Single-crystal growth and characterization of disilver(I) monofluorophosphate(V), Ag2PO3F: Crystal structure, thermal behavior, vibrational spectroscopy, and solid-state F-19, P-31, and Ag-109 MAS NMR spectroscopy

摘要

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) angstrom, b = 5.5854(5) angstrom, c = 14.7840(13) angstrom, and beta = 90.178(2)degrees. The crystal structure of 1 [R(F-2 > 2 sigma(F-2) = 0.0268, wR(F-2 all) = 0.0665] is composed of three crystallographically independent Ag+ cations and PO3F2- anions as single building units. The oxygen environment around each of the Ag+ cations is different, with one Ag+ in distorted octahedral ((d) over bar (Ag-O) = 2.553 angstrom), one in nearly rectangular ((d) over bar (Ag-O) = 2.445 angstrom), and one in distorted tetrahedral ((d) over bar (Ag-O) = 2.399 angstrom) coordination. Additional Ag-F contacts to more remote F atoms located at distances >2.80 angstrom 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 angstrom for the P-O bonds and one considerably longer P-F bond of 1.575(2) angstrom. Compound 1 was further characterized by vibrational spectroscopy (Raman and IR) and solid-state F-19, P-31, and Ag-109 MAS NMR spectroscopy. The value for the isotropic one-bond P-F coupling constant in 1 is (1)J(PF) = -1045 Hz. Thermal analysis (TG, DSC) revealed a reversible phase transition at 308 degrees 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 degrees C.