Sadamu Takeda

Ferroelectricity and polarity control in solid-state flip-flop supramolecular rotators

Molecular rotation has attracted much attention with respect to the development of artificial molecular motors, in an attempt to mimic the intelligent and useful functions of biological molecular motors. Random motion of molecular rotators--for example the 180 degree flip-flop motion of a rotatory unit--causes a rotation of the local structure. Here, we show that such motion is controllable using an external electric field and demonstrate how such molecular rotators can be used as polarization rotation units in ferroelectric molecules. In particular, m-fluoroanilinium forms a hydrogen-bonding assembly with dibenzo[18]crown-6, which was introduced as the counter cation of [Ni(dmit)(2)](-) anions (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate). The supramolecular rotator of m-fluoroanilinium exhibited dipole rotation by the application of an electric field, and the crystal showed a ferroelectric transition at 348 K. These findings will open up new strategies for ferroelectric molecules where a chemically designed dipole unit enables control of the nature of the ferroelectric transition temperature.

Solid-State Molecular Rotators of Anilinium and Adamantylammonium in [Ni(dmit)2]-Salts with Diverse Magnetic Properties

Supramolecular rotators of hydrogen-bonding assemblies between anilinium (Ph-NH 3 (+)) or adamantylammonium (AD-NH 3 (+)) and dibenzo[18]crown-6 (DB[18]crown-6) or meso-dicyclohexano[18]crown-6 (DCH[18]crown-6) were introduced into [Ni(dmit) 2] salts (dmit (2-) is 2-thioxo-1,3-dithiole-4,5-dithiolate). The ammonium moieties of Ph-NH 3 (+) and AD-NH 3 (+) cations were interacted through N-H (+) approximately O hydrogen bonding with the six oxygen atoms of crown ethers, forming 1:1 supramolecular rotator-stator structures. X-ray crystal-structure analyses revealed a jackknife-shaped conformation of DB[18]crown-6, in which two benzene rings were twisted along the same direction, in (Ph-NH 3 (+))(DB[18]crown-6)[Ni(dmit) 2] (-) ( 1) and (AD-NH 3 (+))(DB[18]crown-6)[Ni(dmit) 2] (-) ( 3), whereas the conformational flexibility of two dicyclohexyl rings was observed in (Ph-NH 3 (+))(DCH[18]crown-6)[Ni(dmit) 2] (-) ( 2) and (AD-NH 3 (+))(DCH[18]crown-6)[Ni(dmit) 2] (-) ( 4). Sufficient space for the molecular rotation of the adamantyl group was achieved in the crystals of salts 3 and 4, whereas the rotation of the phenyl group in salts 1 and 2 was rather restricted by the nearest neighboring molecules. The rotation of the adamantyl group in salts 3 and 4 was evidenced from the temperature-dependent wide-line (1)H NMR spectra, dielectric properties, and X-ray crystal structure analysis. ab initio calculations showed that the potential energy barriers for the rotations of adamantyl groups in salts 3 (Delta E approximately 18 kJmol (-1)) and 4 (Delta E approximately 15 kJmol (-1)) were similar to those of ethane ( approximately 12 kJmol (-1)) and butane (17-25 kJmol (-1)) around the C-C single bond, which were 1 order of magnitude smaller than those of phenyl groups in salts 1 (Delta E approximately 180 kJmol (-1)) and 2 (Delta E approximately 340 kJmol (-1)). 1D or 2D [Ni(dmit) 2] (-) anion arrangements were observed in the crystals according to the shape of crown ether derivatives. The 2D weak intermolecular interactions between [Ni(dmit) 2] (-) anions in salts 1 and 3 led to Curie-Weiss behavior with weak antiferromagnetic interaction, whereas 1D interactions through lateral sulfur-sulfur atomic contacts between [Ni(dmit) 2] (-) anions were observed in salts 2 and 4, whose magnetic behaviors were dictated by ferromagnetic (salt 2) and singlet-triplet (salt 4) intermolecular magnetic interactions, respectively.

Metal–organic frameworks of manganese(II) 4,4′-biphenyldicarboxylates: crystal structures, hydrogen adsorption, and magnetism properties

Reactions of 4,4′-biphenyldicarboxylic acid (H2bpdc) with manganese(II) nitrate under solvothermal conditions yield two types of new metal–organic frameworks, [Mn4(bpdc)4(DMF)3](DMF) (1) (DMF = N,N′-dimethylformamide) and Mn3(bpdc)3(DMA)4 (2) (DMA = N,N′-dimethylacetamide). Structural analysis shows different solvents lead to distinct phases of manganese(II) 4,4′-biphenyldicarboxylate although the same starting materials are employed. Complex 1 features a microporous noninterpenetrated structure with nano-sized channels and a rare cem topological net, while 2 is non-porous with an α-polonium topology. Microporous 1 exhibits significant hydrogen adsorptive capability. Magnetic behaviors of the both complexes suggest the presence of antiferromagnetic interactions.

