Synthesis, crystal structures and thermodynamic properties of two novel lanthanide complexes based on 3,4-diethoxybenzoic acid and 2,2′-bipyridine

Two binuclear lanthanide complexes[Ln(3,4,-DEOBA)(3)DIPY](2) DIPY (Ln = Tb (1), Dy (2); 3,4,-DEOBA = 3,4-diethoxybenzoate; DIPY = 2,2'-bipyridine) have been synthesized and characterized. The single crystals of complexes 1 and 2 were obtained. And the two complexes are isostructural with a coordination number of eight to form a distorted square antiprism. Carboxylic groups adopt two modes coordinating with Ln (III) ions: bidentate chelate, and bridging bidentate. Binuclear complexes 1 and 2 are stitched together via pi-pi stacking interactions to form 1D chain and 2D layer supramolecular structures. The two complexes were characterized by elemental analysis, IR spectra, and powder X-ray diffraction. The luminescence spectra of complexes 1 and 2 show the characteristic emissions of Tb3+ (D-5(4) -> F-7(6-3)) and Dy3+ (F-4(9/2) -> H-6(15/2), H-6(13/2)). The thermal decomposition mechanisms for title complexes were studied by the technology of TG-FTIR. And the heat capacities of two complexes were measured by DSC in the temperature range from 258.15 to 343.15 K. The smoothed heat capacities and thermodynamic functions for complexes 1 and 2 were calculated by fitted polynomial and thermodynamic equations. (C) 2016 Elsevier Ltd.