Formation of Tetraselenodiarsenate(II) Anions in Ultra‐alkaline Medium

Albrecht, Ralf; Jach, Franziska; Ruck, Michael

doi:10.1002/zaac.202100306

Zeitschrift anorg allge chemie

2021

DOI: 10.1002/zaac.202100306

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Formation of Tetraselenodiarsenate(II) Anions in Ultra‐alkaline Medium

Ralf Albrecht

Franziska Jach

Michael Ruck

Abstract: SeO2 and As2O3 were reacted at 200 °C in in a potassium hydroxide hydroflux with a molar water‐base ratio n(H2O) : n(KOH)=1.8. Arsenate(III) disproportionates under these conditions into arsenate(V) and elemental arsenic. The reduction also yielded tetraselenodiarsenate(II) anions, which turned the solution yellow and precipitated at room temperature as plate‐shaped crystals of K4(As2Se4) ⋅ 2H2O. The unexpected redox reaction as well as the formation of a hygroscopic compound in an aqueous solution are attribu… Show more

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Cited by 3 publications

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Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na₂[RE(BO₃)(OH)₂] (RE=Y, Gd−Er)

Li,

Carrillo‐Aravena,

et al. 2024

Chemistry A European J

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Reacting RE2O3 and H3BO3 in an ultra‐alkaline NaOH hydroflux at about 250 °C yielded pure, crystalline samples of Na2[RE(BO3)(OH)2] (RE = Y, Gd–Er). The compounds dehydrate to Na3RE(BO3)2 upon heating in air to about 500 °C. Na2[RE(BO3)(OH)2] (RE = Tb–Er) are photoluminescent under UV radiation. Their UV‐Vis spectra show the typical absorptions associated with 4f‐4f transitions and absorption edges in the UV (band gaps ≥ 5.7 eV). The RE3+ cation is coordinated by seven oxygen atoms, which define a distorted pentagonal bipyramid. The bipyramids share trans‐edges of their base forming infinite chains. Triangular (BO3)3– groups connect the chains into layers. The crystal structure of Na2[Ho(BO3)(OH)2] was investigated at various temperatures in the range 100 K ≤ T ≤ 320 K. Above 310(2) K, the compound crystallizes in the orthorhombic space group Cmcm (β‐phase), below, it undergoes a displacive phase transition of second order resulting in a monoclinic structure in space group C2/c (α‐phase). The critical exponents derived from different structural parameters indicate a cooperative distortion of the borate layers, but a rather uncorrelated adaptation of the sodium cations to their local environment. The other compounds of the series also adopt the structure of the α‐phase at 296 K.

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Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na₂[RE(BO₃)(OH)₂] (RE=Y, Gd−Er)

Li,

Carrillo‐Aravena,

et al. 2024

Chemistry A European J

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Ba(BO₂OH) – A Monoprotonated Monoborate from Hydroflux Showing Intense Second Harmonic Generation

Li¹,

Hegarty²,

Rüsing³

et al. 2022

Zeitschrift anorg allge chemie

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Pure samples of colorless, air‐stable Ba(BO2OH) crystals were obtained from Ba(NO3)2 and H3BO3 under the ultra‐alkaline conditions of a KOH hydroflux at about 250 °C. The product formation depends on the water‐base molar ratio and the molar ratio of the starting materials. B(OH)3 acts as a proton donor (Brønsted acid) rather than a hydroxide acceptor (Lewis acid). Ba(BO2OH) crystallizes in the non‐centrosymmetric orthorhombic space group P212121. Hydrogen bonds connect the almost planar (BO2OH)2− anions, which are isostructural to HCO3−, into a syndiotactic chain. IR and Raman spectroscopy confirm the presence of hydroxide groups, which are involved in weak hydrogen bonds. Upon heating in air to about 450 °C, Ba(BO2OH) dehydrates to Ba2B2O5. Moreover, the non‐centrosymmetric structure of Ba(BO2OH) crystals was verified with power‐dependent confocal Second Harmonic Generation (SHG) microscopy indicating large conversion efficiencies in ambient atmosphere.

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Oxohydroxo‐Tellurates(VI) K₂[TeO₂(OH)₄] and K₂[Fe₂TeO₆(OH)₂] ⋅ 2H₂O from Alkaline Hydroflux

He,

Li,

Albrecht

et al. 2023

Zeitschrift anorg allge chemie

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The ultra‐alkaline conditions of a hydroflux offer the possibility of redox chemistry far from the electrochemical standard potentials. We explored the possibilities of synthesizing tellurium(VI) compounds, using both tellurium(VI) and tellurium(IV) as starting materials. Colorless, block‐shaped crystals of the oxohydroxotellurate(VI) K2[TeO2(OH)4] were synthesized from (NH4)2TeO4 in a KOH hydroflux at 200 °C. In the triclinic crystal structure, [TeO2(OH)4]2− octahedra are connected via hydrogen bonds to form layers, which are separated from each other by potassium cations. Yellow‐colored platelets of the ferrate(III) tellurate(VI) K2[Fe2TeO6(OH)2] ⋅ 2H2O were obtained by oxidation of TeO2 with H2O2 followed by reaction with Fe(NO3)3 ⋅ 9H2O in a KOH hydroflux. In the monoclinic crystal structure, strongly corrugated anionic layers Fe2TeO6(OH)2]2− are covered with water molecules and separated from each other by potassium cations. The octahedrally coordinated iron(III) atoms form a distorted honeycomb network, in which they are antiferromagnetically coupled at room temperature and in external fields up to at least 7 T.

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Formation of Tetraselenodiarsenate(II) Anions in Ultra‐alkaline Medium

Cited by 3 publications

References 38 publications

Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na₂[RE(BO₃)(OH)₂] (RE=Y, Gd−Er)

Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na₂[RE(BO₃)(OH)₂] (RE=Y, Gd−Er)

Ba(BO₂OH) – A Monoprotonated Monoborate from Hydroflux Showing Intense Second Harmonic Generation

Oxohydroxo‐Tellurates(VI) K₂[TeO₂(OH)₄] and K₂[Fe₂TeO₆(OH)₂] ⋅ 2H₂O from Alkaline Hydroflux

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Formation of Tetraselenodiarsenate(II) Anions in Ultra‐alkaline Medium

Cited by 3 publications

References 38 publications

Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na2[RE(BO3)(OH)2] (RE=Y, Gd−Er)

Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na2[RE(BO3)(OH)2] (RE=Y, Gd−Er)

Ba(BO2OH) – A Monoprotonated Monoborate from Hydroflux Showing Intense Second Harmonic Generation

Oxohydroxo‐Tellurates(VI) K2[TeO2(OH)4] and K2[Fe2TeO6(OH)2] ⋅ 2H2O from Alkaline Hydroflux

Contact Info

Product

Resources

About

Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na₂[RE(BO₃)(OH)₂] (RE=Y, Gd−Er)

Hydroflux Synthesis and Structural Phase Transition of Rare‐Earth Borate Hydroxides Na₂[RE(BO₃)(OH)₂] (RE=Y, Gd−Er)

Ba(BO₂OH) – A Monoprotonated Monoborate from Hydroflux Showing Intense Second Harmonic Generation

Oxohydroxo‐Tellurates(VI) K₂[TeO₂(OH)₄] and K₂[Fe₂TeO₆(OH)₂] ⋅ 2H₂O from Alkaline Hydroflux