Cd₄As₂Br₃

Single crystals of Cd₄As₂Br₃ (tetra­cadmium biarsenide tri­bromide) were grown by a chemical transport reaction. The structure is isotypic with the members of the cadmium and mercury pnictidohalides family with general formula M₄A₂X₃ (M = Cd, Hg; A = P, As, Sb; X = Cl, Br, I) and contains two independent As atoms on special positions with site symmetry -3 and two independent Cd atoms, of which one is on a special position with site symmetry -3. The Cd₄As₂Br₃ structure consists of AsCd₄ tetra­hedra sharing vertices with isolated As₂Cd₆ octa­hedra that contain As–As dumbbells in the centre of the octahedron. The Br atoms are located in the voids of this three-dimensional arrangement and bridge the different polyhedra through Cd⋯Br contacts.

Related literature

For structural data of the title compound extracted from X-ray powder diffraction data, see: Suchow & Stemple (1963); Rebbah & Deschanvres (1981). For classification and bond character of cadmium and mercury pnictidohalides, see: Rebbah & Rebbah (1994). For the relationship between the crystal and electronic structures based on the Zintl–Klemn concept for inter­preting and predicting the properties of these phases, see: Shevelkov & Shatruk (2001). For isotypic cadmium pnictidohalides, see: Gallay et al. (1975); Kassama et al. (1994) and for isotypic mercury pnictidohalides, see: Labbé et al. (1989); Shevelkov et al. (1996).

Experimental

Crystal data

• Cd₄As₂Br₃

• M_r = 839.17

• Cubic,

• a = 12.625 (4) Å

• V = 2012.4 (6) ų

• Z = 8

• Mo Kα radiation

• μ = 26.70 mm⁻¹

• T = 150 K

• 0.21 × 0.20 × 0.17 mm

Data collection

• Bruker APEXII diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2001) T_min = 0.005, T_max = 0.011

• 6624 measured reflections

• 1485 independent reflections

• 1238 reflections with I > 2σ(I)

• R_int = 0.088

Refinement

• R[F² > 2σ(F²)] = 0.039

• wR(F²) = 0.092

• S = 1.09

• 1485 reflections

• 29 parameters

• Δρ_max = 1.93 e Å⁻³

• Δρ_min = −1.57 e Å⁻³

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012) and CRYSCAL (Roisnel, 2013).

Supporting information

S1. Comment

Le composé Cd₄As₂Br₃ a été étudié au préalable par diffraction des rayons X sur poudre (Suchow & Stemple, 1963; Rebbah & Deschanvres, 1981). Ce composé appartient à la famille des composés semi-conducteurs de formule générale M₄A₂X₃ (M = Cd, Hg; A = P, As, Sb; X = Cl, Br, I), connue sous le nom de halogénopnictures de cadmium et de mercure (Rebbah & Rebbah, 1994; Shevelkov & Shatruk, 2001). La principale caractéristique de ces composés polyanioniques est la présence de liaisons anion-anion (A—A). Dans le composé Cd₄As₂Br₃ il existe deux types d'atomes d'arsenic ayant une coordination tétraédrique légèrement déformée. Les atomes d'arsenic de type As1 sont entourés de trois atomes Cd1 et un atome As1 de même type formant ainsi un doublet As1₂. Les distances anion-anion As1—As1 [2.3945 (19) Å] et Cd1—As1 [2.5595 (5) Å] sont comparables à celles observées dans d'autres composés polyanioniques de la même famille: Cd₄As₂I₃ [As1—As1 = 2.397 (5) Å et Cd1—As1 = 2.574 (5) Å], Gallay et al. (1975); Hg₄As₂I₃ [As1—As1 = 2.415 (2) Å], Labbé et al. (1989); Hg₄As₂Br₃ [As1—As1 = 2.37 (2) Å], Shevelkov et al. (1996). Les angles Cd1—As1—Cd1 et As1—As1—Cd1 qui valent 107.99 (2)° et 110.91 (2)° respectivement, indiquent un tétraèdre légèrement distordu. Les deux tétraèdres correspondant à une même liaison As1—As1 forment un groupement octaédrique As(1)₂Cd₆. Les atomes d'arsenic de type As2 ne forment pas de paire anionique et sont entourés de quatre atomes de cadmium: un atome Cd2 à 2.5655 (13) Å et trois atomes Cd1 à 2.5400 (6) Å, ces distances sont très voisines de celles autour de l'atome As1. Le tétraèdre As2Cd₄ est aussi légèrement distordu avec des angles Cd1—As2—Cd1 et Cd1—As2—Cd2 de 118.414 (12)° et 97.29 (3)° respectivement. La charpente de cette structure est ainsi form\'ee par des octaèdres As1₂Cd₆ déterminant des files parallèles dans les trois directions. L'interconnexion des ces files est assurées par les tétraèdres As2Cd₄, déterminant des cavités occupées par les atomes de brome. Ces atomes de brome assurent la cohésion de la structure par l'intermédiaire de liaisons Cd—Br en reliant d'une part deux groupements octaédriques As1₂Cd₆ et d'autre part un groupement octaédrique As1₂Cd₆ avec un groupement tétraédrique As2Cd₄. La plus courte distance 2.7596 (7) Å est proche de celles trouvées dans Cd₄P₂Br₃ [2.733 (2) Å, Kassama et al. 1994] ou dans Cd₄PAsBr₃ [2.760 (5) Å, Rebbah & Deschanvres, 1981]. Enfin l'équilibre des charges dans ce composé peut s'écrire: Cd₄⁺²As1^-2As2^-3Br₃^-.

