inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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RbH2AsO4

aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
*Correspondence e-mail: bstoeger@mail.tuwien.ac.at

(Received 26 September 2013; accepted 27 September 2013; online 2 October 2013)

RbH2AsO4, rubidium di­hydrogenarsenate (RDA), was synthesized by partial neutralization of an aqueous H3AsO4 solution with aqueous Rb2CO3. Its paraelectric room-temperature phase is composed of virtually regular tetra­hedral [AsO2(OH)2] anions and Rb+ cations, both located on -4 positions. The [AsO2(OH)2] units are connected via O—H⋯O hydrogen bonds into a three-dimensional network, whereby the H atoms are equally disordered between the O atoms. The Rb+ cations are located in channels running along the <100> directions and coordinated by eight O atoms located at the vertices of a snub disphenoid.

Related literature

For isotypic phases, see: Al-Karaghouli et al. (1978[Al-Karaghouli, A. R., Abdul-Wahab, B., Ajaj, E. & Sequeira, A. (1978). Acta Cryst. B34, 1040-1042.]); Delain (1958[Delain, C. (1958). Acad Des Sci. C. R. 247, 1451-1452.]); Ferrari et al. (1956[Ferrari, A., Nardelli, M. & Cingli, M. (1956). Gazz. Chim. Ital. 86, 1174-1180.]); Helmholtz & Levine (1942[Helmholtz, L. & Levine, R. (1942). J. Am. Chem. Soc. 64, 354-358.]); Novotny & Szekely (1952[Novotny, H. N. & Szekely, G. (1952). Monatsh. Chem. 83, 568-582.]); West (1930[West, J. (1930). Z. Kristallogr. 74, 306-335.]); Tenzer et al. (1958[Tenzer, L., Frazer, B. C. & Pepinsky, R. (1958). Acta Cryst. 11, 505-509.]). For related phases, see: Stöger et al. (2012[Stöger, B., Weil, M. & Zobetz, E. (2012). Z. Kristallogr. 227, 859-868.]). For isoformular phases crystallizing in a different structure type, viz.LiH2PO4, see: Catti & Ivaldi (1977[Catti, M. & Ivaldi, G. (1977). Z. Kristallogr. 146, 215-226.]); Catti & Ferraris (1974[Catti, M. & Ferraris, G. (1974). Acta Cryst. B30, 1-6.]); Nelmes & Choudhary (1978[Nelmes, R. J. & Choudhary, R. N. P. (1978). Solid State Commun. 26, 823-826.]); Fanchon et al. (1987[Fanchon, E., Vicat, J., Tran Qui, D. & Boudjada, A. (1987). Acta Cryst. C43, 1022-1025.]). For phase transition, see: Fairall & Reese (1974[Fairall, C. W. & Reese, W. (1974). Phys. Rev. B, 10, 882-885.]). For physical properties of RDA and isotypic analogs, see: Ichikawa et al. (2001[Ichikawa, M., Amasaki, D., Gustafsson, T. & Olovsson, I. (2001). Phys. Rev. B, 64, 100101-1-100101-4.]); Shen (1984[Shen, Y. R. (1984). In The Principles of the Nonlinear Optics. New York: Wiley.]); Negres et al. (2005[Negres, R. A., Kucheyev, S. O., DeMange, P., Bostedt, C., van Buuren, T., Nelson, A. J. & Demos, S. G. (2005). Appl. Phys. Lett. 86, 171107-1-171107-3.]). For crystal growth, see: Rashkovich (1991[Rashkovich, L. N. (1991). In KDP-family Single Crystals. London: Taylor & Francis.]). For bond-valence analyses, see: Brown & Altermatt (1985[Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244-247.]). The extinction correction is described by Becker & Coppens (1974[Becker, P. J. & Coppens, P. (1974). Acta Cryst. A30, 129-147.]).

