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

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.

Multiple Ca(2+) environments in silicate glasses by high-resolution (43)Ca MQMAS NMR technique at high and ultra-high (21.8 T) magnetic fields.

We here show the (43)Ca 5QMAS NMR spectra at high field (16.4 T) and the first 7QMAS spectrum at ultra-high field (21.8 T) for geologically important Ca-containing glasses. The high-resolution MQMAS spectra present a clear evidence of multiple Ca sites in the amorphous structures that have never been identified by other analytical methods. The present study suggests that the Ca(2+) ions are mainly in 7- and 8-fold coordination sites. This will offer valuable insights for dynamic properties of magmatic liquids. The MQMAS NMR technique at high magnetic field is a unique tool to understand the detailed structural information on a specific element in solids including organic and inorganic compounds.

The NQR observation of spin-Peierls transition in an antiferromagnetic MX-chain complex [NiBr(chxn)2]Br2.

81Br Nuclear quadrupole resonance (NQR) measurement was performed in an S = 1/2 one-dimensional Heisenberg antiferromagnetic metal complex [NiBr(chxn)2]Br2 (chxn: 1R,2R-diaminocyclohexane), having a halogen-bridged MX chain structure -Br-Ni3+-Br-Ni3+-Br-. Two 81Br NQR signals were observed below 40 K, while a single signal was observed above 130 K, showing the presence of two nonequivalent bridging Br sites below 40 K. This NQR result together with previously reported magnetic susceptibility and X-ray results indicate the occurrence of a transition into a spin-Peierls state between 40 and 130 K. This communication reports the first spin-Peierls transition in metal complexes in which pure d electrons contribute to the magnetism. In addition, we demonstrated a new experimental method for studying a spin-Peierls system.