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Hiroki Oshio

Publications and source records attributed to Hiroki Oshio.

16 recordsLinked to original sources
PubMed2006

Electrical conducting bis(oxalato)platinate complex with direct connection of CuII ions.

Reactions of K1.62[Pt(ox)2].2H2O and [Cu(bpy)(H2O)3](NO3)2 yielded partially oxidized one-dimensional (1D) bis(oxalato)platinates of [Cu(bpy)(H2O)n]6[Pt(ox)2]7.7H2O (n = 2, 3, or 4) (1) and [Cu(bpy)(H2O)n]8[Pt(ox)2]10.8H2O (n = 3 or 4) (2). The average oxidation numbers of the platinum ions in 1 and 2 are +2.29 and +2.40, respectively. Complexes 1 and 2 crystallize in the triclinic P and monoclinic C2/c space groups, respectively, and the [Pt(ox)2]n- anions are stacked along the crystallographic b axis with 7-fold periodicity for 1 and 10-fold periodicity for 2. In 1, an oxalato ligand in the platinum chain directly coordinates to a paramagnetic [Cu(bpy)(H2O)3]2+ ion, whereas no such direct coordination was observed for 2. The electrical conductivity of 2 at room temperature along the platinum chain is approximately 3 orders of magnitude smaller (sigma||= 1.3 x 10(-3) S cm(-1)) than that of 1 (sigma|| = 0.9-0.5 S cm(-1)), and the activation energies of 1 and 2 are 29 and 67 meV, respectively. The longest inter-platinum distances in 1 and 2 are 2.762 and 3.0082 A, respectively, and this is responsible for the lower electrical conductivity of 2. An X-ray oscillation photograph taken along the b axis of 1 reveals the 7-fold periodicity in the 1D chain, consistent with the period of the Peierls distortion estimated from the degree of partial oxidation. The semiconducting state of 1 can therefore be regarded as a commensurate Peierls state. The magnetoresistance of 1 at ambient pressure indicates no interaction between conduction electrons in the platinum chain and local spins of the paramagnetic CuII ions. Application of hydrostatic pressures of up to 3 GPa enhances electrical conduction, as is often seen as the usual pressure effect on the electrical conductivity, which is due to enhanced orbital (Pt-5dz2) overlap by pressure application.

Journal Article↗
PubMed2005

High-spin molecules with magnetic anisotropy toward single-molecule magnets.

High-spin molecules with easy-axis magnetic anisotropy show slow magnetic relaxation of spin-flipping along the axis of magnetic anisotropy and are called single-molecule magnets (SMMs). SMMs behave as molecular-size permanent magnets at low temperature and magnetic relaxation occurs by quantum tunneling processes; such molecules are promising candidates for use in quantum devices. We first discuss intramolecular ferromagnetic interactions for preparing high-spin molecules. Second, we determine the magnetic anisotropy for single metal ions with d(n) configurations and discuss how molecular anisotropy arises from single-ion anisotropy of the assembled component metal ions.

Magnetics↗
PubMed2005

A dinuclear MnIII-CuII single-molecule magnet.

The reaction of 1/3 equivalent of CuCl2.2H2O with MnCl2.4H2O and 5-bromo-2-salicylideneamino-1-propanol (H(2)5-Br-sap) in methanol gave dark brown crystals of [MnIIICuIICl(5-Br-sap)2(MeOH)] (1). Complex 1 has an alkoxo-bridged dinuclear core of MnIII and CuII ions, which have elongated octahedral and square-planar coordination geometries, respectively. In dc magnetic susceptibility measurements, chi(m)T values increased as the temperature was lowered, followed by a sudden decrease below 20 K. This behavior is indicative of the occurrence of intramolecular ferromagnetic interactions, and fitting gave an S=5/2 spin ground state with an exchange coupling constant J(MnCu) of +78 cm(-1). Magnetization data collected as a function of temperature and applied magnetic field were analyzed by using a spin Hamiltonian with isotropic Zeeman and axial zero-field splitting (ZFS) terms, and a negative D(5/2) value (-1.86 cm(-1)) was obtained. A high-field EPR (HFEPR) spectrum (342.0 GHz) at 4.2 K was composed of four peaks, and two additional peaks at higher magnetic field appeared as the temperature was increased. The temperature dependences in the HFEPR spectra are indicative of a negative D(5/2) value, and fitting of the data gave D(5/2)=-1.81 cm(-1). In the ac magnetic susceptibility measurements, frequency dependent in-phase (chi(m)') and out-of-phase (chi(m)'') signals with peak maxima at 0.7-1.5 K were observed and small peaks below 0.7 K appeared. The ac susceptibility data supports that 1 is a single-molecule magnet (SMM). Arrhenius plots for the chi(m)'' peaks from 0.7-1.5 K gave the re-orientation energy barrier (DeltaE) of 10.5 K with a pre-exponential factor of 8.2x10(-8) s.

