Caesium cis-tetra­chlorido­dioxido­rhenate(VII)

The title crystal structure, Cs[ReCl₄O₂], consists of cis-tetra­chlorido­dioxido­rhenate(VII) anions and caesium cations. The distorted octa­hedral anion has nearly C_2v symmetry, with a cis arrangement of the oxide ligands. The Re-Cl bond lengths for the Cl atoms trans to the oxide ligands are affected by the trans influence of the Re-O bonds and are longer than for the Cl atoms cis to the oxide ligands [average of 2.472 (2) Å versus average of 2.322 (2) Å, respectively]. There are ten Cl atoms from six cis-tetra­chlorido­dioxido­rhenate(VII) anions in the neighbourhood of the caesium cation.

S1. Comment

Tetrachloridodioxidorhenate(VII) anions were initially studied as the first-stage yellow product in the reaction between gaseous hydrogen chloride and rhenate(VII) anions by Jeżowska-Trzebiatowska (1951). Crystal structures containing tetrachloridodioxidorhenate(VII) anions were recently reported by Supeł & Seppelt (2007) in the form of the tetraethylphosphonium salt and also as the [NO][ReO₂Cl₄] salt. As far as the present authors' knowledge is concerned, the only other structure report of an [ReO₂X₄]^- anion (X = halogen) was published for the [ReO₂F₄]^- anion as the lithium salt (Casteel et al., 1999).

In this paper we report a simple method of obtaining unstable crystals of caesium cis-tetrachloridodioxidorhenate(VII), (I), and its crystal structure at 110 (2) K. This compound is one of the unstable crystalline products that it is possible to obtain in the reaction of caesium rhenate(VII) with acetyl chloride (see Experimental).

The crystal structure of (I) consists of cis-tetrachloridodioxidorhenate(VII) anions and caesium cations. In the distorted-octahedral cis-tetrachloridodioxidorhenate(VII) anion of nearly C_2v symmetry (Fig. 1), the two oxide ligands (O1 and O2) are in a cis arrangement. Such a cis arrangement of the oxide ligands is expected for a d⁰ electron configuration of the central metal ion (Barea et al., 1998). This is contrary to, for example, the d² configuration, where, based on molecular orbital calculations, the trans arrangement is favoured (Demachy & Jean, 1997). This symmetry, as well as the geometric parameters of the anion, corresponds very well to the data reported by Supeł & Seppelt (2007). In the tetraethylphosphonium salt (Supeł & Seppelt, 2007), the Re—O bond lengths are 1.692 (1) and 1.707 (1) Å, the Re—Cl_cis bond lengths are 2.3225 (5) and 2.3302 (5) Å, the Re—Cl_trans bond lengths are 2.4417 (4) and 2.4453 (5) Å, and the O—Re—O bond angle is 102.31 (7)°.

In the original paper reporting the crystal structure of [NO][ReO₂Cl₄] (Supeł & Seppelt, 2007), a difference Fourier peak of 5.28 electrons was present, which could come from partial disorder. Refinement based on the original reflection data obtained from the former authors was performed. Although the inclusion of the highest peak in the new refinement resulted in a drop in the R value, we were unable to propose any disorder model better than the previously published model without disorder. It seems that in the reported crystal structure of [NO][ReO₂Cl₄], only the geometric parameters of the second anion are affected by disorder. Therefore, these parameters will not be taken into account in the summary concerning the geometry of the ReO₂ moiety in [ReO₂X₄]^- anions.

The Re—O bond lengths reported here [1.695 (3) and 1.703 (3) Å] are also comparable with the corresponding values published for the Re—O bond lengths in the [ReO₂F₄]^- anion in its lithium salt [the anion can be described with only one Re—O bond length, 1.678 (9) Å, as only half of the anion is symmetry independent; Casteel et al., 1999]. All in all, according to the data reported so far, and taking into account the present report, the Re—O bond lengths in the cis-ReO₂ moiety in [ReO₂X₄]^- anions should be approximately 1.70 Å.

