Crystal structures, luminescence, and thermodynamic properties of lanthanide complexes with 3,5-dimethoxybenzoic acid and 1,10-phenanthroline

The synthesis and structure determination of five novel lanthanide complexes {[Ln(3,5-DmeoxBA)3(phen)]2 (Ln = Pr(1) Nd (2), Sm (3), Eu (4), and Ho (5); 3,5-DmeoxBA = 3,5-Dimethoxybenzoate; phen = 1,10-phenanthroline)} are reported. In the isomorphous complexes 1 to 5, two Ln3+ ions are connected together by four bridging 3,5-DmeoxBA ligands. Each Ln3+ ion is octa-coordinated, yielding a distorted square-antiprism comformation. The thermal properties of the title complexes were investigated by simultaneous TG/DSC-FTIR techniques. The activation energy E values of the first decomposition stage for complexes 1 to 5 were calculated by integral iso-conversional non-linear (NL-INT) and Starink methods. Heat capacities of the five complexes were measured by differential scanning calorimetry (DSC). And the values of the experimental heat capacities were fitted to a polynomial equation with the least-squares method. Furthermore, based on the fitted polynomial and thermodynamic equations, the smoothed heat capacities and thermodynamic functions (HT–H298.15K), (ST–S298.15K), and (GT–G298.15K) were calculated. The fluorescent property of complex 4 was also studied.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We have synthesized and characterised five novel lanthanide complexes. ► The five complexes are isomorphous. ► The thermal properties were investigated by simultaneous TG/DSC-FTIR techniques. ► The heat capacities of the complexes were measured in the range of (263.15 to 475.65) K by means of DSC. ► The thermodynamic parameters were also obtained on the base of the fitted polynomials.