:1 Butyldiphenylphosphine Complexes of Silver(I) Halides

Abstract

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 ³¹P n.m.r. Crystals of [(PPh₂Bu) AgCl ]₄ and [(PPh₂Bu) AgBr ]₄ are isostructural, crystallizing in the tetragonal space group 14 with a 16.853(4), c 11.697(4) Ǻ and R 0.060 for 999 'observed' reflections for X = Cl, and a 16.944(4), c 11.893(9) Ǻ 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) Ǻ for the chloride, and Ag-P 2.408(6), Ag-Br 2.819(3), 2.806(3) and 2.670(3) Ǻ 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) Ǻ, and R 0.053 for 638 'observed' reflections. However, the tetramers in this complex are rotated by 45° 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) Ǻ. The ligand substituents in this complex exhibit very high thermal motion although no disorder is resolved. Solid-state CPMAS ³¹P 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(^107,109Ag,³¹P) 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.