Infrared and Raman studies of the solids in the Mg(CH 3COO) 2–Zn(CH 3COO) 2–H 2O system

Abstract

The infrared and Raman spectra of Mg(CH 3COO) 2·4H 2O, Zn(CH 3COO) 2·2H 2O and the double salt MgZn(CH 3COO) 4·4H 2O have been recorded and discussed with respect to the internal modes of the acetate ions and the water molecules. MgZn(CH 3COO) 4·4H 2O crystallizes in the triclinic system with lattice parameters: a=10.441(3) A ̊ , b=10.353(3) A ̊ , c=8.949(3) A ̊ , α=105.67(2)°, β=114.77(2)°, γ=77.52(2)°, V=839.8(3) A ̊ 3. The analysis of the spectra of MgZn(CH 3COO) 4·4H 2O reveals the existence of probably at least three crystallographically non-equivalent acetate ions in the lattice. The strength of the hydrogen bonds in the three salts is studied by the method of IR matrix spectroscopy (matrix-isolated HDO molecules). The frequencies of the OD modes reveal that the acetate oxygens are stronger hydrogen bond acceptors than the water oxygens and the non-coordinated acetate oxygens show stronger acceptor abilities as compared to that of the coordinated ones. Comparatively strong hydrogen bonds are formed in Zn(CH 3COO) 2·2H 2O. The number of the bands corresponding to the uncoupled OD vibrations in MgZn(CH 3COO) 4·4H 2O evidences that at least four crystallographically different water molecules are expected to exist in the lattice. The water librations in the salts under study are also discussed.