Vibrational spectroscopic studies of trivalent hexa-aqua-cations: single-crystal Raman spectra between 275 and 1 200 cm –1 of the caesium alums of titanium, vanadium, chromium, iron, gallium, and indium

Oriented single-crystal Raman spectra have been recorded at 80 or 90 K for CsM(SO4)2·12H2O (M = Ti, V, Cr, Fe, Ga, or In), CsM(SeO4)2·12H2O (M = Cr or Fe), and CsFe(SO4)2·12D2O. A complete assignment of the spectra between 275 and 1 200 cm–1 has been made. The total symmetric metal–water stretching modes of the trivalent hexa-aqua-cations occur at 517 (Ti), 525 (V), 540 (Cr), 523 (Fe), 537 (Ga), and 505 cm–1(In), significantly higher than values previously reported. The wavenumbers of these modes vary with the reciprocal of the metal(III)–water bond lengths.