The sandwich dimeric form of a Cs^I complex of 18-crown-6 with bridging iodide ions

The sandwich dimeric structure of di-μ-iodo-bis[(1,4,7,10,13,16-hexaoxa­cyclo­octa­decane)­caesium(I)] p-xyl­ene solvate, [Cs₂I₂(C₁₂H₂₄O₆)₂]·C₈H₁₀, has been characterized by X-ray crystallography. The complex adopts an encapsulate of a molecular dimeric array [Cs(18-crown-6)(μ-I)]₂·C₈H₁₀. Two Cs(18-crown-6)⁺ moieties are doubly linked by two iodide ions. The mol­ecule has crystallographic 2/m (C_2h) symmetry.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.028
• wR factor = 0.075
• Data-to-parameter ratio = 23.8

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S1. Comment

The chemistry of macrocyclic complexes of alkali metal cations has developed intensively since the end of the 1960's because of the strong complexing properties of crown ethers. In this case, the complementarity of the macrocyclic cavity and the cation substrate determines the type of complex (Dietrich et al., 1993). A caesium ion is too large for the 18-crown-6 cavity, thus giving a sandwich dimer complex bridged by SCN^- anions (Dobler & Phizackerley, 1974) or water molecules (Rusanova et al., 1999). We report here the sandwich dimer structure of the title compound (I) with bridging iodide ions.

The title compound adopts a molecular dimeric array consisting of two [Cs(18-crown-6)]⁺ units linked via two iodide ions as shown in Figure 1. Two caesium cations are positioned on a mirror plane and two iodide ions are located on a twofold symmetry axis perpendicular to the mirror plane. The asymmetric unit, therefore, consists of a quarter of Cs₂(18-crown-6)₂I₂.

Important bond distances and angles are presented in Table 1. The caesium ion adopts eightfold coordination. The bond distances between Cs and O atoms in the crown ether span a range of 3.050 (3)–3.320 (3) Å and the average distance is 3.198 Å. The caesium ion is located 1.520 (2) Å above the mean O plane of the crown ring, which has a mean deviation of 0.22 Å. This value is slightly larger than those reported previously for the related complexes, 1.44 Å in [Cs₂(18-crown-6)₂(SCN)₂] (Dobler & Phizackerley, 1974) and 1.48 Å in [Cs₂(18-crown-6)₂(H₂O)₂] (Rusanova et al., 1999). The dihedral angle between the plane consisting of two caesium and two iodide ions and the mean O plane of the crown ether is 76.75 (4)°.

The p-xylene molecules are packed in the voids between the dimer complexes. The centre of p-xylene is located on a position of 2/m symmetry. We also determined the crystal structure of Cs₂(18-crown-6)₂I₂^.toluene. The structure is nearly identical to that of the title compound. The toluene molecule is also located at a special position of 2/m symmetry in the C2/m unit cell, so that the non-centrosymmetric toluene molecules are disordered over the inversion centre to give an image like the p-xylene molecule.

S2. Experimental

Equimolar amounts of caesium iodide and 18-crown-6 were dissolved in anhydrous methanol followed by addition of p-xylene. Slow evaporation in a calcium chloride desiccator yielded crystals suitable for X-ray analysis.

S3. Refinement

The C—H atoms were added at their calculated positions (U = 1.2 times that of the corresponding C atom) and refined using a riding model.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1996); program(s) used to solve structure: SHELXTL (Siemens, 1996); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. The structure of the title compound with the atom-numbering scheme. The displacement ellipsoids are drawn at the 50% probability level. All H atoms have been omitted for clarity. [Symmetry codes: (i) x, -y, z; (ii) -x, y, 1 - z; (iii) -x, -y, 1 - z; (iv) -x, y, -z; (v) x, 1 - y, z; (vi) -x, 1 - y, -z]

di-µ-iodo-bis(1,4,7,10,13,16-hexaoxacyclooctadecanecaesium(I)) p-xylene solvate

Crystal data

C24H48Cs2I2O12·C8H10	F(000) = 1124
Mr = 1154.40	Dx = 1.743 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
a = 15.436 (1) Å	Cell parameters from 7131 reflections
b = 17.4317 (11) Å	θ = 1.8–28.3°
c = 8.1756 (5) Å	µ = 3.11 mm^−1
β = 91.195 (1)°	T = 298 K
V = 2199.4 (2) Å^3	Plate, colourless
Z = 2	0.50 × 0.25 × 0.15 mm

