K₃Al₂As₃O₁₂

Single crystals of K₃Al₂As₃O₁₂, tripotassium dialuminotriarsenate(V), were obtained unintentionally by the reaction of KAsO₃ with a corundum crucible at 973 K. The asymmetric unit contains three K, two Al, three As and 12 O atoms. The structure of the title compound is isotypic with those of other K₃M'₂X₃O₁₂ (M' = Al, Ga; X = P, As) structures and is made up of a three-dimensional network of corner-sharing [AlO₄] and [AsO₄] tetra­hedra. The three K⁺ cations are located in channels running along the [100], [001], [101] and [10] directions, exhibiting different coordination numbers of 9, 8 and 6, respectively. All corresponding [KO_x] polyhedra are considerably distorted.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](Al-O) = 0.001 Å
• R factor = 0.018
• wR factor = 0.039
• Data-to-parameter ratio = 53.2

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT163_ALERT_4_C Missing or Zero su (esd) on z-coordinate for ...        AS1
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          5
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600         16
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          2
PLAT915_ALERT_3_C Low Friedel Pair Coverage ......................         73 Perc.

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           45.12
           From the CIF: _reflns_number_total               9623
           Count of symmetry unique reflns         5761
           Completeness (_total/calc)            167.04%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      3862
           Fraction of Friedel pairs measured     0.670
           Are heavy atom types Z>Si present        yes
PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension .          3
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT033_ALERT_4_G Flack x Parameter Value Deviates from Zero .....      0.008
PLAT794_ALERT_5_G Note: Tentative Bond Valency for Al1     (III)         3.13
PLAT794_ALERT_5_G Note: Tentative Bond Valency for Al2     (III)         2.84

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   6 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   6 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   4 ALERT type 4 Improvement, methodology, query or suggestion
   4 ALERT type 5 Informative message, check

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S1. Comment

During crystal growth studies of KAsO₃, we inadvertently obtained single crystals with composition K₃Al₂As₃O₁₂ from an attacked corundum crucible. Many oxides with general formula M_xM'₂X₃O₁₂ crystallize with three-dimensional framework structures (Devi & Vidyasagar, 2000) and are of technological interest. Most notably, compounds crystallizing in the NASICON (Na₃Zr₂Si₂PO₁₂) structure type are excellent ion conductors and have been intensely studied. A recent review on compounds with the NASICON structure has been given by Anantharamulu et al. (2011).

The structure of K₃Al₂As₃O₁₂ is isotypic with the phosphate analogue K₃Al₂P₃O₁₂ (Devi & Vidyasagar, 2000), the mixed arsenate/phosphate solid solution K₃Al₂As_1.92P_1.08O₁₂ (Boughzala et al., 1997) and K₃Ga₂P₃O₁₂ (Beaurain et al., 2008; Yakubovich et al., 2008). Trithallium dialuminotriphosphate, Tl₃Al₂P₃O₁₂ (Devi & Vidyasagar, 2000), can be considered as isopointal to the title compound, because it features distinctly different coordinations of the Al sites and the cationic network due to the electron lone pairs of the Tl⁺ ions.

Whereas in the NASICON structure type the M' site is octahedrally and the X site tetrahedrally coordinated, in the title compound both sites exhibit a tetrahedral coordination. Two crystallographically different [AlO₄] and three [AlO₄] tetrahedra, all on general positions, are linked via their corners to a complex three-dimensional network, whereby [AlO₄] units connect only to [AsO₄] units and vice-versa. This network can be decomposed into undulating sheets normal to [010] (Al1, Al2, As1, As2) which are connected by [AsO₄] units (As3) (Fig. 1).

The three different K⁺ cations are located in channels running along the [100] and [001] (K1, K2) (Fig. 1) as well as the [101] and [101] (K3) (Fig. 2) directions. Considering K–O distances up to 3.5 Å as relevant for first coordination spheres, the K⁺ cations are coordinated by 9 (K1), 8 (K1) and 6 (K3) O atoms, respectively, all in the form of irregular [KO_x] polyhedra. The total bond valence sums (parameters: R₀ = 2.132 Å, b = 0.37 (Brown & Altermatt, 1985)), 1.08 (K1), 1.04 (K2) and 0.90 (K3) valence units (v.u.) are close to the expected value of 1 v.u. and point to a slight undersaturation of K3. The coordination of the K⁺ cations is very similar in all isotypic structures. The main difference in these structures pertains to the bond lengths of the XO₄ tetrahedra. Corresponding mean bond lengths are 1.746 Å for AlO₄ and 1.680 Å for AsO₄ tetrahedra in the title compound; 1.737 Å for AlO₄ and 1.527 Å for PO₄ tetrahedra in K₃Al₂P₃O₁₂; 1.730 Å for AlO₄ and 1.615 Å for (As/P)O₄ tetrahedra in K₃Al₂As_1.92P_1.08O₁₂; 1.816 Å for GaO₄ and 1.535 Å for PO₄ tetrahedra in K₃Ga₂P₃O₁₂.

