Taro Eguchi

Structural study of phosphate groups in layered metal phosphates byhigh-resolution solid-state31P NMR spectroscopy

In studies of a series of crystals of layered metal phosphate compounds by magic angle spinning (MAS) NMR spectroscopy, it has been found that there is a distinct correlation between the 31 P isotropic chemical shift value and the type of phosphate group. The isotropic 31 P chemical shifts of (H 2 PO 4 ) - , (HPO 4 ) 2- and (PO 4 ) 3- groups appear around δ -10, -20 and -30, respectively. These assignments were made unambiguously by measuring the 31 P MAS NMR spectra with and without 1 H high-power decoupling together with the cross-polarization transfer technique between 1 H and 31 P nuclei (CP MAS spectra).

Molecular motions in polymorphic forms of ethanol as studied by nuclear magnetic resonance

Measurements were made of the temperature dependence of the N.M.R. lineshape between 32 and 159 K and the spin-lattice relaxation time T 1 between 56 and 190 K at 10 MHz to study the molecular motion in various states of ethanol and ethanol-D. The methyl group reorientation about C 3 axis is the main relaxation mechanism in the stable crystalline phase, having an activation energy of 12·6 kJ mol-1 and τc 0 = 3·3 × 10-13 s. The molecular tumbling together with rapid methyl rotation is responsible for the dominant relaxation mechanism in the undercooled liquid and the metastable plastic phase. On the other hand, T 1 in the glassy liquid and the glassy crystal may be described by a quantum picture, i.e. the tunnelling rotation of the methyl group. The slope of the T 1 curve for these glassy states corresponds to the separation between the ground and the first excited torsional levels, which is 1·9 kJ mol-1. The tunnelling splitting was deduced to be 15 ± 5 MHz and the barrier height 8 ± 1 kJ mol-1.

Molecular Motions and Phase Transitions in Solid CH3NH3PbX3 (X = C1, Br, I) as Studied by NMR and NQR

Abstract The temperature dependence of 35C1, 81Br, and 127I NQR frequencies and 1Hspin-lattice relaxation times (T1) for CH3NH3PbX3 (X = Cl, Br, I) was measured through the successive phase transitions in these solids. The isotropic reorientation of the CH3NH3 ions takes place in the higher-temperature phases (tetragonal [I4/mcm] and cubic) of the three salts (Ea= 11 kJ mol -1). T1s in the lowest-temperature phases (orthorhombic) indicate that the cations undergo correlated C3-reorientation in the chloride (Ea = 5.45 kJ mol -1)and in the iodide (Ea = 5.80 kJ mol -1, whereas correlated (Ea = 2.40 kJ mol-1) and uncorrected (Ea = 7.50 kJ mol-1) C3- reorientations are excited in the bromide. It is also revealed that the rotational tunneling of the cations governs T1 at lowtemperature region in the orthorhombic phases of these salts

Preparation and characterization of a new inclusion compound with a 1D molecular arrangement of organic radicals using a one-dimensional organic homogeneous nanochannel template

A new inclusion compound with a one-dimensional molecular arrangement of organic radicals (2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)) was prepared using the template compound of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) by the following two methods: i) adsorption of TEMPO vapor under vacuum at 313 K and ii) slow recrystallization in mesitylene. The arrangement of TEMPO molecules in the TPP 1D nanochannel was confirmed by thermogravimetric analysis (TG), powder XRD and ESR measurements. TEMPO molecules were accommodated in the TPP nanochannel with no decomposition, and were arranged with the orientation of the nitroxide group in the TEMPO molecule perpendicular to the axis of the nanochannel. The TPP/TEMPO inclusion compound can include TEMPO molecules up to one molecule per unit cell in the TPP crystal lattice.

Positron annihilation and 129Xe NMR studies of free volume in polymers

Abstract The existence and the average size of free volume in bisphenol-A polycarbonate (PC), low-density polyethylene (LDPE), poly (2,6-dimethyl-phenyleneoxide)(PPO), and polytetrafluoroethylene (PTFE) were studied by positron annihilation and 129 Xe NMR measurements. The 129 Xe NMR chemical shifts for xenon adsorbed in the polymers indicated that the average pore size of the free volume increased in the following order: PC, LDPE, PPO, and PTFE. This order of the pore size of the free volume agrees well with that estimated from the longest lifetime ( τ 3 ) of ortho -positronium formed in the polymers. The unique correlation that δ −1 ∝ r is established between the 129 Xe NMR chemical shift ( δ ) and the pore size ( r ), which is deduced from the positron annihilation measurements.

