Synthesis, vibrational spectra and thermal stability of Ag3O4 and related Ag7O8X salts (X=NO3-,ClO4-,HSO4-)

The titled compounds were synthesized in high purity and yield by passing an ozone/oxygen mixture (5 vol% O3 in O2) through aqueous solutions of different Ag(I) salts at 273–298 K. Ag3O4 is obtained by ozonolysis of neutral or mildly acidic solutions of AgF (0.05 M) or AgBF4 (0.05 M) at 273 K. Ozonolysis of aqueous solutions of AgNO3, AgClO4, Ag2SO4 and CH3COOAg at 273–298 K afforded Ag7O8NO3, Ag7O8ClO4, Ag7O8HSO4 and Ag2O2, respectively. Products were characterized by XRD, SEM, XPS, FT-IR, Raman spectroscopy and DSC. The spectroscopic data show that Ag3O4 and the Ag7O8X salts behave as metals at room temperature, due to overlap between valence and conduction bands in their electronic structure. The correct valence formulations for these compounds are (Ag2.67+)3O4 and (Ag2.67+)6O8 · Ag+X−, respectively. The thermal stability in air of the ozonolysis products was determined by DSC and also complementary XRD, FT-IR and Raman measurements. Ag3O4 was the least stable product, and thermally decomposed to 1.5Ag2O2(s) + 0.5O2(g) within 20 h at 298 K. Thermal stabilities in air increased in the order Ag3O4 < Ag7O8ClO4, Ag7O8HSO4 < Ag7O8NO3 < Ag2O2. This work resolves long-standing debate about the valence states of silver in Ag3O4 and Ag7O8X salts, and also provides valuable new spectroscopic information for these compounds. Attempts to prepare Ag2O3 by the ozonolysis route proved unsuccessful.

Graphical abstractAg3O4 and several related Ag7O8X salts (X=NO3-,ClO4-,HSO4-) were synthesized by ozonolysis of aqueous solutions of different Ag(I) salts at 273–298 K. Spectroscopic studies show that all of these compounds exhibit remarkable metallic character at 298 K, due to overlap between valence and conduction bands in their electronic structure.Figure optionsDownload full-size imageDownload as PowerPoint slide