Related literature

For structural data of the title compound extracted from X-ray powder diffraction data, see: Suchow & Stemple (1963); Rebbah & Deschanvres (1981). For classification and bond character of cadmium and mercury pnictidohalides, see: Rebbah & Rebbah (1994). For the relationship between the crystal and electronic structures including the Zintl–Klemn approach for interpreting and predicting the properties of these phases, see: Shevelkov & Shatruk (2001). For isotypic cadmium pnictidohalides, see: Gallay et al. (1975); Kassama et al. (1994) and for isotypic mercury pnictidohalides, see: Labbé et al. (1989); Shevelkov et al. (1996).

S2. Experimental

Les cristaux de Cd₄As₂Br₃ ont été préparés par transport en phase vapeur à partir d'un mélange stoechiométrique des éléments Cd, As et de CdBr₂. Le mélange est broyé puis introduit dans un tube en quartz scellé; des cristaux de couleur rouge foncée sont obtenus après un chauffage à 1073 K durant une semaine.

S3. Refinement

La structure a été déterminée par isotypie aux halogénopnictures de cadmium et de mercure de formule générale M₄A₂X₃ (M = Cd, Hg; A = P, As, Sb; X = Cl, Br, I). En fin d'affinement, la carte de densité électronique obtenue est: ρ_max = 1.932 e Å^-3 (localisée à 0.61 Å de C d1) et ρ_min = -1.571 e Å^-3 (localisée à 1.16 Å de Br1).

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012) and CRYSCAL (Roisnel, 2013).

Figures

	Fig. 1. Structure de Cd4As2Br3 montrant les files octaédriques As(1)2Cd6 (en gris) reliées par les tétraèdres As(2)Cd4 (en violet).
	Fig. 2. Environnement tétraèdrique distordu des atomes de As, avec un déplacement des ellipsoīdes à 95% de probabilité.

Tetracadmium diarsenide tribromide

Crystal data

Cd4As2Br3	Dx = 5.54 Mg m^−3
Mr = 839.17	Mo Kα radiation, λ = 0.71073 Å
Cubic, Pa3	Cell parameters from 1340 reflections
Hall symbol: -P 2ac 2ab 3	θ = 2.8–34.9°
a = 12.625 (4) Å	µ = 26.70 mm^−1
V = 2012.4 (6) Å^3	T = 150 K
Z = 8	Prism, red
F(000) = 2904	0.21 × 0.2 × 0.17 mm

Data collection

Bruker APEXII diffractometer	1238 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.088
CCD rotation images, thin slices scans	θmax = 34.9°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Bruker, 2001)	h = −17→15
Tmin = 0.005, Tmax = 0.011	k = −20→10
6624 measured reflections	l = −12→19
1485 independent reflections

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)] = 0.039	w = 1/[σ^2(Fo^2) + (0.0052P)^2 + 11.0012P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.092	(Δ/σ)max = 0.003
S = 1.09	Δρmax = 1.93 e Å^−3
1485 reflections	Δρmin = −1.57 e Å^−3
29 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00161 (12)

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
Cd1	0.02627 (4)	−0.01237 (4)	0.24906 (3)	0.00853 (12)
Cd2	0.21971 (3)	0.21971 (3)	0.21971 (3)	0.00892 (16)
As1	0.44525 (4)	0.44525 (4)	0.44525 (4)	0.00244 (19)
As2	0.10239 (5)	0.10239 (5)	0.10239 (5)	0.00298 (19)
Br1	0.18751 (5)	0.43173 (4)	0.26201 (5)	0.00566 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.0091 (2)	0.0118 (2)	0.00468 (19)	−0.00282 (14)	0.00066 (14)	0.00389 (14)
Cd2	0.00892 (16)	0.00892 (16)	0.00892 (16)	−0.00209 (14)	−0.00209 (14)	−0.00209 (14)
As1	0.00244 (19)	0.00244 (19)	0.00244 (19)	0.00002 (17)	0.00002 (17)	0.00002 (17)
As2	0.00298 (19)	0.00298 (19)	0.00298 (19)	0.00131 (18)	0.00131 (18)	0.00131 (18)
Br1	0.0036 (2)	0.0050 (2)	0.0083 (3)	0.00048 (17)	−0.00135 (18)	−0.00099 (18)

