La4Ga2S8O3: A Rare-Earth Gallium Oxysulfide with Disulfide Ions.

Band gap engineering using multiple anions is an established approach to novel photocatalysts that exhibit suitable band gap energies for water splitting and high photocorrosion resistance. However, few studies have been conducted on photocatalysts with polyanions, including polychalcogenide ions. Here, we present a new quaternary gallium oxysulfide with disulfide pairs (S2)2-, La4Ga2S8O3, grown out of a KI molten salt. Single-crystal X-ray diffraction analysis revealed that the oxysulfide crystallizes in the orthorhombic space group Pbcn with lattice constants of a = 18.3330(6) Å, b = 13.0590(5) Å, and c = 5.9022(3) Å. In the crystal structure, the GaS4-based zigzag chains and OLa4-based fluorite-like strips are independently arranged in two dimensions, which alternately stack via the disulfide pairs along the third direction. The oxysulfide is a direct-type semiconductor with a band gap of 2.45 eV. First-principles calculations combined with X-ray photoemission spectroscopy measurements show that S 3p states derived from the disulfide pairs dominate the valence band maximum and conduction band minimum, and these band-edge positions are suitable for the oxidation and reduction of water. Our comprehensive study based on the electronic structure suggests that the disulfide pairs make La4Ga2S8O3 a potential photocatalyst for water splitting under visible-light irradiation.

Photosensitizer Encryption with Aggregation Enhanced Singlet Oxygen Production.

Chromophores that generate singlet oxygen (1O2) in water are essential to developing noninvasive disease treatments using photodynamic therapy (PDT). A facile approach for formation of stable colloidal nanoparticles of 1O2 photosensitizers, which exhibit aggregation enhanced 1O2 generation in water toward applications as PDT agents, is reported. Chromophore encryption within a fuchsonarene macrocyclic scaffold insulates the photosensitizer from aggregation induced deactivation pathways, enabling a higher chromophore density than typical 1O2 generating nanoparticles. Aggregation enhanced 1O2 generation in water is observed, and variation in molecular structure allows for regulation of the physical properties of the nanoparticles which ultimately affects the 1O2 generation. In vitro activity and the ability of the particles to pass through the cell membrane into the cytoplasm is demonstrated using confocal fluorescence microscopy with HeLa cells. Photosensitizer encryption in rigid macrocycles, such as fuchsonarenes, offers new prospects for the production of biocompatible nanoarchitectures for applications involving 1O2 generation.

Repeatable Actuations of Organic Single Crystal Fibers Driven by Thermosalient-Phase-Transition-Induced Buckling.

Thermosalient crystals are molecular solids that exhibit explosive motions, such as sudden breaks and jumps, due to temperature-induced structural phase transitions between two polymorphs. Therefore, the development of molecular actuators with superior speed and power by deriving mechanical work from explosive motion is a fascinating concept. However, thermosalient transitions often cause crystal disintegration, which hampers repeatable phase transitions between the polymorphs. Here, it is reported that single crystal nano/microfibers of 1, 2, 4, 5-tetrabromobenzene (TBB), whose bulk crystals exhibit thermosalient behavior at ≈40 °C, can repeatedly transform between the low and high temperature polymorphs without disintegration. The structural tolerance against phase transition is attributed to the high flexibility of the nano/microfibers. It is observed that a structure consisting of a TBB fiber with both ends pinned to the substrate repeatedly buckles and straightens when the temperature is varied between 30 and 40 °C. It is demonstrated that buckling can lead to large displacement actuation as compared to a simple length change of the fiber. Moreover, the force generated by the buckling fiber is estimated and it is found that it can generate a force large enough to flick an object ≈104 times heavier than the fiber itself into the air against gravity.

Triple A-Site Cation Ordering in the Ferrimagnetic Y2CuGaMn4O12 Perovskite.

