Synthesis and Properties of New Multinary Silicides R₅Mg₅Fe₄Al_<i>x</i>Si_{18–<i>x</i>} (R = Gd, Dy, Y, <i>x</i> ≈ 12) Grown in Mg/Al Flux

Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1 Mg/Al mixed flux produce well-formed crystals of R₅Mg₅Fe₄Al_<i>x</i>Si_{18–<i>x</i>} (<i>x</i> ≈ 12). These phases have a new structure type in tetragonal space group <i>P</i>4<i>/mmm</i> (<i>a</i> = 11.655(2) Å, <i>c</i> = 4.0668(8) Å, <i>Z</i> = 1 and <i>R</i>₁ = 0.0155 for the Dy analogue). The structure features two rare earth sites and one iron site; the latter is in monocapped trigonal prismatic coordination surrounded by silicon and aluminum atoms. Siting of Al and Si was investigated using bond length analysis and ²⁷Al and ²⁹Si MAS NMR studies. The magnetic properties are determined by the R elements, with the Gd and Dy analogues exhibiting antiferromagnetic ordering at <i>T</i>_N = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic behavior with varying field

Synthesis and Properties of New Multinary Silicides R₅Mg₅Fe₄Al_<i>x</i>Si_{18–<i>x</i>} (R = Gd, Dy, Y, <i>x</i> ≈ 12) Grown in Mg/Al Flux

Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1 Mg/Al mixed flux produce well-formed crystals of R₅Mg₅Fe₄Al_<i>x</i>Si_{18–<i>x</i>} (<i>x</i> ≈ 12). These phases have a new structure type in tetragonal space group <i>P</i>4<i>/mmm</i> (<i>a</i> = 11.655(2) Å, <i>c</i> = 4.0668(8) Å, <i>Z</i> = 1 and <i>R</i>₁ = 0.0155 for the Dy analogue). The structure features two rare earth sites and one iron site; the latter is in monocapped trigonal prismatic coordination surrounded by silicon and aluminum atoms. Siting of Al and Si was investigated using bond length analysis and ²⁷Al and ²⁹Si MAS NMR studies. The magnetic properties are determined by the R elements, with the Gd and Dy analogues exhibiting antiferromagnetic ordering at <i>T</i>_N = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic behavior with varying field

Flux Growth and Magnetoresistance Behavior of Rare Earth Zintl Phase EuMgSn

Reactions of europium and tin in 1:1 Mg/Al mixed flux produce large crystals of EuMgSn. This phase crystallizes with the TiNiSi structure type in orthorhombic space group <i>Pnma</i> (<i>a</i> = 8.0849(7) Å, <i>b</i> = 4.8517(4) Å, <i>c</i> = 8.7504(8) Å, <i>Z</i> = 4, <i>R</i>₁ = 0.0137). The crystal structure features europium cations positioned between puckered hexagonal layers comprised of magnesium and tin atoms. Magnetic susceptibility measurements indicate the europium in this phase is divalent, which suggests that the compound is possibly valence-balanced as Eu²⁺Mg²⁺Sn^4–. However, EuMgSn is a metal as indicated by density of states calculations and electrical resistivity behavior. This phase exhibits antiferromagnetic ordering at <i>T</i>_N = 10.9 K at low field (100 G) and the ordering temperature decreases when a higher magnetic field is applied. ac magnetization and field dependence of resistivity at 4.2 K reveal that there is a spin reorientation at 2 T, in agreement with the metamagnetic transition shown in the dc magnetization versus field data. Temperature dependence of resistivity at 2.5 T indicates that EuMgSn has a large magnetoresistance up to −30% near its magnetic ordering temperature

Competing Phases, Complex Structure, and Complementary Diffraction Studies of R_3‑δFeAl_4‑xMg_<i>x</i>Tt₂ Intermetallics (R = Y, Dy, Er, Yb; Tt = Si or Ge; <i>x</i> < 0.5)