Synthesis and gas-occlusion properties of dinuclear molybdenum(II) dicarboxylates (fumarate, terephthalate, trans-trans-muconate, pyridine-2,5-dicarboxylate, and trans-1,4-cyclohexanedicarboxylate)

The bis-μ-dicarboxylate molybdenum(II) complexes Mo(II)2L2 (L = trans-O2C-CH-CH-CO2 (1), p-O2C-C6H4-CO2 (2), trans-trans-O2C-CH-CH-CH-CH-CO2 (3), 2,5-O2C-C5H3N-CO2 (4), and trans-O2C-C6H10-CO2 (5)) were prepared and their gas-occlusion properties were characterized. The dinuclear complexes have quadruple Mo-Mo bonds, with the ground electronic configuration (σ)2(π)4(δ)2. All of these complexes are capable of occluding a large amount of gas (1 or 2 mol of N2 gas per 1 mol of molybdenum atoms). Investigation of the structures of these complexes indicates that gases are most probably occluded in homogeneous and linear micropores which are composed of micropore units surrounded by four dicarboxylate bridges. 13C-CP/MAS NMR measurements indicate that gas molecules are held in the micropores created by the dicarboxylate ligands.

Metal–organic coordination architectures with 3-pyridin-3-yl-benzoate: crystal structures, fluorescent emission and magnetic properties

Reactions of 3-pyridin-3-yl-benzoic acid (HL) with metal nitrates under hydrothermal conditions yield seven new coordination polymers: Ni(L)2(H2O)2 (1), [Ni(L)2](H2O) (2), Co(L)2(H2O)2 (3), [Zn(L)2](H2O) (4), Cu(L)2 (5), Cd(L)2 (6) and Gd2(L)6(H2O)4 (7). A systematic investigation on coordination chemistry of the ligand and the significant function of supramolecular interactions in managing the resultant crystalline networks has been carried out. On the basis of the X-ray diffraction analysis of these complexes, the results show that complexes 1–5 and 7 form similar one-dimensional (1D) double-chain coordination arrays, among which 1 and 3, as well as 2 and 4, are isostructural. Remarkably, distinct network architectures are further constructed with the aid of weak secondary interactions. Amongst them, complexes 1, 3 and 5 exhibit the classical α-polonium networks, while complexes 2 and 4 present the (3,4)-connected two-dimensional layers. In 7, the intermolecular π–π stacking interactions lead to the formation of a double-strand structure. The CdII complex 6 assembles into a three-dimensional metal–organic framework exhibiting a unique 6-connected roa topology. The trans-configuration of L ligand is only found in the case of 6, whereas the cis-ligands are generally observed in these complexes. The fluorescent emission properties of 4 and 6 as well as the magnetic property of 7 have also been investigated.

Ionic Channel Structures in [(M+)x([18]crown‐6)][Ni(dmit)2]2 Molecular Conductors

The [(M+)x[18]crown-6)] supramolecular cations (SC+), in which M+ and [18]crown-6 are alkali metal ions (M+ = Li+, Na+, and Cs+) and 1,4,7,10,13,16-hexaoxacyclooctadecane, respectively, form ionic channel structures through the regular stacks of [18]crown-6 in [Ni(dmit)2]-based molecular conductors (dmit2+ = 2-thioxo-1,3-dithiole-4,5-dithiolate). In addition to the [Ni(dmit)2] salts that have the ionic channel structures (these salts are abbreviated as type I salts), Li+ and Na+ form dimerized [(M+)2([18]crown-6)2] units in the crystals (type II salts). The K+ and Rb+ are coordinated tightly into the [18]crown-6 cavity to form typical disk-shape SC+ units in the corresponding [Ni(dmit)2] salts (type III salts). The type I, II, and III salts have typical stoichiometries of [(M+)x([18]crown-6)][Ni(dmit)2]2, [(M+)([18]crown-6)(H2O)x(CH3CN)(1.5 - x)][Ni(dmit)2]3 (x = 1 for Li+ or 0.5 for Na+), and [M+([18]crown-6)][Ni(dmit)2]3, respectively: the salts of the same type are isostructural. In agreement with the trimer structures of [Ni(dmit)2] in the type II and III salts, they exhibit semiconducting behavior with electrical conductivities at 300 K (sigma(300 K)) of 0.01-0.1 S cm(-1). Type I salts contain a regular stack of partially oxidized [Ni(dmit)2] units, which form a quasi one-dimensional metallic band within the tight-binding approximation regime. The electrical conductivities at 300 K are 10-30 S cm(-1), and an almost temperature-independent conductivity was observed at higher temperatures. However, the one-dimensional electronic structures in these salts are strongly influenced by the static and dynamic structures of the coexisting ionic channel. The Na+ salt is a semiconductor, whose magnetic behavior is described by the disordered one-dimensional antiferromagnetic chain. On the other hand, the Cs+ salt is a exhibits metallic properties with 2 kF instability at room temperature. The Li+ salt shows a gradual transition from the high-temperature metallic phase to the low-temperature one-dimensional antiferromagnetic semiconductor phase, which was associated with the freezing of Li+ motion at lower temperatures. The preferential crystallization of type I salts was possible by controlling the equilibrium constant (Kc) of the complex formation between M+ ions and the [18]crown-6 molecule. The ionic channel structures were obtained when the KC was low in the electrocrystallization solution, while type II or III salts were formed in the high Kc region.

