Sadafumi Nishihara

Construction of hybrid d10 metal–organic frameworks by flexible aromatic dicarboxylate and N-donor ligands : syntheses, structures and physical properties

Six novel metal coordination polymers with flexible aromatic dicarboxylate ligands and N-donor ligands, Zn2(DPA)2(mbix)(H2O) (1), Cd2(DPA)2(mbix) (2), ZnCd(DPA)2(bix) (3), Cd(SDBA)(mbix)(H2O)2 (4), Cd(SDBA)(bimb) (5) and [Cd(SDBA)(4,4′-bipy)0.5(H2O)]·H2O (6) (H2DPA = diphenic acid, H2SDBA = 4,4′-dicarboxybiphenyl sulfone, mbix = 1,3-bis(imidazol-1-ylmethyl)benzene, bix = 1,4-bis(imidazol-1-ylmethyl)benzene, bimb = 4,4′-bis(imidazol-1-ylmethyl) biphenyl and 4,4′-bipy = 4,4′-bipyridine), have been synthesized and structurally characterized by elemental analysis, IR, TGA and X-ray single crystal diffraction. Complex 1 has a two-dimensional (2D) (3,4)-connected layer network with a novel (62.8)(4.62.83)(4.6.8) topology, whereas complex 2 crystallizes in the chiral space groupP61 and has a guest-free three-dimensional (3D) chiral framework structure with one-dimensional (1D) homochiral chains. Complex 3 shows a complicated 2D framework consisting of a heteroquadrinuclear cluster which comprises a centrosymmetric linear array of two Zn atoms and two Cd atoms which are bridged by carboxylate groups of DPA ligands. Complex 4 presents a puckered chiral layer structure with rare heterostranded double helices. Complex 5 exhibits a 2D chiral structure with an open channel by incorporating the auxiliary bimb ligand, while complex 6 features an uncommon self-penetrating 2D network containing double-stranded helices. The results indicate that the dicarboxylate DPA2− and SDBA2− ligand can adopt varied coordination modes in the formation of the complexes and the configuration and flexibility of the ligands play a key role in directing the related properties of the complexes. The photoluminescence properties of 1–6 were studied in the solid state at room temperature. The nonlinear optical measurements showed that 2 and 5 displayed a second-harmonic-generation (SHG) response of 0.7 and 0.8 times that for urea, respectively. Moreover, the ferroelectric properties of 5 have also been investigated.

Temperature-induced assembly of MOF polymorphs: Syntheses, structures and physical properties

Four new coordination polymers, namely, [Co(BIPA)(titmb)]·H2O (1), [Co3(BIPA)3(titmb)2]·0.73H2O (2), [Ni(SDBA)(bix)]·2H2O (3) and [Ni(SDBA)(bix)(H2O)]·0.38H2O (4) (H2BIPA = 5-bromoisophthalic acid, H2SDBA = 4,4′-dicarboxybiphenyl sulfone, titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-tri-methylbenzene, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), were obtained under hydrothermal conditions. Four complexes were characterized by elemental analyses, IR spectra, thermogravimetric analyses and single-crystal X-ray diffraction. Complexes 1 and 2 are polymorphs formed from Co(II) cations, BIPA2− anions, titmb ligands and water molecules, showing a three-dimensional (3,5)-connected network with the topology of (63)(69.8) for 1 and a three-dimensional (3,4)-connected coordination framework with the topology of (4.6.8)(4.62.83)(6.85)(62.83.10)(83) for 2. Complexes 3 and 4 are also two polymorphs constructed from Ni(II) cations, SDBA2− anions, bix ligands and water molecules. Complex 3 exhibits a two-dimensional lamella structure with (4,4) topology, whereas complex 4 displays a two-dimensional 2-fold interpenetrating (6,3) network. It is shown that the reaction temperature plays a crucial role in the formation of the final products. Moreover, the nonlinear optical and ferroelectric properties of 1 have also been investigated.

