title: Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by 35Cl nuclear quadrupole resonance and multi-temperature X-ray diffraction.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Tsukuba, Tsukuba 305-8571, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tobu
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Ikeda
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Nihei
authors.forename: Kazuma
authors.initials: K
authors.lastname: Gotoh
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ishida
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Asaji
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009025:Morpholines / Q000737:chemistry*; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D016227:Benzoquinones; D009025:Morpholines; C014400:chloranilic acid