Unusual adsorption mechanism for carboxylic acid gases by polyamine-intercalated α-zirconium phosphate

The adsorption mechanism of gaseous carboxylic acid by diethylenetriamine- or pentaethylenehexamine-intercalated α-zirconium phosphate was examined in detail using XRD and solid-state 13C and 31P NMR. The adsorption of acetic acid, propanoic acid, and butyric acid resulted in the co-intercalation of the carboxylic acid molecules into polyamine-intercalated α-zirconium phosphate to expand their interlayer distance by 0.64–0.97 nm. In the case of formic acid, its adsorption induced the rearrangement of the polyamine molecules within the interlayer space.

High-pressure 129Xe NMR study of supercritical xenon confined in the mesopores of FSM-16

Pressure (0–10 MPa) and pore size dependence of 129Xe NMR spectra of xenon confined in FSM-16 (pore diameter d = 1.9, 2.7, 4.1 nm) were measured by a high-pressure NMR probe. In the sample with d = 1.9 nm pores, the 129Xe spectrum of the confined xenon had a peak at ca. 95 ppm (P = 0.3 MPa) and consisted of two components above 2 MPa, a high field one due to relatively mobile xenon and a low field one due to strongly adsorbed xenon. The line-width of the weakly confined xenon broadened with increase in pressure and reached a maximum in the vicinity of the critical point of free xenon gas, while that of the bulk xenon remained almost constant in the whole pressure range of the measurement. In the sample with d = 4.1 nm pores, the line shape of the confined xenon could be described by a single component, implying that a type of critical phenomenon took place in the mesopores with a wide opening in the vicinity of the critical point of the bulk xenon. In order to investigate the exchange between the free and the confined xenon, 2D-exchange NMR spectra was measured.

High-pressure spectroscopic studies of reactions of the clusters [Rh4(CO)12–x{P(OPh)3}x](x= 1–4) with carbon monoxide or syngas

The fragmentation and recombination reactions of the clusters [Rh4(CO)12–xLx][L = P(OPh)3, x= 1–4] under applied pressure of CO or CO–H2(1:1) gases have been studied by multinuclear NMR spectroscopy using a high-pressure, high-resolution cell and by high-pressure, IR spectroscopy. Fragmentation to mixtures of dinuclear species [Rh2(CO)8 –xLx](x= 0–2) is observed. The proportions of the variously substituted dimers in the fragmented mixture depends both on the cluster originally present in the solution and on the rhodium concentration. The dimers undergo a fluxional process analogous to that found in [Co2(CO)8]. Recombination on depressurisation can occur either to predominantly the original Rh4 derivative or to mixtures in which several Rh4 species are present in comparable amounts depending on the rhodium to phosphorus ratio. No evidence has been obtained for the formation of hydride species [RhH(CO)4–xLx](x= 0 or 1).

Preparation and Characterization of Inclusion Compounds Using TEMPOL and an Organic 1-D Nanochannel as a Template

Inclusion of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPOL) radical into an organic one-dimensional (1-D) nanochannels formed in guest-free tris(o-phenylenedioxy)cyclotriphosphazene (TPP) was attempted. The inclusion of TEMPOL molecules adsorbed into the TPP nanochannel and their molecular orientation and dynamics were confirmed by temperature-dependent election spin resonance (ESR) measurements. In the specimens prepared by co-precipitation, the existence of 1-D spin diffusion was suggested from the ESR line shape, but the diffusion was not as effective as in the case of the TPP and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) inclusion compound reported in our previous article. These results imply a new methodology for the preparation of a new organic magnet using TPP as a template.

Adsorption of Carboxylic Acids by Diethylenetriamine Intercalation Compound of α-Zr(HPO4)2 · H2O

Abstract Two kinds of diethylenetriamine (2E3A) intercalation compounds of α-zirconium phosphate with different interlayer distances could be obtained by regulating the reaction time and temperature. Phase I (d = 10.2 Å) slowly transforms to Phase II(d = 15. 8 Å) with transformation enthalpy of 30 kJ-mol−1 in 2E3A aqueous solution. The conformation of 2E3A in Phase I and Phase II were confirmed to be bent and all trans (straight) forms by31P MAS NMR and XRD measurements. Two phases have different adsorption behavior for gaseous carboxylic acids. Phase II can adsorb considerable amount of carboxylic acids whereas Phase I adsorb a little.