Experimental

Crystal data
  • RbH2AsO4

  • Mr = 226.4

  • Tetragonal, [I \overline 42d ]

  • a = 7.7865 (9) Å

  • c = 7.466 (2) Å

  • V = 452.64 (14) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 18.07 mm−1

  • T = 295 K

  • 0.50 × 0.29 × 0.27 mm

Data collection
  • Bruker Kappa APEXII CCD diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2013[Bruker (2013). SAINT-Plus, APEX2 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.004, Tmax = 0.009

  • 9202 measured reflections

  • 955 independent reflections

  • 567 reflections with I > 3σ(I)

  • Rint = 0.076

Refinement
  • R[F2 > 2σ(F2)] = 0.025

  • wR(F2) = 0.032

  • S = 1.25

  • 955 reflections

  • 20 parameters

  • 1 restraint

  • All H-atom parameters refined

  • Δρmax = 1.02 e Å−3

  • Δρmin = −0.53 e Å−3

  • Absolute structure: Flack (1983)[Flack, H. D. (1983). Acta Cryst. A39, 876-881.], 409 Friedel pairs

  • Absolute structure parameter: −0.010 (13)

Table 1
Selected geometric parameters (Å, °)

Rb—O 3.0890 (17)
Rb—Oi 2.9304 (12)
As—O 1.6828 (11)
O—As—Oii 109.80 (5)
O—As—Oiii 109.31 (5)
Symmetry codes: (i) [-x+{\script{1\over 2}}, y, -z+{\script{3\over 4}}]; (ii) -x, -y, z; (iii) y, -x, -z.

Data collection: APEX2 (Bruker, 2013[Bruker (2013). SAINT-Plus, APEX2 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT-Plus (Bruker, 2013[Bruker (2013). SAINT-Plus, APEX2 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT-Plus; program(s) used to refine structure: JANA2006 (Petříček et al., 2006[Petříček, V., Dušek, M. & Palatinus, L. (2006). JANA2006. Institute of Physics, Praha, Czech Republic.]); molecular graphics: ATOMS (Dowty, 2006[Dowty, E. (2006). ATOMS. Shape Software, Kingsport, Tennessee, USA.]); software used to prepare material for publication: publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information


Comment top

During formation studies and subsequent structure analysis of compounds in the system K2O–As2O5–H2O (Stöger et al., 2012), related alkali phosphates and arsenates with formula type MH2XO4 (M = K, Rb, Cs, NH4; X = P, As) came into attention. With the exception of CsH2PO4, dihydrogenphosphates and -arsenates MH2XO4 (M = K, Rb, Cs, NH4; X = P, As) are isotypic at room temperature and said to belong to the KH2PO4 (KDP) family. Members of the KDP family are ferroelectrics with low Tc (Ichikawa et al., 2001) and feature non-linear optical (NLO) properties (Shen, 1984). They have been intensely studied for their physical properties paired with a simple crystal-chemistry. Moreover, they are of technical importance in optical applications due to their favourable transparency, high damage threshold (Negres et al., 2005) and ready access to large single crystals (Rashkovich, 1991). Notably, KDP is used as a standard NLO active compound to evaluate the performance of novel NLO materials.

Structural data was published for all members of the KDP family with the exception of RbH2AsO4 (RDA): KH2PO4 (West, 1930), RbH2PO4 (Al-Karaghouli et al., 1978), (NH4)H2PO4 (Tenzer et al., 1958), KH2AsO4 (Helmholtz & Levine, 1942), CsH2AsO4 (Ferrari et al., 1956) and (NH4)H2AsO4 (Delain, 1958). The germanate SrH2GeO4 (Novotny & Szekely, 1952) crystallizes likewise in the KDP structure type. The dihydrogenphosphates and arsenates with larger or smaller alkali metals crystallize in different structure types: LiH2PO4 (Catti & Ivaldi, 1977), NaH2PO4 (Catti & Ferraris, 1974), CsH2PO4 (Nelmes & Choudhary, 1978) and LiH2AsO4 (Fanchon et al., 1987).

At room temperature RDA, like all members of the KDP family, exists in the tetragonal paraelectric phase. Below Tc = 110 K it transforms into the orthogonal ferroelectric phase (Fairall & Reese, 1974). The room temperature phase of RDA crystallizes in I42d symmetry. The crystal structure is made up of one [AsO2(OH2)]- anion and one Rb+ cation, both located on 4 positions. The [AsO2(OH2)] tetrahedra are virtually regular (As—O bond lengths 1.6828 (11) Å; O—As—O angles 109.80 (5)° and 109.31 (5)°). They are connected via hydrogen bonding in the <100> directions, forming a three dimensional network (Figs. 1 and 2). Thus, every O atom is either donor or acceptor of an O—H···O hydrogen bond, whereby the proton is equally disordered between both oxygen atoms.

