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Takayoshi Nakamura

Publications and source records attributed to Takayoshi Nakamura.

At least 19 recordsLinked to original sources
PubMed2006

Flexible and shape-selective guest binding at Cu(II) axial sites in 1-dimensional Cu(II)-1,2-bis(4-pyridyl)ethane coordination polymers.

A series of guest-binding Cu(II) coordination polymers, {[Cu(bpetha)2(acetone)2].2PF6}n (bpetha = 1,2-bis(4-pyridyl)ethane) (1), {[Cu(bpetha)2(DMF)2].2PF6}n (2), {[Cu(bpetha)(2)(MeCN)(2)].2PF6.2MeCN}n (3), {[Cu(bpetha)2(H2O)2].2PF6.3THF.2H2O}n (4), {[Cu(bpetha)2(H2O)2].2PF6.3dioxane}n (5), and {[Cu(bpetha)2(H2O)2].2PF6.2-PrOH.2H2O}n (6), have been synthesized and crystallographically characterized. Their framework stabilities and guest-exchange properties have also been investigated. All compounds form a similar framework motif, a "double chain", in which the bpetha ligands bridge Cu(II) centers to form 1-D [Cu(bpetha)2]n double chains. A variety of Lewis base guest molecules, such as H2O, acetone, DMF, MeCN, THF, dioxane, and 2-PrOH, are incorporated into the assembly of the 1-D double chains. These chains flexibly change their forms of assembly in a guest-dependent manner. Interestingly, acetone, DMF, and MeCN guests with a carbonyl or cyanide group coordinate directly to the axial sites of the Cu(II) centers; in contrast, THF, dioxane, and 2-PrOH guests with an ether or alcohol group are incorporated into the frameworks not via coordination bonds but via weak interactions (hydrogen bonds and van der Waals forces). This selectivity is probably due to steric effects at coordinated oxygen or nitrogen atoms of the guests. Crystal-to-crystal transformations triggered by guests are observed, during which guests coordinated to the Cu(II) axial sites are readily removed and replaced by other guests.

Journal Article↗
PubMed2006

Functionalities of one-dimensional dynamic ultramicropores in nickel(II) coordination polymers.

Ni(II) coordination polymers with a 4,4'-azobis(pyridine) (azpy) ligand, {[Ni2(NCX)4(azpy)4].G}n (X = S, G (guest molecule) = MeOH (1.MeOH); X = S, G = EtOH (1.EtOH); X = S, G = H2O (1.H2O); X = S, G = no guest (1); X = Se, G = MeOH (2.MeOH); X = Se, G = H2O (2.H2O); X = Se, G = no guest (2)), have been synthesized and structurally characterized with their porosity. These compounds have one-dimensional periodic ultramicropores that contain the small guest molecules, H2O, MeOH, or EtOH, whose hydroxy groups interact with the S or Se atoms of isothiocyanate or isoselenocyanate, respectively, via -S(Se)...HO- hydrogen bonds. Although the molecular dimensions of the MeOH guest are considerably larger than the window size of the ultramicropore, 1.MeOH and 2.MeOH easily release their guest molecules without decomposition of the framework to form 1 and 2 without any guest molecules. This shows that 1 and 2 have dynamic ultramicropores constructed from the interpenetrating framework. The guest desorption experiments using 1.MeOH and 1.EtOH reveal that the difference in the desorption behavior is due to van der Waals interactions that depend on the molecular shape of the guest molecule in the ultramicropores and/or an entrance blocking effect that depends on the minimum dimensions of the guest molecule for the pore windows. A marked difference in the N2 and CH4 adsorption isotherms was observed and is associated with the strength of the host-guest interaction.

Journal Article↗
PubMed2006

Formation of p-phenylenediamine-crown ether-[PMo12O40]4- salts.

Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)3[PMo12O40]3- forms a one-electron-reduced Keggin cluster of [PMo12O40]4-, bearing a S = 1/2 spin, while proton transfer from the proton donor of (H+)3[PMo12O40]3- to the proton acceptor of PPD yielded mono- and diprotonated cations of 4-aminoanilinium (HPPD+) and p-phenylenediammonium (H2PPD2+). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD2+)(crown ethers) were successfully introduced into three new alpha-[PMo12O40]4- salts of (H2PPD2+)2([12]crown-4)4[PMo12O40]4- (1), (HPPD+)4([15]crown-5)4[PMo12O40]4- (2), and (HPPD+)2(H2PPD2+)([18]crown-6)4[PMo12O40]4- (3) as the countercation. The protonated states of PPD and molecular-assembly structures of the supramolecular cations depended on the size of the crown ethers. In salt 3, a novel mixed-protonated state of HPPD+ and H2PPD2+ was confirmed to be complexed in the cation structure. According to the changes in the cation structures, the anion arrangements were modulated from those of the two-dimensional layer for salt 1 to the isolated cluster for salts 2 and 3. The temperature-dependent magnetic susceptibilities of salts 1-3 were consistent with the isolated spin arrangements of [PMo12O40]4-. The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent Mo(V) to hexavalent Mo(VI) ions within the [PMo12O40]4- cluster. Temperature-dependent electron spin resonance spectra of salt 2 revealed the delocalization-localization transition of the S = 1/2 spin at 60 K. The spin on the [PMo12O40]4- cluster was localized on a specific Mo(V) site below 60 K, which was thermally activated with an activation energy of 0.015 eV.

Journal Article↗
PubMed2006

Structural phase transition of magnetic [Ni(dmit)2]- salts induced by supramolecular cation structures of (M+)([12]crown-4)2.

Sandwich-type supramolecular cation structures of (M(+))([12]crown-4)(2) complexes (M(+) = Li(+), Na(+), K(+), and Rb(+)) were introduced as countercations to the [Ni(dmit)(2)](-) anion, which bears an S = (1)/(2) spin, to form novel magnetic crystals (dmit(2-) = 2-thione-1,3-dithiole-4,5-dithiolate). The zigzag arrangement of Li(+)([12]crown-4)(2) cations in Li(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salt induced weak intermolecular interactions of [Ni(dmit)(2)](-) dimers, whose magnetic spins were isolated from each other. The molecular arrangements of cations and anions in M(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salts (M(+) = Na(+), K(+), and Rb(+)) were isostructural to each other. In the case of Na(+)([12]crown-4)(2)[Ni(dmit)(2)](-), the space group C2/m changed to C2/c with a lowering in temperature from 298 to 100 K. This structural change occurred at 222.5 K as a first-order phase transition. The space group C2/m (T = 298 K) in the salt K(+)([12]crown-4)(2)[Ni(dmit)(2)](-) also changed to C2/c (T = 100 K), which transition occurred at 270 K. Crystal structural analyses at 298 and 100 K revealed changes in both supramolecular cation conformation and [Ni(dmit)(2)](-) anion arrangements. The transition from C2/m to C2/c crystals generated a dipole moment in the Na(+)([12]crown-4)(2) and K(+)([12]crown-4)(2) structures, which were reconstructed to cancel the net dipole moment of the C2/c crystals. These cation transformations led to changes in intermolecular interactions between the [Ni(dmit)(2)](-) anions via structural rearrangements. The crystal structure of C2/c was stabilized in Rb(+)([12]crown-4)(2)[Ni(dmit)(2)](-) at 298 K. The [Ni(dmit)(2)](-) configuration in these salts with the C2/c space group was a one-dimensional uniform chain, which showed the temperature-dependent magnetic susceptibility of a one-dimensional linear Heisenberg antiferromagnetic chain.

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PubMed2006

Surface pressure induced charge transfer between fullerene and tetrathiafulvalene derivative in Langmuir-Blodgett films.

Structures and electronic states of a 1:1 mixture of bis-tetrathiafulvalene annulated macrocycle (1) and C60 in Langmuir films at the air-water interface and Langmuir-Blodgett (LB) films on solid substrates were examined. Compression of the Langmuir films induced for the first time a phase transition from a weakly interacting state without charge transfer (CT) to a neutral CT state. The scanning force microscope images of LB films transferred onto mica by a single withdrawal showed quite different spatial patterns depending on the CT states. When deposited at around 1 mNm(-1), a domain structure with 3 nm height was obtained, which corresponded to the state without CT interaction. Contrastingly, once the CT interaction was induced by applying surface pressure, a network structure was observed with a height of 6 nm. The CT band, whose transition moment was almost parallel to the substrate surface, was observed at 11.5 x 10(3) cm(-1) in the polarized UV-VIS-NIR spectra of the films deposited at 9 mNm(-1). The phase transition was irreversible, although the surface pressure-area isotherm showed a reversible behavior below 9 mNm(-1). The morphology and electronic state of the film was controllable merely by changing the surface pressure at the air-water interface.

Electrochemistry↗
PubMed2005

Pore surface engineering of microporous coordination polymers.

