Construction of two novel lanthanide complexes supported by 2-bromine-5-methoxybenzoate and 2,2′-bipyridine: Syntheses, crystal structures and thermodynamic properties

Two novel lanthanide complexes with the general formula [Ln(2-Br-5-MOBA) 3 (2,2′-DIPY)] 2 (Ln   =   Pr(1), Dy(2); 2-Br-5-MOBA   =   2-bromine-5-methoxybenzoate; 2,2′-DIPY   =   2,2′-bipyridine) have been successfully synthesized and characterized. The complexes 1 and 2 are isostructural and nine-coordinated with distorted monocapped square antiprismatic coordination geometry by the single-crystal X-ray diffraction analyses. Two complexes are all assembled into the 1D, 2D, 3D supramolecular structures by C H⋯O hydrogen bonding and π–π stacking interactions. The thermal decomposition mechanism for title complexes were obtained by TG/DSC-FTIR technology. The molar heat capacities of the complexes 1 and 2 are measured by a DSC instrument over the temperature range from 263.15   K to 365.15   K. On the basis of the fitted polynomial and thermodynamic equations, the smoothed values of heat capacities and thermodynamic functions ( H T - H 298.15K ), and ( S T - S 298.15K ) of the two complexes are calculated. In addition, the fluorescence spectra indicate that the complex 2 exhibits the characteristic emission of Dy(III) ion ( 4 F 9/2   →   6 H 13/2–15/2 ).