Related literature

For a recent review on NASICON-type materials, see: Anantharamulu et al. (2011). For isotypic K₃M'₂X₃O₁₂ structures, see: Beaurain et al. (2008) and Yakubovich et al. (2008) for K₃Ga₂P₃O₁₂; Boughzala et al. (1997) for the solid solution K₃Al₂(As_1.92P_1.08)O₁₂; Devi & Vidyasagar (2000) for K₃Al₂P₃O₁₂. For the isopointal structure of Tl₃Al₂P₃O₁₂, see: Devi & Vidyasagar (2000). For background to the bond-valence method, see: Brown & Altermatt (1985).

S2. Experimental

K₂CO₃ and H₃AsO₄ were obtained commercially and used without purification. 10 g 80%_wt H₃AsO₄ were titrated against an aqueous K₂CO₃ solution using methyl red as indicator. The water was evaporated and the residue recrystallized from water to obtain KH₂AsO₄. This solid was then heated in a corundum crucible at 973 K, cooled to 633 K over 24 h and quenched. Few colourless crystals of the title compound were isolated from the reaction mixture.

S3. Refinement

The first refinement cycle was performed using the published atomic coordinates of K₃Al₂As_1.92P_1.08O₁₂ (Boughzala et al., 1997) as starting parameters.

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus (Bruker, 2008); program(s) used to solve structure: coordinates taken from an isotypic structure; program(s) used to refine structure: JANA2006 (Petříček et al., 2006); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The crystal structure of K3Al2As3O12 viewed down [100], showing sheets of corner-sharing [AsO4] and [AlO4] tetrahedra extending parallel to (010). Displacement ellipsoids are drawn at the 90% probability level.
	Fig. 2. The crystal structure of K3Al2As3O12 viewed down [101]. Displacement ellipsoids are drawn at the 90% probability level.

tripotassium dialuminotriarsenate(V)

Crystal data

K3Al2As3O12	F(000) = 1112
Mr = 588	Dx = 2.939 Mg m^−3
Orthorhombic, Pna21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2n	Cell parameters from 54411 reflections
a = 8.7943 (2) Å	θ = 3.3–44.8°
b = 17.4400 (2) Å	µ = 8.63 mm^−1
c = 8.6610 (3) Å	T = 100 K
V = 1328.36 (6) Å^3	Plate, colourless
Z = 4	0.10 × 0.06 × 0.01 mm

Data collection

Bruker APEXII CCD diffractometer	9623 independent reflections
Radiation source: X-ray tube	8606 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.038
ω and ϕ scans	θmax = 45.1°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −17→17
Tmin = 0.49, Tmax = 0.92	k = −34→34
52293 measured reflections	l = −15→17

Refinement

Refinement on F^2	Primary atom site location: isomorphous structure methods
R[F^2 > 2σ(F^2)] = 0.018	Weighting scheme based on measured s.u.'s w = 1/(σ^2(I) + 0.0004I^2)
wR(F^2) = 0.039	(Δ/σ)max = 0.003
S = 0.80	Δρmax = 0.33 e Å^−3
9623 reflections	Δρmin = −0.31 e Å^−3
181 parameters	Absolute structure: Flack (1983), 3882 Friedel pairs
0 restraints	Absolute structure parameter: 0.008 (3)
1 constraint

