Shin'ichi Ishimaru

New rotator phase revealed in di-n-alkylammonium bromides studied by solid-state NMR, powder XRD, electrical conductivity and thermal measurements

1 H NMR linewidth and relaxation times, powder XRD, electrical conductivity and differential scanning calorimetry have been performed on (C n H 2n+1 ) 2 NH 2 Br (n=2, 3 and 4). A new ‘rotator’ phase was revealed at 342481, 293538 and 254563 K, respectively, where rod-like cations perform uniaxial reorientation about the molecular long axis and, at the same time, translational self-diffusion at elevated temperatures. The highly disordered structure was also revealed by the transition entropies, the sum of which, at temperature above 130 K, approached the melting entropy, being as small as ca. 20 J K -1 mol -1 . These properties of the rotator phase are quite analogous to those detected in monoalkylammonium chlorides whose rotator phase can be described as a ‘low-dimensional plastic crystal’. The tetragonal crystal structure in the present rotator phase has space group I4/mmm close to the P4/nmm found for that of the monoalkylammonium salts.

Hydrogen transfer in hydrogen-bonded chloranilic acid studied by 35Cl NQR I – a 1:2 complex with 1,4-diazine

Abstract 35 Cl NQR frequencies and spin-lattice relaxation time ( T 1Q ) and 1 H NMR relaxation times ( T 1H ) in a H-bonded three molecular system, chloranilic acid–1,4-diazine (1:2) were measured to reveal H-motions in a symmetric two H-bonds in solid. A single 35 Cl NQR frequency observed implies that the time-averaged structure of chloranilic acid is roughly monovalent in accordance with p K a values in both acid and base. T 1H temperature dependence was explained by a single relaxation mechanism due to the correlated H-transfer in two H-bonds, while that of T 1Q yielded two relaxation processes. One of these undetected by 1 H NMR was explained by the uncorrelated H-transfer.

New mesophases in ionic crystals: piperidinium perchlorate and nitrate studied by 1H, 2H, 14N and 35Cl NMR

Abstract Measurements of 1H, 2H, 14N and 35Cl NMR, differential thermal analysis, differential scanning calorimetry and powder X-ray diffraction were carried out in solid piperidinium perchlorate and nitrate above room temperature. Two and one solid-solid phase transitions were observed for the perchlorate and nitrate, respectively. The crystal structure in the highest-temperature phase of the perchlorate is CsCl-type cubic ( a = 6.02(6) A and Z = 1 ) while that of the nitrate is NaCl-type cubic ( a = 9.35(5) A and Z = 4 ). In this phase of the perchlorate self-diffusion of the cation and isotropic rotation of both cation and anion were revealed. In the highest-temperature phase of the nitrate, the isotropic rotation of both ions was detected. These phases are highly disordered and especially the phase of the perchlorate can be assigned to an anionic plastic phase.

Spin solitons in halogen-bridged one-dimensional mixed-valence complexes, [MII(en)2][MIVBr2(en)2](ClO4)4 (M: Pt, Pd) studied by 1H NMR and EPR

Temperature and Larmor frequency dependences of 1H NMR spin–lattice relaxation time (T1) in 1-D mixed-valence complexes [M(en)2][MBr2(en)2](ClO4)4 (M: Pt, Pd; en: ethylenediamine) were observed in the ranges 90–330 K and 15–60 MHz. EPR spectra observed for the Pd complex showed the presence of paramagnetic PdIII sites of a temperature independent concentration of 10−4 per Pd site, and a motional narrowing upon heating attributable to thermally activated motions of these sites. The NMR T1 data giving an ω1/2 frequency dependence in the range 100–150 K were successfully analysed by applying the Devreuxs treatment of rapidly 1-D diffusing electron spins. Comparing the present results with the electrical conductivity data, the diffusing paramagnetic spins could be explained by kink-type neutral solitons analogous to the spin soliton model reported for trans-polyacetylene. Diffusion rates of 1012–1013 and 1013–1014 rad s−1 were estimated in Pt and Pd complexes, respectively, below ca. 150 K. This diffusion in the present 1-D structure complexes was shown to be much easier than that in [Pd(chxn)2][PdBr2(chxn)2]Br4 (chxn: 1R,2R-cyclohexanediamine) with 2-D hydrogen bond networks.

