Hard magnetic ferrites with high coercive field

The solid-state reaction between SrCO₃ and -FeOOH was investigated by means of thermal analysis, X-ray diffraction, electron microscopy and magnetic measurements. The high reactivity of this mixture is discussed in comparison with that of the mixture of SrCO₃ and -Fe₂O₃.     

Photoinduced magnetization in a two-dimensional cobalt octacyanotungstate

A new type of cyano-bridged Co-W bimetallic assembly, CsI[{CoII(3-cyanopyridine)2}{WV(CN)8}].H2O was synthesized. This compound exhibited a temperature-induced phase transition and a photoinduced magnetization. Irradiating with light induced a spontaneous magnetization with a magnetic phase transition temperature at 30 K. This photoinduced magnetization is due to the phase transition from CoIII(LS; S = 0)-WIV(S = 0) to CoII(HS; S = 3/2)-WV(S = 1/2) phases by the irradiation.     

Synthesis, structures, and magnetic properties of a series of cyano-bridged Fe-Mn bimetallic complexes

The preparation and crystal structures of five cyano-bridged Fe-Mn complexes, [(bipy)2Fe(II)(CN)2Mn(II)(bipy)2]2(ClO4)4 (1), [(bipy)2Fe(II)(CN)2Mn(II)(DMF)3(H2O)]2(ClO4)4 (2), {[(Tp)Fe(III)(CN)3]2Mn(II)(DMF)2(H2O)}2 (3), {[(Tp)Fe(III)(CN)3]2Mn(II)(DMF)2}n (4), and Na2[Mn(II)Fe(II)(CN)6] (5) (bipy = 2,2'-bipyridine, Tp = tris(pyrazolyl)hydroborate), are reported here. Compounds 1-4 contain the basic Fe2(CN)4Mn2 square building units, of which 1-3 show the motif of discrete molecular squares of Fe2(CN)4Mn2 and 4 possesses a 1D double-zigzag chain-like structure, while compound 5 is a 3D cubic framework analogous to that of Prussian blue. Compounds 1 and 2 show weak ferromagnetic interactions between two Mn(II) ions through the bent -NC-Fe(II)-CN- bridges. Compound 3 shows weak antiferromagnetic coupling between the Fe(III) and Mn(II) ions, while compound 4 displays a metamagnetic-like behavior with TN = 5.2 K and Hc = 10.5 kOe. Compound 5 exhibits a ferromagnetic ordering with Tc= 3.5 K, coercive field, Hc, = 330 G, and a remnant magnetization of 503 cm3 Oe mol(-1).     

Coexistence of long-range ferromagnetic ordering and glassy behavior in one-dimensional bimetallic cyano-bridged polymers

Two new one-dimensional (1-D) 3d-5d cyano-bridged bimetallic assemblies, ([Co(3)(II)(DMF)(12)][W(V)(CN)(8)](2)])(infinity) (1) and ([Mn(3)(II)(bipy)(2)(DMF)(8)][W(V)(CN)(8)](2))(infinity) (2), have been synthesized and characterized, where bipy stands for 2,2'-bipyridine and DMF represents N,N-dimethylformamide. The X-ray analyses show that the two complexes belong to the P(-)1 space group with Z = 1 and C(52)H(84)N(28)O(12)Co(3)W(2), a = 11.690(3) A, b = 12.703(3) A, c = 13.712(3) A, alpha = 86.889(4) degrees, beta = 73.256(4) degrees, and gamma = 77.033(4) degrees for 1 and C(60)H(72)N(28)O(8)Mn(3)W(2), a = 10.672(2) A, b = 13.024(3) A, c = 16.000(3) A, alpha = 78.32(3) degrees, beta = 75.69(3) degrees, and gamma = 66.63(3) degrees for 2. The structures of the two complexes are similar and consist of 12-atom rhombic M(2)W(2)(CN)(4) (M = Co (1), Mn (2)) units, which act as a basic component to be repeatedly connected through W-C-N-M-N-C-W linkages to form a one-dimensional infinite 3,2-chain; these chains are well separated by the DMF molecules or 2,2'-bipyridines coordinated to the metal ions Co(2+) for 1 and Mn(2+) for 2. Magnetic studies, including linear and nonlinear ac susceptibility measurements, demonstrate that the long-range magnetic ordering and spin glass behavior coexist in the two 1-D compounds.     

