Interionic forces in crystals—II. Infrared spectra of SO4 groups and “octahedrally” coordinated water in some alums, Tutton salts, and the double salts obtained by dehydrating them

Abstract

Abstract Infrared spectra of 22 alums (including α, β and γ types) show simple v 3 and v 4 sulfate vibrational peaks indicating essentially T d symmetry, plus numerous peaks due to water coordinated about the M''' and M' ions. There are few simple correlations of spectra with change in either cation, but the position of v 3 is slightly affected by change from α to β structure. Infrared spectra of 18 Tutton salts are more sensitive to the nature of the M' cation than to the M'' cation. The effective SO 4 symmetry is C 3 v . Infrared spectra of 24 dehydrated alums fall into two main symmetry patterns for SO 4 , C 3 v , for Al''' and C 2 v , (probably) for other M''' ions. The spectral lines are remarkably sharp and intense, and depend more on the nature of the M''' than on the M' cations. The rock and wag frequencies for waters “octahedrally” coordinated to M''', M'', and M' cations can be systemized in terms of ionic charge and presence or absence of d orbitals in the cation.