Low-temperature thermodynamic properties of dimeric tris(2,2,6,6-tetramethyl-3,5-heptanedionato) europium

• Published in: The Journal of chemical thermodynamics Vol. 140; p. 105904
• Main Authors: Bespyatov, M.A., Cherniaikin, I.S., Stabnikov, P.A., Tsygankova, A.R., Kuzin, T.M., Gelfond, N.V.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-2020
• Subjects: Adiabatic calorimetry; Europium (III) beta-diketonates; Low-temperature heat capacity; Thermochromism; Thermodynamic functions; Low-temperature heat capacity; Thermodynamic functions; Europium (III) beta-diketonates; Adiabatic calorimetry; Thermochromism
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/j.jct.2019.105904

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•The sample of [Eu(C11H19O2)3]2 was synthesized and purified.•The temperature dependence of heat capacity of [Eu(C11H19O2)3]2 has been measured.•An anomaly of heat capacity has been discovered with a maximum at Tc = 262.36 K.•A reversible color change of the sample upon cooling below 245 K was detected.•Thermodynamic functions in a range (0–312) K have been calculated.
A sample of dimeric tris(2,2,6,6-tetramethyl-3,5-heptanedionato) europium ([Eu(C11H19O2)3]2 or dipivaloylmethanate europium) was synthesized. Chemical analysis, elemental analysis and X-ray crystallography were used to characterize composition and structure of the complex. Low-temperature heat capacity of the sample was measured by adiabatic method in a temperature range from 8.63 K to 312.90 K. The Debye temperature at 0 K was calculated. Thermodynamic functions (entropy, enthalpy, reduced Gibbs energy) in a range (0–312) K have been calculated using the obtained experimental heat capacity data. An anomaly in the functional behaviour of heat capacity was detected in a temperature range from 250 K to 270 K, with a maximum at Tc = (262.36 ± 0.01) K. A reversible colour change (thermochromism) of europium dipivaloylmethanate crystals upon cooling below 245 K was detected. Anomalous contributions to entropy and enthalpy have been revealed. The nature of the effects detected is discussed.