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

	x	y	z	Uiso*/Ueq
As1	0.156896 (11)	0.215743 (6)	0.0009	0.004155 (18)
As2	0.293241 (12)	0.313601 (6)	0.511929 (16)	0.004909 (19)
As3	0.236068 (12)	0.502941 (6)	0.085202 (18)	0.005355 (19)
K1	0.01017 (3)	0.402188 (14)	0.84037 (3)	0.00837 (4)
K2	0.95033 (3)	0.354962 (14)	0.30906 (3)	0.00818 (4)
K3	0.68161 (3)	0.488891 (15)	0.11580 (3)	0.01179 (5)
Al1	0.34851 (4)	0.34012 (2)	0.14668 (4)	0.00492 (7)
Al2	0.13204 (4)	0.16767 (2)	0.65562 (4)	0.00520 (7)
O1	0.29089 (10)	0.15184 (5)	0.03110 (9)	0.00824 (17)
O2	0.02014 (10)	0.20900 (5)	0.13689 (9)	0.00746 (16)
O3	0.21755 (9)	0.30785 (4)	0.00781 (10)	0.00643 (14)
O4	0.06929 (10)	0.20939 (5)	0.82779 (9)	0.00730 (16)
O5	0.17013 (13)	0.37287 (6)	0.58794 (12)	0.0139 (2)
O6	0.47459 (12)	0.34183 (7)	0.53518 (11)	0.0168 (2)
O7	0.27956 (11)	0.22138 (5)	0.57055 (11)	0.01044 (18)
O8	0.26654 (10)	0.30933 (6)	0.31927 (9)	0.00936 (18)
O9	0.07409 (11)	0.46866 (6)	0.15273 (11)	0.01076 (18)
O10	0.29028 (11)	0.57855 (5)	0.19818 (10)	0.00894 (17)
O11	0.23407 (11)	0.52699 (6)	0.90078 (10)	0.01074 (19)
O12	0.37999 (10)	0.43772 (5)	0.12022 (10)	0.00883 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
As1	0.00437 (3)	0.00356 (3)	0.00453 (3)	0.00007 (3)	−0.00035 (3)	−0.00027 (3)
As2	0.00554 (3)	0.00472 (4)	0.00447 (3)	−0.00042 (3)	0.00028 (3)	0.00036 (3)
As3	0.00642 (4)	0.00336 (3)	0.00628 (3)	−0.00018 (3)	−0.00018 (3)	−0.00019 (3)
K1	0.00698 (7)	0.01015 (8)	0.00797 (6)	−0.00039 (6)	0.00040 (5)	0.00102 (6)
K2	0.00765 (8)	0.00734 (8)	0.00955 (7)	0.00014 (6)	0.00017 (6)	0.00078 (6)
K3	0.01516 (10)	0.00792 (9)	0.01230 (8)	−0.00147 (7)	−0.00295 (7)	−0.00020 (6)
Al1	0.00487 (12)	0.00439 (12)	0.00550 (10)	−0.00023 (9)	−0.00019 (9)	−0.00024 (9)
Al2	0.00592 (12)	0.00438 (12)	0.00532 (10)	0.00071 (10)	−0.00068 (9)	−0.00031 (9)
O1	0.0078 (3)	0.0069 (3)	0.0101 (3)	0.0029 (2)	−0.0011 (2)	−0.0004 (2)
O2	0.0062 (3)	0.0094 (3)	0.0067 (2)	−0.0020 (2)	0.0017 (2)	−0.0006 (2)
O3	0.0075 (2)	0.0046 (2)	0.0072 (2)	−0.0014 (2)	−0.0019 (2)	0.0005 (2)
O4	0.0078 (3)	0.0089 (3)	0.0052 (2)	0.0016 (2)	−0.0019 (2)	−0.0019 (2)
O5	0.0193 (4)	0.0088 (3)	0.0138 (3)	0.0037 (3)	0.0083 (3)	−0.0016 (3)
O6	0.0101 (3)	0.0274 (5)	0.0130 (3)	−0.0102 (3)	−0.0069 (3)	0.0108 (3)
O7	0.0121 (3)	0.0056 (3)	0.0136 (3)	0.0006 (2)	0.0041 (2)	0.0026 (2)
O8	0.0094 (3)	0.0144 (4)	0.0043 (2)	−0.0031 (3)	−0.0001 (2)	0.0002 (2)
O9	0.0084 (3)	0.0083 (3)	0.0155 (3)	−0.0023 (2)	0.0031 (2)	0.0001 (3)
O10	0.0131 (3)	0.0043 (3)	0.0094 (3)	−0.0018 (2)	0.0003 (2)	−0.0010 (2)
O11	0.0138 (3)	0.0121 (4)	0.0063 (3)	0.0010 (3)	−0.0004 (2)	0.0016 (2)
O12	0.0085 (3)	0.0044 (3)	0.0136 (3)	0.0006 (2)	−0.0019 (2)	0.0002 (2)

Geometric parameters (Å, º)

