X-Ray crystal structure of [Ag4((mu)-dppm)2((mu)-C2F5COO)4]. Synthesis and spectroscopy of silver(I) perfluorinated carboxylate complexes with bis(diphenylphosphino)methane

Complexes of Ag(I) carboxylates with dppm = bis(diphenylphosphino)methane of general formula [Ag2(RCOO)2(dppm)], where R = CF3, C2F5, C3F7, C4F9, C6F13, C9F19, were obtained and characterized with 1H, 13C, 19F, 31P NMR and IR. The X-ray crystal structure of [Ag4(µ-dppm)2((mu)-C2F5COO)4] determined at 100(1) K (R= 0.0316) revealed a centrosymmetric tetranuclear aggregate with the silver atoms bridged by two dppm and four pentafluoropropionates forming two monoatomic (mu)2-((eta)^1-O) and two triple (mu)3-((eta)^2-O, (eta)^1-O ) bridges. Of the two crystallographically independent Ag(I) atoms one has distorted tetrahedral geometry with one Ag-P bond and three Ag-O bonds, while the second has trigonal planar geometry with an Ag-P and two Ag-O bonds. The 31P CP MAS NMR spectra demonstrate splitting due to 1J(107,109Ag-31P) and 2J(P-P) coupling between crystallographically inequivalent phosphorus atoms. Variable-temperature 31P NMR spectra were recorded between 323 and 223 K and 1J(107Ag-31P), 3J(107Ag-31P), 1J(109Ag31P), 3J(109Ag-31P) spin-spin coupling constants calculated. Analysis of coordination shifts and coupling constants is in favor, in solution, of binuclear trigonal Ag(I) complexes with bridging carboxylates and dppm.