Yoshihide Tsunobuchi

Light-induced spin-crossover magnet

The light-induced phase transition between the low-spin (LS) and high-spin (HS) states of some transition-metal ions has been extensively studied in the fields of chemistry and materials science. In a crystalline extended system, magnetically ordering the HS sites of such transition-metal ions by irradiation should lead to spontaneous magnetization. Previous examples of light-induced ordering have typically occurred by means of an intermetallic charge transfer mechanism, inducing a change of valence of the metal centres. Here, we describe the long-range magnetic ordering of the extended Fe(II)(HS) sites in a metal-organic framework caused instead by a light-induced excited spin-state trapping effect. The Fe-Nb-based material behaves as a spin-crossover magnet, in which a strong superexchange interaction (magnetic coupling through non-magnetic elements) between photo-produced Fe(II)(HS) and neighbouring Nb(IV) atoms operates through CN bridges. The magnetic phase transition is observed at 20 K with a coercive field of 240 Oe.

High Proton Conductivity in Prussian Blue Analogues and the Interference Effect by Magnetic Ordering

We observed high proton conductivities of 1.2 x 10(-3) and 1.6 x 10(-3) S cm(-1) on Co[Cr(CN)(6)](2/3).zH(2)O and V[Cr(CN)(6)](2/3).zH(2)O, respectively, and an interference effect between magnetic ordering and ionic conduction below the magnetic phase transition temperature.

Synthesis of a metal oxide with a room-temperature photoreversible phase transition

Photoinduced phase-transition materials, such as chalcogenides, spin-crossover complexes, photochromic organic compounds and charge-transfer materials, are of interest because of their application to optical data storage. Here we report a photoreversible metal-semiconductor phase transition at room temperature with a unique phase of Ti(3)O(5), lambda-Ti(3)O(5). lambda-Ti(3)O(5) nanocrystals are made by the combination of reverse-micelle and sol-gel techniques. Thermodynamic analysis suggests that the photoinduced phase transition originates from a particular state of lambda-Ti(3)O(5) trapped at a thermodynamic local energy minimum. Light irradiation causes reversible switching between this trapped state (lambda-Ti(3)O(5)) and the other energy-minimum state (beta-Ti(3)O(5)), both of which are persistent phases. This is the first demonstration of a photorewritable phenomenon at room temperature in a metal oxide. lambda-Ti(3)O(5) satisfies the operation conditions required for a practical optical storage system (operational temperature, writing data by short wavelength light and the appropriate threshold laser power).

Spin Crossover by Encapsulation

Encapsulation by synthetic hosts can transform the spin states of square planar Ni(II)(acen) and Co(II)(tap) complexes. Upon encapsulation, the red Ni(II) diamagnetic state was converted into a green paramagnetic state, whereas the Co(II) low spin (S = 1/2) state was changed into a coupled (S = 1/2 and S = 3/2) state. The host cages are noninnocent and host-guest interactions within the confined cavity influence the resultant properties of the enclathrated metal complexes.

Vanadium Octacyanoniobate-Based Magnet with a Curie Temperature of 138 K

In this work, we prepared a three-dimensional vanadium octacyanoniobate-based magnet, K(0.10)V(II)(0.54)V(III)(1.24)[Nb(IV)(CN)(8)].(SO(4))(0.45).6.8H(2)O. This compound exhibits ferrimagnetism with a Curie temperature of 138 K, in which the sublattice magnetizations of V(II) (S = (3)/(2)) and V(III) (S = 1) are antiparallelly ordered to that of Nb(IV) (S = (1)/(2)). The estimated superexchange interaction constants of V(II)-Nb(IV) and V(III)-Nb(IV) are -51 and -25 cm(-1), respectively.

Vanadium(II) Heptacyanomolybdate(III)-Based Magnet Exhibiting a High Curie Temperature of 110 K

We prepared a vanadium heptacyanomolybdate-based magnet, V(II)(2)[Mo(III)(CN)(7)].(pyrimidine)(2).4.5H(2)O (VMo), with a Curie temperature (T(C)) of 110 K, which is the highest T(C) value in [Mo(III)(CN)(7)]-based magnets. Additionally, Mn(II)(2)[Mo(III)(CN)(7)].(pyrimidine)(2).2H(2)O (MnMo) of a monoclinic structure (P2(1)/n) with T(C) = 47 K was prepared to confirm the crystal structure of VMo.

Supramolecular approach to the formation of magneto-active physical gels

Magnetic fibers were obtained through self-assembly of a nitroxide radical gelator derived from an L-isoleucine-based scaffold. Spins in the fibers are aligned one-dimensionally due to the parallel β-sheet conformation of the intermolecular hydrogen bonds. The spin nanowires exhibit magnetic behavior reproducible by the Bonner–Fisher model.

Magnetization-induced second harmonic generation in a three-dimensional manganese octacyanoniobate-based pyroelectric ferrimagnet

The magnetization-induced second harmonic generation (MSHG) is observed using a three-dimensional MnII–NbIV pyroelectric ferrimagnet, [{MnII(H2O)2}{MnII(pyrazine)(H2O)2}{NbIV(CN)8}]·4H2O, in which electric polarization is along the b-axis and the magnetic easy axis is along the a-axis. The SH intensity gradually increases due to superparamagnetism below 90 K, and then rapidly increases near the Curie temperature (TC = 48 K) due to spontaneous magnetization.

Tetra­potassium hepta­cyanido­molybdate(III) dihydrate

The asymmetric unit of the title compound, KI 4[MoIII(CN)7]·2H2O, consists of one [Mo(CN)7]4− anion, four K+ cations, and two water molecules. The [MoIII(CN)7]4− anion has a seven-coordinated capped-trigonal-prismatic coordination geometry. The site-occupancy factors of the disordered water molecules were set at 0.90, 0.60 and 0.50. The H-atom positions could not be determined for two of the water molecules. The H atoms of the water with a site-occupancy factor of 0.90 were refined using O—H and H⋯H distance restraints.

Poly[[di­aqua­deca-μ2-cyanido-κ20C:N-hexa­cyanido-κ6C-bis­(μ2-5-methyl­pyrimidine-κ2N:N′)bis­(5-methyl­pyrimidine-κN)tricopper(II)ditungstate(V)] dihydrate]

In the title complex, {[Cu3[W(CN)8]2(C5H6N2)4(H2O)2]·2H2O}n, the coordination polyhedron of the eight-coordinated WV atom is a bicapped trigonal prism, in which five CN groups are bridged to CuII ions, and the other three CN groups are terminally bound. Two of the CuII ions lie on a centre of inversion and each of the three independent CuII cations is pseudo-octahedrally coordinated. In the crystal structure, cyanido-bridged-Cu—W—Cu layers are linked by pillars involving the third independent CuII ion, generating a three-dimensional network with non-coordinating water molecules and 5-methylpyrimidine molecules. O—H⋯O and O—H⋯N hydrogen bonds involve the coordinating and non-coordinating water molecules, the CN groups and the 5-methylpyrimidine molecules.