Directional synthesis and assembly of bimetallic nanosnowmen with DNA

Synthesizing and assembling nanoscale building blocks to form anisotropic nanostructures with the desired composition and property are of paramount importance for the understanding and use of nanostructured materials. Here we report a salt-tuned synthetic strategy using DNA-modified Au nanoparticles (DNA-AuNPs) to form Au-Ag head-body nanosnowman structures in >95% yield. We propose a mechanism for the formation of asymmetric Au-Ag nanosnowmen from DNA-AuNPs, salts, and Ag-precursor-loaded polymers. Importantly, we show that oriented assemblies of various nanostructures are readily obtained using nanosnowmen with asymmetrically modified DNA as building blocks.     

A polar oxide with a large magnetization synthesized at ambient pressure

The perovskite Bi2Mn4/3Ni2/3O6 is polar and combines relative permittivity behavior consistent with ferroelectricity with the magnetic response of a concentrated spin-glass. Bi2Mn4/3Ni2/3O6 is accessible by ambient pressure synthesis despite the instability of the end-members BiMnO3 and BiNiO3 under these conditions.     

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged CoIII-FeII complexes

The effects of pressure and temperature on the energy (Eop) of the metal-to-metal charge transfer (MMCT, FeII-->CoIII) transition of the cyano-bridged complexes trans-[L14CoNCFe(CN)5]- and cis-[L14CoNCFe(CN)5]- (where L14=6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus-Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in Eop due to both pressure and temperature were found to be less than the shifts in the energy difference (DeltaE degrees]) between the CoIII-FeII and CoII-FeIII redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of CoII, are discussed in order to account for this trend. To study the effect of pressure on CoIII electronic absorption bands, a new cyano-bridged complex, trans-[L14CoNCCo(CN)5], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans-[L14CoNCFe(CN)5].5H2O.     

Solvent dependent assembly and disassembly of a hydrogen bonded helical structure in a Co-Mo bimetallic complex

The effect of solvent on the assembly and disassembly of a hydrogen bonded helical structure in a bimetallic cobalt complex of a molybdenum-containing metalloligand and their spontaneous resolution has been demonstrated.     

Giant field dependence of the low temperature relaxation of the magnetization in a dysprosium(III)-DOTA complex

The square antiprismatic Na[Dy(DOTA)(H(2)O)]·4H(2)O complex was characterised by single crystal X-ray diffraction and ac magnetic susceptometry. Two competing mechanisms for magnetic relaxation as well as the remarkable increase of six orders of magnitude in the relaxation time upon application of a static magnetic field were detected.     

Cyano-bridged gadolinium(III)-tungstate(V) bimetallic assembly with a one-dimensional chain structure

In this paper, we report the crystal structure and magnetic properties of the cyano-bridged gadolinium-tungstate bimetallic assembly, GdIII(DMF)6[WV(CN)8](DMF =N,N-dimethylformamide). X-Ray single crystal analysis shows that this compound crystallizes in the monoclinic system of space group P2(1)/c with cell constants a= 16.40(2)A, b= 11.08(1)A, c= 21.18(2)A, beta= 91.09(8) degrees, and Z= 4. The crystal consists of one-dimensional linear chains, in which [GdIII(DMF)6]3+ and [WV(CN)8]3- ions are linked in an alternating fashion. The magnetic data show that this compound is a paramagnet with an antiferromagnetic coupling of -0.58 cm-1 between GdIII(S= 7/2) and WV(S= 1/2).     

Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)(4)(H(2)O)(3)(micro-CN)Fe(CN)(5).H(2)O (DMF = N,N-dimethylformamide)

Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)4(H2O)3(mu-CN)Fe(CN)5.H2O (1) (DMF = N,N-dimethylformamide) is described in this paper. The chiMT values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing the molecule-based magnetic materials.     

Pt nanoparticles decorated with a discrete number of DNA molecules for programmable assembly of Au-Pt bimetallic superstructures

Discrete DNA decorations of Pt nanoparticles (PtNPs) are realized for the first time, which provide a valence control over the quasi-molecular self-assembly of Au-Pt bimetallic heteronanostructures with DNA as the guide.     

