Biomedical subjects
Publications and source records attributed to Hayao Kobayashi.
A porous molecular crystal with guest ethanol molecules, [Mn3(HCOO)6](C2H5OH), was found to be a new type of multifunctional molecular system, which exhibits a ferroelectric transition at 165 K and a ferrimagnetic transition at 8.5 K. [Mn3(HCOO)6](C2H5OH) will give a hint to design "multiferroic" molecular materials where ferroelectric and ferromagnetic orders coexist.
The synergy between the electrical conductivity within the stacks of Ni(dmit)2 in the newly electrocrystallized [Fe(qsal)2][Ni(dmit)2]3.CH3CN.H2O and the spin conversion of Fe(qsal)2 is evidenced. In addition, the presence of a light-induced excited spin state trapping effect suggests that this complex is a prototypal photoswitchable spin-crossover molecular conductor.
The synthesis, crystal structure, and electrical, optical, and magnetic properties of kappa-BETS2[Fe(III)(C2O4)Cl2], where BETS is bis(ethylenedithio)tetraselenafulvalene, are reported. The black plate crystals consist of parallel donor layers, two per unit cell, displaying a kappa-type packing of BETS(0.5+) within the bc plane and anionic magnetic chains, [Fe(C2O4)Cl2-]n, running along the c axis. It displays metallic behavior down to 4.2 K, and analysis of the optical reflectivity data gives unscreened plasma energies of 0.69 eV (E parallel c) and 0.40 eV (E perpendicular c). The optical anisotropy is larger than that seen for other kappa phases and is described well by transfer integrals obtained from extended Hückel calculations. However, the transfer integrals need to be scaled down uniformly by a factor of 1.21 to reproduce the absolute experimental plasma frequencies. The band structure consists of a one-dimensional (1D) band and a hole pocket, characteristics of kappa phases. The magnetic properties were modeled by the sum of a 1D antiferromagnetic chain contribution from the d spins of Fe3+, a temperature-independent paramagnetic contribution, and a Curie impurity term. At 4.5 K, there is a signature of long-range magnetic ordering to a canted-antiferromagnetic state in the zero-field-cooled-field-cooled magnetizations, and at 2 K, a small hysteresis loop is observed.
A single-component molecular conductor [Au(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) undergoes an antiferromagnetic phase transition at unprecedentedly high temperature (TN = 110 K). Black microcrystals of alloys, [Ni1-xAux(tmdt)2] (0.0 < x < 1.0) were prepared. The Au-rich system exhibited an antiferromagnetic transition. Metallic single crystal was obtained for x = 0.25.
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A new molecular conducting material, [BDTA][Ni(dmit)2]2, with a novel multiband electronic structure has been prepared by simple mixing of precursor salts of the components.
[Co3(HCOO)6](CH3OH)(H2O) (1), the isostructural analogue of the porous magnet of coordination framework [Mn3(HCOO)6](CH3OH)(H2O), and its desolvated form [Co3(HCOO)6] (2) were prepared and characterized by X-ray and neutron diffraction methods, IR, thermal analyses, and BET, and their magnetic properties were measured. The parent compound, 1, crystallizes in the monoclinic system, space group P21/c, a = 11.254(2) A, b = 9.832(1) A, c = 18.108(3) A, beta = 127.222(2) degrees , V = 1595.5(4) A3, Z = 4, R1 = 0.0329 at 180 K. It possesses a unit cell volume that is 9% smaller than [Mn3(HCOO)6](CH3OH)(H2O) due to the smaller radius of Co2+ ion. Compared with the parent compound 1, the desolvated compound 2 has slightly larger lattice with cell parameters of a = 11.2858(4) A, b = 9.8690(4) A, c = 18.1797(6) A, beta = 127.193(2) degrees , V = 1613.0(1) A3, R1 = 0.0356 at 180 K. The cell parameters of 2, obtained from neutron powder data at 2 K, are a = 11.309(2) A, b = 9.869(1) A, c = 18.201(3) A, beta = 127.244(8) degrees , V = 1617.3(5) A3. The pore volume reduces from 33% to 30% by replacing Mn by Co. The material exhibits a diamond framework based on Co-centered CoCo4 tetrahedral nodes, in which all metal ions have octahedral coordination geometry and all HCOO groups link the metal ions in syn-syn/anti modes. It displays thermal stability up to 270 degrees C. The compound easily loses guest molecules without loss of crystallinity, and it partly reabsorbs water from the atmosphere. Significant N2 sorption was observed for the desolvated framework suggesting that the material possesses permanent porosity. The magnetic properties show a tendency to a 3D long-range magnetic ordering, probably antiferromagnetic with a spin canting arrangement below 2 K.
