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Open AccessArticle

(K,Na)2[AsB6O12]2[B3O3(OH)3], a New Microporous Material, and Its Comparison to Teruggite

1
Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University, University Emb. 7/9, 199034 Saint Petersburg, Russia
2
Laboratory of Nature-Inspired Technologies and Environmental Safety of the Arctic, Kola Science Centre, Russian Academy of Sciences, Fersmana 14, 184209 Apatity, Russia
3
Nanomaterials Research Center, Federal Research Center, Kola Science Center, RAS, Fersmana Str. 14, 184209 Apatity, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(12), 781; https://doi.org/10.3390/min9120781
Received: 12 November 2019 / Revised: 7 December 2019 / Accepted: 10 December 2019 / Published: 13 December 2019
Single crystals of the novel boroarsenate (K,Na)2[As2B12O24][B3O3(OH)3] (I) were obtained using the borax flux method. The crystal structure of I was found to be triclinic, P-1, a = 8.414(5), b = 10.173(6), c = 15.90(1) Å, α = 79.56(1), β = 78.68(1), γ = 70.91(1), V = 1251(1) Å3, Z = 2. The crystal structure of I is based upon the novel [AsB6O12] microporous boroarsenate framework formed by B and As coordination polyhedra. This framework can be subdivided into borate units that are interlinked by AsO4 tetrahedra. In the case of I, the borate substructure is a chain consisting of triborate rings, ☐2Δ, formed by two (BO3) triangles and one (BO4) tetrahedron connected through shared common oxygen atoms. The chains are extended along [0 1 ¯ 1] and are interlinked by (AsO4) tetrahedra in the [011] direction. As a result, the framework has large channels parallel to [100], having an effective diameter of 4.2 × 5.6 Å2. The channels contain occluded electroneutral ring triborate complexes, [B3O3(OH)3]0, formed by three (BO2(OH)) triangles sharing common O atoms, as well as K+ and Na+ cations. The triborate [B3O3(OH)3]0 units correspond to similar clusters found in the crystal structure of the α-form of metaboric acid, HBO2. According to information-based complexity calculations, the crystal structure of I should be described as complex, with IG = 5.781 bits/atom and IG,total = 625.950 bits/cell. Teruggite, Ca4Mg[B6As(OH)6O11]2(H2O)14, the only known boroarsenate of natural origin, has almost twice as much information per unit cell, with IG,total = 1201.992 bits/cell. The observed difference in structural complexity between I and teruggite is the consequence of their chemistry (hydration state) and different formation conditions. View Full-Text
Keywords: crystal structure; boroarsenate; microporous framework; structural complexity; Shannon information; terrugite crystal structure; boroarsenate; microporous framework; structural complexity; Shannon information; terrugite
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Pankova, Y.A.; Krivovichev, S.V. (K,Na)2[AsB6O12]2[B3O3(OH)3], a New Microporous Material, and Its Comparison to Teruggite. Minerals 2019, 9, 781.

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