Ferroelectric Properties and Nano-Scaled Domain Structures in (1-x)BiFeO3-xBaTiO3 (0.33 < x < 0.50)

We have investigated ferroelectric domain structures in the pseudo-cubic structure of (1-x)BiFeO3-xBaTiO3 with 0.33 < x < 0.50 by the transmission electron microscopy (TEM). High-resolution lattice image reveals that the psudo-cubic structures in the x = 0.33, 0.40 and 0.50 compounds are characterized as nano-scaled coexisting state of the polar rhombohedral structure and the non-polar cubic one. Furthermore, P-E hysteresis curve measurements showed that the x = 0.33, 0.40 and 0.50 compounds are regarded as ferroelectric materials with the spontaneous polarizations of 41 μC/cm2, 21 μC/cm2, and 5 μC/cm2, respectively.

On the Nature of the Structural and Magnetic Phase Transitions in the Layered Perovskite-Like (CH3NH3)2[FeIICl4]

In view of renewed interest in multiferroic for molecular systems, we re-examine the structural and magnetic properties of the potentially ferroic layered perovskite-like (CH3NH3)2[Fe(II)Cl4] due to its high-temperature magnetic ordering transition. The structures from several sets of diffraction data of single crystals consist of square-grid layers of corner-sharing FeCl6 octahedra and changes from the high-symmetry I4/mmm (T > 335 K) to the low-symmetry Pccn (T < 335 K). In the former the iron and bridging chlorine atoms are within the layer and the organic cations sit in the middle of each square grid, while in the latter the octahedra are tilted in pairs, two in and two out, progressively by up to 12° and the nitrogen atoms follow their motion to be nearer to the two-in pairs. Crystals are stable up to 450 K and display three phase transitions, two structural at 332 and 233 K and one magnetic at 95 K. The temperature dependences of the dc magnetization (zero-field and field-cooling modes) in different applied fields (10-10,000 Oe) on several aligned single crystals independently reveal a hidden-canted antiferromagnetic ground state of at least four sublattices and not the reported canted antiferromagnetic ground state. A metamagnetic critical field of only 200 Oe transforms it to a canted antiferromagnet. The estimated canting angle is 1.4° in zero field, and it folds to ca. 2.8° in a field of 50 kOe at 2 K. The easy axis is along 010, the hard axis is along 100, and the intermediate and canting axis is 001. Using the available extracted parameters the phase diagram has been constructed. This study provides evidence of a complex and intricate manifestation of the orientation, temperature, and field dependence of the interplay between anisotropy and coherent lengths, which would need further studies.

High Magnetic Hardness for the Canted Antiferromagnetic, Ferroelectric, and Ferroelastic Layered Perovskite-like (C2H5NH3)2[FeIICl4]

An unusual high magnetic hardness for the layered perovskite-like (C2H5NH3)2[Fe(II)Cl4], in addition to its already found canted antiferromagnetism, ferroelasticity, and ferroelectricity, which are absent for (CH3NH3)2[Fe(II)Cl4], has been observed. The additional CH2 in the ethylammonium compared to methylammonium allows more degrees of freedom and therefore numerous phase transitions which have been characterized by single-crystal structure determinations from 383 to 10 K giving the sequence from tetragonal to orthorhombic to monoclinic (I4/mmm ↔ P42/ncm ↔ Pccn ↔ Pcab ↔ C2/c) accompanied by both tilting and rotation of the FeCl6 octahedra. The magnetic properties on single crystal and powder samples at high temperature are similar for both compounds, but at TN (C2H5NH3)2[Fe(II)Cl4] is a proper canted antiferromagnet unlike the hidden canting observed for (CH3NH3)2[Fe(II)Cl4]. The canting angle is 0.6° toward the c-axis, and thus the moments lie in the easy plane of the iron-chloride layer defined by a critical exponent β = 0.18. The isothermal magnetizations for the field along the three orthogonal crystallographic axes show wider hysteresis for H ∥ c and is present at all temperature below 98 K. The coercive field increases as the temperature is lowered, and at T < 20 K it is difficult to reverse all the moments with the available 50 kOe of the SQUID for both single crystal and powder samples. The shape of the virgin magnetization after zero-field-cool (ZFC) indicates that the high coercive field is due to domain wall pinning. Thus, there are unusual associated anomalies such as asymmetric hysteresis and history dependence. The difference in magnetic hardness of the two compounds suggests that magnetic, electric, and elastic domains are intricately manifested and therefore raise the key question of how the different domains interact.

