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We previously demonstrated that electrode architectures comprising nanoscale birnessite-like MnO x affixed to three-dimensional carbon nanofoam (CNF) scaffolds offer performance advantages when used as cathodes in rechargeable zinc-ion cells. To discern chemical and physical changes at the MnO x @CNF electrode upon deep charge/discharge in aqueous Zn2+-containing electrolytes, we deploy electroanalytical methods and ex situ characterization by microscopy, elemental analysis, x-ray photoelectron spectroscopy, x-ray diffraction, and x-ray pair distribution function analyses. Our findings verify that redox processes at the MnO x are accompanied by reversible precipitation/dissolution of crystalline zinc hydroxide sulfate (Zn4(OH)6(SO4)· x H2O), mediated by the more uniformly reactive electrode structure inherent to the CNF scaffold. [ABSTRACT FROM AUTHOR]

The syntheses of two noncentrosymmetric (NCS) vanadium oxide-fluoride compounds that originate from the same synthetic reagent concentrations are presented. Hydrothermal and low-temperature syntheses allow the isolation of metastable products that may form new phases (or decompose) upon heating and allow creation of chemically similar but structurally different materials. NCS materials synthesis has been a long-standing goal in inorganic chemistry: in this article, we compare two chemically similar NCS inorganic materials, NaVOF4(H2O) (I) and NaVO2-xF2+x (II; x = 1/3). These materials originate from the same, identical reagent mixtures but are synthesized at different temperatures: 100 °C and 150 °C, respectively. Compound I crystallizes in Pna21: a = 9.9595(4) Å, b = 9.4423(3) Å, and c = 4.8186(2) Å. Compound II crystallizes in P21: a = 6.3742(3) Å, b = 3.5963(2) Å, c = 14.3641(7) Å, and β = 110.787(3)°. Both materials display second-harmonic-generation activity; however, compound I is type 1 non-phase-matchable, whereas compound II is type 1 phase-matchable. [ABSTRACT FROM AUTHOR]

The potassium vanadium oxide-fluoride phase β-KVOF3 was prepared by in-situ reduction with hydrothermal methods and characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. The compound is orthorhombic [space group Pnma, a = 7.1596(2) Å, b = 7.5392(2) Å, c = 13.0506(4) Å, Z = 8]. The material is structurally similar and isoformulaic to d1 materials of formulae AVOF3 ( A+ = alkali metal, ammonium, or organic cation). Magnetic susceptibility data were successfully fit with a Heisenberg chain model. In-situ reduction of V5+ to V4+ during the hydrothermal reaction conditions was observed in the presence of Br- anions. The role of bromide ions in this reduction is explained and employed to reduce a d0 vanadium species to obtain a material with magnetic behavior. [ABSTRACT FROM AUTHOR]

The potassium vanadium oxide-fluoride phase β-KVOF3 was prepared by in-situ reduction with hydrothermal methods and characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. The compound is orthorhombic [space group Pnma, a = 7.1596(2) Å, b = 7.5392(2) Å, c = 13.0506(4) Å, Z = 8]. The material is structurally similar and isoformulaic to d1 materials of formulae AVOF3 ( A+ = alkali metal, ammonium, or organic cation). Magnetic susceptibility data were successfully fit with a Heisenberg chain model. In-situ reduction of V5+ to V4+ during the hydrothermal reaction conditions was observed in the presence of Br- anions. The role of bromide ions in this reduction is explained and employed to reduce a d0 vanadium species to obtain a material with magnetic behavior. [ABSTRACT FROM AUTHOR]

A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2>; M = Mo, n = 4, X = CI, Br4/2, I4/2) illustrates generation of polar structures with the use of A- shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d° early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn--Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11_n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3ml or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or A-shaped bimetallic BBUs and related packing effects. These A-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs. [ABSTRACT FROM AUTHOR]

We present structural and electrochemical analyses of a new double-wolframite compound: AgNa(VO2F2)2 or SSVOF. SSVOF is fully ordered and displays electrochemical characteristics that give insight into electrode design for energy storage beyond lithium-ion chemistries. The compound contains trioxovanadium fluoride octahedra that combine to form one-dimensional chain-like basic building units, characteristic of wolframite (NaWO4). The 1D chains are stacked to create 2D layers; the cations Ag+ and Na+ lie between these layers. The vanadium oxide-fluoride octahedra are ordered by the use of cations (Ag+, Na+) that differ in polarizability. In the case of sodium-ion batteries, thermodynamically, the use of a sodium anode introduces a 300 mV loss in overall cell voltage as compared to a lithium anode; however, this can be counter-balanced by introduction of fluoride into the framework to raise the reduction potentials via an inductive effect. This allows sodium-ion batteries to have comparable voltages to lithium systems. With SSVOF as a baseline compound, we have identified new materials design rules for emerging sodium-ion systems that do not apply to lithium-ion systems. These strategies can be applied broadly to provide materials of interest for fundamental structural chemistry and appreciable voltages for sodium-ion electrochemistry. [ABSTRACT FROM AUTHOR]

Three new vanadium oxide-fluoride phases, Na2(M(H2O)2)(V2O4F6) (M = Co2+, Ni2+, and Cu2+), were prepared by hydrothermal techniques in hydrofluoric acid. The compounds contain the dioxo vanadium fluoride dimeric anion: [V2O4F6]4-. The harder (Na+) and softer (M = Co2+, Ni2+, and Cu2+) cations coordinate to the harder fluoride and softer oxide anions, respectively. In contrast to monoxo vanadium fluorides, the dioxo vanadium fluoride exhibits an increased nucleophilicity of the oxide anions. This increased nucleophilicity allows the anion to bond covalently with late transition metals to form 2D layers that contain both an early transition metal (V5+) and a late transition metal (Co2+, Ni2+, or Cu2+). [ABSTRACT FROM AUTHOR]

Three new vanadium oxide-fluoride phases, Na2(M(H2O)2)(V2O4F6) (M = Co2+, Ni2+, and Cu2+), were prepared by hydrothermal techniques in hydrofluoric acid. The compounds contain the dioxo vanadium fluoride dimeric anion: [V2O4F6]4-. The harder (Na+) and softer (M = Co2+, Ni2+, and Cu2+) cations coordinate to the harder fluoride and softer oxide anions, respectively. In contrast to monoxo vanadium fluorides, the dioxo vanadium fluoride exhibits an increased nucleophilicity of the oxide anions. This increased nucleophilicity allows the anion to bond covalently with late transition metals to form 2D layers that contain both an early transition metal (V5+) and a late transition metal (Co2+, Ni2+, or Cu2+). [ABSTRACT FROM AUTHOR]

β-KVOF3 is prepared by in-situ reduction under hydrothermal conditions using a mixture of V2O5 and KBr (3:2) in aq. [ABSTRACT FROM AUTHOR]

The new compounds (IV) and (VI) crystallize isostructurally in the monoclinic space group P21/c with Z = 2 (single crystal XRD). [ABSTRACT FROM AUTHOR]

The cause of polar distortion orientation of ordered one-dimensional chains of basic building units is illustrated with subtle alterations in the heterotypic structures of the previously known compound CuNbOF5(H2O)2(pyz)3 and the new hybrid materials (III), (V), and (VI), whose crystal structures are determined by single crystal XRD. [ABSTRACT FROM AUTHOR]