MIn(HAsO₄)₂(M= K, Rb, Cs): three new hydrogenarsenates adopting two different structure types

Abstract

Potassium indium bis[hydrogen arsenate(V)], KIn(HAsO 4 ) 2 , rubidium indium bis[hydrogen arsenate(V)], RbIn(HAsO 4 ) 2 , and caesium indium bis[hydrogen arsenate(V)], CsIn(HAsO 4 ) 2 , were grown under mild hydrothermal conditions (T = 493 K, 7-8 d). KIn(HAsO 4 ) 2 adopts the KSc(HAsO 4 ) 2 structure type (space group C2/c), while RbIn(HAsO 4 ) 2 and CsIn(HAsO 4 ) 2 crystallize in the space group R3c and are the first arsenate representatives of the RbFe(HPO 4 ) 2 structure type. All three compounds have tetrahedral-octahedral framework topologies. The M + cations, located in voids of the respective framework, are slightly disordered in RbIn(HAsO 4 ) 2 . In KIn(HAsO 4 ) 2 , there is a second Katom position with a very low occupancy, which may suggest that the K atom can easily move in the channels extending along [101]. Chemical contextMetal arsenates often form tetrahedral-octahedral framework structures that frequently show potentially interesting properties, such as ion conductivity, ion exchange and catalytic properties (Masquelier et al., 1990(Masquelier et al., , 1994a(Masquelier et al., ,b, 1995(Masquelier et al., , 1996(Masquelier et al., , 1998Mesa et al., 2000;Ouerfelli et al., 2007a Ouerfelli et al., ,b, 2008 PintardScré pel et al., 1983;Rousse et al., 2013). In the course of a detailed study of the system M + -M 3+ -As-O-(H) by hydrothermal syntheses, a large variety of new arsenate(V) compounds and structure types were found (Kolitsch, 2004; Schwendtner, 2006; Schwendtner & Kolitsch, 2004a,b, 2005,b,c,d, 2017a.The three new title compounds belong to the family of hydrogenarsenate compounds with the general formula M + M 3+ (HAsO 4 ) 2 . Including the three compounds reported here, nine compounds with this general formula are known. They crystallize in four different structure types. KIn(HAsO 4 ) 2 is a further representative of the KSc(HAsO 4 ) 2 structure type (Schwendtner & Kolitsch, 2004a), which is also adopted by AgGa(HAsO 4 ) 2 and AgAl(HAsO 4 ) 2 (Schwendtner & Kolitsch, 2017c (Schwendtner & Kolitsch, 2017c). The asymmetric unit contains one K, one In, one As, one H and four O atoms (Fig. 1a). The slightly distorted InO 6 octahedra share corners with six HAsO 4 tetrahedra, thus forming a three-dimensional anionic framework with narrow channels parallel to [110] and [101] (Fig. 2a,b) which host the K atoms. There are two K-atom positions (K1 and K2), at a distance of 2.653 (15) Å from each other. The K1 position is located on an inversion centre and has a refined occupancy of 0.976 (2), while K2, which lies between two K1 positions, is located on a twofold axis (like the In atom) and has a refined occupancy of 0.024 (2). Both K-atom positions show a [4 + 4]-coordination with average K-O bond lengths of 2.949 and 3.016 Å for K1 and K2, respectively (Table 1). This is slightly longer than the reported average K-O bond length for lations after Gagné & Hawthorne (2015) show bond-valence sums (BVSs) of 0.99 valence units (v.u.) for K1 and 0.85 v.u. for K2, indicating an 'underbonded' charact...

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

“…Since application of the appropriate twin matrices did not improve the refinement and no O ligands were found for this position, it was omitted from the refinement. A very similar situation SEM micrographs of hydrothermally synthesized crystals of (a) -RbAl-(HAsO 4 ) 2 , (b) -CsFe(HAsO 4 ) 2 , (c) -CsFe(HAsO 4 ) 2 and (d) CsFe 2 -As(HAsO 4 ) 6 was encountered for isotypic -CsIn(HAsO 4 ) 2 (Schwendtner & Kolitsch, 2017d).…”

“…Among the many different structure types found during that study, one atomic arrangement, the RbFe(HPO 4 ) 2 -type (Lii & Wu, 1994), was found to be extremely versatile and allowed the incorporation of a wide variety of cations. Two new representatives of this structure type, which was previously also known for RbM 3+ (HPO 4 ) 2 (M 3+ = Al, Ga; Lesage et al, 2007), M + In(HAsO 4 ) 2 (M + = Rb, Cs; Schwendtner & Kolitsch, 2017d) and RbFe(HAsO 4 ) 2 (Schwendtner & Kolitsch, 2018), are presented in this study, namely RbAl(HAsO 4 ) 2 and CsFe(HAsO 4 ) 2 . Two chemically identical compounds, crystallizing in the space group R32, represent a novel but closely related structure type.…”

M + M 3+ 2As(HAsO4)6 (M + M 3+ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO6 octahedra

“…The unitcell parameters a and V correlate well with the size of both cations, but the influence of the M + cations is stronger. It seems that in order to incorporate the small AsO 6 octahedron in the structure the cell widens along the a axis to incorporate the large M + cations and is strongly compressed along c. This effect is also visible in the hydrogen bonds that are very strong in the RbFe(HPO 4 ) 2 -type arsenates with D-HÁ Á ÁA bond lengths ranging from 2.598 (2) to 2.634 (2) Å , while for the RbAl 2 As(HAsO 4 ) 6 -type arsenates they range from 2.727 (2) to 2.7481 (19) Å (Schwendtner & Kolitsch, 2017b, 2018athis paper).…”

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

“…One atomic arrangement, the RbFe(HPO 4 ) 2 type (Lii & Wu, 1994;rhombohedral, R3c), and its two relatives, the CsAl 2 As-(HAsO 4 ) 6 type (Schwendtner & Kolitsch, 2018a, rhombohedral, R3c) and the RbAl(HAsO 4 ) 2 type (Schwendtner & Kolitsch, 2018a, rhombohedral, R32), were found to exhibit a large crystal-chemical flexibility, which allows the incorporation of a wide variety of M + and M 3+ cations. So far the RbFe(HPO 4 ) 2 -type is represented by eight arsenate members with the following M + M 3+ combinations: TlAl, (NH 4 )Ga, RbIn, RbGa, RbAl, RbFe, CsIn and CsFe (Schwendtner & Kolitsch, 2017b, 2018a. Six arsenates of the CsAl 2 As-(HAsO 4 ) 6 type are known with the following M + M 3+ combinations: RbGa, CsGa, TlGa, RbAl, CsAl and CsFe (Schwendtner & Kolitsch, 2018a,c,d).…”

“…The refinement of CsGa(HAsO 4 ) 2 revealed a considerable residual electron-density peak of 5.1 e Å À3 1.27 Å away from As and 1.62 Å away from the O1 site. The corresponding position can be generated by a mirror plane in (110) and therefore was assumed to be an alternative flipped As position (sharing the same O1 atom), similar to what was encountered in related TlAl(HAsO 4 ) and CsIn(HAsO 4 ) 2 (R3c type; Schwendtner & Kolitsch, 2017b). An inclusion of the alternative position led to a considerable drop in the conventional R factor and weight parameters and the highest residual electron densities also decreased considerably.…”