Electrical Network of Single‐Crystalline Metal Oxide Nanoclusters Wired by π‐Molecules

In a mixed-valence polyoxometalate, electrons are usually delocalized within the cluster anion because of low level of inter-cluster interaction. Herein, we report the structure and electrical properties of a single crystal in which mixed-valence polyoxometalates were electrically wired by cationic π-molecules of tetrathiafulvalene substituted with pyridinium. Electron-transport characteristics are suggested to represent electron hopping through strong interactions between cluster and cationic π-molecules.

Syntheses, Structures and Luminescent Properties of Zinc(II) and Cadmium(II) Complexes With the Ditopic Ligand 1,3-Bis(imidazol-1-ylmethyl)benzene

Three new complexes, namely [Zn(mbix)(SO4)]·CH3OH (1), Cd(mbix)2(NO3)2 (2) and [Cd(mbix)2(H2O)2]·(NO3)2 (3), have been obtained by reactions of flexible bidentate ligand 1,3-bis(imidazol-1-ylmethyl)benzene (mbix) with corresponding zinc(II) and cadmium(II) salts. The structures of these complexes have been determined by the X-ray single crystal diffraction analysis. Complex 1 features a 2D wavy network with (4,4) topology. Complex 2 has a 2D grid network with left- and right-handed helical chains, while complex 3 exhibits twofold parallel interpenetration structure. The differences of three complexes demonstrate that the coordination geometry of metal ions and the ratio of reactants have a great impact on the structure of the supramolecular architectures. The luminescent properties of three complexes are also investigated.Graphical AbstractThree complexes have been constructed by different zinc(II) and cadmium(II) salts with the flexible mbix ligand. The results demonstrate that the metal ion and the ratio of reagents have an important effect on the structure of these complexes.

Appearance of magnetization jumps in magnetic hysteresis curves in spinel oxide FeV2O4

We report the appearance of magnetization jumps in the magnetic hysteresis curves of the spinel oxide FeV2O4, in which two different magnetic transition ions appeared, both of them having orbital degrees of freedom. The spin-glass-like transition was observed from ac magnetic susceptibilities and the transition temperature was estimated to be Tg=85.5 K. The magnetization jumps appear below 90 K at B=0. In addition, jumps at B=±1.2 T appear below 4.6 K. The magnetization jumps at B=0 may be correlated with spin-glass-like behaviors.

A heterospin pressure sensor

The effect of external pressure on the magnetic properties was studied for the first time for heterospin crystals based on the Cu(II) complex with nitroxide [Cu(hfac)2NN-PzMe], which exhibits a spin-crossover-like phenomenon. An increase in the hydrostatic pressure to 0.14 GPa caused a significant shift of the magnetic anomaly temperature (from 150 K to 300 K). This complex actually functions as a highly sensitive external pressure sensor.

Characteristic responses of a phospholipid molecular layer to polyols.

Polyols (sugar alcohols) are widely used in foods, pharmaceutical formulations and cosmetics, and therefore it is important to understand their effects on cell membranes and skin. To address this issue, we examined the effect of polyols (1,2-ethanediol (ethylene glycol), 1,3-butanediol, 1,2,3-propanetriol (glycerol), and 1,2,3,4-butanetetraol) on artificial membrane systems (liposomes, monolayers, or dry films) prepared from phospholipid (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)). 1,2-Ethanediol and 1,3-butanediol had little effect on the size of the DMPC liposomes or the surface pressure (π)-surface area (A) isotherm of DMPC monolayers at an air-water interface, whereas 1,2,3-propanetriol or 1,2,3,4-butanetetraol increased both liposome size and surface pressure. Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and differential scanning calorimetry (DSC) were used to evaluate the interaction between DMPC and polyols. These experimental results suggest that the chemical structure of polyol plays an important role in the characteristic interaction between polyol and DMPC.