Search

Heteroanionic compounds, which contain two or more types of anions, have emerged as a promising class of materials with diverse properties and functionalities. In this paper, I review the experimental findings on Ca 3 ReO 5 Cl 2 and related compounds that exhibit remarkable pleochroism and novel quantum magnetism. I discuss how the heteroanionic coordination affects the optical and magnetic properties by modulating the d-orbital states of the transition metal ions. Subsequently, I compare these materials with other heteroanionic and monoanionic compounds and highlight the potential of A 3 MO 5 X 2 materials for future exploration of materials and phenomena.

Photoelectrochemical (PEC) water splitting is a highly demanded technology for the realization of sustainable society. Various types of photoanodes have been developed to achieve high efficiency of PEC water splitting. Plasmonic field enhancement and light confinement effects are often adopted to improve PEC performance. However, their synergistic effects have not been studied. In this work, a mesoporous TiO 2 layer was deposited on an Al plate with a nanovoid array structure, which acts as a photoanode and simultaneously exhibits a light confinement effect and surface plasmon resonance. The solo and synergy effects were investigated through experimental photocurrent measurements and theoretical simulations using the finite-difference time-domain method. The highest improvement in PEC performance was confirmed when the synergy effect occurred.

The high-entropy concept was applied to the synthesis of transition-metal antimonides, M 1- x Pt x Sb (M = equimolar Ru, Rh, Pd, and Ir). High-entropy antimonide samples crystallized in a pseudo-hexagonal NiAs-type crystal structure with a P 6 3 / mmc space group were successfully synthesized through a conventional solid-state reaction and subsequent quenching. A detailed investigation of the composition and equilibration conditions confirmed the reversible phase transition between a multiphase state at low temperature and an entropy-driven single-phase solid solution at high temperatures. Electrical resistivity, magnetization, and heat capacity measurements of single-phase M 1- x Pt x Sb ( x = 0.2) samples revealed a bulk superconducting transition at 2.15(2) K. This study demonstrates that the high-entropy concept provides numerous opportunities for the discovery of new functional materials such as superconductors.

Reductive fluorination, which entails the substitution of O 2- from oxide compounds with F - from fluoropolymers, is considered a practical approach for preparing transition-metal oxyfluorides. However, the current understanding of the fundamental reaction paths remains limited due to the analytical complexities posed by high-temperature reactions in glassware. Therefore, to expand this knowledgebase, this study investigates the reaction mechanisms behind the reductive fluorination of WO 3 using polytetrafluoroethylene (PTFE) in an Ni reactor. Here, we explore varied reaction conditions (temperature, duration, and F/W ratio) to suppress the formation of carbon byproducts, minimize the dissipation of fluorine-containing tungsten (VI) compounds, and achieve a high fluorine content. The gas-solid reaction paths are analyzed using infrared spectroscopy, which revealed tetrafluoroethylene (C 2 F 4 ), hexafluoropropene (C 3 F 6 ), and iso-octafluoroisobutene ( i -C 4 F 8 ) to be the reactive components in the PTFE-decomposition gas during the reactions with WO 3 at 500 °C. CO 2 and CO are further identified as gaseous byproducts of the reaction evincing that the reaction is prompted by difluorocarbene (:CF 2 ) formed after the cleavage of C═C bonds in i -C 4 F 8 , C 3 F 6 , and C 2 F 4 upon contact with the WO 3 surface. The solid-solid reaction path is established through a reaction between WO 3 and WO 3- x F x where solid-state diffusion of O 2- and F - is discerned at 500 °C.

Some inorganic solids undergo phase transitions that result in the formation of "molecules" in their crystalline frameworks, which are frequently accompanied by dramatic changes in physical properties; the metal-insulator transition (MIT) in vanadium dioxide, for instance, is accompanied by the formation of dimer molecules with conventional two-center-two-electron bonding. We have discovered the creation of a linear ruthenium trimer with atypical three-center-four-electron bonding in ruthenium monophosphide at its MIT. Our detailed structural investigation and electronic structure calculations reveal that charge transfer from polymerized phosphorous to ruthenium automatically tunes the electron density to precisely four per trimer at the MIT, with all conduction electrons present at high temperatures being trapped by the trimer's molecular orbitals at low temperatures. Our results demonstrate that molecules are essential even in solid crystals, as they impact their electronic properties.