Based on the aforementioned results, some general conclusions concerning the [ReO₂Cl₄]^- anion geometry can be made and the obtained values of the geometric parameters can be compared with the analogous rhenium d² system with a trans arrangement of the oxide ligands. A survey of the current literature on rhenium compounds reveals an example of a compound suitable for this purpose, potassium dioxidotetracyanorhenate(V). The crystal structure of this complex was first determined by Łukaszewicz & Głowiak (1961), then by Murmann & Schlemper (1971), and finally by neutron diffraction by Fenn et al. (1971). The criterion of the suitability of this compound consists of the presence of two oxide ligands in a trans arrangement, Re^V as the central metal atom, and four remaining ligands of the same kind and possibly resembling chloride ligands. In this crystal structure, the complex trans-[ReO₂(CN)₄]^3- anions differ from the cis-[ReO₂Cl₄]^- anions by the oxidation state of the central Re atom (Re^V instead of Re^VII), as well as by the arrangement of the two oxide ligands (trans instead of cis) and the type of the four remaining ligands (cyano instead of chloride ligands). The Re—O bond length reported for this compound (Murmann & Schlemper, 1971) is 1.781 (3) Å. This means that, in the trans-dioxidorhenium(V) moiety, the Re—O bond should be 0.6–0.8 Å longer than in the cis-dioxidorhenium(VII) moiety.

The Re–Cl bond lengths reported here for the Cl ligands cis to the oxide ligands (Cl3 and Cl4) are 2.330 (2) and 2.313 (2) Å, respectively. The distances of the Cl ligands trans to the oxide ligands (Cl1 and Cl2) from the central Re1 atom are longer [2.472 (2) and 2.471 (2) Å, respectively]. These values for the Re—Cl_trans bond lengths are comparable with the analogous values published for other rhenium(VII) compounds. For cis-tetrachloridodioxidorhenate(VII) anions, Supeł & Seppelt (2007) reported values of 2.4417 (4) and 2.4453 (5) Å in the tetraethylphosphonium salt, and 2.488 (2) and 2.529 (2) Å for [NO]ReO₂Cl₄. In caesium cis-trichloridotrioxidorhenate(VII) reported by Lis (1983), the Re—Cl_trans bond lengths are 2.517 (8) and 2.494 (5) Å. In another example, ReO₃Cl(THF)₂ reported by Noh & Girolami (2007), the Re—Cl_trans bond length is 2.427 (2) Å. In all these cases, the lengthening of the Re—Cl bond is the result of the trans influence of the Re—O bond (Shustorovich et al., 1975). Based on these data, it seems that the Re—Cl_trans (to the oxide O atom) bond should be as much as 0.10–0.25 Å longer than the Re—Cl_cis bond.

There are ten Cl atoms from six cis-tetrachloridodioxidorhenate(VII) anions in the neighbourhood of the Cs⁺ cation, at distances in the range 3.50–3.73 Å (see Table 2 for symmetry codes and the shortest interatomic distances; Fig. 2). Two anions are in contact with the Cs⁺ cation via three Cl ligands (Cl1^iv, Cl2^iv and Cl4^iv, and Cl3ⁱ, Cl1ⁱ and Cl2ⁱ). Four anions are in contact via only one Cl ligand (Cl1, Cl3ⁱⁱ, Cl1ⁱⁱⁱ and Cl4^v). For one cis-tetrachloridodioxidorhenate(VII) anion in contact with the Cs⁺ cation via the Cl2 ligand, an additional contact involving the O1 ligand can be distinguished (Table 1). Thus, the Cs⁺ cation is surrounded by 11 ligands from ten anions, lying in the vertices of a `staggered 164 stack' based on the considerations of King (1970).

The crystal structure is stabilized by a three-dimensional network of short Cs···Cl contacts (Fig. 3). The shortest distance between two Cs⁺ cations is approximately 4.85 Å. The shortest intermolecular distance between two Re centres from two independent anions is approximately 4.73 Å.

Related literature

For related literature, see: Barea et al. (1998); Casteel et al. (1999); Demachy & Jean (1997); Fenn et al. (1971); Jeżowska-Trzebiatowska (1951); King (1970); Lis (1983); Murmann & Schlemper (1971); Noh & Girolami (2007); Sheldrick (2008); Shustorovich et al. (1975); Supeł & Seppelt (2007); Łukaszewicz & Głowiak (1961).

