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abstracts
Permanent magnet material with high maximum energy product is demanded for industrial applications such as high-efficiency motors for hybrid and electric vehicles. Maximum energy product depends on the coercive force and the saturation magnetization. In order to achieve the high maximum energy product, current Nd-Fe-B magnets are doped with heavy rare-earth element Dy to enhance the coercive force at the expense of reducing the saturation magnetization. Viewed from another side, a supply of Dy is highly concerned because of the inequitable distribution of rare-earth resources on the Earth. Therefore, development of a Dy-free Nd-Fe-B magnet is desired. In this context, we have fabricated the Dy-free Nd-Fe-B nanocrystalline magnet and performed the small-angle neutron scattering (SANS) experiment to reveal the mechanism of its coercive force. Hot-deformed Nd-Fe-B nanocrystalline magnets with and without the diffusion process of Pr-Cu eutectic alloy were prepared [1]. Coercive forces were 1.46 T and 2.64 T for as-deformed and Pr-Cu infiltrated sample, respectively. Magnetic field dependent SANS experiment was performed to observe the magnetization reversal process. The reversal magnetic field was swept from 0 T to 5 T. SANS intensities exhibit maxima around the coercive force for both as-deformed and infiltrated sample, which indicates the evolution of the magnetic domain structure. In addition, suppressed intensity variation in infiltrated sample compared to that in as-deformed sample indicates the magnetic isolation of Nd2Fe14B grains, which is responsible for the high coercive force. We will compare the results for Pr-Cu infiltrated sample with Nd-Cu infiltrated one [1]. This work was supported by the Elements Strategy Initiative Center for Magnetic Materials under the outsourcing project of the MEXT, Japan. We thank HZB for the allocation of neutron beamtime (Proposal No. MAT-04-2110). The sample preparation was performed under the MagHEM project.
abstracts
Diboronic acid and racemic tetrol are found to form a self-assembled macrocyclic boronic ester in the presence of appropriate guest molecules[1]. In the crystal, stacking of macrocyclic ring is observed to form infinite channel structure accommodating guest molecules by supramolecular interactions. In such structure, it is important to investigate the guest uptake and release mechanism via the crystal structure determination of the guest-free apohost. However, the apohost crystal can only be obtained by guest release process by heating, which results to form powder crystals. In this study, the structure of apohost was determined by "Structure Determination from Powder X-ray Diffraction data" technique [2][3] and the structural change by guest sorption and desorption processes were investigated. The powder X-ray diffraction pattern of the toluene inclusion crystal and the apohost crystal, which was obtained by heating of the inclusion crystal, are significantly different. However, even after the guest release, the apohost structure determined from the powder X-ray diffraction data was found to retain its crystal packing with one dimensional guest free channel. Interestingly, the apohost crystal easily absorbs the toluene and other aromatic molecules when the vapor was applied, and the crystal transforms into the guest inclusion crystal. Also, such vapor application is interesting method to switch the physicochemical property of the crystal. When naphthalene vapor was applied to the apohost crystal, naphthalene inclusion crystal was readily formed, and it became fluorescent crystal. This property was switched off by heating and guest desorption. In summary, the macrocyclic boronic ester is promising compound that forms inclusion supramolecular crystal, which can be utilized as guest storage / release, separate, protect, and other physicochemical functional material.
abstracts
N-salicylideneaniline derivatives are known to show photochromism by UV light, and it depends on the molecular conformation in the crystal. The twisted molecule is photochromic but the planar one is not[1,2]. N-salicylidene-2-aminopyridine (2SAP) always has a planar conformation due to the chemical structure without steric hindrance, therefore 2SAP is known as non-photochromic. However, by confining the molecule in a cavity of the macrocyclic boronic ester 1[3], the conformation and photochromism can be controlled. The inclusion crystal of 1 (homo-parallel form) has a special feature to have a channel type crystal structure in which the macrocyclic ring aligned one-dimensionally to include guest molecules. Interestingly, the crystals can reversibly absorb/desorb guests maintaining the crystal structure, because the channel structure is robust. To exchange the included guests, the crystal of 1(homo-parallel form) was immersed in the melt of 2SAP at 90°C. The obtained inclusion crystal showed photochromism. In the crystal structure, the shape of residual electron density for 2SAP indicated the conformation of 2SAP was twisted due to the confining in the cavity, which is the reason for photochromism. On the other hand, the recrystallization of 1 and 2SAP from THF / hexane solution unexpectedly gave hetero-antiparallel form of 1 because of the dynamic covalent bond formation in the boronic esters (Fig.). As this hetero-antiparallel form has planar cavity in the molecule, the conformation of the included guest molecule, 2SAP, is also planar as always seen. Therefore the inclusion crystal is non-photochromic. Thus, photochromism change of 2SAP was realized by conformational control through confining in the cavity of macrocyclic boronic ester.
