Hydrates [Na2(H2O)x](2-thiobarbiturate)2 (x=3, 4, 5): crystal structure, spectroscopic and thermal properties

The hydrates [Na-2(H2O)(3)(Htba)(2)] (1) and [Na-2(H2O)(4)(Htba)(2)] (2), where H(2)tba is 2-thiobarbituric acid, were obtained under different thermal conditions from aqueous solutions and were structurally characterized. The molecular and supramolecular structures were compared to the known structure of [Na-2(H2O)(5)(Htba)(2)] (3). In polymeric 1-3, the Htba-ions are linked to Na+ through O and S forming octahedra. The decrease of the number of coordination water molecules led to an increase of the total number of bridge ligands (mu(2)-H2O, Htba(-)) and a change of the Htba-coordination. These factors induced higher distortion of the octahedra. It was assumed that hydrates, with a different number of coordinated water molecules, are more probable when the central metal has weaker bonds with O water molecules and with other ligands. The net topologies of 1-3 were compared. Thermal decomposition and IR spectra were analyzed for 1 and 2. [GRAPHICS] .