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

Abstract

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.