Multivalent supramolecular assembly with ultralong organic room temperature phosphorescence,high transfer efficiency and ultrahigh antenna effect in water

Multivalent supramolecular assemblies have recently attracted extensive attention in the applications of soft materials and cell imaging. Here, we report a novel multivalent supramolecular assembly constructed from 4-(4-bromophenyl)pyridine-1-ium bromide modified hyaluronic acid (HABr), cucurbit[8]uril (CB[8]) and laponite® clay (LP), which could emit purely organic room-temperature phosphorescence (RTP) with a phosphorescence lifetime of up to 4.79 ms in aqueous solution via multivalent supramolecular interactions. By doping the organic dyes rhodamine B (RhB) or sulfonated rhodamine 101 (SR101) into the HABr/CB[8]/LP assembly, phosphorescence energy transfer was realized with high transfer efficiency (energy transfer efficiency = 73–80%) and ultrahigh antenna effect (antenna effect value = 308–362) within the phosphorescent light harvesting system. Moreover, owing to the dynamic nature of the noncovalent interactions, a wide-range spectrum of phosphorescence energy transfer outputs could be obtained not only in water but also on filter paper and a glass plate by adjusting the donor–acceptor ratio and, importantly, white-light emission was obtained, which could be used in the application of information encryption.

An ultralong lifetime supramolecular assembly was constructed via multivalent supramolecular interactions and achieved phosphorescence light harvesting. Multicolor (including white) broad-spectrum outputs could be achieved in water and also on filter paper and a glass plate.     

One-dimensional octacyanomolybdate-based Cu(II)--Mo(V) bimetallic assembly with a novel rope-ladder chain structure

A new type of one-dimensional cyanide-bridged Cu(II)--Mo(V) bimetallic assembly, [Cu(cyclam)](3)[Mo(CN)(8)](2)x5H(2)O (cyclam = 1,4,8,11-tetraazacyclotetradecane), was prepared by self-assembling Mo(CN)(8)(3)(-) and Cu(cyclam)(2+) ions in a 2:3 stoichiometric ratio. The overall molecular view is delineated as a novel rope-ladder chain structure. It displays a dominant ferromagnetic behavior within a pentanuclear Cu(3)Mo(2) unit (J(p) = 3.88 cm(-)(1)). Interunit ferromagnetic interactions (J(c) = -0.03 cm(-)(1)) through a longer magnetic pathway of Cu--Mo and weak antiferromagnetic couplings (zJ' = -0.46 cm(-)(1)) resulting from interchain interactions are obtained.     

Photoinduced intramolecular charge separation in a polymer solid below the glass transition temperature

Photoinduced intramolecular charge separation (CS) in a polar polymer glass, cyanoethylated pullulan (CN-PUL), was studied below the glass transition temperature (Tg=395 K). A series of three carbazole (Cz: donor)-cyclohexane (S: spacer)-acceptor (A: acceptor) molecules (Cz-S-A) was used as intramolecular donor-acceptor dyads. The photoinduced CS rate was evaluated by the fluorescence decay measurement at temperatures from 100 to 400 K. The CS rate (kCS) increased above 200 K even far below Tg where micro-Brownian motions of the whole polymer chain are frozen. Below 200 K, on the other hand, kCS showed weak dependence on temperature. The temperature dependence of kCS is discussed in terms of the dielectric relaxation time of the polymer matrix. Consequently, CS below Tg was well explained by a thermally nonequilibrium electron transfer (ET) formula above 200 K and by a two-mode quantum-mechanical ET formula below 200 K. The increase in kCS above 200 K is mainly caused by a thermally activated low-frequency matrix mode originating from the side-chain relaxation of polar cyano groups. The weak temperature dependence of kCS can be explained by a nuclear-tunneling effect caused by a high-frequency matrix mode (variant Planck's over 2piomegH=250 cm-1) and an intramolecular vibrational mode (variant Planck's over 2piomegaQ=1300 cm-1). The high-frequency mode of the polymer matrix was attributed to a vibrational or librational motion of polar groups in the CN-PUL glassy solid.     