We report the synthesis, crystal structure, and magnetic properties of the two new quantum antiferromagnets A 3 ReO 5 Cl 2 (A = Sr, Ba). The crystal structure is isostructural with the mineral pinalite Pb 3 WO 5 Cl 2 , in which the Re 6+ ion is square pyramidally coordinated by five oxide atoms and forms an anisotropic triangular lattice (ATL) made of S = 1/2 spins. The magnetic interactions J and J ' in the ATL are estimated from magnetic susceptibilities to be 19.5 (44.9) and 9.2 (19.3) K, respectively, with J '/ J = 0.47 (0.43) for A = Ba (Sr). For each compound, the heat capacity at low temperatures shows a large T -linear component with no signature of long-range magnetic order above 2 K, which suggests a gapless spin liquid state of one-dimensional character of the J chains in spite of the significantly large J ' couplings. This is a consequence of one-dimensionalization by geometrical frustration in the ATL magnet; a similar phenomenon has been observed in two compounds with slightly smaller J '/ J values: Cs 2 CuCl 4 ( J '/ J = 0.3) and the related compound Ca 3 ReO 5 Cl 2 (0.32). Our findings demonstrate that 5d mixed-anion compounds provide a unique opportunity to explore novel quantum magnetism.

Single crystals of a novel Na-Pt-Si ternary compound, Na 3 Pt 10 Si 5 , were synthesized by heating the constituent elements at 1423 K. It crystallizes in a non-centrosymmetric trigonal structure of space group R 32 ( Z = 3) with lattice constants of a = 10.1536(3) Å and c = 10.1539(3) Å at 300 K. The structure consists of a three-dimensional framework made of Pt and Si atoms, and the Na atoms are contained in the tunnels of the framework. The large magnitude and the temperature dependence of the atomic displacement parameter of the Na site reveal a large thermal vibration indicative of a "rattling" motion of Na atoms in the oversized tunnel. The electronic structure calculations explain the observed metallic properties on the basis of the covalent bonds between the Pt and Si atoms in the framework and the ionic bonding of the Na atoms to the framework. A type II superconductivity with a transition temperature of 2.9 K and an upper critical field of 2.5 kOe are observed for a polycrystalline sintered bulk sample of Na 3 Pt 10 Si 5 prepared by heating at 1353 K in Na vapor. Heat capacity measurements reveal a strong coupling superconductivity that is probably caused by an electron-phonon interaction enhanced by the rattling motion of the Na atoms.

Transition metal compounds sometimes exhibit attractive colors. Here, we report a new oxychloride, Ca 3 ReO 5 Cl 2 , that shows unusually distinct pleochroism; that is, the material exhibits different colors depending on the viewing direction. This pleochroism is a consequence of the coincidental complex crystal field splitting of the 5d orbitals of the Re 6+ ion in a square-pyramidal coordination of low symmetry in the energy range of the visible spectrum. Since the relevant d-d transitions show characteristic polarization dependence according to the optical selection rule, the orbital states are "visible" in Ca 3 ReO 5 Cl 2 .

The synthesis of reduced coordination (less than 6), unchelated manganese oxygen cluster systems is described. Addition of phenols to Mn(NR(2))(2) (R = SiMe(3)) results in protolytic amide ligand replacement, and represents the primary entry into the described chemistry. Addition of PhOH to Mn(NR(2))(2) results in the formation of the heteroleptic dimer Mn(2)(μ-OPh)(2)(NR(2))(2)(THF)(2) (1). Usage of the sterically larger 2,6-diphenylphenol (Ph(2)C(6)H(3)OH) as the ligand source results in the formation of a 3-coordinate heteroleptic dimer without THF coordination, Mn(2)(μ-OC(6)H(3)Ph(2))(2)(NR(2))(2) (2). Attempts to generate 2 in the presence of THF or Et(2)O resulted in isolation of monomeric Mn(OC(6)H(3)Ph(2))(2)L(2) (3, L = THF, Et(2)O). Use of the sterically intermediate 2,4,6-trimethylphenol (MesOH) resulted in formation of the linear trinuclear cluster Mn(3)(μ-OMes)(4)(NR(2))(2)(THF)(2) (4). Reaction of Mn(NR(2))(2) with PhOH in the presence of water, or reaction of 1 with water, results in the formation of a 5-coordinate, unchelated Mn-O cluster, Mn(8)(μ(5)-O)(2)(μ-OPh)(12)(THF)(6) (5). Preparation, structures, steric properties, and magnetic properties are presented. Notably, complex 5 exhibits a temperature-dependent phase transition between a 4-spin paramagnetic system at low temperature, and an 8-spin paramagnetic system at room temperature.