Iron oxide Fe2O3 has four polymorphs: α-, β-, γ-, and ε-phases. α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite) are abundant in nature, whereas β- and ε-Fe2O3 phases are very rare and must be artificially synthesized in the laboratory. Pure ε-Fe2O3 phase was first synthesized in 2004 using a combination of reverse-micelle and sol–gel techniques, and it shows the largest coercive field value (Hc) among metal oxide-based magnets of 20 kOe at room temperature. Successively, several kinds of metal-substituted ε-iron oxides, ε-MxFe2−xO3 (M = In, Ga, and Al), have been synthesized, and their magnetic properties are controlled by the degree of the metal substitution. Such iron oxides with a high Hc are attractive from industrial application viewpoints, e.g., magnetic recordings and electromagnetic wave absorbers. A series of ε-MxFe2−xO3 shows high-frequency electromagnetic wave absorption due to zero-field ferromagnetic resonance at 35–182 GHz in the millimeter range, which is useful for next-generation high-speed wireless communications. In this article, we describe (i) the synthesis, crystal structure, and magnetic properties of ε-Fe2O3, (ii) generation mechanism of ε-Fe2O3, the origin of the gigantic coercive field, and theoretical analysis of magnetic ordering, (iii) metal-substituted ε-iron oxides, ε-MxFe2−xO3, and (iv) electromagnetic wave absorption in the millimeter wave range.
ε-Iron oxide (ε-Fe2O3) and metal-substituted ε-iron oxides (ε-MxFe2−xO3), which exist as nanoscale size particles, demonstrate gigantic magnetic coercive fields of up to 20 kOe and high-frequency electromagnetic wave absorption.
An optically active AuI4CoIII2 complex with mixed D-penicillaminate (D-pen) and 1,2-bis(diphenylphosphino)ethane (dppe), [Au4Co2(dppe)2(D-pen)4]2+, was selectively formed from [Au2(dppe)(D-pen)2]2− and CoIII. When this complex was crystallized with monovalent anions (ClO4−, BF4−, NO3−, Cl−, Br−, and N3−), the AuI4CoIII2 complex cations were self-assembled to form +12-charged supramolecular octahedrons that are closely packed in a face-centered cubic (fcc) structure. In this structure, ten monovalent anions are accommodated in each hydrophilic tetrahedral interstice to create an adamantane-shaped anionic cluster, while two anions are each encapsulated in each octahedral interstice and in the center of each supramolecular octahedron. The use of divalent anions (SO42− and SiF62−) also produced an analogous fcc structure made up of the +12-charged supramolecular octahedrons. In this case, six divalent anions are accommodated in each hydrophilic tetrahedral interstice to form an octahedron-shaped anionic cluster, completing a giant zinc blende lattice structure where all cations and anions are separately aggregated into the +12-charged octahedrons and the −12-charged octahedrons, respectively. The site selective aggregation of two kinds of inorganic anions (PF6−/Br−, BF4−/Br−, and NO3−/Br−) in the fcc structure, along with the synthesis and characterization of an analogous AuI4CrIII2 complex, is also reported.
The cationic AuI4MIII2 (M = Co and Cr) hexanuclear complexes are crystallized with certain inorganic anions to form ionic crystals, in which inorganic anions are aggregated into amazing anionic clusters accompanied by the aggregation of the AuI4MIII2 cations into supramolecular octahedrons.
We have succeeded in preparing single crystals of the layered copper hydroxide [Cu7(OH)12(CH3CH2CO2)2]·(CH3CH2CO2H)2·(H2O)6 (1) through hydrolysis of a copper propionate solution. X-ray structure analysis showed that this material did not have the botallackite-type structure common in the layered copper hydroxide derivatives, but instead a two-dimensional distorted triangular lattice magnetic network of Cu(II) ions with S = 1/2 was formed. Magnetic measurements revealed dominance of antiferromagnetic interactions between neighboring Cu(II) ions in the copper hydroxide layer, and an antiferromagnetic ordering behavior around 3 K. We also discuss the structural and magnetic differences between 1 and related materials.
