Infrared and Raman studies of the solids in the Mg(CH3COO)2–Zn(CH3COO)2–H2O system

The infrared and Raman spectra of Mg(CH3COO)2·4H2O, Zn(CH3COO)2·2H2O and the double salt MgZn(CH3COO)4·4H2O have been recorded and discussed with respect to the internal modes of the acetate ions and the water molecules. MgZn(CH3COO)4·4H2O crystallizes in the triclinic system with lattice parameters: a=10.441(3)Å, b=10.353(3)Å, c=8.949(3)Å, α=105.67(2)°, β=114.77(2)°, γ=77.52(2)°, V=839.8(3)Å3. The analysis of the spectra of MgZn(CH3COO)4·4H2O 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(CH3COO)2·2H2O. The number of the bands corresponding to the uncoupled OD vibrations in MgZn(CH3COO)4·4H2O 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.