Calcium and strontium thiobarbiturates with discrete and polymeric structures

Three new alkaline earth metal complexes, [Ca-2(H2O)(8)((2)-HTBA-O,O)(2)(HTBA-O)(2)] (1), [Ca(H2O)(5)(HTBA-O)(2)]2H2O (2), and [Sr(H2O)(4)((2)-HTBA-O,S)(2)](n) (3) (H(2)TBA=2-thiobarbituric acid, C4H4N2O2S), were synthesized and characterized by FT-IR spectroscopy, TG-DSC, and single-crystal and powder X-ray diffraction analysis. The single-crystal X-ray diffraction data revealed that 1 and 2 are discrete structures, whereas 3 is a polymer. In 1 and 2, Ca2+ is seven-coordinate and forms a monocapped trigonal prism. In 1, the prisms are pairwise connected with the assistance of two [(2)-HTBA-O,O](-) ligands. In 3, Sr2+ is coordinated by four monodentate HTBA(-) via S or O donors and four waters, with the formation of a distorted square antiprism. The antiprisms are connected by (2)-O,S bridging HTBA(-). Hydrogen bonding involving coordinated water and - interactions plays an important role in construction of the supramolecular 3-D structures in 1-3. Infrared spectroscopic data supported the structural data. The thermal stability of 1-3 decreases in the order 1>2>3. Dehydration of 1-3 was a multi-step process, followed by exothermic oxidative degradation of the 2-thiobarbiturate moiety between 290 and 800 degrees C.