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

Abstract

Two binuclear lanthanide complexes [Ln(3,4,-DEOBA)3DIPY]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 π–π 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+ (5D4→7F6-3) and Dy3+ (4F9/2→6H15/2, 6H13/2). 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 343.15K. The smoothed heat capacities and thermodynamic functions for complexes 1 and 2 were calculated by fitted polynomial and thermodynamic equations.