The two-dimensional thio­phosphate CsCrP₂S₇

The quaternary title compound, caesium chromium(III) hepta­thio­diphosphate(V), CsCrP₂S₇, has been synthesized using the reactive halide flux method. It is isotypic with other AMP₂S₇ (A = alkali metal; M = Cr, V or In) structures and consists of two-dimensional _∞²[CrP₂S₇]⁻ layers extending parallel to (001) which are separated from each other by Cs⁺ ions (symmetry 2). The layer is built up from slightly distorted octa­hedral [CrS₆] units (symmetry 2) and bent [P₂S₇] units consisting of two corner-sharing [PS₄] tetra­hedra. The [CrS₆] octa­hedra share two edges and two corners with the [PS₄] tetra­hedra. There are only van der Waals inter­actions present between the layers. The Cs⁺ ions are located in this van der Waals gap and stabilize the structure through weak ionic inter­actions. The classical charge balance of the title compound can be expressed as [Cs⁺][Cr³⁺][P⁵⁺]₂[S²⁻]_7.

Related literature

For AMP₂S₇-related quaternary thio­phosphates, see: Kopnin et al. (2000) for KMP₂S₇ (M = Cr, V, In); Durand et al. (1993) for RbVP₂S₇; Gutzmann et al. (2005) for CsVP₂S₇. For the related mixed-metallic phase KV_1-xCr_xP₂S₇, see: Sekizawa et al. (2004). Related structures were reported by Coste et al. (2001); Derstroff et al. (2002); Toffoli et al. (1982); Wang et al. (1989).

Experimental

Crystal data

• CrCsP₂S₇

• M_r = 471.34

• Monoclinic, C 2

• a = 8.5867 (7) Å

• b = 9.5461 (7) Å

• c = 6.7504 (6) Å

• β = 97.572 (3)°

• V = 548.50 (8) ų

• Z = 2

• Mo Kα radiation

• μ = 5.87 mm⁻¹

• T = 290 K

• 0.14 × 0.02 × 0.02 mm

Data collection

• Rigaku R-AXIS RAPID diffractometer

• Absorption correction: multi-scan (ABSCOR; Higashi, 1995) T_min = 0.608, T_max = 1.000

• 2714 measured reflections

• 1268 independent reflections

• 1052 reflections with I > 2σ(I)

• R_int = 0.039

Refinement

• R[F² > 2σ(F²)] = 0.029

• wR(F²) = 0.073

• S = 1.18

• 1268 reflections

• 52 parameters

• 1 restraint

• Δρ_max = 1.01 e Å⁻³

• Δρ_min = −1.09 e Å⁻³

• Absolute structure: Flack (1983), 593 Friedel pairs

• Flack parameter: −0.01 (3)

Table 1
Selected geometric parameters (Å, °)

Cr—S1	2.414 (2)
Cr—S2	2.440 (2)
Cr—S3^i	2.430 (2)
P—S1	2.025 (3)
P—S2	2.024 (3)
P—S3	2.012 (2)
P—S4	2.134 (2)

P^ii—S4—P	107.50 (14)
Symmetry codes: (i) ; (ii) -x+1, y, -z+1.

Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO; data reduction: RAPID-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: locally modified version of ORTEP (Johnson, 1965); software used to prepare material for publication: WinGX (Farrugia, 1999).

Supporting information

S1. Comment

During an attempt to prepare new chromium thiophosphates with the use of halide fluxes, a new compound was isolated. Here we report the synthesis and structure of the new layered quaternary thiophosphate, CsCrP₂S₇.

The title compound is a new member of the previously reported isotypic AMP₂S₇ family (A = alkali metal; M = Cr, V, or In) (Kopnin et al., 2000; Durand et al., 1993; Gutzmann et al., 2005, Sekizawa et al. , 2004). The structure of CsCrP₂S₇ consists of layers with composition _∞²[CrP₂S₇]^- which are composed of [CrS₆] octahedra and bent [P₂S₇^4-] units made up of two corner-sharing [PS₄] tetrahedra. As usually found in other chromium sulfides (Derstroff et al., 2002), each Cr atom is surrounded by six S atoms in a (slightly distorted) octahedral arrangement. In the title compound they share two edges and two corners with the [PS₄] tetrahedra to form the two-dimensional infinite layer extending parallel to (001) (Fig. 1). There are only van der Waals interactions between the layers and the Cs⁺ ions in this van der Waals gap stabilize the structure through weak ionic interactions (Fig. 2).

