Influence of alkyl substituents in 1,3-diethyl-2-thiobarbituric acid on the coordination environment in M(H2O)(2)(1,3-diethyl-2-thiobarbiturate)(2) M = Ca2+, Sr2+

Abstract

Two new isostructural complexes, [Ca(H2O)(2) (mu(2)-Detba-O,O')(2)](n) (1) and [Sr(H2O)(2)(mu(2)-Detba-O,O')(2)](n) (2) (HDetba = 1,3-diethyl-2-thiobarbituric acid), were synthesized and characterized by single-crystal and powder X-ray diffraction analysis, TG-DSC, FT-IR, and emission spectroscopy. The single-crystal X-ray diffraction data revealed that 1 and 2 are polymeric where M2+ (M = Ca, Sr) is a six-coordinate octahedral binding four Detba(-) ions and two water molecules. The octahedra are linked through bridging Detba(-) ions forming a 2-D layer. Two intermolecular hydrogen bonds O-H center dot center dot center dot S in the crystal form a 3-D net. The comparison of M(Detba)(2) and M(Htba)(2) (H(2)tba = 2-thiobarbituric acid) structures showed that the coordination number of metals in M(Detba)(2) does not exceed six and there are no pi-pi interactions, unlike compounds with Htba(-); Detba(-) ions are only bridges in HDetba coordination compounds. Thermal decomposition of 1 and 2 includes dehydration, which mainly ends at 200 degrees C, and organic ligand oxidation at 300-350 degrees C with a release of CO2, SO2, H2O, NH3, and isocyanate. Upon excitation at 220 nm, 1 and 2 exhibit an intense emission maximum at 557 nm.