Four dinuclear trivalent lanthanide complexes of the general formula [Ln2(2-Br-5-MOBA)6(phen)2] (Ln = Nd(), Sm(), Ho(), Er(); 2-Br-5-MOBA = 2-bromine-5-methoxybenzoate, phen = 1,10-phenanthroline) were prepared and structurally characterized. The complexes to are isostructural with a coordination number of nine. The carboxylic acid ligands adopt bridging, bidentate chelating, and tridentate chelating bridging modes to coordinate with Ln(iii) ions. The structures of the complexes were confirmed on the basis of elemental analysis, molar conductance, thermogravimetric analysis (TGA), and IR and UV spectra. The heat capacities and thermal circulating processes of the prepared complexes were performed on a differential scanning calorimeter under a nitrogen atmosphere. Two remarkable solid-solid phase transitions existed both in the heat capacities and thermal circulating processes. The bacteriostatic activities of the complexes were evaluated against Candida albicans, Escherichia coli and Staphylococcus aureus. Besides, the luminescent property of complex was also investigated, and the magnetic properties of complexes and were also discussed in detail.

The crystal structures of complexes [Tb (3-Br-4-MBA) 3 phen] 2 (1), [Ho(3-Br-4-MBA) 3 (phen)H 2 O] 2 (2) and [Er(3-Br-4-MBA) 3 (phen)H 2 O] 2 (3) (3-Br-4-MBA=3-bromine-4-methylbenzoate, phen=1,10-phenanthroline) have been solved by single-crystal X-ray diffraction methods. All obtained products were examined and characterized by elemental analysis, molar conductivity, IR, UV and XRD techniques. The thermogravimetric analysis of 1 to 3 was studied, indicating that the decomposition processes of 2 and 3 are different from 1. The mass loss of the first step for 2 and 3 is attributed to the H 2 O molecules. The three-dimensional IR accumulation spectra of gaseous of 1 to 3 were also recorded. Complex 1 emits strong and bright green fluorescence under UV light at the room temperature. The bacteriostatic activities of the three complexes against bacteria, such as Escherichia coli and Staphylococcus aureus, and fungus (Candida albicans) were tested.

In the temperature range of 280 to 350 K, there is a solid-to-solid phase transition for each complex, which is further evidenced by four thermal circulating processes with the scanning rate of 10 K min−1.