Rigorous evidence of metallicity of a molecular crystal consisting of single-component neutral molecules is disclosed by observing the Fermi surface through magnetic quantum oscillations. Torque magnetometry measurements of de Haas-van Alphen oscillatory signals in a single crystal of [Ni(tmdt)2] molecules (tmdt = trimethylenetetrathiafulvalenedithiolate) were performed by using a sensitive microcantilever at low temperatures in high magnetic fields to 45 T. The observed signals for all directions of magnetic field revealed unambiguously the presence of three-dimensional Fermi surfaces for both holes and electrons. The results are consistent with electronic band structure calculations for [Ni(tmdt)2].
We present the synthesis, characterization by IR, TGA, single crystal X-ray structure and magnetic properties of a novel series of NaCl-type frameworks of [AmineH(+)][Mn(HCOO)(3)(-)], templated by alkylammonium. The anionic NaCl-framework of [Mn(HCOO)(3)(-)] is counter-balanced by the alkylammonium cations located in the cavities of the framework to which they are hydrogen-bonded. The divalent manganese ions have octahedral geometry and are bridged by the formate in an anti-anti mode of coordination. All the compounds exhibit long-range antiferromagnetism below 9 K with a slight non-collinear arrangement of the moments. The canting, likely due to second-order spin-orbit coupling, is via a Dzyaloshinski-Moriya antisymmetric exchange mechanism. A spin-flop is observed in each case at fairly low fields. An orthorhombic to monoclinic transformation was observed for the protonated cyclotrimethyleneamine that is accompanied by localization of the cations into two positions below 240 K from the rapid dynamic flipping of the ring observed at room temperature.
To contribute to the development of single-component molecular metals, several nickel complexes with cyclohexeno-condensed or ethylenedioxy-substituted TTF (tetrathiafulvalene) dithiolate ligands, (R(4)N)(n)[Ni(chdt)(2)] [R = Me, n = 2 (1); R = (n)Bu, n = 1 (2); n = 0 (3)] and (R(4)N)(n)[Ni(eodt)(2)] [R = Me, n = 2 (4); R = (n)Bu, n = 1 (5); n = 0 (6)], were prepared. X-ray structures were determined on the monoanionic species 2 and 5. The tetra-n-butylammonium complex of the monoanionic [Ni(chdt)(2)] (2) with a 1:1 composition revealed that its magnetic susceptibility gave a good agreement with the Bonner-Fisher model (J/k(B) = -28 K), which was derived from the one-dimensional chains of anions with a regular interval. On the other hand, the magnetic susceptibility of the tetra-n-butylammonium complex of the monoanionic [Ni(eodt)(2)] (5) showed the Curie-Weiss behavior (C = 0.376 K.emu.mol(-1) and Theta = -4.6 K). Both of the monoanionic species 2 and 5 indicate that they belong to the S = 1/2 magnetic system and have relatively large and anisotropic g-values, suggesting the contribution of the nickel 3d orbital. Electrical resistivity measurements were performed on the compressed pellets of the neutral species 3 and 6. Fairly large conductivities were obtained (sigma(rt) = 1-10 S.cm(-1)). In addition, despite the measurements on the compressed pellets of powder samples, the neutral species 6 showed metallic behavior down to ca. 120 K and retained high conductivity even at 0.6 K [sigma(0.6 K)/sigma(rt) approximately 1/30], suggesting the crystal to be essentially metallic down to very low temperature. The electrical behavior and Pauli paramagnetism of 6 indicate the system to be a new single-component metal.
The infrared spectra of the crystal of transition metal complex molecules with extended-TTF ligands, Ni(tmdt)2, which is the first single-component molecular metal that has a stable metallic state even at low temperatures, exhibited an extremely low-energy electronic absorption around 2200 cm-1 (tmdt = trimethylenetetrathiafulvalenedithiolate). The systematic shift of the absorption peaks for molecules similar to Ni(tmdt)2, which range from metallic to semiconducting crystals, shows that the single-component molecular conductors are composed of molecules with unprecedentedly small HOMO-LUMO gaps.
Mn3(HCOO)6, a 3D highly stable and flexible porous diamondoid framework based on Mn-centered MnMn4 tetrahedral nodes, exhibits a wide spectrum of guest inclusion behaviour and long-range magnetic ordering with guest-modulated critical temperature.