Copper↗
PubMed2004

Single-molecule magnets of ferrous cubes: structurally controlled magnetic anisotropy.

Tetranuclear Fe(II) cubic complexes were synthesized with Schiff base ligands bridging the Fe(II) centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4].2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4].2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4].MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1-6, the alkoxo groups of the Schiff base ligands bridge four Fe(II) ions in a mu3-mode forming [Fe4O4] cubic cores. The Fe(II) ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4-6 are shorter than those in 1-3. Dc magnetic susceptibility measurements for 1-6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, -0.64, -0.66, and -0.67 cm(-1) for 1-6, respectively. Ac magnetic susceptibility measurements for 4-6 showed both frequency dependent in- and out-of-phase signals, while 1-3 did not show out-of-phase signals down to 1.8 K, meaning 4-6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4-6. The bridging ligands R-sap2- in 1-3 and R-sae2- in 4-6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn-Teller distortions at Fe(II) centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry.

Journal Article↗
PubMed2003

Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [Ru(II)(2)Fe(II)(2)(mu-CN)(4)(bpy)(8)](PF6)(4).CHCl(3).H(2)O.

A cyanide-bridged molecular square of [Ru(II) (2)Fe(II) (2)(mu-CN)(4)(bpy)(8)](PF(6))(4).CHCl(3).H(2)O, abbreviated as [Ru(II) (2)Fe(II) (2)](PF(6))(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru(II) (2)Fe(II) (2)](4+) is nearly a square and is composed of alternate Ru(II) and Fe(II) ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru(II) (2)Fe(II) (2)](PF(6))(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70 V (vs. SSCE), which correspond to the four one-electron redox processes of [Ru(II) (2)Fe(II) (2)](4+) right arrow over left arrow [Ru(II) (2)Fe(II)Fe(III)] (5+) right arrow over left arrow [Ru(II) (2)Fe(III) (2)](6+) right arrow over left arrow [Ru(II)Ru(III)Fe(III) (2)](7+) right arrow over left arrow [Ru(III) (2)Fe(III) (2)](8+). Electrochemically generated [Ru(II) (2)Fe(II)Fe(III)](5+) and [Ru(II) (2)Fe(III) (2)](6+) showed new absorption bands at 2350 nm (epsilon =5500 M(-1) cm(-1)) and 1560 nm (epsilon =10 500 M(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe(II) to Fe(III) and from Ru(II) to Fe(III) ions, respectively. The electronic interaction matrix elements (H(AB)) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [Ru(II) (2)Fe(II)Fe(III) (2)](5+) state and 1990 cm(-1) and 0.065 for the [Ru(II) (2)Fe(III) (2)](6+) states.

Journal Article↗
PubMed2002

Cyanide-bridged molecular squares with ferromagnetically coupled dpi, dsigma, and ppi spin system.

Cyanide-bridged molecular squares of [Fe(II)(2)Cu(II)(2)(mu-CN)(4)(dmbpy)(4)(impy)(2)](ClO(4))(4).4CH(3)OH.C(6)H(6) (1) and of [Fe(III)(2)Cu(II)(2)(mu-CN)(4)(dmbpy)(4)(impy)(2)](ClO(4))(6).4CH(3)OH.4H(2)O (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine; impy = 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy) were prepared. In the squares of 1 and 2, the Fe(II/III) (low spin) and Cu(II) ions are alternately bridged by the cyanide groups, in which the cyanide carbon atoms coordinated to the Fe(II) ions and Cu(II) ions are coordinated by imino nitroxide. Magnetic susceptibility measurements for 1 and 2 revealed that the Cu(II) ion and imino nitroxide are ferromagnetically coupled with a fairly strong coupling constant (J(Cu-radical) > 300 K) and act as triplet species. In 1 the Cu(II)-radical moieties are magnetically separated by the Fe(II) ions. In the square of 2, dpi (Fe(III)), dsigma (Cu(II)), and ppi (imino nitroxide) spins are alternately assembled, and this situation allowed the square to have an S = 3 spin ground state. The exchange coupling constant of Fe(III) and the Cu(II)-radical moiety in 2 was estimated to be J = 4.9 cm(-1) (H = -2JSigmaS(Fe).S(Cu-radical)).