Ionic plastic phases in trimethylammonium trifluoroacetate studied by 1H and 19F NMR spectroscopy, X-ray diffraction and thermal measurements

1H and 19F NMR, differential scanning calorimetric and X-ray powder diffraction measurements were carried out in solid trimethylammonium trifluoroacetate, (CH3)3NHCOOCF3. Two solid–solid phase transitions were observed at 307 and 330 K. The structures of the solid phases obtained above 330 K and between 307 and 330 K are CsCl-type cubic and tetragonal, respectively. In the two phases, both cations and anions perform self-diffusion and isotropic rotation. From the dynamic behaviour of the ions together with thermal data, both phases are assignable as ionic plastic phases.

Dynamic behavior of acetonitrile molecules adsorbed in AlPO4-5 and SAPO-5 studied by 1H and 2H NMR

Abstract We studied dynamic behavior of acetonitrile molecules adsorbed in molecular sieves AlPO 4 -5 and SAPO-5 by 1 H and 2 H solid state NMR methods and compared the result with that in bulk acetonitrile. The isotropic rotation of molecules is observed in AlPO 4 -5 above 200 K but they are bound to Bronsted acid sites on the wall in SAPO-5 even at room temperature. An anomalous frequency dependency of 1 H NMR T 1 observed in acetonitrile in SAPO-5 implies a large distribution of the environment around the molecules. This distribution of environment is attributable to the random arrangement in positions of acid sites and acetonitrile molecules. It was shown that molecules in AlPO 4 -5 are movable compared with those in bulk although the interaction with the pore wall seems to hinder motions.

Phase Transition and Cation Dynamics in (CH 3ND 3)Bi 2Cl 11 Crystal as Studied by 1H and 2H NMR

The temperature dependence of the 1 H NMR spin-lattice relaxation time ( T 1 ) and 2 H spectra were measured in (CH 3 NH 3 ) 5 Bi 2 Cl 11 and (CH 3 ND 3 ) 5 Bi 2 Cl 11 to investigate dynamic nature of the paraelectric-ferroelectric phase transition. T 1 anomaly was observed in the close vicinity of the transition temperature of 306.5 K and attributed to critical fluctuation associated with the phase transition. The precessional motion of the methylammonium cation derived from the observed 2 H spectra seems to be concerned with the order-disorder transition expected from the X-ray study.

Dynamic behaviour of triethylamine molecules adsorbed in aluminophosphate (AlPO4-5) and silicoaluminophosphate (SAPO-5) molecular sieves

1 H NMR spectra, second moments of line and spin–lattice relaxation times were measured for triethylamine (TEA) adsorbed in aluminophosphate (AlPO4-5) and silicoaluminophosphate (SAPO-5) molecular sieves in the temperature range 90 K to room temperature. Two modes of motions, molecular reorientations about the pseudo-C3 axis and the isotropic rotation were observed in both systems. The fact that the former motion in SAPO-5 is hindered more than in AlPO4-5 was attributed to the hydrogen-bond formation between Bronsted acid sites and lone-pair electrons in TEA. This difference in interaction was shown to be the origin of the distribution of the motional correlation time (τ) in SAPO-5 less than in AlPO4-5 in which the presence of molecular C3 axes in micropores oriented more randomly than in SAPO-5 result in a marked τ distribution.

Dynamics of n-octylammonium ions intercalated in saponite

Abstract Dynamic behavior of n-octylammonium ions intercalated into saponite was investigated by 2H and 1H solid NMR method. Obtained data indicate distributions in the rate of cationic axial reorientations characterized by the heterogeneity of charge distribution in the saponite layer plane. Above ca. 400 K, in-plane random reorientations of cations were observed as a new kind of motion in the 2-D ionic system.

35Cl NQR Studies of Hydrogen Transfer in Crystalline p-Chlorobenzoic Acid

35Cl NQR frequencies and spin-lattice relaxation times T1Q were measured in p-ClC6H4CO2H(PCB A) and p-ClC6H4CO2D(PCBA-d1) at 77-333 K. T1Q in PCB A gave a shallow minimum of 8.0 ms at ca. 110 K, which could be explained by a double proton transfer mechanism in the carboxylic acid dimer referring to 1H NMR data giving a T1H minimum at almost the same temperature. PCBA-d1, showed temperature dependent NQR frequencies quite analogous to those in PCBA, whereas their T1Q behaviour was quite different in its minimum value and its temperature as well as temperature gradient. These results were explained by suppressed deuteron tunnelling and the Ubbelohde effect.