K₂ScSn(AsO₄)₃: an arsenate-containing langbeinite

The title compound, dipotassium tri-μ-arsenato-scandium(III)tin(IV), is the first arsenate-containing langbeinite to be characterized by single-crystal methods and crystallizes in the aristotype P2₁3 cubic symmetry for this structure type in which the K⁺ ions and the octa­hedral scandium and tin cations lie on crystallographic threefold axes. The Sc^III and Sn^IV ions show a slight segregation over the two octa­hedral sites, with Sc/Sn populations of 0.582 (5):0.418 (5) on one site and 0.418 (5):0.582 (5) on the other. Bond-valence-sum calculations indicate that the K⁺ ions are significantly underbonded in this structure and the O atoms show large anisotropic displacement parameters, as also seen in other langbeinites. The crystal studied was found to be a merohedral twin with a 0.690 (16):0.310 (16) domain ratio.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

dipotassium tri-µ-arsenato-scandium(III)tin(IV)

Crystal data

K2ScSn(AsO4)3	Dx = 3.897 Mg m^−3
Mr = 658.62	Mo Kα radiation, λ = 0.71073 Å
Cubic, P213	Cell parameters from 6789 reflections
Hall symbol: P 2ac 2ab 3	θ = 3.4–33.8°
a = 10.3927 (4) Å	µ = 12.41 mm^−1
V = 1122.50 (7) Å^3	T = 298 K
Z = 4	Cube, colourless
F(000) = 1216	0.10 × 0.10 × 0.10 mm

Data collection

Bruker SMART1000 CCD diffractometer	1522 independent reflections
Radiation source: fine-focus sealed tube	1423 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.046
ω scans	θmax = 34.2°, θmin = 3.4°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −13→16
Tmin = 0.370, Tmax = 0.370	k = −16→13
12634 measured reflections	l = −16→16

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)] = 0.027	w = 1/[σ^2(Fo^2) + (0.025P)^2 + 7.5919P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.063	(Δ/σ)max = 0.002
S = 0.97	Δρmax = 1.43 e Å^−3
1522 reflections	Δρmin = −1.40 e Å^−3
60 parameters	Absolute structure: Flack (1983), 638 Friedel pairs
0 restraints	Absolute structure parameter: 0.310 (16)

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	Occ. (<1)
K1	0.56858 (12)	0.56858 (12)	0.56858 (12)	0.0332 (5)
K2	0.79379 (17)	0.79379 (17)	0.79379 (17)	0.0496 (7)
Sc1	0.36206 (4)	0.36206 (4)	0.36206 (4)	0.00854 (18)	0.582 (5)
Sn1	0.36206 (4)	0.36206 (4)	0.36206 (4)	0.00854 (18)	0.418 (5)
Sc2	0.08755 (3)	0.08755 (3)	0.08755 (3)	0.01036 (12)	0.418 (5)
Sn2	0.08755 (3)	0.08755 (3)	0.08755 (3)	0.01036 (12)	0.582 (5)
As1	0.27347 (4)	0.37301 (4)	0.04504 (4)	0.01062 (10)
O1	0.2652 (5)	0.4234 (5)	0.1973 (4)	0.0399 (12)
O2	0.4228 (4)	0.3475 (6)	−0.0029 (5)	0.0446 (12)
O3	0.2014 (6)	0.2312 (5)	0.0196 (6)	0.0551 (16)
O4	0.1963 (5)	0.4770 (5)	−0.0483 (5)	0.0479 (14)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0332 (5)	0.0332 (5)	0.0332 (5)	−0.0040 (5)	−0.0040 (5)	−0.0040 (5)
K2	0.0496 (7)	0.0496 (7)	0.0496 (7)	−0.0047 (7)	−0.0047 (7)	−0.0047 (7)
Sc1	0.00854 (18)	0.00854 (18)	0.00854 (18)	0.00023 (13)	0.00023 (13)	0.00023 (13)
Sn1	0.00854 (18)	0.00854 (18)	0.00854 (18)	0.00023 (13)	0.00023 (13)	0.00023 (13)
Sc2	0.01036 (12)	0.01036 (12)	0.01036 (12)	−0.00140 (11)	−0.00140 (11)	−0.00140 (11)
Sn2	0.01036 (12)	0.01036 (12)	0.01036 (12)	−0.00140 (11)	−0.00140 (11)	−0.00140 (11)
As1	0.01130 (18)	0.01061 (18)	0.00995 (18)	−0.00112 (13)	−0.00005 (13)	0.00235 (13)
O1	0.064 (3)	0.044 (3)	0.0122 (17)	0.026 (2)	−0.0073 (18)	−0.0090 (16)
O2	0.025 (2)	0.056 (3)	0.053 (3)	0.008 (2)	0.019 (2)	0.014 (2)
O3	0.073 (4)	0.039 (3)	0.054 (3)	−0.040 (3)	0.000 (3)	0.001 (2)
O4	0.055 (3)	0.054 (3)	0.035 (2)	0.027 (2)	0.002 (2)	0.029 (2)

