Calcium chloride rhenate(VII) dihydrate

The crystal structure of calcium chloride rhenate(VII) dihydrate, CaCl(ReO₄)·2H₂O, investigated at 85 K, consists of calcium cations, chloride anions, rhenate(VII) anions and water mol­ecules. In the nearly tetra­hedral rhenate(VII) anion, all constituent atoms lie on special positions of m2m (Re) and m (O) site symmetries. The Cl⁻ anion and water O atom lie on special positions of m2m and 2 site symmetries, respectively. The Ca²⁺ ion, also on a special position (m2m), is eight-coordinated in a distorted square-anti­prismatic coordination mode. The crystal has a layered structure stabilized by Ca—O coordination bonds and O—H...Cl hydrogen bonds.

S1. Comment

Currently all rhenate(VII) salts of the metals of the first and second main groups of the periodic table are known except for beryllium rhenate(VII) (e.g. Krebs & Hasse, 1982; Todorov & Macicek, 1995). Most of these compounds have been investigated as easy-to-prepare crystalline hydrates. The other properties explored include thermal decomposition patterns monitored by thermogravimetric measurements [e.g. lithium rhenate(VII) monohydrate; Abakumov et al., 2001]. Calcium chloride rhenate(VII) dihydrate was obtained in an effort to crystallize a new calcium rhenate(VII) hydrate as a result of the reaction between calcium chloride and rhenic(VII) acid in aqueous solution. Previously reported data on calcium rhenate(VII) include three crystal structure determinations of the dihydrate salt (Matveeva et al., 1980; Picard et al., 1988; Baur & Kassner, 1992).

The title crystal structure consists of calcium cations, chloride anions, rhenate(VII) anions and water molecules of crystallization.

Atom Re1 lies on a special position of m2m site symmetry and the rhenate(VII) O atoms (O2 and O3) occupy special positions of m site symmetry. The rhenate(VII) anion has a slightly distorted tetrahedral geometry, as shown by the O—Re—O bond angles, which deviate slightly from the ideal tetrahedral values (Table 1). The Re—O bond lengths are equal and in good agreement with values observed for similar compounds [e.g. Sr(ReO₄)₂·2H₂O (Todorov et al., 1996), Ba(ReO₄)₂·H₂O (Todorov & Macicek, 1995) and LiReO₄·H₂O (Abakumov et al. 2001)].

The chloride anion and water atom O1 lie on special positions of m2m and 2 site symmetries, respectively.

The calcium ion lies on a special position of m2m symmetry and is eight-coordinated in a distorted square-antiprismatic mode (Fig. 1). The four ligands forming the square basal plane are water molecules [Ca—O = 2.531 (2) Å; Table 1]. The other basal plane is formed by four O atoms from four different rhenate(VII) anions [Ca—O = 2.359 (2) and 2.401 (2) Å; see Fig. 1 for the relevant symmetry operations]. The two basal planes are parallel. The central Ca²⁺ ion deviates by 1.245 (2) and 1.272 (2) Å from the two basal planes formed by the water and rhenate(VII) ligands, respectively. There are no chloride anions within the Ca²⁺ coordination sphere. This coordination pattern of the Ca²⁺ ion is comparable to that reported for calcium rhenate(VII) dihydrate (Baur & Kassner, 1992); however, in that crystal structure the Ca²⁺ ion does not lie on a special position and the distortion of the coordination polyhedron is greater than in the case of the title compound.

The packing (Fig. 2) comprises layers consisting of Ca²⁺ cations and chloride anions alternating with rhenate(VII) anion layers perpendicular to [010]. Neighbouring layers are joined by Ca—O coordination bonds. Within each Ca²⁺ cation–chloride anion layer, cation and anion columns can be distinguished (Fig. 3). Each Cl^- anion participates in four O—H···Cl hydrogen bonds where four symmetry-related water molecules act as donors (Fig. 3). Thus R⁴₂(8) structural motifs are formed (Etter et al., 1990). Each such motif consists of the following atoms: Cl1, H1, O1, H1(x, -y + 1, -z + 1), Cl1(-x + 1, -y + 1, z - 1/2), H1(-x + 1, -y + 1, -z + 1), O1(-x + 1, -y + 1, -z + 1) and H1(-x + 1, y, z).

Related literature

For related literature, see: Abakumov et al. (2001); Baur & Kassner (1992); Etter et al. (1990); Krebs & Hasse (1982); Matveeva et al. (1980); Picard et al. (1988); Todorov & Macicek (1995); Todorov et al. (1996).

