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A new ternary phase, TiIrB, was synthesized by arc-melting of the elements and characterized by powder X-ray diffraction. The compound crystallizes in the orthorhombic Ti1+xRh2−x+yIr3−yB3 structure type, space group Pbam (no. 55) with the lattice parameters a = 8.655(2), b = 15.020(2), and c = 3.2271(4) Å. Density Functional Theory (DFT) calculations were carried out to understand the electronic structure, including a Bader charge analysis. The charge distribution of TiIrB in the Ti1+xRh2−x+yIr3−yB3-type phase has been evaluated for the first time, and the results indicate that more electron density is transferred to the boron atoms in the zigzag B4 units than to isolated boron atoms. [ABSTRACT FROM AUTHOR]

Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V3B4 have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H2SO4) increases with increasing boron chain condensation in vanadium borides: Using a −23 mV overpotential decrement derived from −0.296 mV (for VB at −10 mA cm−2 current density) and −0.273 mV (for V3B4) we accurately predict the overpotential of VB2 (−0.204 mV) as well as that of unstudied V2B3 (−0.250 mV) and hypothetical "V5B8" (−0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical VxBy phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships. [ABSTRACT FROM AUTHOR]

Transition‐metal borides belong to a small class of non‐noble‐metal electrocatalysts that exhibit excellent activity toward the hydrogen evolution reaction (HER) already in bulk form; those containing graphene‐like (flat) boron layers, such as α‐MoB2, are particularly promising. In this study, the first tungsten‐based boride HER electrocatalysts were studied experimentally and theoretically. Tungsten, the diborides of which (α‐ and β‐WB2) contain both the active graphene‐like (flat) boron layer and the less active phosphorene‐like (puckered) boron layer, could be successfully substituted (up to 30 at %) for molybdenum in α‐MoB2. The resulting α‐Mo1−xWxB2 exhibited better HER activity and stability than the binaries WB2 and MoB2, especially at high current density in acidic electrolytes. DFT calculations showed that the graphene‐like boron layer is the most active among the studied surfaces and that tungsten promotes hydrogen generation by facilitating bonding between hydrogen atoms in contrast to molybdenum. These results should pave the way for high‐current‐density, abundant, and inexpensive bulk and nanoscale HER catalysts by applying structure–activity relationships. [ABSTRACT FROM AUTHOR]

The new ternary compound Nb1–xOs1+xB (x = 0.17) was synthesized by arc‐melting of the elements in a water‐cooled crucible under an argon atmosphere and was characterized by powder and single‐crystal X‐ray diffraction as well as energy‐dispersive X‐ray spectroscopy (EDX). The compound crystallizes with a new orthorhombic structure type in the space group Pnma (no. 62) with the lattice parameters a = 11.283(2) Å, b = 3.0101(4) Å, and c = 12.883(2) Å. The structure contains isolated boron atoms in osmium trigonal prisms, and boron chains in face‐sharing niobium trigonal prisms. Electronic structure relaxation has confirmed the crystallographic parameters, and crystal orbital Hamilton population (COHP) bonding analysis was used to understand the chemical bonding. It is shown that a local stabilizing effect from replacing Nb with Os is favored despite a global destabilization. [ABSTRACT FROM AUTHOR]

Tuning of the magnetic properties of intermetallic materials is increasingly gaining interest in the chemistry community. We report on the successful synthesis and magnetic characterizations of the two new quaternary boride series MRh6- nRu nB3 (M = Co, Ni; 1 ≤ n ≤ 5). Powder samples have been synthesized by arc-melting the elements under purified argon in a water-cooled copper crucible. The products were characterized by powder X-ray diffraction through Rietveld refinements as well as EDX measurements. All phases crystallize in the hexagonal Th7Fe3 structure type (space group P63 mc, no. 186, Z = 2). In the Co-based series, the lattice parameters decrease linearly with increasing ruthenium content, whereas in the Ni-based series they remain nearly constant for the Rh-rich side then decrease with increasing Ru content. Significant ferromagnetic interactions are observed for the Co-based series, and they decrease linearly with increasing Ru content with magnetic moments decreasing from 0.74 µB (CoRh5RuB3) to 0.13 µB (CoRhRu5B3) at 5 K and 5 T. Pauli paramagnetism dominates the Ni-based series. [ABSTRACT FROM AUTHOR]

Molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo2B, α-MoB, β-MoB, and MoB2 by arc-melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X-ray photoelectron spectroscopy (XPS) for the first time; MoB2 and β-MoB show excellent activity in the same range as the recently reported α-MoB and β-Mo2C phases, while the molybdenum richest phase Mo2B show significantly lower HER activity, indicating a strong boron-dependency of these borides for the HER. In addition, MoB2 and β-MoB show long-term cycle stability in acidic solution. [ABSTRACT FROM AUTHOR]

The synergistic combination of experiment and density functional theory has led to the discovery of the first ferromagnetic material, Nb6Fe1−xIr6+xB8, containing in its crystal structure iron chains embedded in stacked B6 rings. The strong ferromagnetic Fe–Fe interactions found in the iron chains induce an unexpected strengthening of the B–B interactions in the B6 rings. Beside these strong B–B interactions, strong interlayer metal–boron bonds (Ir–B and Nb–B) ensure the overall structural stability of this phase, while the magnetic Fe–Fe interactions are mainly responsible for the observed ferromagnetic ordering below TC=350 K. [ABSTRACT FROM AUTHOR]

Ta3Ru5B2, Zr2.86(5)Ru5.14(5)B2, and Hf2.83(2)Ru5.17(2)B2 have been successfully synthesized as polycrystalline powders as well as single crystals and characterized by powder and single- crystal X-ray diffraction and EDX analysis. Furthermore, their electronic structures and bonding characteristics have been analyzed by DFT calculations. The three phases are isotypic and crystallize with a Ti3Co5B2-type structure (space group P4/mbm). Their electronic densities of states, which all possess a large pseudogap at the Fermi level, closely follow the rigid band model. Bonding analyses indicated that Ru-B and Ru-M (M = Zr, Hf, Ta) heteroatomic interactions are mainly responsible for their structural stability and that the homoatomic M-M interactions behave differently when connecting either two tetragonal or two pentagonal Ru prisms at the same distance. [ABSTRACT FROM AUTHOR]

Polycrystalline samples and single crystals of four members of the new complex boride series Ti3−xRu5−yIryB2+x (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti3Co5B2 structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti3Ru2.9Ir2.1B2). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti2Ru2.8Ir2.2B3). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir−B and Ru/Ir−Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides. [ABSTRACT FROM AUTHOR]

Highlights from the article: Cover Feature: High-Current-Density HER Electrocatalysts: Graphene-like Boron Layer and Tungsten as Key Ingredients in Metal Diborides (ChemSusChem 16/2019) Keywords: DFT calculations; electrocatalysis; hydrogen evolution reaction; high current density; tungsten borides DFT calculations, electrocatalysis, hydrogen evolution reaction, high current density, tungsten borides.

The ternary borides Ta3Ru5B2, Zr2.86Ru5.14B2, and Hf2.83Ru5.17B2 are synthesized by arc-melting of stoichiometric mixtures of the elements (Ar, Cu crucibles). [ABSTRACT FROM AUTHOR]

The polycrystalline title compound and single crystals thereof are prepared by arc-melting of a stoichiometric pelletized mixture of the elements (Cu crucible under Ar) and characterized by XRD and EDX. [ABSTRACT FROM AUTHOR]

