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New pyrazine (pz)- and 4,4′-bipyridine (4,4′-bpy)-bridged octahedral hexanuclear rhenium(III) cluster dimers, [{Re6(μ3-S)8Cl5}2(μ-L)]6–(L = pz, [1]6–; L = 4,4′-bpy, [2]6–), with 2 × 24 d-electrons {Re6(24e)}2were obtained in a single-step reaction via photoirradiation of [Re6(μ3-S)8Cl6]4–with L in a 2:1 ratio at room temperature. The {Re6(23e)}2dimers, [{Re6(μ3-S)8Cl5}2(μ-L)]4–(L = pz, [1′]4–; L = 4,4′-bpy, [2′]4–), were synthesized through two-electron oxidation of [1]6–and [2]6–, respectively. The single-crystal X-ray structures of [1]6–and [1′]4–were determined, revealing structural distortion of the Re6core of [1′]4–due to the Jahn–Teller effect. The cyclic voltammograms of [1]6–and [2]6–showed two steps of one-electron redox processes attributable to Re6(23e)Re6(24e)/{Re6(24e)}2and {Re6(23e)}2/Re6(23e)Re6(24e), respectively. The separation between the two redox potentials is small (0.056 V for [1]6–and 0.039 V for [2]6–). The magnetic susceptibilities of [1′]4–and [2′]4–were almost temperature-independent, with values of 2.98 and 2.85 μB, respectively, indicating paramagnetism. These results suggest weak electronic interaction between two cluster units bridged by pz or 4,4′-bpy in the intercluster mixed valence state. The compounds [1]6–and [2]6–show photoluminescence in the near-infrared region at 296 K in the solid state.

Schizophyllan, a triple helical polysaccharide, exhibits cooperative order–disorder transition (CODT) in aqueous solutions. The transition transforms the ordered structure (triple helix I) formed between the branched side chains and solvent molecules into the disordered structure (triple helix II) without dissociation of the triple helix. The CODT behaviors in H2O–imidazole mixtures containing HCl with different molar ratios of imidazole/HCl were investigated by adiabatic calorimetry and differential scanning calorimetry on two schizophyllan solutions with different molar masses. The transition temperature (Tr) and the transition enthalpy (ΔHr) significantly depended on both of the mole fractions of imidazole and imidazole/HCl. The composition dependences of Trand ΔHrin H2O–imidazole mixtures were analyzed with linear cooperative transition theory for the solvent-stabilizing effect in the mixture with active compounds. Theoretical analyses confirmed that both imidazole and imidazolium ions in the solutions competitively interact with the side chain of the triple helix.

Orbital angular momentum plays a vital role in various applications, especially magnetic and spintronic properties. Therefore, controlling orbital angular momentum is of paramount importance to both fundamental science and new technological applications. Many attempts have been made to modulate the ligand-field-induced quenching effects of orbital angular momentum to manipulate magnetic properties. However, to date, reported changes in the magnitude of orbital angular momentum are small in both molecular and solid-state magnetic materials. Moreover, no effective methods currently exist to modulate orbital angular momentum. Here we report a dynamic bond approach to realize a large change in orbital angular momentum. We have developed a Co(II) complex that exhibits coordination number switching between six and seven. This cooperative dynamic bond switching induces considerable modulation of the ligand field, thereby leading to substantial quenching and restoration of the orbital angular momentum. This switching mechanism is entirely different from those of spin-crossover and valence tautomeric compounds, which exhibit switching in spin multiplicity.

Two crystal polymorphs of Ni(cyclam)I2(cyclam = 1,4,8,11-tetraazacyclotetradecane) were synthesized, and their magnetic properties were investigated. Temperature-dependent X-ray structural analysis and magnetic measurements revealed gradual spin transition in molecular-crystal polymorph trans-[Ni(cyclam)I2] (1a), whereas the zigzag-chain polymorph catena-[Ni(cyclam)(μ-I)]I (1b) did not show an obvious spin transition. The entropy difference between high- and low-spin states of 1aestimated by assuming the spin-equilibrium model is much smaller than those in typical iron(II)-based spin-crossover (SCO) complexes, suggesting that the normal mode softening is less remarkable in 1a. In this system, it is clearly evidenced that the interaction mode responsible to the spin equilibrium in octahedral nickel(II) complexes is highly anistropic, i.e., z-elongation and x,y-shortening of the coordination octahedron.

