Noncentrosymmetric Triangular Magnet CaMnTeO6: Strong Quantum Fluctuations and Role of s0 versus s2 Electronic States in Competing Exchange Interactions.

Noncentrosymmetric triangular magnets offer a unique platform for realizing strong quantum fluctuations. However, designing these quantum materials remains an open challenge attributable to a knowledge gap in the tunability of competing exchange interactions at the atomic level. Here, a new noncentrosymmetric triangular S = 3/2 magnet CaMnTeO6 is created based on careful chemical and physical considerations. The model material displays competing magnetic interactions and features nonlinear optical responses with the capability of generating coherent photons. The incommensurate magnetic ground state of CaMnTeO6 with an unusually large spin rotation angle of 127°(1) indicates that the anisotropic interlayer exchange is strong and competing with the isotropic interlayer Heisenberg interaction. The moment of 1.39(1) µB, extracted from low-temperature heat capacity and neutron diffraction measurements, is only 46% of the expected value of the static moment 3 µB. This reduction indicates the presence of strong quantum fluctuations in the half-integer spin S = 3/2 CaMnTeO6 magnet, which is rare. By comparing the spin-polarized band structure, chemical bonding, and physical properties of AMnTeO6 (A = Ca, Sr, Pb), how quantum-chemical interpretation can illuminate insights into the fundamentals of magnetic exchange interactions, providing a powerful tool for modulating spin dynamics with atomically precise control is demonstrated.

Borate-Based Compounds as Mixed Polyanion Cathode Materials for Advanced Batteries.

Rational design of new and cost-effective advanced batteries for the intended scale of application is concurrent with cathode materials development. Foundational knowledge of cathode materials' processing−structure−properties−performance relationship is integral. In this review, we provide an overview of borate-based compounds as possible mixed polyanion cathode materials in organic electrolyte metal-ion batteries. A recapitulation of lithium-ion battery (LIB) cathode materials development provides that rationale. The combined method of data mining and high-throughput ab initio computing was briefly discussed to derive how carbonate-based compounds in sidorenkite structure were suggested. Borate-based compounds, albeit just close to stability (viz., <30 meV at−1), offer tunability and versatility and hence, potential effectivity as polyanion cathodes due to (1) diverse structures which can host alkali metal intercalation; (2) the low weight of borate relative to mature polyanion families which can translate to higher theoretical capacity; and a (3) rich chemistry which can alter the inductive effect on earth-abundant transition metals (e.g., Ni and Fe), potentially improving the open-circuit voltage (OCV) of the cell. This review paper provides a reference on the structures, properties, and synthesis routes of known borate-based compounds [viz., borophosphate (BPO), borosilicate (BSiO), and borosulfate (BSO)], as these borate-based compounds are untapped despite their potential for mixed polyanion cathode materials for advanced batteries.

Ln2 (SeO3 )2 (SO4 )(H2 O)2 (Ln=Sm, Dy, Yb): A Mixed-Ligand Pathway to New Lanthanide(III) Multifunctional Materials Featuring Nonlinear Optical and Magnetic Anisotropy Properties.

Bottom-up assembly of optically nonlinear and magnetically anisotropic lanthanide materials involving precisely placed spin carriers and optimized metal-ligand coordination offers a potential route to developing electronic architectures for coherent radiation generation and spin-based technologies, but the chemical design historically has been extremely hard to achieve. To address this, we developed a worthwhile avenue for creating new noncentrosymmetric chiral Ln3+ materials Ln2 (SeO3 )2 (SO4 )(H2 O)2 (Ln=Sm, Dy, Yb) by mixed-ligand design. The materials exhibit phase-matching nonlinear optical responses, elucidating the feasibility of the heteroanionic strategy. Ln2 (SeO3 )2 (SO4 )(H2 O)2 displays paramagnetic property with strong magnetic anisotropy facilitated by large spin-orbit coupling. This study demonstrates a new chemical pathway for creating previously unknown polar chiral magnets with multiple functionalities.

Crystal Structure and Electronic Properties of New Compound Zr6.5Pt6Se19.

