Supramolecular structures, thermal decomposition mechanism and heat capacity of the novel binuclear Tb(III) and Dy(III) complexes with 2,3-dimethoxybenzoic acid and 5,5′-dimety-2,2′-bipyridine

Two novel binuclear lanthanide complexes [Tb(2,3-DMOBA)(3)(5,5 '-DM-2,2 '-bipy)](2)center dot C2H5OH (1) and [Dy(2,3-DMOBA)(3)(5,5 '-DM-2,2 '-bipy)](2)center dot C2H5OH (2) (2,3-DMOBA = 2,3-dimethoxybenzoate, 5,5 '-DM-2,2 '-bipy = 5,5 '-dimety-2,2 '-bipyridine) have been successfully synthesized and structurally validated by single-crystal diffraction. The results of single-crystal analyses indicate the complexes contains one free ethanol molecule, and each center Ln(III) is nine-coordinated, exhibiting a distorted monocapped square anti-prismatic coordination geometry. The two center Ln(III) are bound by four 2,3-DMOBA ligands, two of which are bridging bidentate and the other two are bridging-chelating. The adjacent binuclear complexes can form 1D supramolecular structure by a pair of alternating identical C-H center dot center dot center dot O hydrogen bonding interactions, which further form 2D sheet structures. The thermal behavior of these complexes is investigated by TG-DSC/FTIR. What is more, the heat capacities of the complexes 1-2 are measured by DSC at 259.15-346.15 K, and the result indicates that the heat capacity values of the complexes gradually increased with the increase in temperature. In addition, the thermodynamic functions values (H-T - H-298.15K) and (S-T - S-298.15K) of the complexes 1-2 are calculated according to the fitted polynomial equations and the thermodynamic equation. The luminescence property of complex 1 is studied.