Conspectus: Boron's unique chemical properties and its reactions with metals have yielded the large class of metal borides with compositions ranging from the most boron-rich YB66 (used as monochromator for synchrotron radiation) up to the most metal-rich Nd2Fe14B (the best permanent magnet to date). The excellent magnetic properties of the latter compound originate from its unique crystal structure to which the presence of boron is essential. In general, knowing the crystal structure of any given extended solid is the prerequisite to understanding its physical properties and eventually predicting new synthetic targets with desirable properties. The ability of boron to form strong chemical bonds with itself and with metallic elements has enabled us to construct new structures with exciting properties. In recent years, we have discovered new boride structures containing some unprecedented boron fragments (trigonal planar B4 units, planar B6 rings) and low-dimensional substructures of magnetically active elements (ladders, scaffolds, chains of triangles). The new boride structures have led to new superconducting materials (e.g., NbRuB) and to new itinerant magnetic materials (e.g., Nb6Fe1-xIr6+xB8). The study of boride compounds containing chains (Fe-chains in antiferromagnetic Sc2FeRu5B2), ladders (Fe-ladders in ferromagnetic Ti9Fe2Rh18B8), and chains of triangles (Cr3 chains in ferrimagnetic and frustrated TiCrIr2B2) of magnetically active elements allowed us to gain a deep understanding of the factors (using density functional theory calculations) that can affect magnetic ordering of such low-dimensional magnetic units. We discovered that the magnetic properties of phases containing these magnetic subunits can be drastically tuned by chemical substitution within the metallic nonmagnetic network. For example, the small hysteresis (measure of magnetic energy storage) of Ti2FeRh5B2 can be successively increased up to 24-times by gradually substituting Ru for Rh, a result that was even surpassed (up to 54-times the initial value) for Ru/Ir substitutions. Also, the type of long-range magnetic interactions could be drastically tuned by appropriate substitutions in the metallic nonmagnetic network as demonstrated using both experimental and theoretical methods. It turned out that Ru-rich and valence electron poor metal borides adopting the Ti3Co5B2 or the Th7Fe3 structure types have dominating antiferromagnetic interactions, while in Rh-rich (or Ir-rich) and valence electron rich phases ferromagnetic interactions prevail, as found, for example, in the Sc2FeRu5-xRhxB2 and FeRh6-xRuxB3 series. Fascinatingly, boron clusters (e.g., B6 rings) even directly interact in some cases with the magnetic subunits, an interaction which was found to favor the Fe-Fe magnetic exchange interactions in the ferromagnetic Nb6Fe1-xIr6+xB8. Using less expensive transition metals, we have recently predicted new itinerant magnets, the experimental proof of which is still pending. Furthermore, new structures have been discovered, all of which are being studied experimentally and computationally with the aim of finding new superconductors, magnets, and mechanically hard materials. A new direction is being pursued in our group, as binary and ternary transition metal borides show great promise as efficient water splitting electrocatalysts at the micro- and nanoscale. [ABSTRACT FROM AUTHOR]

The synergistic combination of experiment and density functional theory has led to the discovery of the first ferromagnetic material, Nb6Fe1−xIr6+xB8, containing in its crystal structure iron chains embedded in stacked B6 rings. The strong ferromagnetic Fe–Fe interactions found in the iron chains induce an unexpected strengthening of the B–B interactions in the B6 rings. Beside these strong B–B interactions, strong interlayer metal–boron bonds (Ir–B and Nb–B) ensure the overall structural stability of this phase, while the magnetic Fe–Fe interactions are mainly responsible for the observed ferromagnetic ordering below TC=350 K. [ABSTRACT FROM AUTHOR]

Highly crystalline Nb6Fe1-xIr6+xB8 (68% yield) is prepared from the elements in the molar ratio of Nb:Fe:Ir:B = 6:1:6:9 by rapid arc melting and quenching. [ABSTRACT FROM AUTHOR]

The new title compound is synthesized by arc melting of the elements in a water-cooled Cu crucible under argon (ratio 7:6:8 for Nb:Os:B, 80% yield). [ABSTRACT FROM AUTHOR]

Ta2OsB2 (I) and TaRuB (II) are prepared by arc-melting of stoichiometric amounts of the elements. [ABSTRACT FROM AUTHOR]

DFT calculations for the ternary phases Sc2M6B (M: Ir, Pd, Ni) reveal the presence of pseudogaps near their Fermi levels between 61 and 68 valence electrons leading to the prediction of new phases Sc2Ir6‐xPdxB and Sc2Ir6‐xNixB (x = 0—6) in the double‐perovskite‐like Ti2Rh6B‐type structure. [ABSTRACT FROM AUTHOR]

Sc2FeRu5-xIrxB2 (x: 1, 2, 3, 4) are prepared by arc melting of the elements several times under Ar (20 s, 40 A). [ABSTRACT FROM AUTHOR]

Polycrystalline samples of the boride series Ti9-xM2+xRu18B8 (M: Cr, Co, Mn, Ni) and single crystals of Ti8Co3Ru18B8 are prepared by arc melting of the elements. [ABSTRACT FROM AUTHOR]