We report the structures and the electronic properties of a novel terphenoquinone derivative having a benzo[1,2-b:4,5-b′]dithiophene (BDT) unit as a central ring. This molecule exhibits the open-shell biradical characters resulting from the thermally accessible open-shell structure. X-ray structure analysis and magnetic measurements clarify that this molecule has a closed-shell ground state, which is lower than the open-shell biradical state by 10.4 kJ mol−1. The electronic absorption and electrochemical measurements reveal the small HOMO–LUMO gap about 1.3 eV of this molecule.We synthesized a novel terphenoquinone derivative having a benzo[1,2-b:4,5-b′]dithiophene (BDT) unit as a central ring. This molecule shows open-shell characters at room temperature resulting from the thermally accessible triplet state. The X-ray structure analysis and the magnetic measurements clarified that this molecule has a closed-shell ground state, which is lower than the triplet state by 10.4 kJ mol−1.

A large magnetic anisotropywas achieved around the DyIIIion, and a single‐molecule magnet behavior has been observed up to 35 K for the dinuclear complex DyIII–ZnII. The magnetic relaxation occurs through three different pathways depending on the temperature and the presence of an external dc field (see scheme).

Stärkeres magnetisches Moment mit weniger Elektronen: Der α‐Keggin‐Einzelmolekülmagnet {Mn13} wurde hergestellt und oxidiert (siehe Bild); die Ein‐ und Zwei‐Elektronen‐Oxidationsprodukte konnten isoliert werden. Die Spingrundzustände der stärker oxidierten Verbindungen liegen trotz des Elektronenverlustes höher, was zur Verstärkung der magnetischen Eigenschaften führt.

Zwei gemischtvalente Eisen‐Cobalt‐ Clusterwurden mithilfe mehrzähniger Polypyridylliganden synthetisiert (siehe Bild: FeIIorange, FeIIIgelb, CoIIblau, O rot). Eine siebenkernige Helix und ein Komplex mit einem [3×3]‐Gitter entstehen abhängig vom Metallionenverhältnis. Den Ergebnissen von ESI‐MS‐Messungen zufolge könnte der helicale Cluster eine Zwischenstufe auf dem Weg zum gitterförmigen Komplex sein.

Designer SMM: An ErIII‐based single‐molecule magnet (SMM) was synthesized by designing the ligand‐field anisotropy around an ErIIIion in an equatorial arrangement of donors using a rigid and planar macrocyclic Schiff base ligand including three ZnIIions. The resulting ErIIIZnII3complex (see picture; C gray, O red, N blue) behaves as a SMM with an energy barrier of 24.6(9) K for flipping of the molecular magnetic moment.

A single magnet in a triple decker!TbIII–phthalocyaninate triple‐decker 1, which has a center of symmetry, showed two magnetic relaxation processes in the low‐temperature region in the presence of a direct current (dc) magnetic field. These results suggest that the single‐molecule magnet/magnetic properties of 1undergo a significant transition in a dc magnetic field.

Four dinuclear LnIIICuIIcomplexes with Ln=Tb (1), Dy (2), Ho (3), and Er (4) were synthesized to investigate the relationship between their respective magnetic anisotropies and ligand‐field geometries. These complexes were crystallographically isostructural, and a uni‐axial ligand field was achieved by using three phenoxo oxygen groups. Complexes 1and 2displayed typical single‐molecule magnet (SMM) behaviors, of which the out‐of‐phase susceptibilities were observed in the temperature range of 1.8–5.0 K (1) and 1.8–20.0 K (2). The Cole–Cole plots exhibited a semicircular shape with αparameters in the range of 0.08–0.18 (2.6–4.0 K) and 0.07–0.24 (3.5–7.0 K). The energy barriers Δ/kBwere estimated from the Arrhenius plots to be 32.9(4) K for 1and 26.0(5) K for 2. Complex 3displayed a slow magnetic relaxation below 3.0 K, whereas complex 4did not show any frequency‐dependent behavior for both in‐phase and out‐of‐phase susceptibilities, which indicates that easy‐axis anisotropy was absent. The temperature dependence of the dc susceptibilities for the field‐aligned samples of 1–3revealed that the χMTvalue continuously increased as the temperature was lowered, which indicates the presence of low‐lying Stark sublevels with the highest |Jz| values. In contrast, complex 4displayed a smaller and temperature‐independent χMTvalue, which also indicates that easy‐axis anisotropy was absent. Simultaneous analyses were carried out for 1–3to determine the magnetic anisotropy parameters on the basis of the Hamiltonian that considers B20, B40, and B60.

A novel topologically frustrated pentanuclear cluster helicate [{CuII(μ‐L)3}2CuII3(μ3‐OH)]3+(L−=3,5‐bis(2‐pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky–Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high‐field/multi‐frequency (HF/MF)‐ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu5‐cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system.