A new member of A-site columnar-ordered A2A'A″B4O12 quadruple perovskites with the composition of Y2CuGaMn4O12 was prepared by a high-pressure, high-temperature method at 6 GPa and about 1500 K. Its crystal structure and cation distributions were studied by powder synchrotron X-ray and neutron diffraction. There is a triple A-site cation ordering with some degrees of anti-site disorder among sites occupied by 3d transition metals: [Y2]A[Cu0.8Mn0.2]A'[Ga0.8Mn0.2]A″[Mn3.6Cu0.2Ga0.2]BO12. It has the space group P42/nmc (no. 137) between 1.5 and 873 K with a = 7.33884 Å and c = 7.66251 Å at 297 K. Despite anti-site disorder, it exhibits a long-range ferrimagnetic order at TC = 115 K with the ordered moment of 2.19 µB at each B site and 0.89 µB at the A' or A″ site. Magnetic moments are aligned along the c axis; all moments are ordered ferromagnetically at the B sites, and the moments at the A' or A″ site are ordered in the opposite direction. Cu2+ doping drastically changes magnetic properties as "parent" Y2MnGaMn4O12 just shows spin-glass magnetic properties without long-range ordering. Anisotropic thermal expansion was observed in Y2CuGaMn4O12: the lattice parameter a almost linearly decreases from 1.5 K to TC and then monotonically increases up to 873 K (almost linearly from 300 K); the parameter c monotonically increases from 1.5 to 300 K and then decreases up to 600 K.

Long-Range Order in Supramolecular π Assemblies in Discrete Multidecker Naphthalenediimides.

We report herein the solution and solid-state studies of conformationally flexible multidecker naphthalenediimides (NDIs) in which the chromophoric NDI units intramolecularly assemble into a series of discrete π-stacks. The X-ray crystallography reveals the existence of exclusively all-syn NDIs orientations in lower congeners while all-anti in a higher congener, suggesting short- to long-range π···π interactions throughout the slipped πNDI chromophoric array. The UV/vis and fluorescence spectra evaluate the discrete π-stacks by remarkable optical changes upon cooling in solution. Furthermore, we carried out a systematic electrochemical investigation to gain an insight into redox properties of the long-range π-stacked structures. The higher congener (5NDI) shows a ten-electron reversible reduction process in a small working potential window (∼0.8 V). To our knowledge, this is an unusual observation in an organic molecular system to undergo up to ten-electron reduction. These results pave the way to design multidecker π-stacks in which structural control with specific electronic properties would be engineered.

Amino-Functionalization of Vinyl-Substituted Aromatic Diimides by Quantitative and Catalyst-Free Hydroamination*.

Development of facile and versatile synthetic tools for decorating π-conjugated molecules has attracted considerable interest because of their potential application in creating novel functional π-systems. Reported herein are quantitative catalyst-free hydroamination reactions of a series of aromatic diimide compounds having vinyl groups at the π-core, which have been confirmed by NMR, UV-vis absorption spectroscopy, mass analysis, and single-crystal X-ray structural analysis. Kinetic studies revealed that the hydroamination reaction of a vinyl-substituted naphthalenediimide with an aliphatic amine proceeded rapidly under benign conditions. Similarly, the two vinyl groups attached to aromatic diimides reacted with amines simultaneously, resulting in the formation of amine bisadducts and macromolecules. An amino group appended perylenediimide through an ethylene spacer at the π-core exhibited distinct fluorescence switching in response to acid and base.

Structural Transition with a Sharp Change in the Electrical Resistivity and Spin-Orbit Mott Insulating State in a Rhenium Oxide, Sr3Re2O9.

We report the successful synthesis, crystal structure, and electrical properties of Sr3Re2O9, which contains Re6+ with the 5d1 configuration. This compound is isostructural with Ba3Re2O9 and shows a first-order structural phase transition at ∼370 K. The low-temperature (LT) phase crystallizes in a hettotype structure of Ba3Re2O9, which is different from that of the LT phase of Sr3W2O9, suggesting that the electronic state of Re6+ plays an important role in determining the crystal structure of the LT phase. The structural transition is accompanied by a sharp change in the electrical resistivity. This is likely a metal-insulator transition, as suggested by the electronic band calculation and magnetic susceptibility. In the LT phase, the ReO6 octahedra are rotated in a pseudo-a0a0a+ manner in Glazer notation, which corresponds to C-type orbital ordering. Paramagnetic dipole moments were confirmed to exist in the LT phase by muon spin rotation and relaxation measurements. However, the dipole moments shrink greatly because of the strong spin-orbit coupling in the Re ions. Thus, the electronic state of the LT phase corresponds to a Mott insulating state with strong spin-orbit interactions at the Re sites.

