Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by 35Cl nuclear quadrupole resonance and multi-temperature X-ray diffractionElectronic supplementary information (ESI) available: CCDC 876320-876326 and 887991. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2cp41241a

• Main Authors: Tobu, Yasuhiro, Ikeda, Ryuichi, Nihei, Taka-aki, Gotoh, Kazuma, Ishida, Hiroyuki, Asaji, Tetsuo
• Format: Article
• Language: English
• ISSN: 1463-9076; 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. The hydrogen atom distribution in the OHO hydrogen bond in morpholinium hydrogen chloranilate is discussed from the results of NQR as well as multi-temperature X-ray diffraction.