The different thermally induced intermolecular electron transfer (IET) processes that can take place in the series of complexes [M(Cat‐N‐BQ)(Cat‐N‐SQ)]/[M(Cat‐N‐BQ)2], for which M=Co (2), Fe (3) and Ni(4), and Cat‐N‐BQ and Cat‐N‐SQ denote the mononegative (Cat‐N‐BQ−) or dinegative (Cat‐N‐SQ2−) radical forms of the tridentate Schiff‐base ligand 3,5‐di‐tert‐butyl‐1,2‐quinone‐1‐(2‐hydroxy‐3,5‐di‐tert‐butylphenyl)imine, have been studied by variable‐temperature UV/Vis and NMR spectroscopies. Depending on the metal ion, rather different behaviors are observed. Complex 2has been found to be one of the few examples so far reported to exhibit the coexistence of two thermally induced electron transfer processes, ligand‐to‐metal (IETLM) and ligand‐to‐ligand (IETLL). IETLLwas only found to take place in complex 3, and no IET was observed for complex 4. Such experimental studies have been combined with ab initio wavefunction‐based CASSCF/CASPT2 calculations. Such a strategy allows one to solicit selectively the speculated orbitals and to access the ground states and excited‐spin states, as well as charge‐transfer states giving additional information on the different IET processes.

Grid magnet: A Co8ring and a Co9grid complex are synthesized using a multidentate polypyridine‐type ligand and are shown to exhibit all antiferromagnetic interactions between metal centers, with the grid complex displaying SMM properties as a result of alternating high spin/low spin metal centers in the outer 8‐membered ring.

CobaltII radical complexes with centric and acentric counter anions, [CoClbisimpyMeOH2]X [bisimpy = 2,6bis4′,4′,5′,5′tetramethyl4′,5′dihydro1′Himidazol1′oxyl2′ylpyridine; X = PF61, and ClO42], crystallize in the centrosymmetric and polar space groups, respectively. Compound 1is paramagnetic, whereas spin canting in 2leads to a metamagnetic transition with a critical field of 1300 Oe at 1.8 K. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

Copper cubes: An oxygen‐bridged heptacopper(II) structure, [Cu7(μ3‐OH)6(μ3‐X)2(D‐pends)3], bearing D‐penicillaminedisulfide (D‐H2pends) as an auxiliary ligand was synthesized (see figure). This structure has a novel corner‐sharing double‐cubane framework without an intramolecular inversion center (i), which exhibits different magnetic behavior to that found in related double‐cubane heptacopper(II) clusters with i.

The reaction of N‐(2‐hydroxy‐5‐nitrobenzyl)iminodiethanol (=H3(5‐NO2‐hbide)) with Mn(OAc)2⋅ 4 H2O in methanol, followed by recrystallization from 1,2‐dichloroethane, yielded a wheel‐shaped single‐molecule magnet (SMM) of [MnII3MnIII4(5‐NO2‐hbide)6]⋅5 C2H4Cl2(1). In 1, seven manganese ions are linked by six tri‐anionic ligands and form the wheel in which the two manganese ions on the rim and the one in the center are MnIIand the other four manganese ions are MnIIIions. Powder magnetic susceptibility measurements showed a gradual increase with χmTvalues as the temperature was lowered, reaching a maximum value of 53.9 emu mol−1K. Analyses of magnetic susceptibility data suggested a spin ground state of S=19/2. The zero‐field splitting parameters of Dand ${B{{0\hfill \atop 4\hfill}}}$were estimated to be −0.283(1) K and −1.64(1)×10−5K, respectively, by high‐field EPR measurements (HF‐EPR). The anisotropic parameters agreed with those estimated from magnetization and inelastic neutron scattering experiments. AC magnetic susceptibility measurements showed frequency‐dependent in‐ and out‐of‐phase signals, characteristic data for an SMM, and an Arrhenius plot of the relaxation time gave a re‐orientation energy barrier (ΔE) of 18.1 K and a pre‐exponential factor of 1.63×10−7s. Magnetization experiments on aligned single crystals below 0.7 K showed a stepped hysteresis loop, confirming the occurrence of quantum tunneling of the on magnetization (QTM). QTM was, on the other hand, suppressed by rapid sweeps of the magnetic field even at 0.5 K. The sweep‐rate dependence of the spin flips can be understood by considering the Landau–Zener–Stückelberg (LZS) model.

Three cobalt(II) complexes, [Co(X)2(4NOpy)4] (X = NCO−, NCS−, and Br−; 4NOpy= 4-(N-tert-butylaminoxyl)pyridine) were prepared, and their molecular structures were characterized by X-ray structure analysis. The molecular geometry of [Co(X)2(4NOpy)4] (X = NCO−and NCS−) is a compressed octahedron, in which the counter ions occupy the apical positions with short bond distances of 2.064–2.098 Å. In the crystalline state, from plots of χmolvs Tand χ′molvs T, [Co(NCO)2(4NOpy)4] and [Co(NCS)2(4NOpy)4] are antiferromagnets with TN= 4.5 and 15 K, respectively. In frozen solution, on the other hand, both complexes and [Co(Br)2(4NOpy)4] functioned as single-molecule magnets. The χ″molvs Tplot for [Co(Br)2(4NOpy)4] gave a effective activation barrier (Ueff) of 20 K for the reorientation of the spin. From the field dependence of magnetization at various temperatures below 5 K for [Co(X)2(4NOpy)4] (X = NCO−, NCS−, and Br−) the values of the zero-field splitting parameters, D/kB, were estimated to be −14, −9.7, and −4.5 K with S= 5/2, respectively. Theoretical studies based on the ligand-field theory model for [Co(NCO)2(4NOpy)4] gave an exchange coupling parameter, J/kB, of 29 K and a thermodynamic activation barrier, U, of 60 K.