Pore surface control of microporous coordination polymers is of great interest due to the potentially exciting functionalities it presents, such as highly selective separation, chemisorption, and novel catalysts and sensors. A discussion of our unique strategy aimed at surface engineering using metalloligands, i.e., introduction of coordinatively unsaturated metal centers, is presented.

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PubMed2005

Cooperativity of dynamics of 18-crown-6 molecule forming one-dimensional chain in Cs2(18-crown-6)3[Ni(dmit)2]2.

Heat capacity of Cs2(18-crown-6)3[Ni(dmit)2]2 was measured by adiabatic calorimetry. A broad thermal anomaly was observed around 225 K. The entropy gain (about 52 J K(-1) mol(-1)) is much larger than that expected for twofold disordering of 18-crown-6 assumed in the previous structure analysis. The shape of thermal anomaly was qualitatively explained by a linear Ising model developed for cooperative disordering in polymers. The 18-crown-6 molecules forming a one-dimensional chain in the crystal are orientationally disordered with moderate cooperativity.

Journal Article↗
PubMed2005

Magnetism of [Ni(dmit)2] salts with [meso- and (1S, 2S)-diphenyl-1,2-ethanediammonium]([18]crown-6)2 supramolecular cations.

Meso- and (1S, 2S)-diphenyl-1,2-ethanediammonium (DPEDA2+) complexed with [18]crown-6 were introduced into [Ni(dmit)2]-based magnetic salts as countercations. The configurational difference of DPEDA2+ modulated the crystal structure and magnetic behavior of the salts. A two-dimensional (2D) Heisenberg antiferromagnetic square lattice was observed in (meso-diphenyl-1,2-ethane diammonium2+)([18]crown-6)2[Ni(dmit)2](-)2, which was the first example of a 2D magnetic lattice in [Ni(dmit)2]- salts.

Journal Article↗
PubMed2005

Synthesis and crystallographic characterization of low-dimensional and porous coordination compounds capable of supramolecular aromatic interaction using the 4,4'-azobis(pyridine) ligand.

Coordination compounds with a 4,4'-azobis(pyridine) (azpy) ligand, {[M2(azpy)6(H2O)5] x 4PF6 x azpy x H2O}n (M = Ni(II) (1) or Co(II) (2)) (0-dimensional (0-D) dimer), {[Zn(azpy)3(H2O)2] x 2PF6 x 2azpy x 4H2O}n (3) (1-dimensional (1-D) fishbone-type chain), {[Ag(azpy)] x PF6}n (4) (1-D linear chain), {[Mn(NCS)2(azpy)2] x azpy}n (5) (2-dimensional (2-D) grid sheet), and {[Ni(NCS)2(azpy)2] x 3toluene}n (6) (2-D grid sheet), were synthesized and structurally characterized. Compounds 1 and 2 have a 0-D dimer motif, in which one M(II) (M(II) = Ni(II) or Co(II)) coordination site is shared by unidentate azpy and H2O ligands, each with half-occupancy, i.e., exhibiting static disorder. Compounds 3 and 4 afford 1-D fishbone-type and 1-D linear chain motifs, respectively. Azpy mediates pi-pi and pi-p interactions between these low-dimensional structures. Compounds 5 and 6 possess a 2-D grid sheet motif. These sheets assemble to form microporous frameworks that incorporate aromatic guests, such as coordination-free azpy (5) and toluene (6). There exist not only pi-pi and pi-p interactions but also CH-pi interactions between the framework azpy ligands and guests. It should be noted that the azpy ligand is a good candidate for the construction of new assembling systems of coordination compounds through its aromatic interactions.

Journal Article↗
PubMed2005

Molecular rotor of Cs2([18]crown-6)3 in the solid state coupled with the magnetism of [Ni(dmit)2].

Nanoscale molecular rotors that can be driven in the solid state have been realized in Cs2([18]crown-6)3[Ni(dmit)2]2 crystals. To provide interactions between the molecular motion of the rotor and the electronic system, [Ni(dmit)2]- ions, which bear one S=1/2 spin on each molecule, were introduced into the crystal. Rotation of the [18]crown-6 molecules within a Cs2([18]crown-6)3 supramolecule above 220 K was confirmed using X-ray diffraction, NMR, and specific heat measurements. Strong correlations were observed between the magnetic behavior of the [Ni(dmit)2]- ions and molecular rotation. Furthermore, braking of the molecular rotation within the crystal was achieved by the application of hydrostatic pressure.