Photoinduced hydrogen production using a multilayered molecular assembly composed of zinc tetraphenylporphine and Nafion® membrane

A photoinduced proton reduction to produce H₂ was found to take place in the system using zinc tetraphenylporphine (ZnTPP) incorporated into a Nafion® membrane coated on a platinum electrode (denoted as Pt/Nf[ZnTPP]). When visible light (λ > 390 nm) was irradiated on the Pt/Nf[ZnTPP] system, a photocurrent was generated under applied potentials below −0.10 (v. Ag/AgCl). The action spectrum for the photocurrent agreed with the absorption spectrum of the Nf[ZnTPP] membrane, showing that the present photochemical process is induced on light absorption by the ZnTPP. By measuring the emission decay of ZnTPP under the photoelectrochemical conditions, it was exhibited that the emission from the singlet excited ZnTPP is quenched by the cathodic potentials. The amount of the H₂ produced increased with the cathodic potentials. These results indicated that, in the photochemical primary process, a reductive quenching takes place by electron injection from the Pt electrode to the singlet excited ZnTPP forming ZnTPP^.–, subsequently leading to the H₂ formation by a bimolecular catalysis of the ZnTPP. Copyright © 2000 John Wiley & Sons, Ltd.     

Preparations,IR spectra and crystal structures of cyano-bridged bimetallic complexes of zinc(II) and cadmium(II) with tetracyanopalladate(II)

The novel heteronuclear compounds [Zn(hydet-en)₂Pd(CN)₄] (1) and [Cd(hydet-en)₂Pd(CN)₄] (2) {hydet-en: N-(2-hydroxyethyl-ethylenediamine)} have been synthesized and characterized by elemental analyses and IR spectra. The crystal structures of 1 and 2 have been determined by X-ray diffraction. Structural analysis shows that both compounds have shown a polymeric chain, in which the Zn(II)/Pd(II) and Cd(II)/Pd(II) centres are linked by two CN groups. Both zinc and cadmium atoms are six coordinate with two trans cyanide–nitrogen and four hydet-en N atoms in a distorted octahedron arrangement; the palladium atoms in 1 and 2 are four coordinate with four cyanide-C atoms in a square planar arrangement. The chains in both compounds are connected through weak interchain hydrogen bonds, N–H?···?O, N–H?···?N and O–H?···?N, thereby forming a three-dimensional network.     

Mixed-phase PdRu bimetallic structures with high activity and stability for formic acid electrooxidation

Aiming at investigating the effect of structure on electrocatalytic properties, Pd(50)Ru(50) nanoparticles (NPs) with three different structures were carefully designed in a one-pot polyol process for application in formic acid electrooxidation. The three structures are: (1) single-phase PdRu nanodendrites (denoted as PR-1), (2) a mixed-phase mixture of PdRu nanodendrites and monometallic Ru NPs (denoted as PR-2), and (3) a mixed-phase mixture of monometallic Pd and Ru NPs (denoted as PR-3). From PR-1 to PR-3, the structure was varied from single-phase to mixed-phase. The relative position of Ru was altered from completely Pd-connected (PR-1), to a mixture of Pd-connected and monometallic (PR-2), and completely monometallic (PR-3). All PdRu NPs outperform the commercial Pd/C. PR-2 exhibits the highest peak current density, but its stability is slightly lower than that of PR-3. When both the current density and the durability are taken into consideration, PR-2 is the best choice of catalyst for formic acid oxidation. It indicates that both the Pd-connected Ru NPs and monometallic Ru NPs in the mixed-phase PR-2 are essential to improve the electrocatalytic properties. Our study also illustrates that the electrochemical active surface area (ECSA) and hydrogen storage capacity of the as-prepared PdRu NPs are greatly enhanced after several hundred scans in formic acid, indicating the possibility for highly restorable catalysts in direct formic acid fuel cells.     

Biocatalytic synthesis of a nanostructured and crystalline bimetallic perovskite-like barium oxofluorotitanate at low temperature

Silicatein, an enzymatic biocatalyst from the marine sponge Tethya aurantia, is demonstrated to catalyze and template the hydrolysis/condensation of the molecular precursor BaTiF6 at low temperature to form nanocrystalline BaTiOF4, an orthorhombic oxofluorotitanate. The kinetics of hydrolysis and growth were studied in-situ via pH profiling and quartz crystal microbalance (QCM) techniques. The composition and structure of the resulting BaTiOF4 microstructures on the silicatein surface were characterized using FT-IR spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. The silicatein-mediated hydrolysis/condensation of BaTiF6 generates nanocrystalline BaTiOF4 (a high-temperature intermediate to BaTiO3) at 16 degrees C without any added acid or base, and the growth is templated along the protein filaments into floret microstructures. The unique combination of silicatein and the single-source molecular precursor has allowed a multimetallic perovskite-like material to be biocatalytically synthesized, in vitro, for the first time.