Structure, luminescent and thermal properties of two novel lanthanide complexes with 3,4-diethoxybenzoic acid and 5,5′-dimethy-2,2′-bipyridine

Abstract

Two new lanthanide complexes [Tb(3,4,-DEOBA)3 5,5′-DME-2,2′-BIPY]2 (1), [Dy(3,4,-DEOBA)35,5′-DME-2,2′-BIPY]2 (2)(3,4,-DEOBA=3,4-diethoxybenzoate,5,5′-DME-2,2′-BIPY=5,5′-dimethy-2,2′-bipyridine) have been synthesized and characterized by elemental analysis, IR spectra and powder X-ray diffraction. The single crystal of the complex 1 has been obtained. There are two kinds of coordination modes in complex, 1 and the Tb3+ ion is eight-coordinated. The luminescence spectra of complexes 1 and 2 show the characteristic emission of Tb3+ ion (5D4 → 7F6-3) and Dy3+ ion (4F9/2 → 6H15/2,6H13/2). The results of thermal decomposition mechanism of the title complexes show that two complexes are thermally stable. And the pathway of thermal decomposition has been investigated by the coupled TG-FTIR technique. In the thermal decomposition of the title complexes, neutral ligands lose firstly, and then 3,4-DEOBA decompose into gaseous molecules of H2O and CO2. The kinetics of the first decomposition stage for two complexes are investigated by using the integral isoconversional nonlinear (NL-INT) method, which suggests that the first decomposition step of two complexes is complex reactions. The heat capacities of title complexes were measured by DSC in the temperature range from 258.15 to 343.15 K. The smoothed heat capacities and thermodynamic functions of the complexes are calculated based on the fitted polynomial and thermodynamic equations. The antibacterial performance study of complexes shows that two complexes have good antibacterial activity against Candida albicans, Staphylococcus aureus and no bacteriostatic activity on Escherichia coli.