Exotic magnetism on the quasi-FCC lattices of the d3d^3 double perovskites La2_2NaB′'O6_6 (B′' == Ru, Os)

We find evidence for long-range and short-range ($\zeta$ $=$ 70 \AA~at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices of the monoclinic double perovskites La$_2$NaRuO$_6$ and La$_2$NaOsO$_6$ respectively. Incommensurate magnetic order on the FCC lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbour and next nearest neighbour exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap $\Delta$ $\sim$ 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally-coordinated $3d^3$ systems, so the large gap observed for La$_2$NaRuO$_6$ may result from the significantly enhanced value of spin-orbit coupling in this $4d^3$ material.Comment: 5 pages, 4 figure

Flux Crystal Growth of the RE2Ru3Ge5 (RE = La, Ce, Nd, Gd, Tb) Series and Their Magnetic and Metamagnetic Transitions

Previously synthesized only as powders, single crystals of the RE2Ru3Ge5 (RE = La, Ce, Nd, Gd, Tb) series of compounds have now been obtained from molten In. These materials crystallize with the U2Co3Si5-type structure in orthorhombic space group Ibam with lattice parameters a ≈ 10.00–9.77 Å (La–Tb), b ≈ 12.51–12.35 Å, and c ≈ 5.92–5.72 Å. The structure is a three-dimensional framework consisting of RuGe5 and RuGe6 units, as well as Ge–Ge zigzag chains. This structure type and those of the other five (Sc2Fe3Si5, Lu2Co3Si5, Y2Rh3Sn5, Yb2Ir3Ge5, and Yb2Pt3Sn5) to compose the RE2T3X5 phase space are discussed in depth. For the three compounds with RE = Nd, Gd, Tb, multiple magnetic transitions and metamagnetic behavior are observed. Electronic band structure calculations performed on La2Ru3Ge5 indicate that these materials have a negative band gap and are semimetallic in nature

Hydroflux Crystal Growth of Platinum Group Metal Hydroxides: Sr₆NaPd₂(OH)₁₇, Li₂Pt(OH)₆, Na₂Pt(OH)₆, Sr₂Pt(OH)₈, and Ba₂Pt(OH)₈

Crystals of five complex metal hydroxides containing platinum group metals were grown by a novel low-temperature hydroflux technique, a hybrid approach between the aqueous hydrothermal and the molten hydroxide flux techniques. Sr₆NaPd₂(OH)₁₇ (<b>1</b>) crystallizes in orthorhombic space group <i>Pbcn</i> with lattice parameters <i>a</i> = 19.577(4) Å, <i>b</i> = 13.521(3) Å, and <i>c</i> = 6.885(1) Å. This compound has a three-dimensional framework structure with Sr­(OH)_<i>n</i> polyhedra, Na­(OH)₆ octahedra, and Pd­(OH)₄ square planes. Isostructural phases Li₂Pt­(OH)₆ (<b>2</b>) and Na₂Pt­(OH)₆ (<b>3</b>) crystallize in trigonal space group <i>P</i>-3 with lattice parameters of <i>a</i> = 5.3406(8) Å and <i>c</i> = 4.5684(9) Å and <i>a</i> = 5.7984(8) Å and <i>c</i> = 4.6755(9) Å, respectively. Structures of these materials consist of layers of A­(OH)₆ (A = Li (<b>2</b>), Na (<b>3</b>)) and Pt­(OH)₆ octahedra. Sr₂Pt­(OH)₈ (<b>4</b>) crystallizes in monoclinic space group <i>P</i>2₁/<i>c</i> with lattice parameters <i>a</i> = 5.9717(6) Å, <i>b</i> = 10.997(1) Å, <i>c</i> = 6.0158(6) Å, and β = 113.155(2)°, while Ba₂Pt­(OH)₈ (<b>5</b>) crystallizes in orthorhombic space group <i>Pbca</i> with lattice parameters <i>a</i> = 8.574(2) Å, <i>b</i> = 8.673(2) Å, and <i>c</i> = 10.276(2) Å. Both of these compounds have three-dimensional structures composed of Pt­(OH)₆ octahedra surrounded by either Sr­(OH)₈ or Ba­(OH)₉ polyhedra. Decomposition of these materials into condensed metal oxides, which is of importance to possible catalytic applications, was monitored via thermogravimetric analysis. For example, Na₂Pt­(OH)₆ (<b>3</b>) converts cleanly via dehydration into α-Na₂PtO₃

Metallic Borides, La₂Re₃B₇ and La₃Re₂B₅, Featuring Extensive Boron–Boron Bonding

La₂Re₃B₇ and La₃Re₂B₅ have been synthesized in single-crystalline form from a molten La/Ni eutectic at 1000 °C in the first example of the flux crystal growth of ternary rare-earth rhenium borides. Both compounds crystallize in their own orthorhombic structure types, with La₂Re₃B₇ (space group <i>Pcca</i>) having lattice parameters <i>a</i> = 7.657(2) Å, <i>b</i> = 6.755(1) Å, and <i>c</i> = 11.617(2) Å, and La₃Re₂B₅ (space group <i>Pmma</i>) having lattice parameters <i>a</i> = 10.809(2) Å, <i>b</i> = 5.287(1) Å, and <i>c</i> = 5.747(1) Å. The compounds possess three-dimensional framework structures that are built up from rhenium boride polyhedra and boron–boron bonding. La₃Re₂B₅ features fairly common B₂ dumbbells, whereas La₂Re₃B₇ has unique one-dimensional subunits composed of alternating triangular B₃ and trans-B₄ zigzag chain fragments. Also observed in La₃Re₂B₅ is an unusual coordination of B by an octahedron of La atoms. Electronic band structure calculations predict that La₂Re₃B₇ is a semimetal, which is observed in the electrical resistivity data as measured on single crystals, with behavior obeying the Bloch–Grüneisen model and a room-temperature resistivity ρ_300 K of ∼375 μΩ cm. The electronic band structure calculations also suggest that La₃Re₂B₅ is a regular metal