S2. Experimental

The title compound was obtained in the reaction of calcium chloride with rhenic(VII) acid in aqueous solution. The crystals were obtained in the form of colourless, transparent blocks. A crystal suitable for X-ray analysis was cut from a larger crystal.

S3. Refinement

The water H atom was located in a difference Fourier map and refined isotropically. The highest peaks in the difference Fourier map are near atom Re1 (the peak of 3.33 e Å^-3 at 0.56 Å from Re1 and the peak of 1.83 e Å^-3 at 0.61 Å from Re1).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Bruker, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The coordination environement of the calcium ion. [Symmetry codes: (ii) -x, -y + 1, -z + 1; (iii) x, y, -z + 1/2; (v) -x, -y + 1, z - 1/2; (vii) -x + 1/2, -y + 1/2, z - 1/2; (viii) x - 1/2, -y + 1/2, -z + 1; (ix) -x, y, -z + 1/2.]
	Fig. 2. The crystal packing, showing layers of Ca^2+ cations and Cl^- anions along with ReO4^- anion layers perpendicular to [010]. The hydrogen bonds are indicated with dashed lines.
	Fig. 3. A view of the Ca^2+ cation and Cl^- anion layer along [010], showing cation and anion chains extending along [001] and the hydrogen-bonding scheme (dashed lines).

Calcium chloride rhenate(VII) dihydrate

Crystal data

CaCl(ReO4)·2H2O	F(000) = 656
Mr = 361.76	Dx = 3.641 Mg m^−3
Orthorhombic, Cmcm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2c 2	Cell parameters from 7496 reflections
a = 7.009 (2) Å	θ = 2–35°
b = 14.148 (4) Å	µ = 19.5 mm^−1
c = 6.656 (2) Å	T = 85 K
V = 660.0 (3) Å^3	Blocks, colourless
Z = 4	0.09 × 0.08 × 0.05 mm

Data collection

Kuma KM-4 CCD diffractometer	985 independent reflections
Radiation source: sealed tube	935 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.065
ω & ϕ scans	θmax = 37.5°, θmin = 5.2°
Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2006)	h = −11→12
Tmin = 0.265, Tmax = 0.423	k = −24→22
8292 measured reflections	l = −11→11

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.016	All H-atom parameters refined
wR(F^2) = 0.037	w = 1/[σ^2(Fo^2) + (0.0203P)^2 + 0.5702P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max = 0.001
985 reflections	Δρmax = 3.32 e Å^−3
35 parameters	Δρmin = −2.60 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0091 (3)

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

	x	y	z	Uiso*/Ueq
Re1	0	0.242666 (9)	0.75	0.00391 (5)
Ca1	0	0.41009 (5)	0.25	0.00467 (11)
Cl1	0.5	0.38338 (6)	0.75	0.00865 (14)
O1	0.2028 (3)	0.5	0.5	0.0074 (3)
O2	0	0.31571 (14)	0.5423 (3)	0.0113 (4)
O3	0.1996 (3)	0.17157 (14)	0.75	0.0099 (4)
H1	0.264 (4)	0.462 (3)	0.539 (5)	0.021 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re1	0.00337 (7)	0.00457 (7)	0.00379 (7)	0	0	0
Ca1	0.0044 (3)	0.0055 (2)	0.0041 (3)	0	0	0
Cl1	0.0075 (3)	0.0093 (3)	0.0091 (4)	0	0	0
O1	0.0073 (8)	0.0067 (7)	0.0082 (8)	0	0	−0.0003 (6)
O2	0.0154 (10)	0.0096 (8)	0.0087 (8)	0	0	0.0037 (6)
O3	0.0058 (8)	0.0097 (8)	0.0144 (9)	0.0030 (6)	0	0

Geometric parameters (Å, º)

Re1—O2	1.726 (2)	Ca1—O3^i	2.401 (2)
Re1—O3	1.723 (2)	Ca1—Ca1^ii	4.189 (2)
Ca1—O1	2.531 (2)	O1—H1	0.74 (3)
Ca1—O2	2.359 (2)
O3—Re1—O2	110.45 (5)	O1—Ca1—O1^ii	68.33 (9)
O2—Ca1—O2^iii	111.07 (11)	O1—Ca1—O1^iii	82.20 (6)
O3^i—Ca1—O3^iv	122.48 (10)	O2—Ca1—O3^i	74.20 (4)
O1—Ca1—O1^v	119.67 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···Cl1	0.74 (3)	2.44 (3)	3.135 (2)	159 (4)