New tetrathiafulvalene (TTF)-type electron-donor molecules annelated with imidazole or benzimidazole moiety were designed and synthesized by the phosphite-mediated coupling reactions of imidazole- or benzimidazole-annelated 1,3-dithiole-2-thiones. The effect of imidazole-annelation on the redox properties was evaluated by theoretical calculation and electrochemical measurement, and the imidazole-annelation slightly enhances the electron-donating abilities of parent TTF and benzo-TTF skeletons. The substitution of the imidazole ring with an electron-withdrawing cyano group caused a large high potential shift of the oxidation potentials in the cyclic voltammetry and an intense intramolecular charge-transfer absorption band in the electronic spectrum. The self-assembling ability was investigated by crystal structure analysis, where solvent or counter anion mediated one-dimensional hydrogen-bonded arrays of imidazole rings were linked through π-stacks and S···S interactions to construct multidimensional networks. The donor molecules afforded weak charge-transfer complexes with tetracyanoquinodimethane (TCNQ) and fully ionic complexes with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and 2,3,5,6-tetrafluoro-TCNQ. In the crystal structures of TCNQ complex and iodine salt of a benzimidazole-annelated derivative, π-stacking motifs, donor–acceptor alternating stack, and π-stacking dimer, respectively, were interacted through hydrogen-bonds.
To investigate the influence of the number of substituents on supramolecular assemblies of hydrogen-bonded disk-like (phenylethynyl)benzene derivatives with chiral L-alanine dodecyl groups, a tris(phenylethynyl)benzene derivative 3 and a tetrakis(phenylethynyl)benzene derivative 4 were synthesized. The behavior of these supramolecular assemblies was compared with that of the previously reported hexakis(phenylethynyl)benzene derivative 6. It is clearly shown that the stability of the supramolecular helical columnar structure is enhanced by increasing the number of substituents, namely the number of amide groups contributing to the hydrogen bonding. In addition, along with 6, 4 also exhibits a solvent-induced supramolecular helical sense inversion. Furthermore, 4 exhibits a thermally reversible supramolecular helical sense inversion at a critical solvent composition.
Diarylethenes are photosensitive π-conjugated molecules, being of great promise in potential applications to various molecular devices. Although the switching properties of diarylethenes have been widely investigated experimentally and theoretically, little is known about their rectifying diode-like behavior. In this study, electron-transport properties of asymmetric diarylethenes incorporating two different heterocyclic five-membered rings with opposite electronic demands are investigated with the nonequilibrium Green function combined with density functional theory. The aim of this study is to derive the effect of the heteroatomic defects on not only switching but also rectifying characteristics of the asymmetric diarylethenes. Obtained results show that a silicon atom involved in the diarylethenes plays an important role in the current rectifying as well as switching performance. It is found that maximum rectification ratios of the asymmetric diarylethenes increase linearly with an increase in electronegativity difference between the asymmetrically arranged heteroatoms. The silicon- and oxygen-containing asymmetric diarylethene is suggested to be a good potential candidate for a novel molecular electronic device combining a switch and a diode.
The liquid junction potential between electrolyte solutions in different solvents has been studied, paying attention to why the values of the component related to ion solvation are actually much smaller than the values expected from the differences in ionic standard chemical potentials.
Magnetic removal of cesium ions (Cs) by γ-poly(glutamic acid)-coated magnetite particles (PGA-MPs) was investigated using a variety of waters. Cs was sufficiently removed from fresh water in a pH range from 7.0 to 9.0, with a removal efficiency of higher than 80% by using 5 wt % PGA-MPs, while that from artificial seawater was limited to 30%. Zeolite particles were employed as a supplementary adsorbent to adsorb Cs before the collection of zeolite with PGA-MPs. The addition of 1 wt % zeolite particles enhanced the recovery of Cs up to 97.7 ± 0.2% for fresh water and the amount of PGA-MPs required for the treatment was reduced to 0.2 wt %. Nevertheless, such improvement was not observed for artificial seawater treatment. The zeolite supplementation method performed sufficiently on the recovery of Cs in tap water and spring water, and their recoveries were both higher than 93% with R.S.D. of less than 1%. These results strongly suggest that the provided procedure can be practically applied to the removal of Cs from various inland waters.
