Synthesis, Crystal Structure, and Thermal Properties of a Holmium(III) Benzoate Complex with 1,10-Phenanthroline

Abstract

A binuclear holmium(III) benzoate 1,10-phenanthroline ternary complex, [Ho(BA)3phen]2, was synthesized and characterized by elemental analysis, IR and UV spectroscopy, molar conductance, single crystal X-ray diffraction, and thermogravimetric/differential thermogravimetric (TG-DTG) techniques. The crystal of the complex is in a triclinic crystal system, space group p1̅ with a = 10.7162(18) Å, b = 11.845(3) Å, c = 12.227(2) Å, α = 105.141(11)°, β = 93.845(8)°, γ = 112.880(5)°, and Z = 1. Each Ho(III) cation in the crystal is eight-coordinated including two O atoms of one chelating bidentate carboxylate group, four O atoms of four bridging bidentate carboxylate groups, and two N atoms of one 1,10-phenanthroline molecule, yielding a distorted square antiprismatic comformation. The thermal analysis of [Ho(BA)3phen]2 has been performed by simultaneous TG/DSC-FTIR techniques. By the Malek method, SB(m,n) was defined as a kinetic model for the second-step thermal decomposition. The activation energy E of this step is 296.99 kJ·mol−1, and the pre-exponential factor ln A is 39.99 s−1. The thermodynamic parameters, Gibbs energy (ΔG≠), enthalpy (ΔH≠), and entropy (ΔS≠) of activation, at the peak temperatures were also calculated. The heat capacity of [Ho(BA)3phen]2 was measured by differential scanning calorimetry (DSC) over the temperature range from (254 to 470) K. In addition, the values of the experimental heat capacities were fitted to a polynomial equation with the least-squares method.