La3 Ga3 Ge2 S3 O10 : An Ultraviolet Nonlinear Optical Oxysulfide Designed by Anion-Directed Band Gap Engineering.

Chalcogenide-containing compounds have been widely studied as infrared nonlinear optical (NLO) materials. However, they have never been applied in the ultraviolet (UV) region owing to the high energy levels of chalcogen anions, leading to band gap narrowing. We report the synthesis of a new UV NLO oxysulfide La3 Ga3 Ge2 S3 O10 with an exceptionally wide band gap of 4.70 eV due to from the unique anion-ordered frameworks comprising 1D 1 ∞ [(Ga3/5 Ge2/5 )3 S3 O3 ] triangular tubes and 0D (Ga3/5 Ge2/5 )2 O7 dimers of corner-sharing (Ga/Ge)S2 O2 and (Ga/Ge)O4 tetrahedra, respectively. Second harmonic generation (SHG) measurements revealed that La3 Ga3 Ge2 S3 O10 was phase matchable with twice the SHG response of KH2 PO4 . The results of theoretical calculations suggest that the strong SHG response is mainly attributable to the S-3p and O-2p orbitals in the occupied states. The anion-directed band-gap engineering may give insights into the application of NLO oxychalcogenides in the UV regions.

Two-Step Divergent Synthesis of Monodisperse and Ultra-Long Bottlebrush Polymers from an Easily Purifiable ROMP Monomer.

The longest bottlebrush polymers reported so far (up to 7 µm in length) were synthesized in two steps from a norbornene derivative bearing two 2-bromoisobutylate moieties (NB). The key to this achievement is the excellent reactivity of NB in ring opening metathesis polymerization, which proceeded in a well-controlled manner with quantitative conversion of NB for monomer-initiator ratios ranging up to 10,000. The resultant polymer derived from NB was readily converted to various bottlebrush polymers in a divergent synthetic route by grafting vinyl monomers from the 2-bromoisobutylate units in NB via atom transfer radical polymerization. The structure of the ultra-long bottlebrush polymer was directly observed using atomic force microscopy.

Na Doping in PbTe: Solubility, Band Convergence, Phase Boundary Mapping, and Thermoelectric Properties.

Many monumental breakthroughs in p-type PbTe thermoelectrics are driven by optimizing a Pb0.98Na0.02Te matrix. However, recent works found that x > 0.02 in Pb1-xNaxTe further improves the thermoelectric figure of merit, zT, despite being above the expected Na solubility limit. We explain the origins of improved performance from excess Na doping through computation and experiments on Pb1-xNaxTe with 0.01 ≤ x ≤ 0.04. High temperature X-ray diffraction and Hall carrier concentration measurements show enhanced Na solubility at high temperatures when x > 0.02 but no improvement in carrier concentration, indicating that Na is entering the lattice but is electrically compensated by high intrinsic defect concentrations. The higher Na concentration leads to band convergence between the light L and heavy Σ valence bands in PbTe, suppressing bipolar conduction and increasing the Seebeck coefficient. This results in a high temperature zT nearing 2 for Pb0.96Na0.04Te, ∼25% higher than traditionally reported values for pristine PbTe-Na. Further, we apply a phase diagram approach to explain the origins of increased solubility from excess Na doping and offer strategies for repeatable synthesis of high zT Na-doped materials. A starting matrix of simple, high performing Pb0.96Na0.04Te synthesized following our guidelines may be superior to Pb0.98Na0.02Te for continued zT optimization in p-type PbTe materials.

Langbeinite Phosphates KPbM2(PO4)3 (M = Cr, Fe): Synthesis, Structure, Thermal Expansion, and Magnetic Properties Investigation.

