Bis(benzo-15-crown-5-κ5 O)strontium bis­(triiodide)

Christine Walbaum; Ingo Pantenburg; Gerd Meyer

doi:10.1107/S1600536808012373

. 2008 Apr 30;64(Pt 5):m747. doi: 10.1107/S1600536808012373

Bis(benzo-15-crown-5-κ⁵ O)strontium bis(triiodide)

Christine Walbaum ^a, Ingo Pantenburg ^a,^*, Gerd Meyer ^a

PMCID: PMC2961288 PMID: 21202264

Abstract

The title compound, [Sr(C₁₄H₂₀O₅)₂](I₃)₂, obtained by slow evaporation of an ethanol/dichloromethane solution (1:1) of SrCl₂, benzo-15-crown-5 and I₂, is built of sandwich-like [Sr(benzo-15-crown-5)₂]²⁺ cations and isolated linear I₃ ⁻ anions which are arranged in alternating layers parallel to (010). The triiodide anions are located in general positions, whereas the cations are located on centres of inversion.

Related literature

For related literature, see: Pantenburg et al. (2002 ▶); Walbaum et al. (2007 ▶) and references cited therein. For bond-length data, see: Allen et al. (1987 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

[Sr(C₁₄H₂₀O₅)₂](I₃)₂
M _r = 1385.62
Monoclinic,
a = 12.0127 (17) Å
b = 12.8666 (12) Å
c = 13.085 (2) Å
β = 90.245 (18)°
V = 2022.5 (5) Å³
Z = 2
Mo Kα radiation
μ = 5.96 mm⁻¹
T = 293 (2) K
0.2 × 0.2 × 0.15 mm

Data collection

Stoe IPDS-I diffractometer
Absorption correction: numerical [X-RED (Stoe & Cie, 2001 ▶); after optimizing the crystal shape using X-SHAPE (Stoe & Cie, 1999 ▶)] T _min = 0.393, T _max = 0.465
18994 measured reflections
4869 independent reflections
1779 reflections with I > 2σ(I)
R _int = 0.124

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.069
S = 0.71
4869 reflections
207 parameters
H-atom parameters constrained
Δρ_max = 0.54 e Å⁻³
Δρ_min = −0.72 e Å⁻³

Data collection: IPDS (Stoe & Cie, 1996 ▶); cell refinement: IPDS; data reduction: IPDS; program(s) used to solve structure: SIR92 (Altomare et al., 1993 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2004 ▶); software used to prepare material for publication: CIF-Editor (Wieczorrek, 2004 ▶).

Supplementary Material

Crystal structure: contains datablocks global_, I. DOI: 10.1107/S1600536808012373/nc2102sup1.cif

e-64-0m747-sup1.cif^{(20.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808012373/nc2102Isup2.hkl

e-64-0m747-Isup2.hkl^{(233.7KB, hkl)}

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

Table 1. Selected geometric parameters (Å, °).

I2—I1	2.8754 (13)
I2—I3	2.9210 (13)
Sr1—O13	2.679 (5)
Sr1—O13ⁱ	2.679 (5)
Sr1—O4	2.682 (5)
Sr1—O4ⁱ	2.682 (5)
Sr1—O1	2.691 (5)
Sr1—O1ⁱ	2.691 (5)
Sr1—O7ⁱ	2.706 (5)
Sr1—O7	2.706 (5)
Sr1—O10ⁱ	2.778 (5)
Sr1—O10	2.778 (5)

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I1—I2—I3

177.54 (4)

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Symmetry code: (i) Inline graphic .

supplementary crystallographic information

Comment

Polyiodide anions are synthesized by the addition of elemental iodine to iodide ions and can be incorporated into crystalline solids in the presence of suitable cations. They show considerable diversity in I - I bond lengths, covering the whole range between a strongly covalent bond and the sum of the van der Waals radii of two iodine atoms. However, the bond lengths are never uniform. As a consequence, the structural diversity of polyiodide ions is remarkably high. To date, no systematic procedure for the synthesis and crystallization of iodine-rich polyiodides is known, and this remains the ultimate goal of our work. We try to control the structures and composition of polyiodide matrices by variation of the shape, charge and size of the corresponding cations. In previous work, we have shown that bulky low-charged cations of the general formula [M(crown-ether)]^x⁺ (where M is an element of group 1 or 2, or a rare earth-metal, crown-ether is benzo-18-crown-6, benzo-15-crown-5 or dibenzo-18-crown-6 and x = 1, 2 or 3) positively influence the stabilitity of polyiodides in the solid state (Walbaum et al., 2007).

[Sr(benzo-15-crown-5)₂](I₃)₂ is isotypic with the respective Ba compound (Pantenburg et al., 2002). The Sr²⁺ ion (2a; 1,0,1) is located slightly above the centre of two benzo-15-crown ligands and coordinated in a sandwich-like manner by ten O atoms. The Sr—O distances vary between 2.679 (5) Å and 2.778 (5) Å (Table 1). Distances and angles within the crown-ether moiety are in good agreement with published data [mean values from the Cambridge Structural Database (Allen, 2002): CH₂—O = 1.43 (3) Å, CH₂—CH₂ = 1.51 (2) Å, O—CH₂—CH₂ = 108.9 (13)°, CH₂—O—CH₂ = 111.4 (10)°]. The triiodide anion is almost symmetrical (I1—I2 = 2.8754 (13) Å, I2—I3 = 2.9210 (13) Å) and only slightly angular (I1—I2—I3 = 177.54 (4)°).

Although polyiodide ions tend to form even larger arrays through weak attractions between the anions, the shortest distance between the triiodide anions in [Sr(benzo-15-crown-5)₂](I₃)₂ is 4.6623 (19) Å (I2—I1ⁱ; (i) = -x + 2, -y + 1, -z + 2) (Fig. 2). Thus, the anions may be considered as isolated. Distances between the [Sr(benzo-15-crown-5)₂]²⁺ cations and the anions are also rather large, beginning with (I—H) = 3.138 (1) Å, (I—C) = 3.872 (9) Å, and (I—O) = 3.896 (5) Å.

Experimental

[Sr(benzo-15-crown-5)₂](I₃)₂ was prepared by dissolving SrCl₂ (0.05 g, 0.3 mmol), C₁₄H₂₀O₅ (0.08 g, 0.3 mmol), and I₂ (0.08 g, 0.3 mmol) in ethanol/dichloromethane (1:1) (40 ml). Red crystals were obtained after a few days by slow evaporation of the solvent under ambient conditions.