Micro- and sub-micro particles of complex [Mn12O12(O2CC6H5)16(H2O)4] (1) with controlled size and polymorphism have been prepared by dense-gas crystallization techniques, showing a remarkable particle size influence on the magnetization relaxation rates.

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 dnconfigurations and discuss how molecular anisotropy arises from single‐ion anisotropy of the assembled component metal ions.

The reaction of 1/3 equivalent of CuCl2⋅2 H2O with MnCl2⋅4 H2O and 5‐bromo‐2‐salicylideneamino‐1‐propanol (H25‐Br‐sap) in methanol gave dark brown crystals of [MnIIICuIICl(5‐Br‐sap)2(MeOH)] (1). Complex 1has an alkoxo‐bridged dinuclear core of MnIIIand CuIIions, which have elongated octahedral and square‐planar coordination geometries, respectively. In dc magnetic susceptibility measurements, χmTvalues 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 JMnCuof +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 D5/2value (−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 D5/2value, and fitting of the data gave D5/2=−1.81 cm−1. In the ac magnetic susceptibility measurements, frequency dependent in‐phase (χm′) and out‐of‐phase (χm′′) 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 1is a single‐molecule magnet (SMM). Arrhenius plots for the χm′′ peaks from 0.7–1.5 K gave the re‐orientation energy barrier (ΔE) of 10.5 K with a pre‐exponential factor of 8.2×10−8s.

[NEt4][Pt(ppy)(C3S5)] (ppy−= C-deprotonated 2-phenylpyridine(−); C3S52−= 4,5-disulfanyl-1,3-dithiole-2-thionate(2−)), [NEt4]-, [NBun4][Pt(ppy)(C8H4S8)] (C8H4S82−= 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2−)) and [NEt4][Pt(ppy)(C10–C6S8)] (C10–C6S82−= 2-{bis(decylthio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2−)) were prepared. They showed an intense electronic absorption band due to an intramolecular mixed metal/dithiolate ligand-to-ppy ligand charge transfer transition, which is somewhat sensitive to the solvent. The complexes exhibited first oxidation potentials of −0.27 to +0.02 V (vs Ag/Ag+) due to the dithiolate ligand-centered oxidation. They were oxidized by TCNQ and iodine to afford [Pt(ppy)(L)] and [Pt(ppy)(L)](I1.0–4.2) (L = C3S52−, C8H4S82−, and C10–C6S82−). Electrical conductivities of the oxidized C8H4S8- and C10–C6S8-species measured for compacted pellets at room temperature were 6.2 × 10−6–7.8 × 10−3S cm−1, while those of the oxidized C3S5-species were very low [(3.8–6.2) × 10−9S cm−1]. The X-ray crystal structure of [NBun4][Pt(ppy)(C8H4S8)] was clarified.