While both the [CrS₆] octahedron and the [PS₄] tetrahedron show angular distortions, the Cr—S and P—S distances are rather regular and in good agreement with those found in other related phases (e.g. Coste et al., 2001). Atom S4 is bridging two P atoms in the [P₂S₇^4-] units. The bridging P—S4 bond is longer than those of the terminal bonds, a characteristic feature for two condensed PS₄ tetrahedra (Toffoli et al., 1982) or PO₄ tetrahedra (Wang et al., 1989).

The Cs⁺ ion is surrounded by twelve S atoms if an arbitrarily choosen cut-off of 4.2 Å for the Cs—S bonding interactions is used. The anharmonic behavior of the alkali metal ion, as observed in the isotypic K or Rb analogues (Kopnin et al., 2000; Durand et al., 1993), is not found here. The harmonic behavior of the Cs⁺ ion in the title compound could be due to the larger ionic radius and hence to a larger coordination number (Gutzmann et al., 2005). The classical charge balance of the title compound can be expressed as [Cs⁺][Cr³⁺][[P⁵⁺]₂[S^2-]₇.

Related literature

For AMP₂S₇-related quaternary thiophosphates, see: Kopnin et al. (2000) for KMP₂S₇ (M = Cr, V, In); Durand et al. (1993) for RbVP₂S₇; Gutzmann et al. (2005) for CsVP₂S₇. For the related mixed-metallic phase KV_1-xCr_xP₂S₇, see: Sekizawa et al. (2004). Related structures were reported by Coste et al. (2001); Derstroff et al. (2002); Toffoli et al. (1982); Wang et al. (1989).

S2. Experimental

The title compound, CsCrP₂S₇, was prepared by the reaction of the elemental Cr, P and S with the use of the reactive alkali metal halide flux technique. A combination of the pure elements, Cr powder (CERAC 99.95%), P powder (CERAC 99.5%) and S powder (Aldrich 99.999%) were mixed in a fused silica tube in a molar ratio of Cr: P: S = 1: 2: 6 with CsCl/LiCl. The mass ratio of the reactants and the alkali halide flux was 1: 3. The tube was evacuated to 0.133 Pa, sealed and heated gradually (50 K/h) to 923 K, where it was kept for 72 h. The tube was cooled to 473 K at 3 K/h and then was quenched to room temperature. The excess halides were removed with distilled water and dark brown needle shaped crystals were obtained. The crystals are stable in air and water. Semi-qualitative analysis of the crystals with XRF indicated the presence of Cs, Cr, P, and S. No other element was detected.

S3. Refinement

A difference Fourier synthesis calculated with phase based on the final parameters shows that the highest residual electron density (1.01 e/ų) is 0.89 Šfrom the Cs site and the deepest hole (-1.09 e/ų) is 1.74 Šfrom the S3 site.

Computing details

Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: locally modified version of ORTEP (Johnson, 1965); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. The interconnection mode of the [CrS6] octahedron and the [P2S7^4-] units with the atom labelling scheme. Displacement ellipsoids are drawn at the 80% probability level.
	Fig. 2. A perspective view of CsCrP2S7 down the b axis showing the stacking of the layers. Filled, dark gray, pale gray, and open circles represent Cr, P, Cs, and S atoms, respectively. The Cs—S bonds are omitted for clarity. The displacement ellipsoids are drawn at the 80% probability level.

caesium chromium(III) heptathiodiphosphate(V)

Crystal data

CrCsP2S7	F(000) = 442
Mr = 471.34	Dx = 2.854 Mg m^−3
Monoclinic, C2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C 2y	Cell parameters from 10764 reflections
a = 8.5867 (7) Å	θ = 3.0–27.5°
b = 9.5461 (7) Å	µ = 5.87 mm^−1
c = 6.7504 (6) Å	T = 290 K
β = 97.572 (3)°	Needle, dark brown
V = 548.50 (8) Å^3	0.14 × 0.02 × 0.02 mm
Z = 2