A new ternary nonstoichiometric Zr6.5Pt6Se19 has been discovered as a part of effort to dope Zr into the layered transitional metal chalcogenide PtSe2. With a new structure type (oC68), it is the first Pt-based ternary chalcogenide with group 4 elements (Ti, Zr, and Hf). The crystal structure adopts the orthorhombic space group Cmmm with lattice parameters of a = 15.637(6) Å, b = 26.541(10) Å, c = 3.6581(12) Å, and V = 1518.2(9) Å3. This unusual structure consists of several building units: chains of edge-sharing selenium trigonal prisms and octahedra centered by zirconium atoms, chains of corner-shared square pyramid, and square planar centered by Pt atoms. The condensation of these building blocks forms a unique structure with bilayered Zr5.54Pt6Se19 slabs stacking along the b direction and large channels parallel to the c direction within the bilayered slabs. Band structure calculations suggest that partial occupancy of Zr atoms creates a pseudo gap at the Fermi level and is likely the main cause for the stability of this new phase.

Synthesis of the Elusive S = 1/2 Star Structure: A Possible Quantum Spin Liquid Candidate.

Materials with two-dimensional, geometrically frustrated, spin-1/2 lattices provide a fertile playground for the study of intriguing magnetic phenomena such as quantum spin liquid (QSL) behavior, but their preparation has been a challenge. In particular, the long-sought, exotic spin-1/2 star structure has not been experimentally realized to date. Here we report the synthesis of [(CH3)2(NH2)]3[CuII3(µ3-OH)(µ3-SO4)(µ3-SO4)3]·0.24H2O with an S = 1/2 star lattice. On the basis of the magnetic susceptibility and heat capacity measurements, the layered Cu-based compound exhibits antiferromagnetic interactions but no magnetic ordering or spin freezing down to 2 K. The spin-frustrated material appears to be a promising QSL candidate.

A Mixed-Valent Iron (II/III) Diamond Chain with Single-Ion Anisotropy.

The geometrically frustrated diamond spin chain system has yielded materials with a diversity of interesting magnetic properties but is predominantly limited to compounds with single-spin components. Here, we report the compound [(CH3)2NH2]6[FeIII4FeII2(µ3-O)2(µ3-OH)2(µ3-SO4)8] (1), which features the mixed-valent iron(II/III) diamond chain: ∞[FeIII-(FeIII)2-FeIII-(FeII)2]. 57Fe Mössbauer spectroscopy shows that two-thirds of the total spins in the ∞[FeIII4FeII2] diamond chain are spin-5/2 (high-spin FeIII), while the remaining one-third are spin-2 (high-spin FeII). To date, 1 is the only diamond-chain compound composed of more than one type of dimer, namely, (FeIII)2 and (FeII)2. On the basis of temperature-dependent 57Fe Mössbauer spectroscopy data, an alternating noncollinear 90° magnetic structure is proposed. Both the (FeIII)2 and (FeII)2 dimers are antiferromagnetically coupled and align in the direction along the chain axis ≈ [010], whereas the moments of the bridging FeIII monomers are oriented orthogonally. The spin canting, arising from the anisotropy of the FeII ions, leads to ferrimagnetic ordering at low temperatures.

Synthesis and Structure of a Nonstoichiometric Zr3.55Pt4Sb4 Compound.

A nonstoichiometric ternary antimonide, Zr3.55Pt4Sb4, with a new structure type (hP24), has been synthesized via arc-melting. Its crystal structure was determined by single-crystal X-ray diffraction with hexagonal space group P63/mmc and lattice parameters a = 4.391(3) Å, c = 30.53(2) Å, and V = 509.7(8) Å3. It features the unique Pt4Sb4 slab with Pt-Pt bonds and is reminiscent to hexagonal diamond substructures. Three different Zr atoms, occupying three different sites, aid in the close-packing of the Pt and Sb atoms. Electronic structure calculations show the half occupancy of one Zr site creates a pseudogap at the Fermi level and optimizes the Pt-Sb bonding interactions. This enhances the electronic stability and accounts for the very narrow phase width observed for this nonstoichiometric compound. Furthermore, strong Zr-Pt and Zr-Sb interactions play a crucial role in the chemical bonding of the title compound. Electrical transport measurements show metallic behavior of this compound down to 2 K, consistent with the band structure calculations.

Sulfate-Bridged, Octanuclear Chromic and Ferric Wheels.

