A series of lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been synthesized with the formulae of [La(2-cl-4,5-dfba)(3)phen](n)center dot nH(2)O (1), [Nd(2-cl-4,5-dfba)(3)phenH(2)O](2) (2), [Ln(2-cl-4,5-dfba)(3)phen](2) (Ln = Eu (3), Ho (4)). The complexes are characterized by elemental analysis, infrared and fluorescent spectra and X-ray single-crystal diffraction. The structures of the four complexes are very different. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror growth pattern. Each La3+ ion is coordinated to four bridging carboxylic groups, two tridentate chelating-bridging carboxylic groups, simultaneous with one phen molecule, giving the coordination number of nine. In the molecular structures of complexes 2 and 3, two Ln(3+) ions are linked by four carboxyl groups, forming two binuclear molecules. In addition, each Nd3+ ion in complex 2 is bonded to one H2O molecule and one carboxyl group by monodentate mode, one phen molecule by bidentate chelating, and each Eu3+ ion is also chelated to one phen molecule and one carboxyl group in complex 3. And in complex 4, the Ho3+ ion yields a eight-coordinated distorted square anti-prism coordination geometry. The three-dimensional IR accumulation spectra of gaseous products for complexes 1 to 4 are analyzed and further authenticated the thermal decomposition processes with TG-DTG curves. The heat capacities of complexes 2 to 4 are measured and fitted to a polynomial equation by the least squares method on the basis of the reduced temperature x (x = [T-(T-max + T-min)/2]/[(T-max - T-min)/2]). Then the smoothed molar heat capacities and thermodynamic functions of complexes 2 to 4 are calculated. The fluorescence intensity of complex 3 is markedly improved as well. (C) 2012 Elsevier Ltd. All rights reserved.