New langbeinite-type phosphates KPbCr2(PO4)3 and KPbFe2(PO4)3 are synthesized by solution method and characterized by powder X-ray diffraction, infrared spectra, thermogravimetric and differential thermal analysis, scanning electron microscope, and energy dispersive X-ray analysis. Rietveld refinement reveals that both of the compounds crystallize in the cubic system with P213 space group, and the calculated lattice parameters for Cr and Fe phases are 9.7332(2) and 9.8325(7) Å, respectively. The electron micrographs confirm the crystalline nature of the samples from their surface morphologies. Infrared spectra display the characteristic features of P-O and M-O vibrational bands for both of the phases. Thermal analysis of KPbCr2(PO4)3 and KPbFe2(PO4)3 indicates that they are thermally stable up to 1273 K. The axial thermal expansion is studied by high-temperature X-ray diffraction between 298 and 1073 K. The average thermal expansion coefficients of KPbCr2(PO4)3 and KPbFe2(PO4)3 are identified as 8.9 × 10-6 and 10.8 × 10-6 K-1, respectively. Magnetic study reveals both of the compounds follow Curie-Weiss behavior in the higher-temperature region, and antiferromagnetic interactions are dominant.

Study of Polycrystalline Bulk Sr3OsO6 Double-Perovskite Insulator: Comparison with 1000 K Ferromagnetic Epitaxial Films.

Polycrystalline Sr3OsO6, which is an ordered double-perovskite insulator, is synthesized via solid-state reaction under high-temperature and high-pressure conditions of 1200 °C and 6 GPa. The synthesis enables us to conduct a comparative study of the bulk form of Sr3OsO6 toward revealing the driving mechanism of 1000 K ferromagnetism, which has recently been discovered for epitaxially grown Sr3OsO6 films. Unlike the film, the bulk is dominated by antiferromagnetism rather than ferromagnetism. Therefore, robust ferromagnetic order appears only when Sr3OsO6 is under the influence of interfaces. A specific heat capacity of 39.6(9) × 10-3 J mol-1 K-2 is found at low temperatures (<17 K). This value is remarkably high, suggesting the presence of possible Fermionic-like excitations at the magnetic ground state. Although the bulk and film forms of Sr3OsO6 share the same lattice basis and electrically insulating state, the magnetism is entirely different between them.

High-Pressure Synthesis, Crystal Structures, and Properties of A-Site Columnar-Ordered Quadruple Perovskites NaRMn2Ti4O12 with R = Sm, Eu, Gd, Dy, Ho, Y.

The formation of NaRMn2Ti4O12 compounds (R = rare earth) under high pressure (about 6 GPa) and high temperature (about 1750 K) conditions was studied. Such compounds with R = Sm, Eu, Gd, Dy, Ho, Y adopt an A-site columnar-ordered quadruple-perovskite structure with the generic chemical formula A2A'A″B4O12. Their crystal structures were studied by powder synchrotron X-ray and neutron diffraction between 1.5 and 300 K. They maintain a paraelectric structure with centrosymmetric space group P42/nmc (No. 137) at all temperatures, in comparison with the related CaMnTi2O6 perovskite, in which a ferroelectric transition occurs at 630 K. The centrosymmetric structure was also confirmed by second-harmonic generation. It has a cation distribution of [Na+R3+]A[Mn2+]A'[Mn2+]A″[Ti4+4]BO12 (to match with the generic chemical formula) with statistical distributions of Na+ and R3+ at the large A site and a strongly split position of Mn2+ at the square-planar A' site. We found a C-type long-range antiferromagnetic structure of Mn2+ ions at the A' and A″ sites below TN = 12 K for R = Dy and found that the presence of Dy3+ disturbs the long-range ordering of Mn2+ below a second transition at lower temperatures. The first magnetic transition occurs below 8-13 K in all compounds, but the second magnetic transition occurs only for R = Dy, Sm, Eu. All compounds show large dielectric constants of a possible extrinsic origin similar to that of CaCu3Ti4O12. NaRMn2Ti4O12 with R = Er-Lu crystallized in the GdFeO3-type Pnma perovskite structure, and NaRMn2Ti4O12 with R = La, Nd contained two perovskite phases: an AA'3B4O12-type Im3̅ phase and a GdFeO3-type Pnma phase.

Synthesis and Atomic Structure of the Yb-Ga-Au 1/1 Quasicrystal Approximant.

