Rb2Sb4O11

Govindaraasan Kalpana; Mark T Weller

doi:10.1107/S1600536809016109

. 2009 May 7;65(Pt 6):i41. doi: 10.1107/S1600536809016109

Rb₂Sb₄O₁₁

Govindaraasan Kalpana ^a,^*, Mark T Weller ^a

PMCID: PMC2969830 PMID: 21582976

Abstract

The title compound, dirubidium tetraantimonate(V), Rb₂Sb₄O₁₁, has been synthesized by flux reaction. It is isotypic with known A ₂Sb₄O₁₁ (A = K, Cs) structures and consists of an (Sb₄O₁₁)²⁻ skeleton and two Rb atoms as charge-compensating cations. Distorted SbO₆ octahedra share edges and corners, resulting in a layered assembly. Alternate stacking of the layers along the c axis leads to the formation of tunnels. The Rb⁺ ions, surrounded by nine and ten O atoms, respectively, are located in these tunnels. Some atoms in the structure are on special positions of m symmetry (two Sb atoms, both Rb atoms and four O atoms) and 2 symmetry (one O atom).

Related literature

Isotypic structures have been reported by Hong (1974 ▶) [K₂Sb₄O₁₁] and by Hirschle et al. (2001 ▶) [Cs₂Sb₄O₁₁]. For Rb—O distances in the crystal structure of Rb₃Ti₂(TiO)(PO₄)₃P₂O₇, see: Duhlev (1994 ▶).

Experimental

Crystal data

Rb₂Sb₄O₁₁
M _r = 833.94
Monoclinic,
a = 19.5045 (11) Å
b = 7.5681 (4) Å
c = 7.2115 (4) Å
β = 95.203 (3)°
V = 1060.12 (10) Å³
Z = 4
Mo Kα radiation
μ = 19.26 mm⁻¹
T = 120 K
0.12 × 0.12 × 0.11 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2007 ▶) T _min = 0.110, T _max = 0.120
7605 measured reflections
1312 independent reflections
1234 reflections with I > 2σ(I)
R _int = 0.038

Refinement

R[F ² > 2σ(F ²)] = 0.028
wR(F ²) = 0.072
S = 1.41
1312 reflections
91 parameters
18 restraints
Δρ_max = 1.89 e Å⁻³
Δρ_min = −1.91 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: DENZO (Otwinowski & Minor, 1997 ▶) and COLLECT; data reduction: DENZO nd COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2006 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809016109/wm2230sup1.cif

e-65-00i41-sup1.cif^{(20.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809016109/wm2230Isup2.hkl

e-65-00i41-Isup2.hkl^{(64.9KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Sb1—O4	1.940 (4)
Sb1—O3ⁱ	1.956 (5)
Sb1—O1ⁱⁱ	1.986 (3)
Sb1—O2	2.089 (5)
Sb2—O3ⁱⁱⁱ	1.903 (5)
Sb2—O6^iv	1.970 (3)
Sb2—O2^v	1.977 (5)
Sb2—O5ⁱⁱⁱ	1.993 (5)
Sb2—O2ⁱⁱⁱ	2.129 (5)
Sb3—O8	1.9281 (15)
Sb3—O4	1.959 (4)
Sb3—O7^vi	1.978 (4)
Sb3—O7	1.979 (4)
Sb3—O6	2.005 (4)
Sb3—O5	2.0261 (14)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

Acknowledgments

The authors thank the EPSRC for funding, the EPSRC National Crystallography Service for the use of the KappaCCD diffractometer and Dr Mark E. Light for useful discussions.

supplementary crystallographic information

Comment

Single crystals of the title compound (1), were formed inadvertently during one of our flux syntheses aimed at producing new oxides in the quaternary Rb/Sb/B/O system. There are two A₂Sb₄O₁₁ (A = K, Cs) compounds known and their structures were determined by single-crystal X-ray diffraction (Hong, 1974 and Hirschle et al., 2001). A₂Sb₄O₁₁(A = K, Cs) crystallize in the centrosymmetric space group C2/m and have two-dimensional structures with Sb in octahedral coordination. In K₂Sb₄O₁₁, the K⁺ ions are mobile in the tunnels. The K⁺ ions have been ion-exchanged with Na⁺, Ag⁺, Rb⁺ and TI⁺ in molten salts, but neither their unit-cell parameters nor their crystal structures are available (Hong, 1974). In Cs₂Sb₄O₁₁, Cs⁺ ions are not mobile (Hirschle et al., 2001). Here, we report the crystal structure of Rb₂Sb₄O₁₁, confirming that it is isotypic with A₂Sb₄O₁₁ (A = K, Cs).

The crystal structure of compound (1) contains two Rb (Rb1 and Rb2), three Sb (Sb1, Sb2 and Sb3) and eight O (O1—O8) atoms (Fig.1). The atoms Sb1, O4, O6 and O7 are on general positions, all other atoms are on special positions, viz. mirror planes and twofold-rotation axes. Each antimony atom is coordinated to six oxygen atoms to form distorted octahedra with Sb—O distances ranging from 1.903 (4) to 2.129 (5) Å, comparable to those in the isotypic antimonates(V) (Hong, 1974; Hirschle et al., 2001). Rb1 is nine fold coordinated and Rb2 is ten fold coordinated to oxygen atoms (Fig. 2 (a) and 2(b)) with Rb—O distances ranging from 2.933 (4) - 3.473 (4) Å, comparable to Rb₃Ti₂(TiO)(PO₄)₃P₂O₇ (Duhlev, 1994). The coordination number of Rb⁺ ion differs from the the 11 coordinated A⁺ ions reported for the isotypic A₂Sb₄O₁₁ (A = K, Cs) compounds, where the non bonding distances of K—O; 3.78 (3) - 3.832 (4) Å, Cs—O; 3.721 (8) - 3.940 (9) Å were considered as bonds.

In the asymmetric unit of the title compound (1) all oxygen atoms are shared between two SbO₆ octahedra, except the oxygen atoms O(2) and O(4), that are common to all three Sb(1)O₆, Sb(2)O₆ and Sb(3)O₆ octahedra (Fig. 1). In compound (1), there are two different layers (1 and 2) formed by edge-sharing of Sb(1)—Sb(1), Sb(2)—Sb(2) and Sb(3)—Sb(3) octahedra to form three types of Sb₂O₁₀ dimers (Fig. 3). Layer 1 is formed by edge-sharing of the Sb₂(2)O₁₀ and Sb₂(3)O₁₀ dimers and layer 2 is formed by Sb₂(1)O₁₀ dimers sharing corners with the layer 1. Alternate stacking of these two layers along the c axis leads to formation of tunnels and Rb⁺ ions are located in these tunnels. The single-crystal data was measured at 123 K and the displacement parameters observed for Rb⁺ are roughly isotropic, indicating that they are not mobile in the channels.

Experimental

A mixture of Rb₂CO₃ (Aldrich, 0.6224 g; 2.70 mmol), Sb₂O₃ (Aldrich, 0.3143 g; 1.08 mmol) and H₃BO₃ (Aldrich,0.5000 g; 8.09 mmol) was ground in a mortar and pestle. The ground mixture was then added into a platinum crucible. The furnace temperature was slowly raised from room temperature and heated at 773 K for 12 hrs, 923 K for a further 12 hrs, and then kept at 1273 K for 24 hrs. The furnace was cooled to room temperature over a period of 48 hrs. The melt was washed with hot water to remove the excess boric acid, filtered and dried in an oven at 353 K. Colourless crystals of compound (1) were obtained from the melt.