Journal Article↗
PubMed1997

Ferromagnetic Interactions between Imino Nitroxides through Diamagnetic Metal Ions: Crystal Structures, Magnetism, and Electronic Properties of [M(I)(imino nitroxide)(2)](PF(6)) (M = Cu(I) and Ag(I)).

An orthogonal arrangement of imino nitroxide ligands in Cu(I) and Ag(I) complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu(I)(CH(3)CN)(4)](PF(6)) and Ag(I)(PF(6)) with imino nitroxides in ethanol solution gave [Cu(I)(immepy)(2)](PF(6)) (1) and [Ag(I)(impy)(2)](PF(6)) (2), respectively (immepy = 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy and impy = 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a = 11.251(2) Å, b = 14.745(3) Å, c = 9.747(2) Å, V = 1617.0(5) Å(3), and Z = 2. Refinement with 991 reflections observed [|I(o)| > 3sigma(I(o))] gave R = 0.044 (R(w) = 0.053). In 1, imino nitroxides coordinate to the Cu(I) ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-)(1) with g = 2.0; H = -JS(1)().S(2)()). The UV-visible absorption spectrum of 1 shows strong bands at 464 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Å, b = 31.295(3) Å, c = 8.921(4) Å, V = 2941(1) Å(3), and Z = 4. Refinement with 1882 reflections [|I(o)| > 3sigma(I(o))] gave R = 0.058 (R(w) = 0.074). In 2, the four coordination sites of the Ag(I) ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (|D| = 0.043 cm(-)(1) and |E| = 0.014 cm(-)(1)). Curie plots for the Deltam = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

Journal Article↗
PubMed1997

A One-Dimensional Helical Copper(II) Imino Nitroxide.

The reaction of [Cu(I)(CH(3)CN)(4)](PF(6)) with a biradical of imino nitroxide in methanol yielded a copper(II) complex [Cu(II)(imapy)](PF6) (2) (Himapy = 2-(1'-oxy-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)-6-(1"-oxyl-4",4",5",5"-tetramethyl-4",5"-dihydro-1"H-imidazol-2"-yl)pyridine)). In 2 one of the nitroxides in the ligand was reduced to a hydroxyamino anion and the Cu(I) ion was oxidized. Complex 2 crystallizes in tetragonal space group P4(3)2(1)2 with a = 14.341(3) Å, c = 24.282(5) Å, V = 4993(1) Å(3), and Z = 8, and the absolute structure for this crystal was determined by using Flack's parameter. Square planar coordination sites of the Cu(II) ion are occupied by two nitrogen and two oxygen atoms, where one of the coordinated oxygen atoms comes from the hydroxyamino group in the next molecule. The Cu(II) ions are bridged by the imino-hydroxyamino anion to form a one-dimensional structure with each Cu(II) ion having the coordinated imino nitroxide. Complex molecules locate on the 4-fold screw axis, which results in a counterclockwise helical arrangement of the imino nitroxides. Magnetic susceptibility measurements revealed that antiferromagnetic interactions are operative. The system was treated as the one-dimensional chain of the Cu(II)-radical species, and coupling constants J(1) and J(2) for the intrachain and Cu(II)-radical interactions were estimated to be -6 and -23 cm(-)(1), respectively.

Journal Article↗
PubMed1996

A Ferromagnetic Interaction between Cu(2+) Centers through a [CrO(4)](2-) Bridge: Crystal Structures and Magnetic Properties of [{Cu(acpa)}(2)(&mgr;-MO(4))] (M = Cr, Mo) (Hacpa = N-(1-Acetyl-2-propyridene)(2-pyridylmethyl)amine).