Effects of rare earth or transition metal doping on the activity of CeO2 to particulate matter oxidation were investigated, and it was found that a Ce–Pr–La–O mixed oxide demonstrates the lowest ignition temperature of carbon, as low as 550 K. Oxygen-temperature-programmed desorption measurements suggested that the amount of O2 desorbed from CeO2 increases with the substitution of Pr, and furthermore, La doping reduces the desorption temperature of the lattice oxygen. Even in the absence of oxygen, carbon oxidation occurs on Ce–Pr–La–O, and the ignition temperature of carbon is almost the same as the desorption temperature of the lattice oxygen. Doping of La and Pr into CeO2 has a positive impact on carbon oxidation because of this decreased desorption temperature of the lattice oxygen.
Wittig reaction of (E)-2-(2-thienyl)ethylene-1-carbaldehyde with [(3-guaiazulenyl)methyl]triphenylphosphonium bromide in ethanol containing sodium ethoxide (=NaOC2H5) at 25 °C for 24 h under argon gives the two (2E,4E)- and (2E,4Z)-geometric isomers of a new compound 1-(3-guaiazulenyl)-4-(2-thienyl)-1,3-butadiene, the only title (2E,4E)-form, of which can be isolated as single crystals. Preparation, chemical and spectroscopic properties, crystal structure, and electrochemical behavior of the target (2E,4E)-form, compared with those of (E)-1-(3-guaiazulenyl)-2-(2-thienyl)ethylene and the structurally related new compound (3-guaiazulenyl)[(E)-2-(2-thienyl)ethenyl]methylium hexafluorophosphate, are documented.
A reusable catalytic system was developed for the catalytic enantioselective borohydride reduction of ketones. The optically active 1-chlorovinylketoiminatocobalt(III) complexes were recovered after the reaction by silica gel column chromatography, and then efficiently catalyzed the enantioselective reduction several times without any loss of reactivity as well as enantioselectivity.
1H NMR studies demonstrated that chiral macrocycle 1 was a good chiral solvating agent, and was effective for the determination of the enantiomeric excess of a wide range of rac-carboxylic acids. Large nonequivalent chemical shifts (up to 0.125 ppm) can be achieved in the presence of 1.0 equiv of 1.
The reaction of bis(phenylseleno)benzene dibromide 1 with tribromoborane afforded bromoselenonium tetrabromoborate 2, which has a weak CT interaction between the two selenium atoms. Using Ag reagents provided the first examples of 5-phenylselenanthrenium salts.
New ionic plastic crystals of NR4BEt3Me (R = Me and Et) and NRxR′4−xBEt3Me (R = Et, R′ = Me and Pr, x = 1–3) were formed in a new region of plastic crystal. In this area, globular cations and anions are assembled by weak interactions. On the basis of our results of 1H and 13C NMR spectra and electrical conductivity measurements, we could conclude that isotropic reorientation and self-diffusion of globular cations and anions were detected in the crystal. X-ray diffraction (XRD) lines observed in RxR′4−xBEt3Me (R = Et, R′ = Me, x = 0–4) revealed a CsCl-type cubic crystal structure. Additionally, DSC spectra revealed that this new class of plastic crystals displays low phase-transition temperatures in the plastic phase and have high melting points. The former tendency is frequently detected in molecular plastic crystals while the latter is often found in ionic plastic crystals.
Skeletal Cu was prepared from Cu–Ti amorphous alloy (amor-CuTi) via heating at various temperatures followed by HF treatment for extraction of Ti moieties. Thermal treatment at somewhat lower crystallization temperature of amor-CuTi followed by HF treatment leads to higher catalytic activity in the hydrogenation reaction of p-nitrophenol to p-aminophenol.