Four new intermetallic phases R_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Si₂ (R = Yb, Dy) and R_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Ge₂ (R = Er, Y) were synthesized in Mg/Al (1:1 mol ratio) molten flux. These phases have a new structure type in tetragonal space group <i>P</i>4<i>/mbm</i> (<i>a</i> = 13.3479(9) Å, <i>c</i> = 4.0996(3) Å, <i>Z</i> = 4, and R1 = 0.0176 for Yb_2.77FeAl_3.72Mg_0.28Si₂). The structure features iron in trigonal prismatic coordination by aluminum atoms. The prisms share trigonal faces to form chains running along the <i>c</i>-axis, similar to the chains seen in several related structures, including that of the previously reported competing phases R₅Mg₅Fe₄Al₁₂Si₆ (R = Gd, Dy, and Y). Occupancies of Mg, Al, and Si sites in Yb_2.77FeAl_3.72Mg_0.28Si₂ were determined by single crystal X-ray and neutron diffraction, bond length analysis, and comparison to atom positions and bond lengths in the isostructural germanides. Electronic structure calculations indicate these phases are polar intermetallics with pseudogaps near the Fermi level. The magnetic properties of these phases are determined by the rare earth ions. Y_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Ge₂ is Pauli paramagnetic; the Yb³⁺ cations in Yb_2.77FeAl_3.72Mg_0.28Si₂ exhibit Curie–Weiss behavior with no ordering in the temperature range observed. Er_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Ge₂ and Dy_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Si₂ order antiferromagnetically at <i>T</i>_N = 2.8 and 4.0 K, respectively; the former undergoes a spin reorientation at ∼4400 G according to the ac field dependence of magnetization

Synthesis of α-arylalkylferrocenes through cesium fluoride-promoted coupling of arylboronic acids with <i>N</i>-tosylhydrazones

<p>A cesium fluoride-promoted reductive coupling reaction of acylferrocene tosylhydrazones with arylboronic acids has been developed, producing highly substituted α-arylalkylferrocenes in moderate to excellent yields. The reaction employs anionic fluorine to facilitate the cleavage of C–B bond. The developed methodology demonstrates a wide substrate scope and high functional groups tolerance. Moreover, the α-arylalkylferrocenes compounds were also obtained on a multi-gram scale.</p

Flux Growth and Magnetoresistance Behavior of Rare Earth Zintl Phase EuMgSn

Reactions of europium and tin in 1:1 Mg/Al mixed flux produce large crystals of EuMgSn. This phase crystallizes with the TiNiSi structure type in orthorhombic space group <i>Pnma</i> (<i>a</i> = 8.0849(7) Å, <i>b</i> = 4.8517(4) Å, <i>c</i> = 8.7504(8) Å, <i>Z</i> = 4, <i>R</i>₁ = 0.0137). The crystal structure features europium cations positioned between puckered hexagonal layers comprised of magnesium and tin atoms. Magnetic susceptibility measurements indicate the europium in this phase is divalent, which suggests that the compound is possibly valence-balanced as Eu²⁺Mg²⁺Sn^4–. However, EuMgSn is a metal as indicated by density of states calculations and electrical resistivity behavior. This phase exhibits antiferromagnetic ordering at <i>T</i>_N = 10.9 K at low field (100 G) and the ordering temperature decreases when a higher magnetic field is applied. ac magnetization and field dependence of resistivity at 4.2 K reveal that there is a spin reorientation at 2 T, in agreement with the metamagnetic transition shown in the dc magnetization versus field data. Temperature dependence of resistivity at 2.5 T indicates that EuMgSn has a large magnetoresistance up to −30% near its magnetic ordering temperature

Competing Phases, Complex Structure, and Complementary Diffraction Studies of R_3‑δFeAl_4‑xMg_<i>x</i>Tt₂ Intermetallics (R = Y, Dy, Er, Yb; Tt = Si or Ge; <i>x</i> < 0.5)

