Low-temperature Heat Capacities and Thermochemistry on the Complex of Erbium Perchlorate with L-α-Glycine [Er2(L-Gly)2(H2O)12](ClO4)6 · 4H2O(s)
You-Ying Dia,* and Zhi-Cheng Tanb
a College of Chemistry and Chemical Engineering, Liaocheng
University, Liaocheng 252059, Shandong Province, P. R. Cnina
b Thermochemistry Laboratory, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian 116023, P. R. China
* Corresponding author: Tel: +86-635-8538299, Fax: +86-635-8239121
E-mail: yydi@lcu.edu.cn, diyouying@126.com
Abstract
A coordination compound of erbium perchlorate with L-α-glycine,
[Er2(Gly)2(H2O)12] (ClO4)6
· 4H2O(s), was synthesized. By chemical analysis, elemental analysis,
FTIR, TG/DTG, and comparison with relevant literature, its chemical composition
and structure were established. The purity was found to be >99.0%, without
melting point. Low-temperature heat capacities were measured by a precision
automated adiabatic calorimeter over the temperature range from 78 to 372 K. An
obvious endothermic peak in the heat capacity curve was observed over the
temperature region of 275–296 K, which was ascribed to a solid-to-solid phase
transition according to the results of TG/DTG analysis. The temperature Ttr,
the enthalpy ∆trHm and the entropy ∆trSm
of the phase transition for the compound were determined to be, Ttrs
= (283.315 ± 0.061) K, (11.026 ± 0.059) kJ mol–1 and (38.918 ± 0.206)
J K–1 mol–1. Two polynomial equations of heat capacities as a
function of the temperature in the regions of 78–275 K and 296–372 K were fitted
by the least square method, respectively. The mechanism about thermal
decomposition of the complex was deduced on the basis of the TG/DTG analysis. In
accordance with Hess law, the standard molar enthalpy of formation for the
complex was determined
as ∆fHmo= –(7794.40±1.01) kJ mol–1, by
an isoperibol solution-reaction calorimeter.
Keywords: Complex of erbium perchlorate with L-α-glycine; Adiabatic calorimetry; Low-temperature heat capacity; Isoperibol solution-reaction calorimetry; Standard molar enthalpy of formation