[Rh(η⁵-C5H5)(C8H4S8)] and [M(η⁵-C5Me5)(C8H4S8)] [M = Rh^III and Ir^III. C8H4S8²⁻ = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2−)] were prepared by reactions of [NMe4]2[C8H4S8] with [Rh(η⁵-C5H5)Cl2]2 or [M(η⁵-C5Me5)Cl2]2 (M = Rh and Ir). They exhibit oxidation potentials of between +0.16 and +0.24 V (versus Ag/Ag⁺) with oxidation of the dithiolate ligand. The geometries and electronic states of their one-electron-oxidized species [M(L)(C8H4S8)]⁺ and [RhX(L)(C8H4S8)] (M = Rh and Ir; X = Br and I; L = η⁵-C5H5 and η⁵-C5Me5), obtained by reactions of the above complexes with bromine, iodine, or the ferrocenium cation are discussed based on their ESR spectra. The oxidized η⁵-C5Me5-metal complexes exhibit electrical conductivities of between 10⁻⁶ and 10⁻⁴ S cm⁻¹, while some oxidized η⁵-C5H5-Rh complexes show conductivities of between 10⁻³ and 10⁻² S cm⁻¹ measured for compacted pellets at room temperature. The X-ray crystal structures of the two-electron-oxidized species [MI(η⁵-C5Me5)(C8H4S8)](I3) (M = Rh and Ir) were also clarified. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Crystals of [Au(ppy)(C8H4S8)]2[PF6] [ppy⁻ = C-deprotonated 2-phenylpyridine(−); C8H4S8²⁻ = 2-{(4,5-ethylenedithio)-1,3-dithiol-2-ylidene}-1,3-dithiole-4,5-dithiolate(2−)] were prepared by current-controlled electrolysis of a benzonitrile solution of [Au(ppy)(C8H4S8)] with [NEt4][PF6] as an electrolyte. The X-ray crystal structure analysis revealed the formation of a columnar stacking of two crystallographically independent cations in formally the 0.5-electron-oxidized state. Cation moieties with some S−S non-bonded contacts (< 3.7 Å) along the a and b axes form a two-dimensional sheet, with the molecular interaction parallel to the ab plane. The electrical conductivities measured for a crystal at room temperature were 9.2 and 0.0028 S cm⁻¹ along the a and c axes, respectively. From the activation energy for the electron conduction determined by the conductivities measured for a compacted pellet the complex was estimated to be metallic from room temperature to 110 K. The energy-band calculation for the oxidized species showed two-dimensional electron conduction through the column. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Electromotive force of galvanic cells with zirconia solid electrolytes was measured to determine the activity of gallium in liquid Ga-In-Te alloys in the temperature range of 1000 to 1200 K along 3 psuedobinary lines of (In_yTe_1−y)-Ga where y= 0.25, 0.50 and 0.75. The mixture of Ga and Ga₂O₃ was used as a reference electrode. The activity curves of Ga are very complicated at 1073 K. Isoactivity curves at 1073 K in the ternary Ga-In-Te alloys were derived by combining the activity data of Ga-In and Ga-Te alloys. Using Darken's equation, 2 binary data of Ga-In and Ga-Te and ternary data in this study, ΔG^XS at 1073 K were derived. The results were compared with those from 3 model calculations proposed by Toop, Kohler and Chou to show better agreement between the experimental values and those by Toop's and Chou's models.

[NMe4]2[Sn(C3S5)3], [NBun4]2[Sn(C3S5)3], [NBun4]2[Sn(C8H4S8)3], [NEt4][Sn(Bun)(C8H4S8)2] and [NBun4][Sn(Ph)(C8H4S8)2] [C3S52-= 4,5-disulfanyl-1,3-dithiole-2-thionate(2-) ; C8H4S82-= 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-ditholate(2-)] were prepared by reactions of Na2[C3S5] or Na2[C8H4S8] with SnCl4·5H2O, Sn(Bun)Cl3and Sn(Ph)Cl3in EtOH. [NBun4]2[Sn(C8H4S8)3] was oxidized by iodine or TCNQ in DMF/CH2Cl2to give [Sn(C8H4S8)3], which exhibited an electrical conductivity of 3.2 × 10-2S cm-1(compacted pellet at room temperature). [NBun4]2[Sn(C3S5)3], [NEt4][Sn(Bun)(C8H4S8)2] and [NBun4][Sn(Ph)(C8H4S8)2] were oxidized by iodine or TCNQ in acetone or in DMF to afford (C3S5)2and (C8H4S8)n. Crystal structures of [NMe4]2[Sn(C3S5)3], [NBun4]2[Sn(C3S5)3], [NBun4][Sn(Ph)(C8H4S8)2] and (C3S5)2were determined by X-ray crystallography.

[Pt(bpy)(C 8 H 4 S 8 )][BF 4 ] (bpy=2,2′-bipyridine; C 8 H 4 S 8 =2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2-)) was prepared by current-controlled electrolysis of a dichloromethane solution of [Pt(bpy)(C 8 H 4 S 8 )] with [NEt 4 ][BF 4 ] as an electrolyte. The X-ray crystal structure analysis revealed a columnar stacking of the one-electron oxidized, cationic moieties with some S-S non-bonded contacts (<3.7 A˚) as well as an S-S layered interaction in another direction. The electrical conductivity measured for a compacted pellet was 5.0×10 S cm at room temperature with activation energy of 0.05 eV. The energy band calculation of the oxidized species showed an essentially one-dimensional electron-conduction through the column.

