Crystal structures and thermal decomposition mechanism of four lanthanide complexes with halogen-benzoic acid and 1,10-phenanthroline

Abstract

This paper describes syntheses and structure determination of four lanthanide complexes [Nd(2-Cl-4-FBA)3phen]2 (1, 2-Cl-4-FBA = 2-chloro-4-fluorobenzoate, phen = 1,10-phenanthroline), [Ln(2,5-DClBA)3phen]2 (Ln = Sm(2) and Tb(3), 2,5-DClBA = 2,5-dichlorobenzoate) and [Sm(2-Cl-4,5-DFBA)3(phen)(H2O)]2 (4, (2-Cl-4,5-DFBA = 2-chloro-4,5-difluorobenzoate). The complexes were characterized by elemental analysis, infrared and ultraviolet spectra, and X-ray single-crystal diffraction. In the molecular structures of 1–4, two Ln3+ ions are linked by four carboxyl groups, with two of them in a bridging bidentate mode and the other two in a bridging-chelating tridentate mode, forming four binuclear molecules. In addition, each Ln3+ ion is also chelated to one phen molecule and one carboxyl group in the complexes, except each Sm3+ ion in 4 which is bonded to one carboxyl group by unidentate mode and one H2O molecule. There are two different coordination polyhedrons for each Nd3+ ion in the two similar molecular structures of 1 and they are a distorted monocapped square antiprismatic and a distorted tricapped triangular prism conformation, respectively. The coordination polyhedron for each Ln3+ ion in 2–4 is a nine-coordinated distorted mono-capped square antiprismatic conformation. The complex 3 exhibits green luminescence under the radiation of UV light. The thermal decomposition behaviors of the complexes have been discussed by simultaneous TG/DSC-FTIR technique. The 3D surface graphs for the FTIR spectra of the evolved gases were recorded and the gaseous products were identified by the typical IR spectra obtained at different temperatures from the 3D surface graphs. Meanwhile, we discussed the non-isothermal kinetics of 1–4 by the integral isoconversional non-linear (NL-INT) method.