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

Abstract

Two novel binuclear lanthanide complexes [Tb(2,3-DMOBA)3(5,5′-DM-2,2′-bipy)]2·C2H5OH (1) and [Dy(2,3-DMOBA)3(5,5′-DM-2,2′-bipy)]2·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···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 (HT − H298.15K) and (ST − S298.15K) 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.