Journal Article↗
PubMed2004

Langmuir-Blodgett films of amphiphilic bis(tetrathiafulvalene) macrocycles with four alkyl chains.

Amphiphilic bis(tetrathiafulvalene) [bis(TTF)] macrocycles with four alkyl chains were fabricated as novel electrically active Langmuir-Blodgett (LB) films. Two TTF units were linked via [24]crown-8, [21]crown-7, and [18]crown-6 macrocycles, forming charge-transfer (CT) salts with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane (F4-TCNQ) at the air-water interface and on solid substrates. The CT salt of the amphiphilic bis(TTF)-macrocycle having a [24]crown-8 ring system formed a uniform surface morphology on mica. Using single-crystal X-ray structural analysis, the layer structure between the hydrophobic chains and the one-dimensional pi-pi stack of the CT salt was confirmed. Our results show that the bis(TTF)-macrocycle was folded at the flexible [24]crown-8 moiety, forming intramolecular pi-pi dimer structures and one-dimensional intermolecular pi-pi stacks with F4-TCNQ dimers. The open-shell electronic structure of the LB films was determined by electronic spectra, electrical conductivity, and electron spin resonance analyses. Asymmetry was introduced into the bis(TTF)-macrocycle by changing the ring size from [24]crown-8 to [21]crown-7. The surface morphology of the CT salts with F4-TCNQ was established as two-dimensional round-shape domains on mica. Further reduction of the macrocyclic ring from [21]crown-7 to [18]crown-6 resulted in a CT salt of the bis(TTF)-macrocycle with F4-TCNQ with a leaf-shape domain morphology and a typical dimension of approximately 1 microm2 on mica. In general, decreasing the macrocyclic ring size from [24]crown-8 to [21]crown-7 or [18]crown-6 affected the inter- and intramolecular interactions and the surface morphologies of LB films.

Journal Article↗
PubMed2004

Proton transfer and a dielectric phase transition in the molecular conductor (HDABCO+)2(TCNQ)3.

One-dimensional dielectric (N.H.N)( infinity ) hydrogen-bonding chains of monoprotonated 1,4-diazabicyclo[2.2.2]octane (HDABCO(+)) were introduced into an electrically conducting 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) salt as the countercation structure. Room-temperature electrical conductivity was approximately 10(-)(3) S cm(-)(1), with a semiconductive behavior. The temperature-dependent dielectric constants of (HDABCO(+))(2)(TCNQ)(3) indicated a dielectric transition at 306 K. A large deuterium isotope effect for the dielectric transition (DeltaT = 70 K) was observed for the deuterated salt, (DDABCO(+))(2)(TCNQ)(3). Thermally activated order/disorder of the protons or deuteriums within the one-dimensional hydrogen-bonding chains of (HDABCO(+))( infinity ) and (DDABCO(+))( infinity ) affected the dielectric responses in the TCNQ-based semiconductors.

Journal Article↗
PubMed2003

Crystal structure and magnetic properties of Gd2([18]crown-6)2(OH)2(CH3CN)2[Ni(dmit)2]4 complex having f- and pi-spins.

Crystal structure and magnetic properties of Gd(2)([18]crown-6)(2)(OH)(2)(CH(3)CN)(2)[Ni(dmit)(2)](2) (dmit(2)(-) = 2-thioxo-1,3-dithiole-4,5-dithiolate) are reported. Gd(3+) ions (S = (7)/(2)) were introduced into the pi-spin network of [Ni(dmit)(2)](-) (S = (1)/(2)) complex as a binuclear supramolecular cation, Gd(2)([18]crown-6)(2)(OH)(2)(CH(3)CN)(2), in which two Gd([18]crown-6) units are bridged with two hydroxide ions. The weak antiferromagnetic interactions between Gd.Gd through hydroxide ions were observed, and [Ni(dmit)(2)](-) formed isolated monomers and dimers in the crystal.

Journal Article↗
PubMed2002

Coupled protonic and electronic conduction in the molecular conductor [2-(2-1H-Benzimidazolyl)-1H-benzimidazolium]-TCNQ.