Embedding of bistable molecules into an organic conductor is expected to yield interesting hysteretic conductive properties. As a typical bistable species switchable under a temperature change, a spin-crossover iron(III) complex was utilized to prepare two charge-transfer salts containing an organic acceptor molecule, [Fe(acpa) 2 ](TCNQ) n (Hacpa = N -(1-acetyl-2-propylidene)-2-pyridyl-methylamine; TCNQ = 2,2'-(2,5-cyclohexadien-1,4-diylidene)-bispropanedinitrile), and their magnetic and electrical properties were studied. While magnetic behavior of dilute spin-crossover complex molecules is well described by an entropy-driven spin equilibrium between low-spin and high-spin states across an energy gap, intermolecular interactions should be taken into account and often abrupt phase transitions are found in densely-packed complex molecules like crystalline solids. In order to delineate these systems in a unified manner, a phenomenological two-state model based on a mean-field approximation was examined. It worked well to reproduce the temperature dependence of electrical conductivities associating with a spin-crossover transition assuming a Slater-type distance dependence for the band gap. spin-crossover phenomena iron(III) complex TCNQ Chesnut model first-order phase transition band gap

The magnetic behavior of the nickel cubane complex [Ni 4 (Ome) 4 -(sal) 4 (MeOH) 4 ](Hsal=salicylaldehyde) was studied by using a Hartshorn bridge equipped with a 3 He/ 4 He dilution refrigerator. This complex has long been known to have a well-isolated high-spin ground state with S =4 and it was suggested to have an easy-axis type anisotropy. AC magnetic susceptibility data clearly show a slow magnetization reversal below 0.3 K, characteristic of single-molecule magnets. The Arrhenius plot of the relaxation rate provides the activation energy of about 5 K.

The spin-crossover phenomena of iron complexes accompany with molecular deformations such as symmetric breathing and trigonal torsion. Thus they can serve as a sensitive probe to molecular surroundings. A confinement effect into interlayer spaces of a clay host compound, NaTSM (sodium fluorotetrasilicic mica), was studied for iron complexes by magnetic susceptibility and 57 Fe Mössbauer spectroscopy. Guest complexes examined are [Fe II -(amp) 3 ] 2+ (amp=2-aminomethylpyridine), [Fe III (acpa) 2 ] + (Hacpa= N -(1-acetyl-2-propylidene)-2-pyridylmethylamine), and [Fe III - (sal 2 trien)] + (H 2 sal 2 trien= N , N ′-disalicylidenetriethylenetetramine). A remarkable reduction of the high spin-low spin energy gap in the interlayer space was observed.

The preparation and physical characterization are reported for the single-molecule magnet salts A[Mn12O12(O2CC6H4F(-o))16(H2O)4] (A+=PPh4+ (2a), Fe(C5Me5)2+ (2b), and Co(C5Me5)2+ (2c)). The effects of the magnetic cation on the magnetization relaxation behavior of the [Mn12]− anions are investigated. All complexes exhibit out-of-phase ac magnetic susceptibility (χ″M) signals in the 4.8–5.1 K range at 1 kHz ac frequency. The temperature of the χ″M peaks is frequency dependent, as expected for a single-molecule magnet. From Arrhenius plots of the frequency dependence of the temperature of the χ″M peaks, the effective energy barriers Ueff for changing the magnetization direction from spin “up” to spin “down” were estimated to be in the 52–57 K range. Magnetization hysteresis loops were observed for all the complexes studied. They show clear hysteresis loops with steps, indicating the effect of the magnetic cation on the magnetization relaxation of the anionic [Mn12]− complex is rather small. The least-squares fittings of variable-field magnetization data show the ground state of complex 2a is best described as S=21/2 with g=1.96 and D=−0.56 K, while complexes 2b and 2c have S=19/2 ground states. The fitting parameters are g=1.96 and D=−0.54 K for complex 2b and g=1.95 and D=−0.57 K for complex 2c. These analyses show the magnetic cation has essentially no effect on the ground state spin or on the parameters g and D for the [Mn12]− anion.

AbstractCo(η5-C5H5)(C8H4S8), Ti(η5-C5H5)2(C8H4S8)2], [NMe4][Ti(η5−C5H5)(C8H4S8)2], and [NMe4] [Zr(η5−C5H5)(C8−H4S8)2] [C8H4S82−= 2−{(4,5-ethylenedithio)−1,3-dithiole-2-ylidene}−1,3-dit hiole−4,5-dithiolate(2−)] were prepared. They exhibited low oxidation potentials [−0.23 − +0.45 V (vs.SCE)] for the C8H4S8ligand oxidation and were oxidized by iodine or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) to afford [Co(η5-C5H5)−(C8H4S8)] (I3), [Ti(η5-C5H5)2(C8H4S8)](I3), [Ti(η5-C5H5)−(C8H4S8)2](I3)0.3, [Ti(η5−C5H5) (C8H4S8)2] (TCNQ)0.3, and [Zr−(η5-C5H5)(C8H4S8)2]. These oxidized species showed electrical conductivities of 0.19 − 1.0 × 10−4S cm−1at room temperature for compacted pellets.