The total bond valence sum (BVS) of the unique O atom calculated using Σexp((r0-r)/b) and the parameters of Brown and Altermatt (1985) for RbI—O (r0=2.263 Å, b=0.37) and AsV—O (r0=1.767 Å, b=0.37) is 1.527 (4) valence units (v.u.). This value is in good agreement with the observed disorder, as it lies halfway between the ideal values of O2- and O- (2 and 1 v.u., respectively).

The Rb+ cation is located in channels running along the <100> directions (Fig. 1). It is coordinated by eight O atoms located at the vertices of a snub disphenoid (Fig. 3). The total BVS of Rb+ calculates as 1.0878 (15) v.u. using the parameters above, which is in excellent agreement with the expected value (1 v.u.). More remote O atoms are located at 4.3005 (12) Å from the Rb+ ion and can therefore not be considered part of the coordination sphere (contribution of 0.004 v.u.).

Related literature top

For isotypic phases, see: Al-Karaghouli et al. (1978); Delain (1958); Ferrari et al. (1956); Helmholtz & Levine (1942); Novotny & Szekely (1952); West (1930); Tenzer et al. (1958). For related phases, see: Stöger et al. (2012). For isoformular phases crystallizing in a different structure type, viz.LiH2PO4, see: Catti & Ivaldi (1977); Catti & Ferraris (1974); Nelmes & Choudhary (1978); Fanchon et al. (1987). For phase transition, see: Fairall & Reese (1974). For physical properties of RDA and isotypic analogs, see: Ichikawa et al. (2001); Shen (1984); Negres et al. (2005). For crystal growth, see: Rashkovich (1991). For bond-valence analyses, see: Brown & Altermatt (1985). The extinction correction is described by Becker & Coppens (1974).

Experimental top

Rb2CO3 and H3AsO4 were obtained commercially and used without purification. 1 g 80% aq. H3AsO4 was dissolved in 10 ml water and titrated against aq. Rb2CO3 using one drop of methyl red in EtOH as indicator. The water was evaporated and the residue recrystallized from a small amount of water and washed with acetone to obtain large single crystals of RbH2AsO4.

Refinement top

An initial model was generated by using the published coordinates of the non-H atoms of the isotypic room temperature phase of RbH2PO4 (Al-Karaghouli et al., 1978).

The structure was refined against F values using the Jana2006 software package (Petříček et al., 2006). The disordered H atom was located in a difference Fourier map and was refined with an occupancy of 0.5. The O—H distance was restrained to 0.850 (1) Å. All non-H atoms were refined with anisotropic displacement parameters.