A novel molecular based proton-electron mixed conductor, (H3BBIM(+))(TCNQ)(Cl(-))(0.5)(H(2)O) (1), where H3BBIM(+) is 2-(2-1H-benzimidazolyl)-1H-benzimidazolium and TCNQ is 7,7,8,8-tetracyano-p-quinodimethane, was synthesized. The salt exhibited peculiar phase transitions as a result of proton-electron coupling phenomena within the crystal. Salt 1 is composed of a closed-shell H3BBIM(+) cation and an open-shell TCNQ anion radical, and was obtained by electrocrystallization in a buffered CH(3)CN solution. Crystal 1 was constructed from the segregated uniform stacks of H3BBIM(+) and TCNQ. The regular stack of partially electron-transferred TCNQ(-0.5) provided a one-dimensional electron-conducting column. Between the regular H3BBIM(+) columns, a channel-like sequence of holes was formed at the side-by-side space that is filled with disordered Cl(-) ions and H(2)O molecules, and which offer a proton-conducting path. The electrical conductivity at room temperature (10 S cm(-1)) was greater by a magnitude of four than the protonic conductivity (1x10(-3) S cm(-1)). Electronic conduction changed from metallic (T>250 K) to semiconducting (250>T>100 K), then insulating (T<100 K). Protonic conductivity was observed above 200 K. The continuous metal-semiconductor transition at 250 K is caused by the formation of the Cl(-) superstructure, whereas the disappearance of protonic conductivity at 200 K is related to the rearrangement of the [Cl(-)-(H(2)O)(2)] sublattice within the channel. The magnetic susceptibility continuously shifted from Pauli paramagnetism (T>250 K) to the one-dimensional linear Heisenberg antiferromagnetic chain (T<250 K). Lattice dimerization in regular TCNQ columns was confirmed by the appearance of vibrational a(g) mode at low temperatures. The strong localization of conduction electrons on each TCNQ dimer caused a Mott transition at 100 K. The melting and freezing of the [Cl(-)-(H(2)O)(2)] sublattice within the channel was correlated to the conduction electrons on the TCNQ stack and the protonic conductivity.

Journal Article↗
PubMed2002

Supramolecular cation assemblies of hydrogen-bonded (NH4+/NH2NH3+)(crown ether) in [Ni(dmit)2]-based molecular conductors and magnets.

Hydrogen-bonded supramolecular cation assemblies of (NH4+/NH2-NH3+)(crown ether), where the crown ether is [12]crown-4, [15]crown-5, or [18]crown-6, were incorporated into electrically conducting [Ni(dmit)2] salts (dmit2- = 2-thioxo-1,3-dithiole-4,5-dithiolate). (NH4+)([12]crown-4)[Ni(dmit)2]3(CH3CN)2 had a pyramidal shape, while ionic channels were observed in (NH4+)(0.88)([15]crown-5)[Ni(dmit)(2)]2 and (NH4+)(0.70)([18]crown-6)[Ni(dmit)(2)]2. Both (NH4+)(0.88)([15]crown-5) and (NH4+)(0.70)([18]crown-6) contained regularly spaced [Ni(dmit)(2)] stacks formed by N-H.O hydrogen bonding between the oxygen atoms in crown ethers and the NH4+ ion. NH4+ occurred nonstoichiometrically; there were vacant ionic sites in the ionic channels. The ionic radius of NH4+ is larger than the cavity radius of [15]crown-5 and [18]crown-6. Therefore, NH4+ ions could not pass through the cavity and were distributed randomly in the ionic channels. The static disorder caused the conduction electrons to be randomly localized to the [Ni(dmit)2] stacks. Hydrazinium (NH2-NH3+) formed the supramolecular cations in (NH2-NH3+)([12]crown-4)2[Ni(dmit)2]4 and (NH2-NH3+)2([15]crown-5)3[Ni(dmit)2]6, possessing a sandwich and club-sandwich structure, respectively. To the best of our knowledge, these represent the first hydrazinium-crown ether assemblies to be identified in the solid. In the supramolecular cations, hydrogen bonding was detected between the ammonium or the amino protons of NH2-NH3+ and the oxygen atoms of crown ethers. The sandwich-type cations coexisted with the [Ni(dmit)2] dimer stacks. Although the assemblies were typically semiconducting, ferromagnetic interaction (Weiss temperature = +1 K) was detected in the case of (NH2-NH3+)2([15]crown-5)3[Ni(dmit)2]6. The (NH2-NH3+)0.8([18]crown-6)[Ni(dmit)2]2 and (NH4+)0.76([18]crown-6)[Ni(dmit)2]2 crystals were isomorphous. The large and flexible [18]crown-6 allowed for maintaining the same ionic channel structure through replacement of the NH4+ cation by NH2-NH3+.

Journal Article↗