S2. Experimental

All operations were performed at room temperature. Caesium rhenate(VII) (0.05 g) was placed in a glass vessel and acetyl chloride (0.2 ml) was added. The vessel was covered with Parafilm. The mixture turned slowly orange and then red with dissolution of the solid rhenate(VII). At this stage, the vessel was covered with a plastic cap. After 1 d, extremely unstable crystals in the form of plates, difficult to handle and reproduce, began to precipitate. Part of the solution with the precipitated crystals was quickly placed on a cool plate, cooled to about 258 K under a nitrogen atmosphere and covered with perfluoroalkylether. All these operations were intended to avoid the decomposition of the crystals. A single-crystal was selected from the cooled mixture and a preliminary X-ray diffraction measurement showed it likely to be composed of caesium cis-tetrachloridodioxidorhenate(VII) acetic anhydride solvate. The measurement provided only the crystal structure model, as the crystals were extremely unstable and some decomposition occurred before they were mounted on the diffractometer. This could lead to the conclusion concerning the apparent reaction shown in the scheme.

After a week, in the remaining reaction mixture among the orange plates, red blocks began to appear with another kind of unstable orange plates. Application of a similar procedure to that described above enabled the performance of X-ray diffraction measurements for both new kinds of crystals. The red blocks consisted of caesium pentachloridooxidorhenate(VI) and the new kind of orange plates consisted of the title compound. Interestingly, the same reaction of acetyl chloride with caesium rhenate(VII) performed at about 267 K yields orange crystals in the form of needles with the same composition as the title compound. At further reaction stages, the red mixture in contact with air turned violet and underwent decomposition to caesium rhenate(VII).

S3. Refinement

The structure was solved using the Patterson method in SHELXS97 (Sheldrick, 2008).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Bruker, 1997) and DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. A view of the cis-tetrachloridodioxidorhenate(VII) anion, with the atom-labelling scheme.
	Fig. 2. The nearest neighbours of the Cs^+ cation. The debatable contact to atom O1 (see Comment) is denoted with a dashed line [No dashed line is visible - please revise diagram]. [Symmetry codes: (i) -x + 1, -y + 2, -z + 1; (ii) x, -y + 3/2, z + 1/2; (iii) x - 1, -y + 3/2, z + 1/2; (iv) x - 1, y, z; (v) -x + 1, y + 1/2, -z + 3/2.]
	Fig. 3. A view of the packing in the crystal structure, showing the three-dimensional network of short Cs···Cl contacts (heavy lines; see Comment). [Symmetry code: (vi) -x, 1 - y, 1 - z.]

Caesium cis-tetrachloridodioxidorhenate(VII)'

Crystal data

Cs[ReCl4O2]	F(000) = 856
Mr = 492.91	Dx = 4.102 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9641 reflections
a = 6.609 (3) Å	θ = 3–35°
b = 10.322 (5) Å	µ = 20.98 mm^−1
c = 11.714 (5) Å	T = 110 K
β = 92.04 (5)°	Plate, orange
V = 798.6 (6) Å^3	0.11 × 0.11 × 0.07 mm
Z = 4

Data collection

Oxford Diffraction XcaliburPX CCD diffractometer	4462 independent reflections
Radiation source: fine-focus sealed tube	2402 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.057
ω and ϕ scans	θmax = 42.0°, θmin = 5.0°
Absorption correction: analytical (ABSPACK and analytical correction; Oxford Diffraction, 2006)	h = −11→8
Tmin = 0.164, Tmax = 0.296	k = −19→13
14688 measured reflections	l = −22→21

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.032	Secondary atom site location: difference Fourier map
wR(F^2) = 0.034	w = 1/[σ^2(Fo^2)] where P = (Fo^2 + 2Fc^2)/3
S = 0.77	(Δ/σ)max = 0.002
4462 reflections	Δρmax = 1.52 e Å^−3
73 parameters	Δρmin = −1.59 e Å^−3