The reaction of [Cu(acpa)](+) with [MO(4)](2)(-) (Hacpa = N-(1-acetyl-2-propyridene)(2-pyridylmethyl)amine and M = Cr and Mo) in water-methanol or water-acetonitrile solution affords dinuclear copper(II) complexes with metalate bridges, [{Cu(acpa)}(2)(&mgr;-CrO(4))].4CH(3)OH.4H(2)O (1) and [{Cu(acpa)}(2)(&mgr;-MoO(4))].4H(2)O (2), respectively. The crystal structures and the magnetic properties have been studied. Complexes 1 and 2 are isomorphous and the structures are made up of discrete dimers in which two copper(II) ions are bridged by the [MO(4)](2)(-) anion. The coordination geometry about the copper(II) ions is square planar with a N(2)O chelate group from acpa and an oxygen atom from [MO(4)](2)(-). Magnetic susceptibility measurements for 1 revealed that a ferromagnetic interaction between copper(II) ions is propagated through the [CrO(4)](2)(-) bridge and the coupling constant (2J) was evaluated to be 14.6(1) cm(-)(1) (H = -2JS(1).S(2)). In 2, two copper(II) ions bridged by [MoO(4)](2)(-) anion are antiferromagnetically coupled with the 2J value of -5.1(4) cm(-)(1). The ferromagnetic interaction in 1 is explained by means of the orbital topology of frontier orbitals. Crystal data: 1, monoclinic, space group P2(1)/m, a = 8.349(2) Å, b = 17.616(3) Å, c = 10.473 Å, beta = 107.40(2) degrees, Z= 2; 2, monoclinic, space group P2(1)/m, a = 8.486(2) Å, b = 18.043(3) Å, c = 9.753(2) Å, beta = 95.82(2) degrees, Z = 2.

Journal Article↗
PubMed1996

Intermolecular Ferromagnetic and Antiferromagnetic Interactions in Halogen-Bridged Copper(I) Imino Nitroxides: Crystal Structures and Magnetic Properties of [Cu(I)(&mgr;-X)(imino nitroxide)](2) (X = I or Br).

Reaction of CuI or CuBr with some imino nitroxides in methanol gave the halogen bridged dinuclear Cu(I) complexes [Cu(&mgr;-I)(impy)](2) (1), [Cu(&mgr;-I)(immepy)](2) (2), [Cu(&mgr;-Br)(immepy)](2) (3), and [Cu(&mgr;-Br)(imph-NO(2))](2) (4), respectively (impy = 2-(2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl, immepy = 2-(6'-methyl-2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl, imph-NO(2) = 2-(4'-nitrophenyl)-4,4,5,5-tetramethyl-4,6-dihydro-1H-imidazolyl-1-oxyl). Crystal structures and magnetic properties have been studied. Complexes 1-4 have dimeric structures where two copper ions are doubly bridged by halide ions in a &mgr;(2) fashion. In 1-3, each copper ion is tetrahedral with a bidentate imino nitroxide and two halide ions, and the two copper ions are separated by 2.592(2), 2.6869(8), and 2.7357(6) Å, respectively. In 4, triangular coordination sites of the copper ions are completed with a nitrogen atom from the imino nitroxide and two bromide ions bridging the two copper ions with a separation of 3.074(2) Å. Ligand imino nitroxides in 1-4 form one-dimensional radical chains, and the chains are linked with halocuprate dimer units. Structural and magnetic susceptibility data support that radicals in 1 and 4 are ferromagnetically stacked, while radicals in 2 and 3 form an antiferromagnetic chain. The magnetic behaviors are discussed in connection with the stacking modes of the radicals and bridging conformations. Crystal data (Mo Kalpha, lambda = 0.71069 Å): 1, orthorhombic, space group P2(1)2(1)2(1), a = 17.807(2) Å, b = 8.595(2) Å, c = 19.336(6) Å, and Z = 4; 2, monoclinic, space group P2(1)/c, a = 9.941(2) Å, b = 18.482(2) Å, c = 8.337(2) Å, beta = 96.41(2) degrees, and Z = 2; 3, monoclinic, space group P2(1)/c, a = 9.964(6) Å, b = 18.167(4) Å, c = 8.009(7) Å, beta = 95.81(6) degrees, and Z = 2; 4, monoclinic, space group P2(1)/c, a = 11.991(7) Å, b = 17.998(8) Å, c = 7.215(6) Å, beta = 104.07(6) degrees, and Z = 2.

Journal Article↗