Data collection

Rigaku R-AXIS RAPID diffractometer	1052 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
ω scans	θmax = 27.5°, θmin = 3.0°
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	h = −10→11
Tmin = 0.608, Tmax = 1.000	k = −12→12
2714 measured reflections	l = −8→8
1268 independent reflections

Refinement

Refinement on F^2	1 restraint
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0208P)^2 + 0.2322P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.029	(Δ/σ)max < 0.001
wR(F^2) = 0.073	Δρmax = 1.01 e Å^−3
S = 1.18	Δρmin = −1.09 e Å^−3
1268 reflections	Absolute structure: Flack (1983), 593 Friedel pairs
52 parameters	Absolute structure parameter: −0.01 (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.

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

	x	y	z	Uiso*/Ueq
Cs	0.5	0.39716 (9)	0	0.0432 (2)
Cr	0	0.48837 (14)	0.5	0.0198 (4)
P	0.3006 (2)	0.63947 (16)	0.4247 (3)	0.0188 (4)
S1	0.15938 (19)	0.51649 (17)	0.2337 (3)	0.0235 (4)
S2	0.1839 (2)	0.65997 (17)	0.6648 (3)	0.0272 (5)
S3	0.3619 (2)	0.81248 (18)	0.2834 (3)	0.0283 (5)
S4	0.5	0.5073 (3)	0.5	0.0218 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cs	0.0254 (4)	0.0753 (6)	0.0289 (4)	0	0.0042 (3)	0
Cr	0.0113 (8)	0.0170 (7)	0.0317 (10)	0	0.0048 (7)	0
P	0.0110 (9)	0.0179 (8)	0.0274 (11)	−0.0028 (6)	0.0022 (8)	−0.0004 (8)
S1	0.0149 (8)	0.0271 (9)	0.0291 (10)	−0.0051 (7)	0.0053 (8)	−0.0056 (8)
S2	0.0235 (11)	0.0249 (9)	0.0355 (12)	−0.0039 (7)	0.0127 (9)	−0.0090 (9)
S3	0.0258 (10)	0.0247 (9)	0.0319 (11)	−0.0102 (8)	−0.0056 (9)	0.0070 (9)
S4	0.0119 (11)	0.0249 (13)	0.0288 (15)	0	0.0039 (10)	0

Geometric parameters (Å, º)

Cr—S1^i	2.414 (2)	P—S1	2.025 (3)
Cr—S1	2.414 (2)	P—S2	2.024 (3)
Cr—S2	2.440 (2)	P—S3	2.012 (2)
Cr—S2^i	2.440 (2)	P—S4	2.134 (2)
Cr—S3^ii	2.430 (2)	S3—Cr^iv	2.430 (2)
Cr—S3^iii	2.430 (2)	S4—P^v	2.134 (2)
S1^i—Cr—S1	167.23 (10)	S3^iii—Cr—S2^i	166.77 (6)
S1^i—Cr—S3^ii	104.20 (7)	S2—Cr—S2^i	95.64 (10)
S1—Cr—S3^ii	84.74 (7)	S3—P—S2	119.23 (11)
S1^i—Cr—S3^iii	84.74 (7)	S3—P—S1	110.24 (12)
S1—Cr—S3^iii	104.20 (7)	S2—P—S1	104.37 (10)
S3^ii—Cr—S3^iii	92.60 (9)	S3—P—S4	110.27 (11)
S1^i—Cr—S2	88.98 (7)	S2—P—S4	109.45 (11)
S1—Cr—S2	82.44 (6)	S1—P—S4	101.73 (10)
S3^ii—Cr—S2	166.77 (6)	P—S1—Cr	86.60 (9)
S3^iii—Cr—S2	87.38 (7)	P—S2—Cr	85.93 (9)
S1^i—Cr—S2^i	82.44 (6)	P—S3—Cr^iv	114.79 (11)
S1—Cr—S2^i	88.98 (7)	P^v—S4—P	107.50 (14)
S3^ii—Cr—S2^i	87.38 (7)

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