Computing details top

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT-Plus (Bruker, 2013); data reduction: SAINT-Plus (Bruker, 2013); program(s) used to solve structure: coordinates of Al-Karaghouli et al. (1978); program(s) used to refine structure: JANA2006 (Petříček et al., 2006); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The crystal structure of the paraelectric room temperature phase of RDA viewed approximately down [100]. [AsO4] tetrahedra are drawn in yellow; Rb, O and H atoms are represented by purple, red and white spheres of arbitrary radii.
[Figure 2] Fig. 2. Crystal structure of the paraelectric room temperature phase of RDA viewed down the tetragonal axis [001]. Atom colour codes as in Fig. 1.
[Figure 3] Fig. 3. Coordination polyhedron of Rb in the paraelectric room temperature phase of RDA. Rb and O are represented by purple and red ellipsoids drawn at 75% probability level. Symmetry codes: (i) -x, -y, z; (ii) y, -x, -z + 1; (iii) -y, x, -z + 1; (iv) -x + 1/2, y, -z + 3/4; (v) x - 1/2, -y, -z + 3/4; (vi) -y, -x + 1/2, z + 1/4; (vii) y, x - 1/2, z + 1/4
Rubidium dihydrogenarsenate top
Crystal data top
RbH2AsO4Dx = 3.321 Mg m3
Mr = 226.4Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I42dCell parameters from 2250 reflections
Hall symbol: I -4 2bwθ = 3.7–44.1°
a = 7.7865 (9) ŵ = 18.07 mm1
c = 7.466 (2) ÅT = 295 K
V = 452.64 (14) Å3Block, clear colourless
Z = 40.50 × 0.29 × 0.27 mm
F(000) = 416
Data collection top
Bruker Kappa APEXII CCD
diffractometer
955 independent reflections
Radiation source: X-ray tube567 reflections with I > 3σ(I)
Graphite monochromatorRint = 0.076
ω and ϕ scansθmax = 45.3°, θmin = 3.8°
Absorption correction: multi-scan
(SADABS; Bruker, 2013)
h = 1515
Tmin = 0.004, Tmax = 0.009k = 1514
9202 measured reflectionsl = 1414
Refinement top
Refinement on FHydrogen site location: difference Fourier map
Least-squares matrix: fullAll H-atom parameters refined
R[F2 > 2σ(F2)] = 0.025Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2)
wR(F2) = 0.032(Δ/σ)max = 0.021
S = 1.25Δρmax = 1.02 e Å3
955 reflectionsΔρmin = 0.53 e Å3
20 parametersExtinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
1 restraintExtinction coefficient: 4440 (110)
0 constraintsAbsolute structure: Flack (1983), 409 Friedel pairs
Primary atom site location: isomorphous structure methodsAbsolute structure parameter: 0.010 (13)
Crystal data top
RbH2AsO4Z = 4
Mr = 226.4Mo Kα radiation
Tetragonal, I42dµ = 18.07 mm1
a = 7.7865 (9) ÅT = 295 K
c = 7.466 (2) Å0.50 × 0.29 × 0.27 mm
V = 452.64 (14) Å3
Data collection top
Bruker Kappa APEXII CCD
diffractometer
955 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2013)
567 reflections with I > 3σ(I)
Tmin = 0.004, Tmax = 0.009Rint = 0.076
9202 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.025All H-atom parameters refined
wR(F2) = 0.032Δρmax = 1.02 e Å3
S = 1.25Δρmin = 0.53 e Å3
955 reflectionsAbsolute structure: Flack (1983), 409 Friedel pairs
20 parametersAbsolute structure parameter: 0.010 (13)
1 restraint
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Rb000.50.01896 (5)
As0000.01382 (5)
O0.15295 (14)0.08872 (11)0.12961 (14)0.0203 (2)
H0.147 (6)0.1975 (7)0.122 (10)0.048 (12)*0.5
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Rb0.02023 (8)0.02023 (8)0.01640 (11)000
As0.01201 (7)0.01201 (7)0.01744 (11)000
O0.0173 (3)0.0172 (3)0.0265 (4)0.0032 (3)0.0093 (3)0.0063 (4)
Geometric parameters (Å, º) top
Rb—O3.0890 (17)Rb—Ovii2.9304 (12)
Rb—Oi3.0890 (17)As—O1.6828 (11)
Rb—Oii3.0890 (17)As—Oi1.6828 (11)
Rb—Oiii3.0890 (17)As—Oviii1.6828 (11)
Rb—Oiv2.9304 (12)As—Oix1.6828 (11)
Rb—Ov2.9304 (12)O—H0.850 (8)
Rb—Ovi2.9304 (12)
O—Rb—Oi52.94 (3)O—As—Oi109.80 (5)
O—Rb—Oii143.26 (3)O—As—Oviii109.31 (5)
O—Rb—Oiii143.26 (3)O—As—Oix109.31 (5)
O—Rb—Oiv82.32 (3)Oi—As—Oviii109.31 (5)
O—Rb—Ov133.06 (3)Oi—As—Oix109.31 (5)
O—Rb—Ovi67.05 (3)Oviii—As—Oix109.80 (5)
O—Rb—Ovii80.84 (3)
Symmetry codes: (i) x, y, z; (ii) y, x, z+1; (iii) y, x, z+1; (iv) x+1/2, y, z+3/4; (v) x1/2, y, z+3/4; (vi) y, x+1/2, z+1/4; (vii) y, x1/2, z+1/4; (viii) y, x, z; (ix) y, x, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O—H···Ox0.850 (8)1.665 (6)2.5125 (13)175 (6)
Symmetry code: (x) x, y+1/2, z+1/4.
Selected geometric parameters (Å, º) top
Rb—O3.0890 (17)As—O1.6828 (11)
Rb—Oi2.9304 (12)
O—As—Oii109.80 (5)O—As—Oiii109.31 (5)
Symmetry codes: (i) x+1/2, y, z+3/4; (ii) x, y, z; (iii) y, x, z.
 

Acknowledgements

The X-ray Centre of the Vienna University of Technology is acknowledged for providing access to the single-crystal diffractometer and for financial support.

References

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