Norihisa Hoshino

Three-way switching in a cyanide-bridged [CoFe] chain

Bistable compounds that exist in two interchangeable phases under identical conditions can act as switches under external stimuli. Among such switchable materials, coordination complexes have energy levels (or phases) that are determined by the electronic states of their constituent metal ions and ligands. They can exhibit multiple bistabilities and hold promise in the search for multifaceted materials that display different properties in different phases, accessible through the application of contrasting external stimuli. Molecular systems that exhibit both thermo- and photoinduced magnetic bistabilities are excellent candidates for such systems. Here we describe a cyanide-bridged [CoFe] one-dimensional chiral coordination polymer that displays both magnetic and electric bistabilities in the same temperature range. Both the electric and magnetic switching probably arise from the same electron-transfer coupled spin-transition phenomenon, which enables the reversible conversion between an insulating diamagnetic phase and either a semiconducting paramagnetic (thermoinduced) or a type of ferromagnetic single-chain magnet (photoinduced) state.

A Light-Induced Phase Exhibiting Slow Magnetic Relaxation in a Cyanide-Bridged [Fe4Co2] Complex†

Single-molecule magnets: A cyanide-bridged hexanuclear complex showed a thermal electron-transfer-coupled spin transition centered at 220 K. Light irradiation at low temperature (LT; HT = high temperature) generated a metastable state showing slow magnetic relaxation in measurements of the alternating-current magnetic susceptibility (χ(m); see picture).

Molecular magnets containing wheel motifs.

An overview of some compounds with structures that can be regarded as derived from an {Fe(7)(mu(3)-OR)(6)(mu-OR)(6)} motif is presented. Many of these compounds act as single-molecule magnets. In addition, the results of a comprehensive study on the single-crystal structures, magnetism, and spin structures for five new iron compounds with structural components related to this are given. This serves to illustrate the methodology that can be used to unravel the complicated magnetic behavior of such systems. Thus, the alkoxo- and phenoxo-bridged multinuclear iron complexes, [Fe(II)(7)(Hbmsae)(6)(OMe)(6)]Cl(2) x 6 H(2)O (6), [Fe(II)Fe(III)(6)(bmsae)(6)(mu(3)-OMe)(6)]Cl(2) x 23 H(2)O (7), [NaFe(III)(6)(bmsae)(6)(mu(3)-OMe)(6)]Cl x 30 H(2)O (8), [Fe(III)(3)(bmsae)(3)Cl(2)(MeOH)(OMe)] x MeOH x Et(2)O (9), and [Fe(III)(2)(Hbmsae)(2)(OMe)(2)Cl(2)][Fe(3)(bmsae)(3)(OMe)Cl(2)(MeOH)](2) x 1.5 MeOH (10), were prepared by the reactions of iron sources with Schiff base ligands (H(2)bmsae = 5-bromo-3-methoxysalicylideneaminoethanol). Heptanuclear complexes of 6 and 7 have wheel structures in which six iron(II) and six iron(III) ions locate on the rim with the central iron(II) ions, respectively, while 8 also has a wheel structure with a diamagnetic sodium ion in the center. 9 is a trinuclear ferric complex with an incomplete cubic structure. In 10, di- and trinuclear complexes exist in the crystal, where the trinuclear complex has an incomplete cubic structure similar to that of 9. Magnetic susceptibility measurements revealed that 6 has an S = 10 spin ground state, while the antiferromagnetic interactions dominate in 7-10.

Undecanuclear mixed-valence 3d–4f bimetallic clusters

Two undecanuclear 3d-4f clusters with the general formula {Mn(III)(4)Mn(IV)Ln(III)(6)}, where Ln = Gd or Tb, were synthesized, with both showing large spin ground states, and the Tb species acting as a single molecule magnet.