Data collection

CCD area-detector diffractometer	2742 independent reflections
Radiation source: fine-focus sealed tube	2385 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
ϕ and ω scans	θmax = 28.3°, θmin = 1.8°
Absorption correction: multi-scan (XPREP, Siemens, 1996)	h = −18→19
Tmin = 0.386, Tmax = 0.627	k = −23→16
7131 measured reflections	l = −10→10

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.075	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0345P)^2 + 2.918P] where P = (Fo^2 + 2Fc^2)/3
2742 reflections	(Δ/σ)max < 0.001
115 parameters	Δρmax = 1.20 e Å^−3
0 restraints	Δρmin = −1.08 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cs1	0.170972 (16)	0.0000	0.36783 (3)	0.04777 (9)
I1	0.0000	0.150813 (17)	0.5000	0.05492 (10)
O1	0.3636 (3)	0.0000	0.5128 (6)	0.0904 (13)
O2	0.29407 (16)	0.14338 (15)	0.4161 (4)	0.0693 (7)
O3	0.20804 (17)	0.14078 (15)	0.1049 (3)	0.0672 (6)
O4	0.1305 (2)	0.0000	0.0011 (4)	0.0645 (9)
C1	0.3762 (3)	0.0690 (3)	0.6022 (6)	0.0924 (15)
H1A	0.4309	0.0667	0.6626	0.111*
H1B	0.3302	0.0750	0.6801	0.111*
C2	0.3764 (3)	0.1343 (3)	0.4910 (6)	0.0806 (12)
H2A	0.3918	0.1805	0.5511	0.097*
H2B	0.4194	0.1263	0.4078	0.097*
C3	0.2924 (3)	0.2057 (2)	0.3048 (5)	0.0711 (10)
H3A	0.3405	0.2014	0.2308	0.085*
H3B	0.2986	0.2536	0.3645	0.085*
C4	0.2104 (3)	0.2058 (2)	0.2110 (5)	0.0711 (10)
H4A	0.1621	0.2037	0.2850	0.085*
H4B	0.2054	0.2525	0.1471	0.085*
C5	0.1301 (3)	0.1360 (2)	0.0124 (5)	0.0774 (11)
H5A	0.1225	0.1821	−0.0530	0.093*
H5B	0.0814	0.1318	0.0850	0.093*
C6	0.1333 (3)	0.0680 (3)	−0.0955 (5)	0.0792 (12)
H6A	0.0845	0.0688	−0.1721	0.095*
H6B	0.1862	0.0688	−0.1575	0.095*
C7	0.0000	0.3329 (4)	0.0000	0.096 (2)
H7A	0.0556	0.3145	−0.0330	0.115*	0.50
H7B	−0.0440	0.3145	−0.0750	0.115*	0.50
H7C	−0.0116	0.3145	0.1080	0.115*	0.50
C8	0.0000	0.4192 (3)	0.0000	0.0596 (11)
C9	0.0726 (2)	0.4604 (2)	−0.0427 (4)	0.0598 (8)
H9	0.1225	0.4342	−0.0720	0.072*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cs1	0.04634 (15)	0.04223 (14)	0.05461 (16)	0.000	−0.00198 (10)	0.000
I1	0.04822 (16)	0.04972 (17)	0.0672 (2)	0.000	0.00949 (13)	0.000
O1	0.100 (3)	0.073 (3)	0.097 (3)	0.000	−0.046 (3)	0.000
O2	0.0538 (13)	0.0588 (14)	0.0953 (19)	−0.0105 (11)	0.0046 (13)	−0.0034 (13)
O3	0.0611 (14)	0.0547 (13)	0.0859 (18)	0.0076 (11)	0.0078 (13)	0.0026 (12)
O4	0.079 (2)	0.066 (2)	0.0484 (17)	0.000	−0.0109 (16)	0.000
C1	0.077 (3)	0.122 (4)	0.077 (3)	−0.026 (3)	−0.025 (2)	−0.004 (3)
C2	0.062 (2)	0.071 (2)	0.108 (3)	−0.015 (2)	−0.006 (2)	−0.025 (2)
C3	0.072 (2)	0.0459 (18)	0.097 (3)	−0.0115 (16)	0.027 (2)	−0.0073 (18)
C4	0.077 (2)	0.0413 (16)	0.096 (3)	0.0063 (16)	0.029 (2)	0.0049 (17)
C5	0.081 (3)	0.068 (2)	0.083 (3)	0.017 (2)	−0.001 (2)	0.027 (2)
C6	0.083 (3)	0.094 (3)	0.060 (2)	0.009 (2)	−0.0113 (19)	0.019 (2)
C7	0.112 (5)	0.059 (3)	0.118 (5)	0.000	0.035 (4)	0.000
C8	0.068 (3)	0.060 (3)	0.051 (2)	0.000	0.005 (2)	0.000
C9	0.0523 (17)	0.072 (2)	0.0554 (17)	0.0096 (15)	0.0059 (14)	−0.0001 (15)