abstracts
Macrocyclic boronic esters (1) are obtained as a self-assembled molecule by condensation reaction between rac-tetrol (2) and 1,4-naphthalenediboronic acid (3) in the presence of toluene molecule [1]. In the crystal, this macrocyclic molecules form a charasteristic one dimensional channel structure that accommodates various small molecules. Interestingly, reversible desorption / absorption phenomena of guest molecules is observed without significant crystal packing change, meaning this crystal may have guest storage, separation, and catalytic abilities. In the course of exploring further functional aspects of the molecule, we give fluorescence property to this crystal by inclusion of acene molecules into this robust one dimensional channel structure. Naphthalene inclusion crystal was obtained by the diffusion method. The crystal structure is isostructural to known crystals, that is, a naphthalene molecule is included in a channel and sandwiched by two naphthalene moieties of the macrocyclic molecule (inter planar distance is about 3.6 angstrom). Under UV light, a blue color fluorescence observed in this crystal, suggesting the guest naphthalene molecule contributes the fluorescence property. After heating by 200 degrees C, the naphthalene was released to leave isostructural apohost crystal without fluorescence property. However, by naphthalene vapor exposure to the apohost crystal, the fluorescence property was recovered, which means naphthalene desorption and absorption are possible in crystalline state. Moreover Anthracene and Tetracene inclusion crystal were obtained, and they also showed light blue and yellow color fluorescence under UV light, respectively. Thus, the fluorescence function was successfully realized by inclusion of acene molecule in the one dimensional channel of the crystals, and furthermore the fluorescent color can be controlled by changing acene molecules.
abstracts
Macrocyclic compound has been attracting increasing attention because of their application for guest absorption and storage, guest selectivity, and reaction environment, which would utilize void space in the compound. Recently, such macrocyclic compound, boronic esters, has found to be formed as dynamic self-assembly of organic molecules through solvent dependent dynamic covalent bond formation between racemic polyol and planar 1,4-benzen(boronic acid)[1]. Thus, it is important to determine the crystal structure of the macrocyclic boronic esters with incorporated guest molecule to reveal the features of the compounds. In this study, structures of boronic ester of 1,4- naphthalene(boronic acid) (1) are presented and compared. The boronic ester with toluene guest molecule crystalized in monoclinic system, C2/c, Z=4, V=5099.7(6) Å3. As expected, toluene molecule was accommodated within a ring sandwiched by two naphthalene rings suggesting π-π interaction (ca. 3.6 Å separations). It is interesting that other structures of 1 with 1,4-dicyanobenzene, chloroform, and THF also have isomorphic structures to 1 with toluene. It clearly shows the guest inclusion ability of this boronic ester by weak intermolecular interactions. In the crystal structures, the boronic ester aligned along b-axis forming one-dimensional stacking with channel structure filled with guest molecules. Also, 1 with chloroform has a pseudo-polymorph phase (P21/c, V=5780.8(13) Å3) that has two additional chloroform molecules inside and outside of the ring; however, it also shows similar one-dimensional stacking structure with channel, implying this boronic ester has an easily stacking molecular shape. Although, the molecules have similar [2+2] ring structure, dihedral angle between two facing naphthalene rings is different in 1 with toluene, which is smaller as 14.10 than 22 to 240 in other structures. It may indicate a flexibility of the macrocyclic ring.
abstracts
Rare earth intermetallic compound Sm2Fe17N3 exhibits notalble magnetic properties such as high Curie temperature and high coercivity which are very suitable for permanent magnets [1,2]. Although microscopic magnetic structure is one of the basic information for magnetic materials, there is no report about the magnetic structure of Sm2Fe17N3 for our knowledge. This is because samarium's neutron absorption cross section is huge enough to make researchers hesitate to have neutron diffraction experiments of Sm compounds. We have carried out powder neutron diffraction measurement of Sm2Fe17N3 with a straightforward solution to the problem by taking long measurement time. Synchrotron x-ray diffraction measurements with single crystal has also been done to obtain initial crystal structure parameters for magnetic structure analysis and we have succeeded to analyze the magnetic structure of Sm2Fe17N3 at room temperature. Among four Fe sites in the unit cell, while one Fe site which is the nearest neighbor of nitrogen shows smaller magnetic moment than normal iron, two Fe sites show enhancement in their magnetic moments. This phenomenon can be understood as 'cobaltization' of Fe by the adjacent nitrogen through hybridization.
