M + M 3+ 2 As(HAsO 4 ) 6 ( M + M 3+ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO 6 octahedra

Single crystals of the title compound, Na(H 2 AsO 4 ), were obtained by partial neutralization of arsenic acid with sodium hydroxide in aqueous solution. The crystal structure of Na(H 2 AsO 4 ) is isotypic with the phosphate analogue and the asymmetric unit consists of two sodium cations and two tetrahedral H 2 AsO 4 À anions. Each of the sodium cations is surrounded by six O atoms of five H 2 AsO 4 À groups, defining distorted octahedral coordination spheres. In the extended structure, the sodium cations and dihydrogen arsenate anions are arranged in the form of layers lying parallel to (010). Strong hydrogen bonds [range of OÁ Á ÁO distances 2.500 (3)-2.643 (3) Å ] between adjacent H 2 AsO 4 À anions are observed within and perpendicular to the layers. The isotypic structure of Na(H 2 PO 4 ) is comparatively discussed. Chemical contextArsenic acid is triprotic and thus can form various salts, depending on the degree of deprotonation (H 2 AsO 4 À , HAsO 4 2À , AsO 4 3À ), the condensation grade of the anion (mono-, di-, tri-, polyarsenate, etc) and the amount of water incorporated in the crystal. With respect to sodium arsenates, numerous crystal structures have been determined so far, including arsenic in tetrahedral and/or in octahedral coordination by oxygen atoms. Arsenate structures with arsenic exclusively in tetrahedral coordination resemble those of the related phosphates and in some cases show isotypism with them (marked by an asterisk): Na 3.25 (AsO 4 )(OH) 0.25 (H 2 O) 12 *

Section: Chemical Contextmentioning

confidence: 99%

Crystal structure of sodium dihydrogen arsenate

Ring¹,

Lindenthal²,

Weil³

et al. 2017

(NH₄)Ga(HAsO₄)₂ and TlAl(HAsO₄)₂ - two new RbFe(HPO₄)₂-type M ⁺ M ³⁺ arsenates

Schwendtner

Kolitsch

2018

Self Cite

CsGa(HAsO₄)₂, the first Ga representative of the RbAl(HAsO₄)₂structure type

Schwendtner

Kolitsch

2019

Self Cite

The crystal structure of hydrothermally synthesized (T = 493 K, 7 d) caesium gallium bis[hydrogen arsenate(V)], CsGa(HAsO4)2, was solved by single-crystal X-ray diffraction. The compound crystallizes in the common RbAl(HAsO4)2 structure type (R32) and consists of a basic tetrahedral–octahedral framework topology that houses Cs+ cations in its channels. The AsO4 tetrahedron is disordered over two positions with site occupancy factors of 0.946 (1) and 0.054 (1). Strong hydrogen bonds strengthen the network. The structure was refined as inversion twin.