Geometric parameters (Å, º)

K1—O2^i	2.980 (6)	Sc1—O1^x	2.086 (4)
K1—O2^ii	2.980 (6)	Sc1—O1^xi	2.086 (4)
K1—O2^iii	2.980 (6)	Sc1—O1	2.086 (4)
K1—O4^iv	3.046 (6)	Sc2—O3^xi	2.032 (5)
K1—O4^v	3.046 (6)	Sc2—O3	2.032 (5)
K1—O4^vi	3.046 (6)	Sc2—O3^x	2.032 (5)
K1—O3^i	3.068 (7)	Sc2—O2^xii	2.040 (4)
K1—O3^ii	3.068 (7)	Sc2—O2^xiii	2.040 (4)
K1—O3^iii	3.068 (7)	Sc2—O2^xiv	2.040 (4)
K2—O1^vii	2.956 (5)	As1—O2	1.651 (4)
K2—O1^viii	2.956 (5)	As1—O3	1.674 (5)
K2—O1^ix	2.956 (5)	As1—O4	1.659 (4)
K2—O4^i	3.185 (6)	As1—O1	1.669 (4)
K2—O4^ii	3.185 (6)	O1—K2^xv	2.956 (5)
K2—O4^iii	3.185 (6)	O2—Sc2^xvi	2.040 (4)
K2—O3^ii	3.322 (6)	O2—K1^xvii	2.980 (6)
K2—O3^i	3.322 (6)	O3—K1^xvii	3.068 (7)
K2—O3^iii	3.322 (6)	O3—K2^xvii	3.322 (6)
Sc1—O4^v	2.008 (4)	O4—Sc1^xviii	2.008 (4)
Sc1—O4^iv	2.008 (4)	O4—K1^xviii	3.046 (6)
Sc1—O4^vi	2.008 (4)	O4—K2^xvii	3.185 (6)
O2^i—K1—O2^ii	101.56 (14)	O3^ii—K2—O3^i	80.0 (2)
O2^i—K1—O2^iii	101.56 (14)	O1^vii—K2—O3^iii	162.73 (15)
O2^ii—K1—O2^iii	101.56 (14)	O1^viii—K2—O3^iii	103.12 (12)
O2^i—K1—O4^iv	95.01 (14)	O1^ix—K2—O3^iii	83.83 (16)
O2^ii—K1—O4^iv	100.72 (15)	O4^i—K2—O3^iii	127.21 (16)
O2^iii—K1—O4^iv	148.84 (14)	O4^ii—K2—O3^iii	82.30 (13)
O2^i—K1—O4^v	100.72 (15)	O4^iii—K2—O3^iii	48.02 (12)
O2^ii—K1—O4^v	148.84 (14)	O3^ii—K2—O3^iii	80.0 (2)
O2^iii—K1—O4^v	95.01 (14)	O3^i—K2—O3^iii	80.0 (2)
O4^iv—K1—O4^v	55.73 (14)	O4^v—Sc1—O4^iv	90.3 (2)
O2^i—K1—O4^vi	148.84 (14)	O4^v—Sc1—O4^vi	90.3 (2)
O2^ii—K1—O4^vi	95.01 (14)	O4^iv—Sc1—O4^vi	90.3 (2)
O2^iii—K1—O4^vi	100.72 (15)	O4^v—Sc1—O1^x	90.7 (2)
O4^iv—K1—O4^vi	55.73 (14)	O4^iv—Sc1—O1^x	88.89 (19)
O4^v—K1—O4^vi	55.73 (14)	O4^vi—Sc1—O1^x	178.7 (2)
O2^i—K1—O3^i	51.10 (12)	O4^v—Sc1—O1^xi	178.7 (2)
O2^ii—K1—O3^i	116.90 (17)	O4^iv—Sc1—O1^xi	90.7 (2)
O2^iii—K1—O3^i	51.46 (13)	O4^vi—Sc1—O1^xi	88.89 (19)
O4^iv—K1—O3^i	132.12 (16)	O1^x—Sc1—O1^xi	90.1 (2)
O4^v—K1—O3^i	94.07 (14)	O4^v—Sc1—O1	88.89 (19)
O4^vi—K1—O3^i	139.67 (16)	O4^iv—Sc1—O1	178.7 (2)
