New fluorescent compounds based on zinc thiocyanate: influence of structure on spectral properties.

New coordination compounds based on zinc thiocyanate, namely (acetone thiosemicarbazone-κ2N1,S)bis(isothiocyanato-κN)zinc(II) monohydrate, [Zn(NCS)2(C4H9N3S)]·H2O, (I), and diaquatetrakis(urea-κO)zinc(II) tetrakis(isothiocyanato-κN)zinc(II), [Zn(CH4N2O)4(H2O)2][Zn(NCS)4], (II), were synthesized and studied by UV-Vis, fluorescence and IR spectroscopy. Coordination salt (II) forms a rare system composed of two different coordination units of the same metal and it is the first example of a compound with two completely different zinc coordination units, of which one contains a tetrakis(urea)zinc unit. Both (I) and (II) possess fluorescence properties and produce blue and green emissions, respectively, upon irradiation with violet light. The spectral properties were correlated with the observed molecular and supramolecular structures. The acetone thiosemicarbazone ligand of (I) exhibits (upon coordination) red shifts of bands corresponding to N=C and C=S stretching vibration frequencies, which is not typical for chelating molecules.