M+M3+2As(HAsO4)6 and α- and β-M+M3+(HAsO4)2 (M+M3+ = RbAl or CsFe): six new compounds crystallizing in three closely related structure types

Three new acid M+ arsenates and phosphates with multiply protonated As/PO4 groups

The crystal structures of Cs(H₂AsO₄)(H₃AsO₄)₂, NH₄(H₂AsO₄)(H₃AsO₄) and Li₂(H₂PO₄)₂ were determined from single-crystal X-ray diffraction data. The two alkali compounds represent novel structure types, while the ammonium compound is homeotypic with its Rb analogue.

The crystal structures of caesium di­hydrogen arsenate(V) bis­[tri­hydrogen arsen­ate(V)], Cs(H₂AsO₄)(H₃AsO₄)₂, ammonium di­hydrogen arsenate(V) tri­hydrogen arsenate(V), NH₄(H₂AsO₄)(H₃AsO₄), and dilithium bis­(di­hydrogen phosphate), Li₂(H₂PO₄)₂, were solved from single-crystal X-ray diffraction data. NH₄(H₂AsO₄)(H₃AsO₄), which was hydro­thermally synthesized (T = 493 K), is homeotypic with Rb(H₂AsO₄)(H₃AsO₄), while Cs(H₂AsO₄)(H₃AsO₄)₂ crystallizes in a novel structure type and Li₂(H₂PO₄)₂ represents a new polymorph of this composition. The Cs and Li compounds grew at room temperature from highly acidic aqueous solutions. Li₂(H₂PO₄)₂ forms a three-dimensional (3D) framework of PO₄ tetra­hedra sharing corners with Li₂O₆ dimers built of edge-sharing LiO₄ groups, which is reinforced by hydrogen bonds. The two arsenate compounds are characterized by a 3D network of AsO₄ groups that are connected solely via multiple strong hydrogen bonds. A statistical evaluation of the As—O bond lengths in singly, doubly and triply protonated AsO₄ groups gave average values of 1.70 (2) Å for 199 As—OH bonds, 1.728 (19) Å for As—OH bonds in HAsO₄ groups, 1.714 (12) Å for As—OH bonds in H₂AsO₄ groups and 1.694 (16) Å for As—OH bonds in H₃AsO₄ groups, and a grand mean value of 1.667 (18) Å for As—O bonds to nonprotonated O atoms.

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

The crystal structure of hydro-thermally 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 tetra-hedral-octa-hedral framework topology that houses Cs⁺ cations in its channels. The AsO₄ tetra-hedron 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.

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

The crystal structures of hydro-thermally synthesized (T = 493 K, 7-9 d) ammonium gallium bis-[hydrogen arsenate(V)], (NH4)Ga(HAsO4)2, and thallium aluminium bis-[hydrogen arsenate(V)], TlAl(HAsO4)2, were solved by single-crystal X-ray diffraction. Both compounds crystallize in the common RbFe(HPO4)2 structure type (R c) and share the same tetra-hedral-octa-hedral framework topology that houses the M + cations in its channels. One of the two Tl sites is slightly offset from its ideal position. Strong O-H⋯O hydrogen bonds strengthen the network.

Two new Rb-Ga arsenates: RbGa(HAsO4)2 and RbGa2As(HAsO4)6

The crystal structures of hydro-thermally synthesized (T = 493 K, 7-9 d) rubidium gallium bis-[hydrogenarsenate(V)], RbGa(HAsO4)2, and rubidium digallium arsenic(V) hexa-[hydrogenarsenate(V)], RbGa2As(HAsO4)6, were solved by single-crystal X-ray diffraction. Both compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations are located in channels of the respective framework. RbGa(HAsO4)2 crystallizes in the RbFe(HPO4)2 structure type (Rc), while RbGa2As(HAsO4)6 adopts the structure type of RbAl2As(HAsO4)6 (Rc), which represents a modification of the RbFe(HPO4)2 structure type. In this modification, one third of the M3+O6 octa-hedra are replaced by AsO6 octa-hedra, and two thirds of the voids in the structure, which are usually filled by M+ cations, remain empty to achieve charge balance.

M+M3+2As(HAsO4)6 (M+M3+ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO6 octa-hedra

The crystal structures of hydro-thermally synthesized (T = 493 K, 7 d) thallium(I) digallium arsenic(V) hexa-kis-[hydrogenarsenate(V)], TlGa2As(HAsO4)6, caes-ium digallium arsenic(V) hexa-kis-[hydrogenarsenate(V)], CsGa2As(HAsO4)6, and caesium dialuminium arsenic(V) hexa-kis-[hydrogenarsenate(V)], CsAl2As(HAsO4)6, were solved by single-crystal X-ray diffraction. The three compounds are isotypic and adopt the structure type of RbAl2As(HAsO4)6 (Rc), which itself represents a modification of the RbFe(HPO4)2 structure type and consists of a tetra-hedral-octa-hedral framework in which the slightly disordered M+ cations are located in channels. The three new compounds contain AsO6 octa-hedra assuming the topological role of M3+O6 octa-hedra. The As-O bond lengths are among the shortest As-O bond lengths known so far in AsO6 octa-hedra.

RbFe(HAsO4)2 and TlFe(HAsO4)2, two new hydrogenarsenates adopting two closely related structure types

Rubidium iron bis-[hydrogen arsenate(V)], RbFe(HAsO4)2, and thallium iron bis-[hydrogen arsenate(V)], TlFe(HAsO4)2, were grown under mild hydro-thermal conditions (T = 493 K, 7 d). RbFe(HAsO4)2 adopts the RbFe(HPO4)2 structure type (space group Rc), while TlFe(HAsO4)2 crystallizes in the (NH4)Fe(HPO4)2 structure type (space group P ). Both compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations are located in channels of the respective framework and are disordered in TlFe(HAsO4)2, which may suggest that the M+ cations can move in the channels.