K1—O1^i	2.7084 (9)	Al1—O8	1.7443 (9)
K1—O3^ii	2.8524 (8)	Al1—O12	1.7396 (9)
K1—O5	2.6496 (11)	Al2—O4	1.7485 (9)
K1—O9^ii	2.9964 (10)	Al2—O6^vii	1.7415 (11)
K1—O9^iii	2.8747 (10)	Al2—O7	1.7616 (10)
K1—O10^iii	2.9344 (10)	Al2—O10^viii	1.7373 (10)
K1—O11	2.9814 (10)	As1—O1	1.6429 (9)
K2—O1^iv	2.7885 (9)	As1—O2	1.6875 (8)
K2—O2^v	3.0134 (9)	As1—O3	1.6936 (8)
K2—O7^iv	3.0260 (10)	As1—O4^ix	1.6893 (8)
K2—O8^v	2.8939 (10)	As2—O5	1.6352 (10)
K2—O9^v	2.6362 (10)	As2—O6	1.6812 (11)
K2—O11^vi	2.7384 (10)	As2—O7	1.6909 (9)
K3—O1^iv	2.7360 (9)	As2—O8	1.6867 (8)
K3—O5^vi	2.7515 (10)	As3—O9	1.6519 (9)
K3—O11^vi	2.5921 (9)	As3—O10	1.7098 (9)
K3—O12	2.7989 (10)	As3—O11^ix	1.6515 (9)
Al1—O2^iv	1.7376 (9)	As3—O12	1.7285 (9)
Al1—O3	1.7578 (9)
O1^i—K1—O3^ii	86.82 (3)	O1^iv—K3—O5^vi	126.59 (3)
O1^i—K1—O5	144.51 (3)	O1^iv—K3—O11^vi	93.38 (3)
O1^i—K1—O9^ii	73.59 (3)	O1^iv—K3—O12	92.90 (3)
O1^i—K1—O9^iii	115.72 (3)	O5^vi—K3—O11^vi	92.38 (3)
O1^i—K1—O10^iii	69.80 (3)	O5^vi—K3—O12	136.86 (3)
O1^i—K1—O11	128.11 (3)	O11^vi—K3—O12	102.95 (3)
O3^ii—K1—O5	88.21 (3)	O2^iv—Al1—O3	112.21 (4)
O3^ii—K1—O9^ii	69.16 (3)	O2^iv—Al1—O8	104.42 (4)
O3^ii—K1—O9^iii	154.71 (3)	O2^iv—Al1—O12	109.74 (5)
O3^ii—K1—O10^iii	148.77 (2)	O3—Al1—O8	102.53 (4)
O3^ii—K1—O11	84.81 (2)	O3—Al1—O12	109.11 (4)
O5—K1—O9^ii	136.06 (3)	O8—Al1—O12	118.68 (5)
O5—K1—O9^iii	79.72 (3)	O4—Al2—O6^vii	107.43 (5)
O5—K1—O10^iii	98.85 (3)	O4—Al2—O7	111.59 (4)
O5—K1—O11	86.28 (3)	O4—Al2—O10^viii	108.39 (4)
O9^ii—K1—O9^iii	104.81 (3)	O6^vii—Al2—O7	112.68 (5)
O9^ii—K1—O10^iii	120.24 (3)	O6^vii—Al2—O10^viii	110.77 (6)
O9^ii—K1—O11	55.61 (2)	O7—Al2—O10^viii	105.95 (5)
O9^iii—K1—O10^iii	56.01 (3)	O1—As1—O2	110.66 (4)
O9^iii—K1—O11	72.39 (3)	O1—As1—O3	114.32 (4)
O10^iii—K1—O11	125.79 (3)	O1—As1—O4^ix	115.08 (4)
O1^iv—K2—O2^v	68.86 (2)	O2—As1—O3	105.42 (4)
O1^iv—K2—O7^iv	112.20 (3)	O2—As1—O4^ix	106.85 (4)
O1^iv—K2—O8^v	119.86 (2)	O3—As1—O4^ix	103.72 (4)
O1^iv—K2—O9^v	78.24 (3)	O5—As2—O6	113.25 (6)
O1^iv—K2—O11^vi	89.12 (3)	O5—As2—O7	115.67 (5)
O2^v—K2—O7^iv	95.73 (2)	O5—As2—O8	109.52 (5)
O2^v—K2—O8^v	65.61 (2)	O6—As2—O7	108.07 (5)
O2^v—K2—O9^v	107.28 (3)	O6—As2—O8	105.28 (4)
O2^v—K2—O11^vi	154.06 (3)	O7—As2—O8	104.19 (5)
O7^iv—K2—O8^v	109.45 (3)	O9—As3—O10	108.48 (5)
O7^iv—K2—O9^v	156.96 (3)	O9—As3—O11^ix	115.16 (5)
O7^iv—K2—O11^vi	79.62 (3)	O9—As3—O12	109.34 (4)
O8^v—K2—O9^v	79.97 (3)	O10—As3—O11^ix	111.13 (5)
O8^v—K2—O11^vi	140.08 (3)	O10—As3—O12	101.71 (4)
O9^v—K2—O11^vi	80.10 (3)	O11^ix—As3—O12	110.16 (5)

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