Na₃Cr₂(AsO₄)₃: trisodium dichromium(III) triarsenate

Trisodium dichromium(III) triarsenate, Na₃Cr₂(AsO₄)₃, has been synthesized by a solid-state reaction and structurally characterized by single-crystal X-ray diffraction. It has the garnet structure type.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](As-O) = 0.002 Å
• R factor = 0.019
• wR factor = 0.039
• Data-to-parameter ratio = 12.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.406     0.508
          Tmin and Tmax expected:      0.286     0.445
          RR =      1.243
          Please check that your absorption correction is appropriate.

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      0.875
          Tmax scaled      0.445 Tmin scaled      0.355

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           29.88
         From the CIF: _reflns_number_total                216
         From the CIF: _diffrn_reflns_limit_ max hkl   17.   17.   10.
         From the CIF: _diffrn_reflns_limit_ min hkl    0.    0.    0.
         TEST1: Expected hkl limits for theta max
         Calculated maximum hkl   17.   17.   17.
         Calculated minimum hkl  -17.  -17.  -17.
          ALERT: Expected hkl max differ from CIF values


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

Until now, in the system Na₂O–Cr₂O₃–As₂O₅, only the structure compounds lying in the limiting binary system have been studied: NaCrO₂ (Ruedorff & Becker, 1977), CrAsO₄ (Attfield et al., 1987), Na₂As₄O₁₁ (Driss et al., 1988), NaAsO₃ (Liebau, 1956), Na₄As₂O₇ (Leung & Calvo, 1973) and Na₃AsO₄ (Palazzi & Remy, 1971).

To our knowledge, only one ternary compound, viz. Na₃Cr₂(AsO₄)₃ (Schwarz & Schmidt, 1972), has been reported, but its structure has not been determined. On investigating this system, we synthesized this arsenate and report here the synthesis and crystal structure determination.

S2. Experimental

The title compound was prepared as previously described by Schwarz & Schmidt (1972), starting from reagent-grade Na₂CO₃ (Fluka, 99%), (NH₄)₂Cr₂O₇ (Prolabo, 99%) and As₂O₃ (Hoping & Williams, 99.5%) mixed in stoichiometric ratios. The sample was heated first at 773 K for 6 h and the at 1173 K for 60 h and finally quenched to room temperature.

Computing details

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4(Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1.

trisodium dichrome (III) triarsenate

Crystal data

Na3Cr2(AsO4)3	Dx = 4.327 Mg m^−3
Mr = 589.73	Mo Kα radiation, λ = 0.71073 Å
Cubic, Ia3d	Cell parameters from 25 reflections
Hall symbol: -I 4bd 2c 3	θ = 10–14°
a = 12.188 (2) Å	µ = 13.50 mm^−1
V = 1810.6 (5) Å^3	T = 293 K
Z = 8	Polyhedral, green
F(000) = 1104	0.1 × 0.08 × 0.06 mm

Data collection

Enarf-Nonius CAD-4 diffractometer	194 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.021
Graphite monochromator	θmax = 29.9°, θmin = 4.1°
ω/2θ scans	h = 0→17
Absorption correction: ψ scan (North et al., 1968)	k = 0→17
Tmin = 0.406, Tmax = 0.508	l = 0→10
735 measured reflections	2 standard reflections every 120 min
216 independent reflections	intensity decay: 1.0%

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)] = 0.019	w = 1/[σ^2(Fo^2) + (0.0156P)^2 + 7.0122P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.039	(Δ/σ)max < 0.001
S = 1.14	Δρmax = 0.33 e Å^−3
216 reflections	Δρmin = −0.40 e Å^−3
18 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00326 (17)

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
As1	0.3750	0.0000	0.2500	0.00339 (18)
Cr1	0.2500	0.2500	0.2500	0.0034 (2)
Na1	0.1250	0.0000	0.2500	0.0112 (4)
O1	0.28819 (14)	−0.09814 (12)	0.29743 (13)	0.0064 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
As1	0.0037 (2)	0.0032 (2)	0.0032 (2)	0.000	0.000	0.000
Cr1	0.0034 (2)	0.0034 (2)	0.0034 (2)	0.00020 (16)	0.00020 (16)	0.00020 (16)
Na1	0.0064 (9)	0.0136 (6)	0.0136 (6)	0.000	0.000	0.0011 (7)
O1	0.0076 (8)	0.0046 (7)	0.0071 (8)	−0.0016 (6)	0.0017 (6)	0.0002 (5)

