Preparation, thermodynamic property and antimicrobial activity of some rare-earth (III) complexes with 3-bromo-5-iodobenzoic acid and 1,10-phenanthroline

Four new rare-earth complexes of general formula [Ln(3-Br-5-IBA)3phen]2 (Ln(III) = Er (1), Tb (2), Dy (3) and Ho (4); 3-Br-5-IBA = 3-bromo-5-iodobenzoate; phen = 1,10-phenanthroline) were synthesized by solution-precipitation method, and investigated using elemental analysis, infrared spectra, ultraviolet spectra and TG/DSC-FTIR technology. The non-isothermal kinetics of the first stage for the complexes was studied by using non-linear integral isoconversional method and double equal-double steps method. The heat capacities of the complexes were measured between 263.15 and 485.55 K by means of differential scanning calorimeter, and the values of the experimental heat capacities were fitted to a polynomial equation with the least-squares method. And the thermodynamic functions [HT − H298.15], [ST − S298.15] and [GT − G298.15] were also derived based on the fitted polynomials and thermodynamic relationships with temperature interval of 10 K. Moreover, the antimicrobial activity test indicated that all these complexes exhibited moderate antimicrobial activity against Candida albicans and Staphylococcus aureus, good antibacterial activity against Escherichia coli. The fluorescence spectra for the complexes 2 and 3 behaved the characteristic transitions of Tb(III) and Dy(III) ions.