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

	x	y	z	Uiso*/Ueq
Re1	0.67638 (3)	0.688959 (13)	0.447624 (14)	0.01305 (4)
Cs1	0.18718 (4)	0.88921 (2)	0.65308 (2)	0.01490 (6)
Cl3	0.52127 (14)	0.82298 (8)	0.31048 (8)	0.0155 (2)
Cl1	0.99603 (14)	0.78427 (8)	0.38315 (8)	0.0158 (2)
Cl2	0.68494 (13)	0.88663 (8)	0.56669 (8)	0.01300 (19)
Cl4	0.87935 (15)	0.60021 (8)	0.59234 (8)	0.0190 (2)
O1	0.4549 (4)	0.6505 (2)	0.5080 (2)	0.0212 (7)
O2	0.7095 (4)	0.5656 (2)	0.3535 (2)	0.0205 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re1	0.01647 (9)	0.00987 (6)	0.01285 (8)	−0.00079 (7)	0.00087 (6)	−0.00059 (7)
Cs1	0.01357 (13)	0.01527 (11)	0.01578 (13)	−0.00073 (10)	−0.00064 (10)	0.00321 (9)
Cl3	0.0155 (5)	0.0164 (4)	0.0144 (5)	−0.0010 (4)	−0.0032 (4)	0.0007 (4)
Cl1	0.0131 (5)	0.0202 (5)	0.0143 (5)	0.0020 (4)	0.0018 (4)	−0.0007 (4)
Cl2	0.0141 (5)	0.0126 (4)	0.0125 (5)	0.0007 (4)	0.0017 (4)	−0.0015 (3)
Cl4	0.0270 (6)	0.0159 (4)	0.0141 (5)	0.0044 (4)	0.0007 (4)	0.0019 (4)
O1	0.0220 (16)	0.0162 (14)	0.0256 (17)	−0.0044 (11)	0.0017 (14)	0.0023 (12)
O2	0.0315 (17)	0.0149 (13)	0.0148 (15)	0.0013 (12)	−0.0035 (13)	−0.0016 (11)

Geometric parameters (Å, º)

Re1—O1	1.695 (3)	Cs1—Cl1^iii	3.6013 (18)
Re1—O2	1.704 (3)	Cs1—Cl2^ii	3.4357 (19)
Re1—Cl1	2.4728 (14)	Cs1—Cl2	3.4761 (19)
Re1—Cl2	2.4710 (12)	Cs1—Cl2^iii	3.5847 (15)
Re1—Cl3	2.3299 (13)	Cs1—Cl3^iii	3.5584 (16)
Re1—Cl4	2.3131 (14)	Cs1—Cl3^iv	3.5751 (17)
Cs1—O1	3.508 (3)	Cs1—Cl4^ii	3.6662 (16)
Cs1—Cl1^i	3.5082 (16)	Cs1—Cl4^v	3.7314 (16)
Cs1—Cl1^ii	3.5331 (18)	Cs1—Cs1^vi	4.856 (2)
O1—Re1—O2	103.18 (13)	Cl4—Re1—Cl2	84.97 (4)
O1—Re1—Cl4	95.05 (10)	Cl3—Re1—Cl2	84.24 (5)
O2—Re1—Cl4	95.40 (10)	O1—Re1—Cl1	168.60 (9)
O1—Re1—Cl3	93.54 (10)	O2—Re1—Cl1	88.20 (10)
O2—Re1—Cl3	93.48 (10)	Cl4—Re1—Cl1	84.37 (5)
Cl4—Re1—Cl3	165.92 (3)	Cl3—Re1—Cl1	85.00 (5)
O1—Re1—Cl2	87.74 (9)	Cl2—Re1—Cl1	80.86 (4)
O2—Re1—Cl2	168.98 (9)

Symmetry codes: (i) x−1, −y+3/2, z+1/2; (ii) x−1, y, z; (iii) −x+1, −y+2, −z+1; (iv) x, −y+3/2, z+1/2; (v) −x+1, y+1/2, −z+3/2; (vi) −x, −y+2, −z+1.