Geometric parameters (Å, º)

Cs1—O4	3.050 (3)	O1—C1^i	1.418 (5)
Cs1—O2	3.159 (2)	O2—C2	1.408 (5)
Cs1—O2^i	3.159 (2)	O2—C3	1.417 (5)
Cs1—O1	3.178 (4)	O3—C5	1.410 (5)
Cs1—O3^i	3.320 (3)	O3—C4	1.427 (5)
Cs1—O3	3.320 (3)	O4—C6^i	1.425 (4)
Cs1—C5^i	3.793 (4)	O4—C6	1.425 (4)
Cs1—C5	3.793 (4)	C1—C2	1.457 (7)
Cs1—C1	3.860 (4)	C3—C4	1.466 (6)
Cs1—C1^i	3.860 (4)	C5—C6	1.480 (6)
Cs1—C4^i	3.862 (4)	C7—C8	1.504 (8)
Cs1—C4	3.862 (4)	C8—C9	1.382 (4)
Cs1—I1	3.8940 (3)	C8—C9^ii	1.382 (4)
O1—C1	1.418 (5)	C9—C9^iii	1.381 (8)
O4—Cs1—O2	103.47 (7)	O1—Cs1—C4^i	88.35 (8)
O4—Cs1—O2^i	103.47 (7)	O3^i—Cs1—C4^i	21.24 (8)
O2—Cs1—O2^i	104.57 (10)	O3—Cs1—C4^i	116.18 (8)
O4—Cs1—O1	122.51 (12)	C5^i—Cs1—C4^i	35.89 (10)
O2—Cs1—O1	52.97 (5)	C5—Cs1—C4^i	110.55 (10)
O2^i—Cs1—O1	52.97 (5)	C1—Cs1—C4^i	108.71 (11)
O4—Cs1—O3^i	52.99 (6)	C1^i—Cs1—C4^i	75.05 (11)
O2—Cs1—O3^i	123.66 (7)	O4—Cs1—C4	72.78 (7)
O2^i—Cs1—O3^i	52.03 (7)	O2—Cs1—C4	37.64 (9)
O1—Cs1—O3^i	93.95 (8)	O2^i—Cs1—C4	132.66 (8)
O4—Cs1—O3	52.99 (6)	O1—Cs1—C4	88.35 (8)
O2—Cs1—O3	52.03 (7)	O3^i—Cs1—C4	116.18 (8)
O2^i—Cs1—O3	123.66 (7)	O3—Cs1—C4	21.24 (8)
O1—Cs1—O3	93.95 (8)	C5^i—Cs1—C4	110.55 (10)
O3^i—Cs1—O3	95.33 (9)	C5—Cs1—C4	35.89 (10)
O4—Cs1—C5^i	38.69 (7)	C1—Cs1—C4	75.05 (11)
O2—Cs1—C5^i	132.85 (9)	C1^i—Cs1—C4	108.71 (11)
O2^i—Cs1—C5^i	72.00 (9)	C4^i—Cs1—C4	136.51 (12)
O1—Cs1—C5^i	115.15 (10)	I1—Cs1—I1^i	84.929 (10)
