Construction of lanthanide complexes based on 2,6-dimethylbenzoic acid and 5,5′-dimethyl-2,2′-bipyridine: Supramolecular structures, thermodynamic properties and luminescence

By using conventional solution method, two novel binuclear lanthanide complexes, [Eu(2,6-DMBA)(3)(5,5'-DM 2,2'bipy)](2)(1), and [Sm(2,6-DMBA)(3)(5,5'-DM-2,2'-bipy)](2)(2) (2,6-DMBA = 2,6-dimethylbenzoate, 5,5'-DM-2,2'-bipy = 5,5'-dimethy-2,2'-bipyridine), have been synthesized at room temperature. The two complexes are characterized by element analysis, single-crystal X-ray diffraction analyses and powder X-ray diffraction. The single-crystal analyses results indicate they are isomorphous in the monoclinic space group of P2(1)c. The binuclear complexes 1 and 2 are linked to form 1D, 2D supramolecular structures through the same C-H center dot center dot center dot O hydrogen bonding interactions. The thermal decomposition process of these complexes is investigated by TG-DSC/FTIR technology and the FTIR spectra of the escaped gas also are measured. In addition within a temperature range from 295.15 K to 410.15 K, heat capacities of the title complexes are measured by a DSC instrument, which indicates that no phase transition occurs in this range, and the heat capacity values of the complexes gradually increases with rising temperature. Not only that, the thermodynamic functions values (H-T-H-298.15K) and (S-T-S-298.15K) of the complexes 1 and 2 are calculated according to the fitted polynomial equations and the thermodynamic equation. The luminescent behaviour of complex 1 is investigated in the solid state. The complex 1 with Eu3+ ion shows strong red luminescence behaviour, and the luminescence lifetime and fluorescent quantum yield are calculated to be 1.442 ms and 18.96%. (C) 2019 Elsevier Ltd.