The Raman spectra of crystalline Na2CrO4 and Na2CrO4·4H2O

Abstract The laser-Raman spectra of crystalline Na 2 CrO 4 and Na 2 CrO 4 ·4H 2 O are reported. Lack of isomorphism with the other alkali—metal chromates results in a unique spectrum for Na 2 CrO 4 . The trend towards higher frequencies with smaller cations, which is evident for the isomorphous alkali—metal chromates, is discontinued with Na 2 CrO 4 . The spectrum of Na 2 CrO 4 ·4H 2 O is unique and considerably more complex than that of the anhydrous salt, owing to a larger number of formula units per unit cell. Evidence from both Raman and infrared data for hydrogen bonding between hydrated water molecules and chromateionsin Na 2 CrO 4 ·4H 2 O is presented. Features of the spectrum of Na 2 CrO 4 ·4H 2 O are interpreted in terms of the effects of hydrogen bonding on the chromate frequencies.