O3^i—Cs1—C5^i	21.57 (8)	Cs1—I1—Cs1^iv	95.071 (10)
O3—Cs1—C5^i	89.67 (9)	C1—O1—C1^i	116.0 (5)
O4—Cs1—C5	38.69 (7)	C1—O1—Cs1	108.0 (3)
O2—Cs1—C5	72.00 (9)	C1^i—O1—Cs1	108.0 (3)
O2^i—Cs1—C5	132.85 (9)	C2—O2—C3	111.7 (3)
O1—Cs1—C5	115.15 (10)	C2—O2—Cs1	120.0 (2)
O3^i—Cs1—C5	89.67 (9)	C3—O2—Cs1	121.6 (2)
O3—Cs1—C5	21.57 (8)	C5—O3—C4	112.5 (3)
C5^i—Cs1—C5	77.38 (15)	C5—O3—Cs1	98.5 (2)
O4—Cs1—C1	129.57 (10)	C4—O3—Cs1	101.3 (2)
O2—Cs1—C1	37.47 (10)	C6^i—O4—C6	112.5 (4)
O2^i—Cs1—C1	72.50 (10)	C6^i—O4—Cs1	122.5 (2)
O1—Cs1—C1	20.45 (10)	C6—O4—Cs1	122.5 (2)
O3^i—Cs1—C1	113.64 (10)	O1—C1—C2	110.1 (4)
O3—Cs1—C1	86.58 (9)	O1—C1—Cs1	51.5 (2)
C5^i—Cs1—C1	134.16 (11)	C2—C1—Cs1	86.9 (2)
C5—Cs1—C1	107.89 (11)	O2—C2—C1	110.2 (3)
O4—Cs1—C1^i	129.57 (10)	O2—C3—C4	109.9 (3)
O2—Cs1—C1^i	72.50 (10)	O3—C4—C3	109.2 (3)
O2^i—Cs1—C1^i	37.47 (10)	O3—C4—Cs1	57.45 (17)
O1—Cs1—C1^i	20.45 (10)	C3—C4—Cs1	88.1 (2)
O3^i—Cs1—C1^i	86.58 (9)	O3—C5—C6	109.1 (3)
O3—Cs1—C1^i	113.64 (10)	O3—C5—Cs1	59.96 (17)
C5^i—Cs1—C1^i	107.89 (11)	C6—C5—Cs1	87.0 (2)
C5—Cs1—C1^i	134.16 (11)	O4—C6—C5	109.6 (3)
C1—Cs1—C1^i	36.30 (17)	C9—C8—C9^ii	117.4 (5)
O4—Cs1—C4^i	72.78 (7)	C9—C8—C7	121.3 (2)
O2—Cs1—C4^i	132.66 (8)	C9^ii—C8—C7	121.3 (2)
O2^i—Cs1—C4^i	37.64 (9)	C9^iii—C9—C8	121.3 (2)

Symmetry codes: (i) x, −y, z; (ii) −x, y, −z; (iii) x, −y+1, z; (iv) −x, y, −z+1.