RAMAN, FTIR and PXRD studies of water in cinchoninum tetrachlorocadmate(II) hemipentahydrate and tetrachlorozincate(II) dihydrate compounds

Two transition metal (Cd(II) and Zn(II)) compounds with cinchonine, i.e. [(cinH2)CdCl4]·2.5H2O and [(cinH2)ZnCl4]·2H2O were studied, to explain the role of water molecules contained in their structure. FT-Raman and FTIR spectroscopy along with powder X-ray diffraction (PXRD) methods were applied to analyse structural changes induced in Zn(II) and Cd(II) derivatives by: (i) loosing crystallisation water as well as (ii) lowering temperature to 10 K. The PXRD patterns point to stronger changes in Cd(II)-cin structure framework on heating, confirmed by appearance of new reflections at low angle region. This fact may suggest differences in water bonding in Zn(II)-cin and Cd(II)-cin compounds. FT-Raman spectroscopy allow to indicate bands which characterise vibrations in which water molecules are involved, i.e. 1606 cm−1 and also to those which are disturbed by disappearance of the water, i.e. 3120, 3100 and 3077 cm−1. Redistribution of relative intensities in 1350–1400 cm−1 region, was a confirmation that Cd(II)-cin structure with doubly protonated cinchonine at N1 and N13 is a stable form. The observed changes in MIR spectra seem to be connected with the rearrangement of the hydrogen bond network and with the reorganisation of the cinchonine constituent moieties as a function of temperature.