Phase transition in hydrazinium hydrogen oxalate. A calorimetric study of the short hydrogen bond system |
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| Institution: | 1. Department of Chemistry, Govt. Degree College, Dharmanagar, Tripura(N) 799253, India;2. Department of Chemistry, Nagaland University, Lumami, Nagaland 798627, India;3. Faculty of Engineering, Department of Fundamental Sciences, Samsun University, Samsun 55420, Turkey;4. Faculty of Arts and Sciences, Department of Physics, Ondokuz Mayıs University, Samsun 55139, Turkey;5. Department of Chemistry, Milki High School, Milki, Malda 732209, India;6. Department of Chemistry, Faculty of Science, University of Maragheh, P.O. Box 55181-83111, Maragheh, Iran;7. Molodogvardeyskaya Str 244, Samara State Technical University, Samara 443100, Russian Federation;8. Department of Inorganic and Structural Chemistry, Howard University, Washington DC 20059, United States;9. Department of Chemistry, University of Washington, Seattle, WA 98195, United States;10. Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, United States;11. Faculty of Chemistry, University of Wroclaw, Wroclaw 50383, Poland |
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| Abstract: | The heat capacity of hydrazinium hydrogen oxalate crystal has been measured between 14 and 300 K. A first-order phase transition was found at 217.6 K. Total transition enthalpy and entropy are 1.09 kJ mol−1 and 4.18 J K−1 mol−1, respectively. The high temperature phase supercooled to 165−170 K. The heat capacity of the supercooled high temperature phase was significantly larger than that of the low temperature phase. By fitting a Schottky heat capacity function to the heat capacity difference, a Schottky energy level was found at (135 ± 4) cm−1 above the ground state and related to the tunneling splitting of the energy levels of the short acidic hydrogen bond. A thermodynamic model of the first-order transition is proposed in which the Schottky anomaly plays the main role. Far-infrared spectra of hydrazinium hydrogen oxalate are reported for the frequency range 400–30 cm−1 at temperatures of 295 and 90 K. |
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