Solvent Responsive Magnetic Dynamics of a Dinuclear Dysprosium Single‐Molecule Magnet

A new dysprosium(III) phosphonate dimer {Dy(notpH4)(NO3)(H2O)}2·8H2O (1) [notpH6=1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid)] that contains two equivalent Dy(III) ions with a three-capped trigonal prism environment is reported. Complex 1 can be transformed into {Dy(notpH4)(NO3)(H2O)}2 (2) in a reversible manner by desorption and absorption of solvent water at ambient temperature. This process is accompanied by a large dielectric response. Magnetic studies reveal that both 1 and 2 show thermally activated magnetization relaxation as expected for single-molecule magnets. Moreover, the magnetic dynamics of the two compounds can be manipulated by controlling the number of solvent molecules at room temperature.

Cyanide-bridged iron(II,III) cube with multistepped redox behavior.

A building unit of Prussian blue was isolated as a cyanide-bridged iron cube of [Fe(II)4Fe(III)4(CN)12(tp)8] x 12 DMF x 2 Et2O x 4 H2O [tp(-) = hydrotris(pyrazolyl)borate]. A cyclic voltammogram showed quasi-reversible four-stepped redox waves, which correspond to [Fe(III)4Fe(II)4]/[Fe(III)5Fe(II)3](+), [Fe(III)5Fe(II)3](+)/[Fe(III)6Fe(II)2](2+), [Fe(III)6Fe(II)2](2+)/[Fe(III)7Fe(II)1](3+), and [Fe(III)7Fe(II)1](3+)/[Fe(III)8](4+) processes. Controlled potential absorption spectral measurements revealed two intervalence charge-transfer bands at 816 and 1000 nm, which were assigned to charge transfers from Fe(II) ions to adjacent and remote Fe(III) ions, respectively, in the cube.

Syntheses, structures and magnetic properties of multinuculear manganese complexes with Schiff base ligands

Abstract Multinulear manganese complexes with Schiff base ligands, [{MnIII4(μ3-O)(sae)4(μ-N3)(CH3OH)}2(μ-N3)]N3 ([1]N3), [MnIII6(μ3-O)2(sae)6(NCS)2] (2) and [MnII4MnIII2(sae)6(CH3OH)2Cl2] (3) (H2sae=2-salicylideneaminoethanol), were prepared and the crystal structures and magnetic properties were studied.

Thermally driven polymorphic transition prompting a naked-eye-detectable bending and straightening motion of single crystals.

The amplification of molecular motions so that they can be detected by the naked eye (10(7) -fold amplification from the ångström to the millimeter scale) is a challenging issue in the development of mechanical molecular devices. In this context, the perfectly ordered molecular alignment of the crystalline phase has advantages, as demonstrated by the macroscale mechanical motions of single crystals upon the photochemical transformation of molecules. In the course of our studies on thermoresponsive amphiphiles containing tetra(ethylene glycol) (TEG) moieties, we serendipitously found that thermal conformational changes of TEG units trigger a single-crystal-to-single-crystal polymorphic phase transition. The single crystal of the amphiphile undergoes bending and straightening motion during both heating and cooling processes at the phase-transition temperatures. Thus, the thermally triggered conformational change of PEG units may have the advantage of inducing mechanical motion in bulk materials.

Structures and magnetic properties of metal cubes

Abstract Structures and magnetic properties of copper(II), nickel(II) and manganese(II) cubes are presented. In the cubes, four metal ions are assembled into the cubes by tridentate Schiff base ligands. Magnetic succeptibility measurements revealed the copper and nickel cubes have high-spin ground state, while the manganese cube has a S =0 spin ground state.

Contrasting Magnetism of [MnIII4] and [MnII2MnIII2] Squares

Two tetranuclear manganese distorted square-shaped clusters, [Mn(III)(4)(L1)(4)(mu(2)-OMe)(4)].2.5H(2)O (1) and [Mn(II)(2)Mn(III)(2)(L2)(4)(H(2)O)(2)](PF(6))(2).CHCl(3).CH(3)OH.1.5H(2)O (2) (H(2)L1 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridinecarboxylic acid methyl ester; H(2)L2 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridinecarboxylic acid ethyl ester), exhibit antiferromagnetic and ferromagnetic interactions between neighboring manganese ions, respectively.