Four new intermetallic phases R_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Si₂ (R = Yb, Dy) and R_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Ge₂ (R = Er, Y) were synthesized in Mg/Al (1:1 mol ratio) molten flux. These phases have a new structure type in tetragonal space group <i>P</i>4<i>/mbm</i> (<i>a</i> = 13.3479(9) Å, <i>c</i> = 4.0996(3) Å, <i>Z</i> = 4, and R1 = 0.0176 for Yb_2.77FeAl_3.72Mg_0.28Si₂). The structure features iron in trigonal prismatic coordination by aluminum atoms. The prisms share trigonal faces to form chains running along the <i>c</i>-axis, similar to the chains seen in several related structures, including that of the previously reported competing phases R₅Mg₅Fe₄Al₁₂Si₆ (R = Gd, Dy, and Y). Occupancies of Mg, Al, and Si sites in Yb_2.77FeAl_3.72Mg_0.28Si₂ were determined by single crystal X-ray and neutron diffraction, bond length analysis, and comparison to atom positions and bond lengths in the isostructural germanides. Electronic structure calculations indicate these phases are polar intermetallics with pseudogaps near the Fermi level. The magnetic properties of these phases are determined by the rare earth ions. Y_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Ge₂ is Pauli paramagnetic; the Yb³⁺ cations in Yb_2.77FeAl_3.72Mg_0.28Si₂ exhibit Curie–Weiss behavior with no ordering in the temperature range observed. Er_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Ge₂ and Dy_3‑δFeAl_4‑<i>x</i>Mg_<i>x</i>Si₂ order antiferromagnetically at <i>T</i>_N = 2.8 and 4.0 K, respectively; the former undergoes a spin reorientation at ∼4400 G according to the ac field dependence of magnetization

Synthesis of symmetrical terphenyl derivatives by PdCl₂-catalyzed Suzuki–Miyaura reaction of dibromobenzene using 3-(diphenylphosphino)propanoic acid as a ligand

<p>A simple and efficient catalytic system for PdCl₂ catalyzing the Suzuki–Miyaura reaction of dibromobenzene and arylboronic acid has been developed by using 3-(diphenylphosphino)propanoic acid as a ligand in dimethylsulfoxide at 100 °C. Using this method, a series of symmetrical terphenyl derivatives were obtained with remarkably good yields, up to 93%.</p

Thermoelectric Properties of Ba_1.9Ca_2.4Mg_9.7Si₇: A New Silicide Zintl Phase with the Zr₂Fe₁₂P₇ Structure Type

Ba_1.9Ca_2.4Mg_9.7Si₇ was grown as large crystals from the reaction of silicon with barium and calcium in Mg/Al flux. This compound is a charge-balanced Zintl phase with the Zr₂Fe₁₂P₇ structure type in hexagonal space group <i>P</i>6̅ (<i>a</i> = 11.196(2) Å, <i>c</i> = 4.4595(9) Å); barium occupies the Zr sites, the lighter alkaline earths (Mg, Ca) mix on the Fe sites, and silicon occupies the phosphorus sites. An isostructural germanide (Ba_1.2Sr_0.9Mg_11.9Ge₇, <i>a</i> = 11.064(1) Å, <i>c</i> = 4.3709(6) Å)) was similarly synthesized from reactions of germanium with barium and strontium in Mg/Al flux. Density of states calculations indicate these phases are semimetals, in agreement with their charge-balanced nature. Measurements of electrical resistivity, thermal conductivity, and Seebeck coefficient were carried out from 300–1000 K to investigate the thermoelectric properties of Ba_1.9Ca_2.4Mg_9.7Si₇. This compound is an n-type semimetal with low thermal conductivity (2 W/(m·K)), moderate Seebeck coefficient (−200 μV/K at 900 K), and a thermoelectric figure of merit ZT of 0.35 at 900 K

Inheritance of Crystallographic Orientation during Lithiation/Delithiation Processes of Single-Crystal α‑Fe₂O₃ Nanocubes in Lithium-Ion Batteries

Iron oxides are very promising anode materials based on conversion reactions for lithium-ion batteries (LIBs). During conversion processes, the crystal structure and composition of the electrode material are drastically changed. Surprisingly, in our study, inheritance of a crystallographic orientation was found during lithiation/delithiation processes of single-crystal α-Fe₂O₃ nanocubes by ex situ transmission electron microscopy. Single-crystal α-Fe₂O₃ was first transformed into numerous Fe nanograins embedded in a Li₂O matrix, and then the conversion between Fe and FeO nanograins became the main reversible electrochemical reaction for energy storage. Interestingly, these Fe/FeO nanograins had almost the same crystallographic orientation, indicating that the lithiated/delithiated products can inherit the crystallographic orientation of single-crystal α-Fe₂O₃. This finding is important for understanding the detailed electrochemical conversion processes of iron oxides, and this feature may also exist during lithiation/delithiation processes of other transition-metal oxides