The Yb-Ga-Au 1/1 quasicrystal approximant (AP) composition ranges from Yb14.0Ga20.6Au65.4 to Yb14.8Ga46.3Au38.9, and single crystals of the 1/1 AP having the composition Yb13.8Ga26.1Au60.1 were obtained by the self-flux technique. X-ray structural analysis demonstrated that the atomic structure [space group Im3; a = 14.6889(9) Å] can be described by the body-centered packing of Tsai-type rhombic triacontahedron (RTH) clusters. The positional disorder in these clusters, interpreted as the average of an orientationally disordered tetrahedron and triangle, results in positional disorder in the outer shells. The elemental distributions and positions of mixtures of Au and Ga atoms in the RTH clusters correspond to those in the isostructural Yb15Al36Au49 1/1 AP.

Formation of an Intermediate Valence Icosahedral Quasicrystal in the Au-Sn-Yb System.

We report on the formation of a new icosahedral quasicrystal (iQC) in the Au-Sn-Yb alloy system. This iQC has a primitive icosahedral lattice with a lattice constant aico of 0.5447(7) nm and a composition that was determined to be Au60.0Sn26.7Yb13.3. X-ray absorption spectroscopy measurement of the near Yb L3 edge demonstrates that the Yb valence in the iQC is an intermediate valence between divalent (4f14) and trivalent (4f13) at ambient pressure and was determined to be 2.18+. The results are compared to those for a corresponding 2/1 cubic approximant crystal. The formation of this new iQC is discussed in terms of the atomic size factor (δ) and the valence electron-to-atom ratio (e/a).

Characterization of Ni3Sn intermetallic nanoparticles fabricated by thermal plasma process and catalytic properties for methanol decomposition.

The intermetallic compound Ni3Sn has potential for application in hydrogen production as a catalyst. Herein, we synthesized Ni3Sn nanoparticles through a thermal plasma process. We characterized the nanoparticles by synchrotron radiation X-ray diffraction and transmission electron microscopy analyses, and analyzed their catalytic properties for methanol decomposition in a temperature range of 513 to 793 K. The Ni3Sn nanoparticles showed a higher selectivity to H2 and CO than pure Ni nanoparticles, but a relatively lower catalytic activity for methanol decomposition compared to pure Ni nanoparticles. Density functional theory calculations revealed that the activation energy barrier for CO dissociation on Ni3Sn (001) was 396 kJ/mol, which was higher than that for Ni (111). Moreover, the activation energy barrier for OH formation on Ni3Sn (001) was 229 kJ/mol, which was significantly higher than that for Ni (111). This supported the experimental results and confirmed that the Ni3Sn catalyst suppresses the formation of carbon and H2O, compared to Ni catalyst.

Carrier generation and electronic properties of a single-component pure organic metal.

Metallic conduction generally requires high carrier concentration and wide bandwidth derived from strong orbital interaction between atoms or molecules. These requisites are especially important in organic compounds because a molecule is fundamentally an insulator; only multi-component salts with strong intermolecular interaction-namely, only charge transfer complexes and conducting polymers-have demonstrated intrinsic metallic behaviour. Herein we report a single-component electroactive molecule, zwitterionic tetrathiafulvalene(TTF)-extended dicarboxylate radical (TED), exhibiting metallic conduction even at low temperatures. TED exhibits d.c. conductivities of 530 S cm-1 at 300 K and 1,000 S cm-1 at 50 K with copper-like electronic properties. Spectroscopic and theoretical investigations of the carrier-generation mechanism and the electronic states of this single molecular species reveal a unique electronic structure with a spin-density gradient in the extended TTF moieties that becomes, in itself, a metallic state.

Intrinsic Triple Order in A-site Columnar-Ordered Quadruple Perovskites: Proof of Concept.

There is an emerging topic in the science of perovskite materials: A-site columnar-ordered A2 A'A''B4 O12 quadruple perovskites, which have an intrinsic triple order at the A sites. However, in many examples reported so far, A' and A'' cations are the same, and the intrinsic triple order is hidden. Here, we investigate structural properties of Dy2 CuMnMn4 O12 (1) and Ho2 MnGaMn4 O12 (2) by neutron and X-ray powder diffraction and prove the triple order at the A sites. The cation distributions determined are [Ho2 ]A [Mn]A' [Ga0.66 Mn0.34 ]A'' [Mn3.66 Ga0.34 ]B O12 and [Dy2 ]A [Cu0.73 Mn0.27 ]A' [Mn0.80 Dy0.20 ]A'' [Mn1.89 Cu0.11 ]B1 [Mn2 ]B2 O12 . There are clear signatures of Jahn-Teller distortions in 1 and 2, and the orbital pattern is combined with an original type of charge ordering in 1. Columnar-ordered quadruple perovskites represent a new playground to study complex interactions between different electronic degrees of freedom. No long-range magnetic order was found in 2 by neutron diffraction, and its magnetic properties in low fields are dominated by an impurity with negative magnetization or magnetization reversal. On the other hand, 1 shows three magnetic transitions at 21, 125, and 160 K.