Heat capacities of the molecule-based antiferromagnet MnCu(obbz)·5H2O (obbz = oxamidobis(benzoato)) have been measured at temperatures from 0.1 to 300 K by means of adiabatic calorimetry. A phase transition due to three-dimensional antiferromagnetic ordering was observed at 2.18 K, above which a heat capacity hump appeared, arising from the short-range ordering characteristic of a low-dimensional magnet. The enthalpy and entropy gained at the magnetic phase transition were evaluated to be 48.6 J mol-1and 12.1 J K-1mol-1, respectively. This entropy gain is close to the value Rln 5 ( = 13.4J K-1mol-1) expected for the spin-manifold of the S= 2 ground state. The heat capacity hump above the magnetic transition temperature is explained well by the S= 2 one-dimensional ferromagnetic Heisenberg model with the exchange interaction J/kB= 0.75 K, where kBis the Boltzmann constant. These results confirm that the present complex behaves as a one-dimensional ferrimagnet, in which strong antiferromagnetic coupling exists between a pair of spins of Mn(II) (S= 5/2) and Cu(II) (S= 1/2) but the magnetic interaction is very weak between the pairs. A first-order phase transition was also found at 268.4 K. This transition may arise from orientational order–disorder mechanism of the crystalline water molecules in the complex.

Reactions of [NBun4]2[PtCl4] with Na2[C6S8R2] [C6S8R22– = 2-{bis(alkylthio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2–); R = C10H21, C14H29 or C18H37] in methanol afforded [NBun4]2[Pt(C6S8R2)2]. The crystal structure of [NBun4]2[Pt{C6S8(C10H21)2}2] was determined by X-ray analysis. The crystal packing structure consists of columns of anion units assembled through the association of alkyl chains, where the metal-center units are separated by the bulky cations. These complexes exhibit oxidation potentials of –0.25 to +0.35 4;V vs. SCE. They were oxidized by bromine or iodine to yield essentially two-electron oxidized species [Pt(C6S8R2)2]0, with ligand-centered oxidation. The oxidized complexes (R = C10H21 and C14H29) exhibit electrical conductivities (σ) of 1.4 × 10–2 to 4.9 × 10–2 4;S 4;cm–1 measured for compacted pellets at room temperature, while the oxidized species with R = C18H37 behaves as an insulator (σ < 10–8 4;S 4;cm–1). Electronic states and molecular interactions of the complexes in the solid state are discussed based on EPR, XPS, electronic absorption and reflectance spectra.

Typical molecular-based magnets, decamethylferrocenium tetracyanoethenide ([DMeFc][TCNE]) and decamethylferrocenium tetracyanoquinodimethanide ([DMeFc][TCNQ]), have been studied by means of adiabatic calorimetry. The Curie temperature of [DMeFc][TCNE] was determined to be Tc - 4.74 K. The excess entropy derived from the observed heat-capacity anomaly was very close to the expected magnetic entropy, 2 R In 2. Detailed analysis of the heat-capacity anomaly revealed that [DMeFc][TCNE] is a good one-dimensional (ID) Ising magnet. Two structural phase transitions were found for the first time at 248.7 and 281.8 K, and attributed to the orientational order-disorder character of the TCNE anion. For [DMeFc][TCNQ] an antiferromagnetic phase transition was observed at TN = 2.54 K. The magnetic lattice anisotropy of the TCNQ salt is smaller than that of the TCNE salt.

AbstractSeveral [M(C3S5)3]n- (M ˭ V(IV), Mo(IV), W(IV); n = 2 and M ˭ Nb(V), Re(V); n = 1) anion complexes were prepared. They exhibited low oxidation potentials of +0.145 – +0.76 V vs. SCE. They were oxidized by reactions with iodine, [Fe(C5Me5)2]+, [Fe(C5H5)2]+, and the TTF+radial cation, as well as the electrolysis, in organic solvents to afford oxidized [M(C3S5)3]m-(0 < m < 1) species having electrical conductivities of 6.0 × 10−5-1.5 × 10−1S cm−1measured for compacted pellets at room temperature. X-ray crystal structures of the [M(C3S5)3]2-(M ˭ Mo, W) complexes and the one-electron-oxidized [M(C3S5)3]−(M ˭ V, W) species as well as ESR and X-ray photoelectron spectra of the oxidized species are discussed.

Spin-crossover phenomena of four iron complexes, [Fe(amp)3]2+ (amp = 2-(aminomethyl)pyridine), [Fe(acac2trien)]+ (H2acac2trien = N,N-bis(1- metnyl-3-oxobutylidene)triethylenetetramine), [Fe(sal2trien)] (H2sal2trien = N,N'- disalicylidenetriethylenetetramine), and [Fe(acpa)2] (Hacpa = N-acetyl-2-propylidene) -2-pyridylmethylamine), intercalating into the montmorillonite interlayer space were examined by the magnetic susceptibility measurement and 57Fe Mössbauer spectroscopy. Confinement of the complexes in the 2D space brings some dispersion and drop of the spin-crossover temperature in comparison with those for their spin equilibria in solution. Twisting deformation of the complexes was proposed to be responsible for the observed variation of the relative stability between high-spin and low-spin species.

