Vibrational Spectra of Ag2CrO4

It has been shown¹ recently that Ag₂CrO₄ has a crystal structure which is unique among simple anhydrous chromates studied to date. Like the chromates of potassium², rubidium³, and cesium⁴, it may be assigned to the space group Pnma - D_2h ¹⁶ with four formula units per unit cell and chromium atoms on C_s sites. However, unlike the alkali-metal chromates, the cations are equally divided between sites of C_s and C_i symmetries. Furthermore, metal-oxygen distances in Ag₂CrO₄ range from 2.34 to 2.62Å, as contrasted with 2.7 to about 3.2Å in K₂CrO₄, and point to a greater degree of convalent bonding between cations and anions.¹ The present infrared and Raman data have been obtained with an interest in determining the spectral manifestations of this unique structure.