Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by 35Cl nuclear quadrupole resonance and multi-temperature X-ray diffraction

• Published in: Physical chemistry chemical physics : PCCP 2012-09, Vol.14 (35), p.12347-12354
• Main Authors: Tobu, Yasuhiro, Ikeda, Ryuichi, Nihei, Taka-aki, Gotoh, Kazuma, Ishida, Hiroyuki, Asaji, Tetsuo
• Format: Article
• Language: English
• Subjects: Benzoquinones - chemistry; Hydrogen Bonding; Magnetic Resonance Spectroscopy; Models, Molecular; Morpholines - chemistry; Thermodynamics; X-Ray Diffraction
• ISSN: 1463-9084
• DOI: 10.1039/c2cp41241a

The temperature dependence of (35)Cl NQR frequencies and the spin-lattice relaxation times T(1) has been measured in the wide temperature range of 4.2-420 K for morpholinium hydrogen chloranilate in which a one-dimensional O-HO hydrogen-bonded molecular chain of hydrogen chloranilate ions is formed. An anomalous temperature dependence of the NQR frequencies was analyzed to deduce a drastic temperature variation of the electronic state of the hydrogen-bonded molecular chain. The hydrogen atom distribution in the OHO hydrogen bond is discussed from the results of NQR as well as multi-temperature X-ray diffraction. Above ca. 330 K, the T(1) showed a steep decrease with an activation energy of ca. 70 kJ mol(-1) and with an isotope ratio (37)Cl T(1)/(35)Cl T(1) = 0.97 ± 0.2. The orientational change of the z axis of electric field gradient tensor in conjunction with the hydrogen transfer between adjacent hydrogen chloranilate ions is suggested as a possible relaxation mechanism.