Geometric parameters (Å, º)

Cd1—As2	2.5400 (5)	As1—As1^vi	2.3945 (19)
Cd1—As1^i	2.5595 (5)	As1—Cd1^vii	2.5594 (9)
Cd1—Br1^ii	2.7933 (11)	As1—Cd1^viii	2.5595 (5)
Cd1—Br1^iii	2.9999 (8)	As1—Cd1^ix	2.5595 (5)
Cd2—As2	2.5655 (13)	As2—Cd1^v	2.5400 (6)
Cd2—Br1^iv	2.7596 (11)	As2—Cd1^iv	2.5400 (5)
Cd2—Br1	2.7596 (7)	Br1—Cd1^x	2.7932 (11)
Cd2—Br1^v	2.7596 (7)	Br1—Cd1^vii	2.9999 (8)
As2—Cd1—As1^i	140.50 (3)	Cd1^vii—As1—Cd1^viii	107.99 (2)
As2—Cd1—Br1^ii	118.24 (3)	As1^vi—As1—Cd1^ix	110.91 (2)
As1^i—Cd1—Br1^ii	97.55 (2)	Cd1^vii—As1—Cd1^ix	107.99 (2)
As2—Cd1—Br1^iii	106.62 (2)	Cd1^viii—As1—Cd1^ix	107.99 (2)
As1^i—Cd1—Br1^iii	91.57 (2)	Cd1^v—As2—Cd1	118.414 (12)
Br1^ii—Cd1—Br1^iii	85.291 (15)	Cd1^v—As2—Cd1^iv	118.414 (14)
As2—Cd2—Br1^iv	125.922 (19)	Cd1—As2—Cd1^iv	118.416 (17)
As2—Cd2—Br1	125.923 (19)	Cd1^v—As2—Cd2	97.29 (3)
Br1^iv—Cd2—Br1	89.07 (3)	Cd1—As2—Cd2	97.29 (3)
As2—Cd2—Br1^v	125.922 (17)	Cd1^iv—As2—Cd2	97.29 (3)
Br1^iv—Cd2—Br1^v	89.07 (3)	Cd2—Br1—Cd1^x	112.19 (2)
Br1—Cd2—Br1^v	89.07 (2)	Cd2—Br1—Cd1^vii	108.48 (2)
As1^vi—As1—Cd1^vii	110.91 (3)	Cd1^x—Br1—Cd1^vii	104.66 (2)
As1^vi—As1—Cd1^viii	110.91 (2)
As1^i—Cd1—As2—Cd1^v	90.34 (7)	Br1^iv—Cd2—As2—Cd1	129.443 (19)
Br1^ii—Cd1—As2—Cd1^v	−117.28 (4)	Br1—Cd2—As2—Cd1	−110.56 (2)
Br1^iii—Cd1—As2—Cd1^v	−23.66 (5)	Br1^v—Cd2—As2—Cd1	9.442 (19)
As1^i—Cd1—As2—Cd1^iv	−114.45 (6)	Br1^iv—Cd2—As2—Cd1^iv	−110.56 (2)
Br1^ii—Cd1—As2—Cd1^iv	37.93 (6)	Br1—Cd2—As2—Cd1^iv	9.443 (19)
Br1^iii—Cd1—As2—Cd1^iv	131.55 (4)	Br1^v—Cd2—As2—Cd1^iv	129.44 (2)
As1^i—Cd1—As2—Cd2	−12.05 (5)	As2—Cd2—Br1—Cd1^x	27.93 (3)
Br1^ii—Cd1—As2—Cd2	140.33 (2)	Br1^iv—Cd2—Br1—Cd1^x	163.39 (3)
Br1^iii—Cd1—As2—Cd2	−126.06 (2)	Br1^v—Cd2—Br1—Cd1^x	−107.53 (3)
Br1^iv—Cd2—As2—Cd1^v	9.443 (19)	As2—Cd2—Br1—Cd1^vii	143.055 (14)
Br1—Cd2—As2—Cd1^v	129.44 (2)	Br1^iv—Cd2—Br1—Cd1^vii	−81.486 (14)
Br1^v—Cd2—As2—Cd1^v	−110.557 (19)	Br1^v—Cd2—Br1—Cd1^vii	7.60 (2)

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