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The platelike crystals of a series of novel molecular conductors, which are based on the pi-donor molecules BDT-TTP (2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene) with a tetrathiapentalene skeleton and lanthanide nitrate complex anions [Ln(NO3)x](3-x)(Ln = La, Ce, (Pr), Tb, Dy, Ho, Er, Tm, Yb, Lu) with localized 4f magnetic moments, were synthesized. Except for the Ce complex, the salts were composed of (BDT-TTP)(5)[Ln(NO(3))(5)] and were isostructural. Even though the Ce crystal had a different composition, (BDT-TTP)(6)[Ce(NO(3))(6)](C(2)H(5)OH)(x)() (x approximately 3), the crystals all had the space group P(-)1. Although the X-ray examination of the Pr salts was insufficient, the existence of two modifications was suggested in these systems by preliminary X-ray examination. Previously, we reported the crystal structures and unique magnetic properties of (BDT-TTP)(5)[Ln(NO(3))(5)] (Ln = Sm, Eu, Nd, Gd). Thus, by combining the results of this work with previous one, we for the first time succeeded in obtaining a complete set of organic conductors composed of the identical pi-donors (BDT-TTP in this case) and all the lanthanide nitrate complex anions (except the complex with Pm(3+)). The crystals were all metallic down to 2 K. Electronic band structure calculations resulted in two-dimensional Fermi surfaces, which was consistent with their stable metallic states. Except for the Lu complex, which lacked paramagnetic moments, the magnetic susceptibilities were measured on the six heavy lanthanide ion complex salts by a SQUID magnetometer (Ln = Tb, Dy, Ho, Er, Tm, Yb). The large paramagnetic susceptibilities, which were caused by the paramagnetic moments of the rare-earth ions, were obtained. The Curie-Weiss law fairly accurately reproduced the temperature dependence of the magnetic susceptibilities of (BDT-TTP)(5)[Ho(NO(3))(5)] in the experimental temperature range (2-300 K) and a comparatively large Weiss temperature (|THETAV;|) was obtained (THETAV;(Ho) = -15 K). A Weiss temperature (THETAV;(Tm) = -8 K) was also obtained for Tm. The |THETAV;| values of other (BDT-TTP)(5)[Ln(NO(3))(5)] salts and (BDT-TTP)(6)[Ce(NO(3))(6)](C(2)H(5)OH)x(x approximately 3) were as follows: |THETAV;|/K = 4 (Er), < or =2 (Ce, Tb, Dy, Yb). The comparatively strong intermolecular magnetic interaction between Ho(3+) ions, which was suggested by the |THETAV;| value, is inconsistent with the traditional image of strongly localized 4f orbitals shielded by the electrons in the outer 5s and 5p orbitals. The dipole interactions between Ln(3+) ions causing the Curie-Weiss behavior and the comparatively large THETAV; value of (BDT-TTP)(5)[Ho(NO(3))(5)] is inconsistent with the data, since the complexes exhibit isostructural properties and there is not a clear relationship between the magnitudes of THETAV; values and those of magnetic moments. Therefore, it is possible that the 4f orbitals of Ho atom are sensitive to the ligand field, which will have an effect on the orbital moment of the Ho(3+) ion and/or produce a small amount of mixing between 4f and ligand orbitals to give rise to "real" intermolecular antiferromagnetic interaction through intermolecular overlapping between pi (BDT-TTP) and ligand orbitals of lanthanide nitrate complex anions.
Highly conducting crystals based on single-component gold complexes with extended-TTF dithiolate ligands [Au(dmdt)(2)](0+) (1) and [Au(tmdt)(2)](0+) (2) were prepared (dmdt = dimethyltetrathiafulvalenedithiolate and tmdt = trimethylenetetrathiafulvalenedithiolate). On the basis of the synchrotron radiation powder diffraction data, the MEM electron density of 2 was successfully obtained. The conductivities of compacted powder samples of 1 and 2 at room temperature were 12 and 15 S cm(-1), respectively. Pauli-like susceptibility of 1 suggested the system to be essentially metallic at least above 50 K, while 2 showed a magnetic transition around 100 K without loss of its high conductivity.
Dual-action organic superconductors, whose conducting properties can be sharply controlled by an external magnetic field, have been discovered in systems consisting of organic conduction layers based on bis(ethylenedithio)tetraselenafulvalene (BETS) molecules and magnetic anions. Owing to the metamagnetic nature of the anion layers, the superconducting state of kappa-BETS2FeBr4 can be switched on or off by applying the external field. In lambda-BETS2Fe0.4Ga0.6Cl4, exhibiting a field-induced superconducting transition for the field parallel to the conduction plane, the insulating, metallic, and superconducting states can be realized in a stepwise manner by slightly tuning the external magnetic field.
A single-component conducting molecular crystal composed of paramagnetic copper complexes, [Cu(dmdt)2]0+, was prepared. The crystal has an unprecedented three-dimensionally packed molecular arrangement and exhibits a fairly high conductivity (1 S cm-1 at room temperature). The magnetic susceptibility measurements revealed that [Cu(dmdt)2]0+ molecule keeps most of S = 1/2 spin moments. The difference of the bond lengths between [Cu(dmdt)2]0+ and [Cu(dmdt)2]2- is consistent with the result of the molecular orbital calculation.