Magnetic studies of the trinuclear center in laccase and ascorbate oxidase approached by EPR spectroscopy and magnetic susceptibility measurements.

The trinuclear centers in Rhus vernicifera laccase and Cucumis sativus ascorbate oxidase have been studied by EPR spectroscopy and magnetic susceptibility measurements over the wide range of 5 K to 300 K. The EPR spectra showed that type II copper receives increasing tetrahedral distortion with raising temperature. Magnetic susceptibilities of laccase showed that both of type I and type II coppers are almost fully paramagnetic since the antiferromagnetic interaction between type III coppers is extremely strong from 5 K to 300 K. On the other hand, the effective magnetic moment of ascorbate oxidase is contributed by ca. 1.7 Cu2+ even below ca. 100 K, since type II Cu is partly in the reduced form. The effective magnetic moment continuously increased with raising temperature because the antiferromagnetic interaction between type III coppers is not as strong as in the case of laccase. The simulation of the SQUID measurement results suggested that the conformational change of the ascorbate oxidase molecule caused the temperature dependence of the antiferromagnetic interaction. The type II Cu EPR signals in laccase and ascorbate oxidase were conspicuously broadened with raising temperature because of the increasing contribution of the triplet state by type III Cus and/or of the rapid relaxation which finally led to only ca. 30% detection of the type II Cu signals at room temperature. The stepwise binding of azide to the trinuclear center made one of type III Cus to be EPR detectable. SQUID measurements indicated that only one Cu in the trinuclear center is paramagnetic and other two Cus are antiferromagnetically coupled for both of the one- and two-azide bound forms. The binding mode of azide to the trinuclear center was discussed based on some models.

Dissipative and Autonomous Square‐Wave Self‐Oscillation of a Macroscopic Hybrid Self‐Assembly under Continuous Light Irradiation

Building a bottom-up supramolecular system to perform continuously autonomous motions will pave the way for the next generation of biomimetic mechanical systems. In biological systems, hierarchical molecular synchronization underlies the generation of spatio-temporal patterns with dissipative structures. However, it remains difficult to build such self-organized working objects via artificial techniques. Herein, we show the first example of a square-wave limit-cycle self-oscillatory motion of a noncovalent assembly of oleic acid and an azobenzene derivative. The assembly steadily flips under continuous blue-light irradiation. Mechanical self-oscillation is established by successively alternating photoisomerization processes and multi-stable phase transitions. These results offer a fundamental strategy for creating a supramolecular motor that works progressively under the operation of molecule-based machines.

Molecular Rotors of Coronene in Charge-Transfer Solids

Ten types of neutral charge transfer (CT) complexes of coronene (electron donor; D) were obtained with various electron acceptors (A). In addition to the reported 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex of 1:1 stoichiometry with a DA-type alternating π column, TCNQ also afforded a 3:1 complex, in which a face-to-face dimer of parallel coronenes (Cor-As) is sandwiched between TCNQs to construct a DDA-type alternating π column flanked by another coronene (Cor-B). Whereas solid-state (2)H NMR spectra of the 1:1 TCNQ complex formed with deuterated coronene confirmed the single in-plane 6-fold flipping motion of the coronenes, two unsynchronized motions were confirmed for the 3:1 TCNQ complex, which is consistent with a crystallographic study. Neutral [Ni(mnt)2] (mnt: maleonitriledithiolate) as an electron acceptor afforded a 5:2 complex with a DDA-type alternating π column flanked by another coronene, similar to the 3:1 TCNQ complex. The fact that the Cor-As in the [Ni(mnt)2] complex arrange in a non-parallel fashion must cause the fast in-plane rotation of Cor-A relative to that of Cor-B. This is in sharp contrast to the 3:1 TCNQ complex, in which the dimer of parallel Cor-As shows inter-column interactions with neighboring Cor-As. The solid-state (1)H NMR signal of the [Ni(mnt)2] complex suddenly broadens at temperatures below approximately 60 K, indicating that the in-plane rotation of the coronenes undergoes down to approximately 60 K; the rotational rate reaches the gigahertz regime at room temperature. Rotational barriers of these CT complexes, as estimated from variable-temperature spin-lattice relaxation time (T1) experiments, are significantly lower than that of pristine coronene. The investigated structure-property relationships indicate that the complexation not only facilitates the molecular rotation of coronenes but also provides a new solid-state rotor system that involves unsynchronized plural rotators.

Macroscopic motion of supramolecular assemblies actuated by photoisomerization of azobenzene derivatives

Submillimetre size self-assemblies composed of oleate and azobenzene derivatives show forceful motions such as screw-type coiling-recoiling motion by photoirradiation.