Geometric parameters (Å, º)

As1—O1^i	1.6983 (16)	Cr1—O1^viii	1.9942 (15)
As1—O1^ii	1.6983 (16)	Na1—O1^ix	2.3919 (17)
As1—O1	1.6984 (16)	Na1—O1^x	2.3919 (17)
As1—O1^iii	1.6984 (16)	Na1—O1^iii	2.3919 (17)
Cr1—O1^iv	1.9941 (15)	Na1—O1	2.3919 (17)
Cr1—O1^v	1.9941 (15)	Na1—O1^xi	2.5337 (17)
Cr1—O1^vi	1.9942 (15)	Na1—O1^xii	2.5337 (17)
Cr1—O1^iii	1.9942 (15)	Na1—O1^xiii	2.5337 (17)
Cr1—O1^vii	1.9942 (15)	Na1—O1^viii	2.5337 (17)
O1^i—As1—O1^ii	102.93 (11)	O1^x—Na1—O1	116.73 (7)
O1^i—As1—O1	112.84 (6)	O1^iii—Na1—O1	67.48 (7)
O1^ii—As1—O1	112.84 (6)	O1^ix—Na1—O1^xi	123.39 (3)
O1^i—As1—O1^iii	112.84 (6)	O1^x—Na1—O1^xi	70.40 (7)
O1^ii—As1—O1^iii	112.84 (6)	O1^iii—Na1—O1^xi	92.07 (4)
O1—As1—O1^iii	102.93 (11)	O1—Na1—O1^xi	75.46 (6)
O1^iv—Cr1—O1^v	180.0	O1^ix—Na1—O1^xii	70.40 (7)
O1^iv—Cr1—O1^vi	90.87 (7)	O1^x—Na1—O1^xii	123.39 (3)
O1^v—Cr1—O1^vi	89.13 (7)	O1^iii—Na1—O1^xii	75.46 (6)
O1^iv—Cr1—O1^iii	89.13 (7)	O1—Na1—O1^xii	92.07 (4)
O1^v—Cr1—O1^iii	90.87 (7)	O1^xi—Na1—O1^xii	165.15 (7)
O1^vi—Cr1—O1^iii	180.00 (9)	O1^ix—Na1—O1^xiii	92.07 (4)
O1^iv—Cr1—O1^vii	90.87 (7)	O1^x—Na1—O1^xiii	75.46 (6)
O1^v—Cr1—O1^vii	89.13 (7)	O1^iii—Na1—O1^xiii	123.39 (3)
O1^vi—Cr1—O1^vii	90.87 (7)	O1—Na1—O1^xiii	70.40 (7)
O1^iii—Cr1—O1^vii	89.13 (7)	O1^xi—Na1—O1^xiii	112.01 (8)
O1^iv—Cr1—O1^viii	89.13 (7)	O1^xii—Na1—O1^xiii	70.04 (8)
O1^v—Cr1—O1^viii	90.87 (7)	O1^ix—Na1—O1^viii	75.46 (6)
O1^vi—Cr1—O1^viii	89.13 (7)	O1^x—Na1—O1^viii	92.07 (4)
O1^iii—Cr1—O1^viii	90.87 (7)	O1^iii—Na1—O1^viii	70.40 (7)
O1^vii—Cr1—O1^viii	180.00 (9)	O1—Na1—O1^viii	123.39 (3)
O1^ix—Na1—O1^x	67.48 (7)	O1^xi—Na1—O1^viii	70.04 (8)
O1^ix—Na1—O1^iii	116.73 (7)	O1^xii—Na1—O1^viii	112.01 (8)
O1^x—Na1—O1^iii	158.94 (7)	O1^xiii—Na1—O1^viii	165.15 (7)
O1^ix—Na1—O1	158.94 (7)

Symmetry codes: (i) −x+3/4, z−1/4, −y+1/4; (ii) −x+3/4, −z+1/4, y+1/4; (iii) x, −y, −z+1/2; (iv) z, −x+1/2, y+1/2; (v) −z+1/2, x, −y; (vi) −x+1/2, y+1/2, z; (vii) y+1/2, z, −x+1/2; (viii) −y, −z+1/2, x; (ix) −x+1/4, z−1/4, y+1/4; (x) −x+1/4, −z+1/4, −y+1/4; (xi) y+1/4, x−1/4, −z+3/4; (xii) y+1/4, −x+1/4, z−1/4; (xiii) −y, z−1/2, −x+1/2.