Keisuke Miyakubo

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.

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.

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.

Characterization of adsorbed xenon in Zeolite-A, X, and Y by high-pressure 129Xe NMR spectroscopy

The local structure of confined xenon in A-, X- and Y-type zeolites (molecular sieve 5A, 13X and zeolite NaY) was investigated by in situ high-pressure 129Xe NMR spectroscopy. Xenon confined in dehydrated samples gives a resonance peak in the chemical shift range from 50 to 100 ppm at 0.1 MPa, and the chemical shift values increase as pressure increases. The pressure dependence of 129Xe chemical shift on xenon confined in the micropores can be approximately described by the Langmuir adsorption model, resulting in the parameters being able to describe pore diameter, adsorption ability of the pore, and the local structure of the confined xenon atoms. Using these parameters, the pore structure, the mobility and the cluster size of xenon in the micropore are discussed for A- and X-type zeolites. Furthermore, the effect of pre-adsorbed water and the binder for pellet preparation on the pore structure is also examined. In the Y-zeolite, a chemical exchange of xenon between the outside and inside of the micropores was observed above 0.75 MPa. Spectral simulation assuming a simple two-site exchange model revealed the exchange rate constant and the population ratio of xenon in the exchange between the outside and the inside the micropores. The exchange of xenon is optimum around the supercritical point of the bulk xenon (∼6 MPa), and decreases above 6 MPa, and this originates from the cooperative phenomenon in the supercritical fluid.

Specific Molecular Motion of Adamantane Induced by Hydrophobic Nanoslits in ACF as Studied Using Solid-State 1H, 2H, and 13C NMR

Molecular motion of adamantane confined in activated carbon fiber (ACF) with slit-width of 1.1 nm was investigated using solid state 1H, 2H, and 13C NMR analyses. Temperature dependence of the 2H spin-lattice relaxation time revealed that adamantane undergoes rapid isotropic reorientation in ACF that is much faster than in bulk plastic crystal. Temperature dependence of the line width of the 1H NMR spectrum also suggests that adamantane undergoes translational motion in ACF. The single minimum potential profile between adamantane and the pore wall might engender the high mobility of guest adamantane molecules as a “two-dimensional fluid.”

Local structure of xenon adsorbed in the nanospaces of zeolites as studied by high-pressure 129Xe NMR

Pressure (0-10 MPa) and local density dependence of 129Xe NMR chemical shift of xenon in various microporous materials was investigated using an in situ high-pressure probe. The density dependence of the chemical shift was analyzed using virial expansion of the chemical shift by xenon density. Results indicate that the second virial coefficient depends on the pore size and shape, and that the void space affects xenon-xenon interaction in both microporous and mesoporous materials. Furthermore, to interpret the magnitude of the virial coefficient in terms of the local structure of the adsorbed xenon, we analyzed the local structure of adsorbed xenon in molecular sieve 5A using Xe(n) clusters, thereby allowing description of the density dependence of the chemical shift. We also demonstrated the cluster models validity by applying it to molecular sieves 13X and ZSM-5. The latter showed that the adsorbed xenon exists as a xenon monomer up to the filling of about 0.6 in micropores. Larger xenon clusters up to n = 4 have been grown with increasing filling of xenon. According to analyses using the Xe(n) cluster model, the second virial coefficient is related closely with the xenon cluster size, which contributes greatly to the chemical shift in the low loading region.

Intermolecular Interactions of Xe Atoms Confined in One-dimensional Nanochannels of Tris(o-phenylenedioxy)cyclotriphosphazene as Studied by High-pressure 129Xe NMR

The pressure dependence of the 129Xe chemical shift tensor confined in the Tris(o-phenylenedioxy) cyclotriphosphazene (TPP) nanochannel was investigated by high-pressure 129Xe NMR spectroscopy. The observed 129Xe spectrum in the one-dimensional TPP nanochannel (0.45 nm in diameter) exhibits a powder pattern broadened by an axially symmetric chemical shift tensor. As the pressure increases from 0.02 to 7.0 MPa, a deshielding of 90 ppm is observed for the perpendicular component of the chemical shift tensor δ⊥, whereas a deshielding of about 30 ppm is observed for the parallel one, δ‖. This suggests that the components of the chemical shift tensor, δ‖ and δ⊥, are mainly dominated by the Xe-wall and Xe-Xe interaction, respectively. Furthermore, the effect of helium, which is present along with xenon gas, on the 129Xe chemical shift is examined in detail. The average distance between the Xe atoms in the nanochannel is estimated to be 0.54 nm. This was found by using δ⊥ at the saturated pressure of xenon, and comparing the increment of the chemical shift value in δ⊥ to that of a β -phenol/Xe compound.

Temperature Dependence of 2H Nuclear Quadrupole Interaction in Very Short Hydrogen Bonds in Some Organic Acidic Salt Crystals

The 2H nuclear quadrupole interaction parameters, e2Qq/h and η, are closely related to the shape of the potential energy surface at hydrogen bonds and depend sensitively on their geometry. We measured the temperature dependence of the 2H NMR spectra of the crystalline acidic salts KDCO3, KD cetylenedicarboxylate, RbD acetylenedicarboxylate, and KD maleate, which contain very short O-D···O type hydrogen bonds. The temperature coefficient decreases with increase in the O···O distance in the hydrogen bond. Ab inito molecular orbital calculations of the electric field gradient tensor based on the temperature dependent structure of each crystal indicate that thermal expansion of the hydrogen bond geometry is not responsible for this tendency. Ab initio calculations also predict that a fictitious off center shift of the hydrogen position in a symmetric hydrogen bond causes very high e2 Qq/h values. This suggests that low energy vibrational excitation may be responsible for large positive d (e2 Qq/h)/dT values in symmetric hydrogen bonds.

Interlayer reaction of polyamine/α-zirconium phosphate intercalation compounds with some aldehydes

Abstract The intercalation compound between α-zirconium phosphate and N,N′-bis-(3-aminopropyl)-1, 3-propanediamine has two different modifications with respect to the conformation of the guest amine molecules: one is “bent form” and the other “straight form”. Reactivity of each phase with a series of aldehydes was examined. 13C CP/MAS NMR indicated that the tetraamine reacts stereoselectively with aldehydes to form cis-imine in the interlayer spacing. Depending on the molecular size of aldehyde, it is found that a significant difference can be recognized in the yields of the imine products for the two phases of intercalation compounds. It is also noted that residual water molecules in the interlayer spacing play an important role in the imine formation reaction.

Syntheses of intercalation compounds of tetraamine in α-Zr(HPO4)2·H2O and the structures of guest molecules by solid state NMR

Abstract Conformational change of N,N ′-Bis-(3-aminopropyl)-1,3-propanediamine (3P4A) intercalated in α-zirconium phosphate (α-ZrP) is reported. It is demonstrated that two kinds of intercalation compounds with different interlayer spacings, i.e., d =2.0 nm and d =1.7 nm, can be isolated by reacting at ca. 333 K and at ca. 298 K in aqueous suspension of 3P4A and α-ZrP, respectively. The lineshape analysis of 13 C CP/MAS NMR spectra suggests that the conformation of 3P4A assumes the ‘straight’ form in the higher temperature product while it assumes the ‘bent’ form in the lower temperature product. According to this model, 31 P MAS NMR spectra can be consistently assigned. It is found that 31 P chemical shift values strongly depend on the bonding state of the amine groups in 3P4A molecule to the phosphate groups of α-ZrP. It is also shown that removing and/or controlling the amount of water molecules in the intercalation compounds are very important for the detailed assignment of the complicated 31 P resonances.