X-Ray crystal structure of [Ag₄(μ-dppm)₂(μ-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(μ-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 μ2-(η1-O) and two triple μ3-(η2-O, η1-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(109Ag–31P), 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.