Single-Crystal Growth and Characterization of Disilver(I) Monofluorophosphate(V), Ag₂PO₃F:  Crystal Structure, Thermal Behavior, Vibrational Spectroscopy, and Solid-State ¹⁹F, ³¹P, and ¹⁰⁹Ag MAS NMR Spectroscopy

Single crystals of disilver(I) monofluorophosphate(V), Ag₂PO₃F (1), were obtained by slow evaporation of a diluted aqueous Ag₂PO₃F solution. Compound 1 adopts a new structure type and crystallizes in the monoclinic space group C2/c with eight formula units and lattice parameters of a = 9.2456(8) Å, b = 5.5854(5) Å, c = 14.7840(13) Å, and β = 90.178(2)°. The crystal structure of 1 [R(F² > 2σ(F²) = 0.0268, wR(F² all) = 0.0665] is composed of three crystallographically independent Ag⁺ cations and PO₃F^2- anions as single building units. The oxygen environment around each of the Ag⁺ cations is different, with one Ag⁺ in distorted octahedral ((Ag−O) = 2.553 Å), one in nearly rectangular ((Ag−O) = 2.445 Å), and one in distorted tetrahedral ((Ag−O) = 2.399 Å) coordination. Additional Ag−F contacts to more remote F atoms located at distances >2.80 Å augment the coordination polyhedra for the two latter Ag⁺ cations. The monofluorophosphate anion deviates slightly from C_3v symmetry and exhibits the characteristic differences in bond lengths, with a mean of 1.510 Å for the P−O bonds and one considerably longer P−F bond of 1.575(2) Å. Compound 1 was further characterized by vibrational spectroscopy (Raman and IR) and solid-state ¹⁹F, ³¹P, and ¹⁰⁹Ag MAS NMR spectroscopy. The value for the isotropic one-bond P−F coupling constant in 1 is ¹J_PF = −1045 Hz. Thermal analysis (TG, DSC) revealed a reversible phase transition at 308 °C, which is very close to the decomposition range of 1. Under release of POF₃, Ag₄P₂O₇ and Ag₃PO₄ are the thermal decomposition products at temperatures above 450 °C.