O2^i—K1—O3^ii	51.46 (13)	O4^vi—Sc1—O1	90.7 (2)
O2^ii—K1—O3^ii	51.10 (12)	O1^x—Sc1—O1	90.1 (2)
O2^iii—K1—O3^ii	116.90 (17)	O1^xi—Sc1—O1	90.1 (2)
O4^iv—K1—O3^ii	94.07 (14)	O3^xi—Sc2—O3	91.7 (2)
O4^v—K1—O3^ii	139.67 (16)	O3^xi—Sc2—O3^x	91.7 (2)
O4^vi—K1—O3^ii	132.12 (16)	O3—Sc2—O3^x	91.7 (2)
O3^i—K1—O3^ii	88.17 (17)	O3^xi—Sc2—O2^xii	80.4 (2)
O2^i—K1—O3^iii	116.90 (17)	O3—Sc2—O2^xii	169.4 (3)
O2^ii—K1—O3^iii	51.46 (13)	O3^x—Sc2—O2^xii	95.5 (2)
O2^iii—K1—O3^iii	51.10 (12)	O3^xi—Sc2—O2^xiii	169.4 (3)
O4^iv—K1—O3^iii	139.67 (16)	O3—Sc2—O2^xiii	95.5 (2)
O4^v—K1—O3^iii	132.12 (16)	O3^x—Sc2—O2^xiii	80.4 (2)
O4^vi—K1—O3^iii	94.07 (14)	O2^xii—Sc2—O2^xiii	93.3 (2)
O3^i—K1—O3^iii	88.17 (17)	O3^xi—Sc2—O2^xiv	95.5 (2)
O3^ii—K1—O3^iii	88.17 (17)	O3—Sc2—O2^xiv	80.4 (2)
O1^vii—K2—O1^viii	94.13 (16)	O3^x—Sc2—O2^xiv	169.4 (3)
O1^vii—K2—O1^ix	94.13 (16)	O2^xii—Sc2—O2^xiv	93.3 (2)
O1^viii—K2—O1^ix	94.13 (16)	O2^xiii—Sc2—O2^xiv	93.3 (2)
O1^vii—K2—O4^i	55.52 (11)	O2—As1—O3	103.4 (3)
O1^viii—K2—O4^i	82.43 (14)	O2—As1—O4	112.5 (3)
O1^ix—K2—O4^i	148.83 (16)	O3—As1—O4	105.3 (3)
O1^vii—K2—O4^ii	82.43 (14)	O2—As1—O1	112.7 (3)
O1^viii—K2—O4^ii	148.83 (16)	O3—As1—O1	113.7 (3)
O1^ix—K2—O4^ii	55.52 (11)	O4—As1—O1	109.0 (2)
O4^i—K2—O4^ii	119.04 (3)	As1—O1—Sc1	131.1 (3)
O1^vii—K2—O4^iii	148.83 (16)	As1—O1—K2^xv	109.7 (2)
O1^viii—K2—O4^iii	55.52 (11)	Sc1—O1—K2^xv	103.26 (17)
O1^ix—K2—O4^iii	82.43 (14)	As1—O2—Sc2^xvi	150.0 (3)
O4^i—K2—O4^iii	119.04 (3)	As1—O2—K1^xvii	104.7 (2)
O4^ii—K2—O4^iii	119.04 (3)	Sc2^xvi—O2—K1^xvii	101.41 (19)
O1^vii—K2—O3^ii	83.83 (16)	As1—O3—Sc2	148.5 (4)
O1^viii—K2—O3^ii	162.73 (15)	As1—O3—K1^xvii	100.6 (3)
O1^ix—K2—O3^ii	103.12 (12)	Sc2—O3—K1^xvii	98.8 (2)
O4^i—K2—O3^ii	82.30 (13)	As1—O3—K2^xvii	88.6 (2)
O4^ii—K2—O3^ii	48.02 (12)	Sc2—O3—K2^xvii	119.6 (2)
O4^iii—K2—O3^ii	127.21 (16)	K1^xvii—O3—K2^xvii	78.65 (15)
O1^vii—K2—O3^i	103.12 (12)	As1—O4—Sc1^xviii	163.7 (4)
O1^viii—K2—O3^i	83.83 (16)	As1—O4—K1^xviii	95.9 (2)