Onboard experiment investigating metal leaching of fresh hydrothermal sulfide cores into seawater.

We observed the initial release rate of metals from four fresh (i.e., without long time exposure to the atmosphere) hydrothermal sulfide cores into artificial seawater. The sulfide samples were collected by seafloor drilling from the Okinawa Trough by D/V Chikyu, powdered under inert gas, and immediately subjected to onboard metal-leaching experiments at different temperatures (5 °C and 20 °C), and under different redox conditions (oxic and anoxic), for 1-30 h. Zinc and Pb were preferentially released from sulfide samples containing various metals (i.e., Mn, Fe, Cu, Zn, Cd, and Pb) into seawater. Under oxic experimental conditions, Zn and Pb dissolution rates from two sulfide samples composed mainly of iron disulfide minerals (pyrite and marcasite) were higher than those from two other sulfide samples with abundant sphalerite, galena, and/or silicate minerals. Scanning electron microscopy confirmed that the high metal-releasing sample contained several galvanic couples of iron disulfide with other sulfide minerals, whereas the low metal-releasing sample contained fewer galvanic couples or were coated by a silicate mineral. The experiments overall confirmed that the galvanic effects with iron disulfide minerals greatly induce the initial release of Zn and Pb from hydrothermal sulfides into seawater, especially under warm oxic conditions.

High-Pressure Phase Relations and Crystal Structures of Postspinel Phases in MgV2O4, FeV2O4, and MnCr2O4: Crystal Chemistry of AB2O4 Postspinel Compounds.

We have investigated high-pressure, high-temperature phase transitions of spinel (Sp)-type MgV2O4, FeV2O4, and MnCr2O4. At 1200-1800 °C, MgV2O4 Sp decomposes at 4-7 GPa into a phase assemblage of MgO periclase + corundum (Cor)-type V2O3, and they react at 10-15 GPa to form a phase with a calcium titanite (CT)-type structure. FeV2O4 Sp transforms to CT-type FeV2O4 at 12 GPa via decomposition phases of FeO wüstite + Cor-type V2O3. MnCr2O4 Sp directly transforms to the calcium ferrite (CF)-structured phase at 10 GPa and 1000-1400 °C. Rietveld refinements of CT-type MgV2O4 and FeV2O4 and CF-type MnCr2O4 confirm that both the CT- and CF-type structures have frameworks formed by double chains of edge-shared B3+O6 octahedra (B3+ = V3+ and Cr3+) running parallel to one of orthorhombic cell axes. A relatively large A2+ cation (A2+ = Mg2+, Fe2+, and Mn2+) occupies a tunnel-shaped space formed by corner-sharing of four double chains. Effective coordination numbers calculated from eight neighboring oxygen-A2+ cation distances of CT-type MgV2O4 and FeV2O4 and CF-type MnCr2O4 are 5.50, 5.16, and 7.52, respectively. This implies that the CT- and CF-type structures practically have trigonal prism (six-coordinated) and bicapped trigonal prism (eight-coordinated) sites for the A2+ cations, respectively. A relationship between cation sizes of VIIIA2+ and VIB3+ and crystal structures (CF- and CT-types) of A2+B23+O4 is discussed using the above new data and available previous data of the postspinel phases. We found that CF-type A2+B23+O4 crystallize in wide ionic radius ranges of 0.9-1.4 Å for VIIIA2+ and 0.55-1.1 Å for VIB3+, whereas CT-type phases crystallize in very narrow ionic radius ranges of ∼0.9 Å for VIIIA2+ and 0.6-0.65 Å for VIB3+. This would be attributed to the fact that the tunnel space of CT-type structure is geometrically less flexible due to the smaller coordination number for A2+ cation than that of CF-type.