The temperature dependence of the magnetic susceptibilities for 4-methacryloyloxy- and 4-acryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl (MOTMP and AOTMP, respectively) was measured. Intermolecular magnetic coupling in these radicals was changed from antiferromagnetic to ferromagnetic by substituting hydrogen at α-position with a methyl group. A magnetic phase transition for MOTMP was observed at 0.14 K in the measurement of the temperature dependence of heat capacity. The circumstantial evidences support that the ordered state is of ferromagnet.

The dinuclear rhenium(IV) complexes with the C3S4Se-ligand [1,3-dithiole-2-selone-4,5- dithiolate(2-)], [PPh4]2- (1) and [NEt4]2[Re2(C3S4Se)5] (2), were prepared. Complex 2 was oxidized by a reaction with [Fe(C5H5)2][PF6] or [TTF]3[BF4]2(TTF·+= the tetrathiafulvalenium radical cation) and by the current-controlled electrolysis to yield [NEt4]x[Re2(C3S4Se)5] (x = 0.15 and 0.5) and [TTF][Re2(C3S4Se)5]. The compounds exhibit electrical conductivities of 3.3 x 10-3- 9.3 x 10-4S cm-1for compact pellets at room temperature. Electrochemical and spectroscopic properties of the complexes are discussed on the basis of cyclic voltammetry and ESR, XPS and IR spectra as well as the magnetic susceptibility of the TTF salt.

Substituted pyridine derivatives (X-py: X=H, 2,4-Me2 , 2-Me, 3-Cl, 3-Br and 4-CN) and bipyridine compounds (2,2′- and 4,4′-pyYpy: –Y–=none, –C2H2 –, –SS– and –C2H4 –) reacted with powdered gel-V2O5 1.6H2O or VOPO4 2H2O suspended in ethanol to afford intercalation compounds. They contained 0.1–0.4 mol of guest molecules per vanadium ion. In the V2O5-intercalation compounds, intercalation essentially occurs through the diffusion of the guest molecules accompanied by the protonation on the nitrogen atoms to some extent in the interlayer space, resulting in a net expansion of the spacings of 4.0–5.0 Å. The long-axis direction of the guest molecules is arranged approximately parallel to the V2O5-sheet, and hydrogen bonds are formed between the N-components of the protonated guest molecules and the V&z.dbd;O sites. The interlayer distances are lengthened with an increase of the amount of the N-protonated pyridyl moieties in the interlayer space. In the VOPO4-intercalation compounds, the net expansions of the interlayer spaces were 7.0–12.0 Å, the guest molecules being arranged approximately perpendicular to the host layer. There is no appreciable relationship between the interlayer distances and the amounts of N-protonated pyridyl moieties.

The new dithiolato ligand with an extended π-electron system, CgH4S82-(2-[(4,5-ethylenedithio)-1,3-dithiole-2-ylidene]-1,3-dithiole-4,5-dithiolate) was synthesized and [NBun4][Au(C8H4S8)2] and Pt(C8H4S8)-(SEt2)2 prepared. Redox potentials of these complexes were determined. Their oxidized species and Na1.5[Ni(C8H4S8)2] exhibit electrical conductivities of 0.06-17 S cm-1 at room temperature for compacted pellets.

The second example of the Ce(III)-based single-molecule magnet (SMM), which involves only one 4f electron as a spin carrier, was realized based on similar magnetostructural correlations with Tb(III)-based SMMs. The estimated energy barrier for spin flipping was ?E/kB= 37(1) K, which is higher than that for the first Ce(III)-SMM, and slow magnetic relaxation was observed up to 15 K.

The article presents a study on the relationship of surface gloss and drawing conditions during the final pass of cold drawing for Ni-plated steel wire. It states that the study employed two kinds of Ni-plated wires which were drawn to the final diameter in one pass through emulsion type lubricant under various experimental conditions. It reveals that there is a direct relationship between the surface gloss of Ni-plated steel wire and the approach semi-angle of the die.

The presence of alkoxyl chains on the single-molecule magnet [(Pc′)2Tbiii] and its planar character favour its 2-D self-assembly on HOPG with the molecular plane parallel to the graphite surface, enabling us to control and/or predict the orientation of the preferential magnetization axis on the surface.

No Abstract

A complex of cobalt(ii)(OCN)2coordinated with four pyridines having a stable tert-butyl aminoxyl exhibited in frozen MTHF a slow magnetic relaxation for the reorientation of magnetization with activation barrier, Δ/kB= 50 K, and a hysteresis loop having a fast relaxation at 0 Oe below 2.5 K.