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

Abstract

The hydrates [Na₂(H₂O)₃(Htba)₂] (1) and [Na₂(H₂O)₄(Htba)₂] (2), where H₂tba 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 [Na₂(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 (μ₂-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.