O1^ix—K2—O3^i	162.73 (15)	Sn1^xviii—O4—K1^xviii	92.40 (17)
O4^i—K2—O3^i	48.02 (13)	As1—O4—K2^xvii	93.6 (2)
O4^ii—K2—O3^i	127.21 (16)	Sc1^xviii—O4—K2^xvii	97.83 (19)
O4^iii—K2—O3^i	82.30 (13)	K1^xviii—O4—K2^xvii	104.82 (18)
O2—As1—O1—Sc1	−43.1 (5)	O4—As1—O3—K2^xvii	44.5 (3)
O3—As1—O1—Sc1	74.2 (5)	O1—As1—O3—K2^xvii	163.82 (19)
O4—As1—O1—Sc1	−168.6 (4)	O3^xi—Sc2—O3—As1	−74.4 (6)
O2—As1—O1—K2^xv	86.4 (3)	O3^x—Sc2—O3—As1	17.4 (7)
O3—As1—O1—K2^xv	−156.4 (3)	O2^xii—Sc2—O3—As1	−115.6 (13)
O4—As1—O1—K2^xv	−39.2 (3)	O2^xiii—Sc2—O3—As1	97.8 (8)
O4^v—Sc1—O1—As1	165.5 (5)	O2^xiv—Sc2—O3—As1	−169.7 (8)
O4^vi—Sc1—O1—As1	75.2 (4)	O3^xi—Sc2—O3—K1^xvii	53.0 (3)
O1^x—Sc1—O1—As1	−103.8 (3)	O3^x—Sc2—O3—K1^xvii	144.74 (17)
O1^xi—Sc1—O1—As1	−13.7 (5)	O2^xii—Sc2—O3—K1^xvii	11.8 (14)
O4^v—Sc1—O1—K2^xv	33.9 (2)	O2^xiii—Sc2—O3—K1^xvii	−134.8 (2)
O4^vi—Sc1—O1—K2^xv	−56.4 (2)	O2^xiv—Sc2—O3—K1^xvii	−42.3 (2)
O1^x—Sc1—O1—K2^xv	124.6 (3)	O3^xi—Sc2—O3—K2^xvii	134.8 (4)
O1^xi—Sc1—O1—K2^xv	−145.3 (2)	O3^x—Sc2—O3—K2^xvii	−133.4 (4)
O3—As1—O2—Sn2^xvi	144.9 (7)	O2^xii—Sc2—O3—K2^xvii	93.6 (13)
O4—As1—O2—Sn2^xvi	31.8 (8)	O2^xiii—Sc2—O3—K2^xvii	−52.9 (3)
O1—As1—O2—Sn2^xvi	−91.8 (7)	O2^xiv—Sc2—O3—K2^xvii	39.6 (3)
O3—As1—O2—Sc2^xvi	144.9 (7)	O2—As1—O4—Sn1^xviii	−69.8 (12)
O4—As1—O2—Sc2^xvi	31.8 (8)	O3—As1—O4—Sn1^xviii	178.3 (11)
O1—As1—O2—Sc2^xvi	−91.8 (7)	O1—As1—O4—Sn1^xviii	55.9 (12)
O3—As1—O2—K1^xvii	−4.7 (3)	O2—As1—O4—Sc1^xviii	−69.8 (12)
O4—As1—O2—K1^xvii	−117.9 (3)	O3—As1—O4—Sc1^xviii	178.3 (11)
O1—As1—O2—K1^xvii	118.5 (2)	O1—As1—O4—Sc1^xviii	55.9 (12)
O2—As1—O3—Sc2	131.5 (8)	O2—As1—O4—K1^xviii	170.1 (2)
O4—As1—O3—Sc2	−110.3 (8)	O3—As1—O4—K1^xviii	58.2 (3)
O1—As1—O3—Sc2	9.0 (9)	O1—As1—O4—K1^xviii	−64.2 (3)
O2—As1—O3—K1^xvii	4.5 (3)	O2—As1—O4—K2^xvii	64.8 (3)
O4—As1—O3—K1^xvii	122.7 (2)	O3—As1—O4—K2^xvii	−47.1 (3)
O1—As1—O3—K1^xvii	−118.0 (2)	O1—As1—O4—K2^xvii	−169.5 (2)
O2—As1—O3—K2^xvii	−73.7 (2)

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