Construction of lanthanide complexes based on 3,4-dichlorobenzoic acid and 5,5′-dimethyl-2,2′-bipyridine: Supramolecular structures, thermodynamic properties and luminescent behaviors

Two novel lanthanide complexes, [Ln(2)(3,4-DCIBA)(6)(5,5'-DM-2,2'-bipy)(2)(C2H5OH)(H2O)] (Ln = Gd(1), Tb (2)); 3,4-DCIBA: 3,4-dichlorobenzoate; 5,5'-DM-2,2'-bipy: 5,5'-dimethyl-2,2'-bipyridine) have been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectrum, thermal analysis and single X-ray diffraction techniques. The binuclear complexes 1-2 are isomorphous and crystallize in the triclinic crystal system and P1 space group, and each metal center is eight-coordinated with distorted square antiprismatic molecular geometry. The structure of this type of complex is unique in that the solvent ethanol molecule participates in the coordination. Complexes 1-2 are stitched together via pi-pi stacking interactions and hydrogen bonding interactions to form the 1D, 2D supramolecular structures. The thermal decomposition mechanisms of two complexes were obtained by TG-DSC/FTIR techniques. The molar heat capacities of the complexes 1 and 2 are measured by a DSC instrument over the temperature range from 255.15 to 323.15 K and thermodynamic functions were calculated by fitted polynomial and thermodynamic equations. The luminescence studies demonstrate that complex 2 exhibits the characteristic emission of Tb3+ ion (D-5(4) -> F-7(6-3)). (C) 2019 Elsevier Ltd. All rights reserved.