Two new amine-templated transition metal-based sulfates, [(CH3)2NH2]17.4 [SO4]0.7 [MIII8(µ2-OH)8(µ2-SO4)16] where M = Cr and Fe, have been synthesized via mild solvothermal synthesis. The compounds are isostructural and were refined in the monoclinic space group P21/n. They feature the rare sulfate-bridged inorganic molecular wheels [CrIII8(OH)8(SO4)16]16- and [FeIII8(OH)8(SO4)16]16-. In both the octanuclear chromic (J = -2.4 cm-1 based on Hex = -J Sî · Sĵ convention) and ferric wheels (J = -38.3 cm-1), the coupling between the adjacent metal ions is antiferromagnetic giving spin-singlet ground states. The variation in the magnitude of the exchange coupling constants is due to the differences in the superexchange mechanisms, namely, a π-pathway for the Cr- and a σ-pathway for the Fe-wheel cluster.

A large spin, magnetically anisotropic, octanuclear vanadium(iii) wheel.

A large spin, magnetically anisotropic, octanuclear vanadium(iii) wheel-like cluster has been synthesized. The coupling between adjacent VIII ions is ferromagnetic giving a ground state of St = 8, the largest known for a vanadium-based complex.

Nb2O2F3: a reduced niobium (III/IV) oxyfluoride with a complex structural, magnetic, and electronic phase transition.

A new niobium oxyfluoride, Nb2O2F3, synthesized through the reaction of Nb, SnO, and SnF2 in Sn flux, within welded Nb containers, crystallizes in a monoclinic structure (space group: I2/a; a = 5.7048(1)Å, b = 5.1610(1)Å, c = 12.2285(2)Å, ß = 95.751(1)°). It features [Nb2X10] units (X = O, F), with short (2.5739(1) Å) Nb-Nb bonds, that are linked through shared O/F vertices to form a 3D structure configurationally isotypic to ζ-Nb2O5. Nb2O2F3 undergoes a structural transition at ∼90 K to a triclinic structure (space group: P1̅; a = 5.1791(5)Å, b = 5.7043(6)Å, c = 6.8911(7)Å, α = 108.669(3)°, ß = 109.922(2)°, γ = 90.332(3)°). The transition is described as a disproportionation or charge ordering of [Nb2](7+) dimers: (2[Nb2](7+) → [Nb2](6+) + [Nb2](8+)), resulting in doubly (2.5000(9) Å) and singly bonded (2.6560(9) Å) Nb2 dimers. The structural transition is accompanied by an unusual field-independent "spin-gap-like" magnetic transition.

Synthesis, structure, and superconductivity in the new-structure-type compound: SrPt6P2.

A metal-rich ternary phosphide, SrPt(6)P(2), with a unique structure type was synthesized at high temperatures. Its crystal structure was determined by single-crystal X-ray diffraction [cubic space group Pa3̅; Z = 4; a = 8.474(2) Å, and V = 608.51(2) Å(3)]. The structure features a unique three-dimensional anionic (Pt(6)P(2))(2-) network of vertex-shared Pt(6)P trigonal prisms. The Sr atoms occupy a 12-coordinate (Pt) cage site and form a cubic close-packed (face-centered-cubic) arrangement, and the P atoms formally occupy tetrahedral interstices. The metallic compound becomes superconducting at 0.6 K, as evidenced by magnetic and resistivity measurements.

Photocatalytic degradation of paraquat using nano-sized Cu-TiO2/SBA-15 under UV and visible light.

Photocatalytic degradation of paraquat using mesoporous-assembled Cu-TiO2/SBA15 under UV and visible light was investigated. The catalyst was synthesized by impregnation of Cu-TiO2 colloids onto SBA-15. The colloids of Cu-TiO2 were prepared via sol-gel method while the mesoporous support was prepared using hydrothermal technique. The catalyst was characterized using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X-ray adsorption spectroscopy. Results from characterizations showed that Cu doped TiO2 had a small crystalline size and was well-dispersed on SBA-15. The inclusion of SBA-15 significantly enhanced the photocatalytic activity of the catalyst. Among the three types of undoped catalyst in this study (P25, TiO2, TiO2/SBA-15), TiO2/SBA-15 yielded the highest degradation of paraquat for all pH under UV illumination. Meanwhile 2 wt.% Cu-TiO2/SBA-15 yielded the highest activity under visible light.