The alluaudite-like arsenate NaCaMg₃(AsO₄)₃

Abstract

The title compound, sodium calcium trimagnesium tris­(arsenate), an alluaudite-like arsenate, was prepared by solid-state reaction at high temperature. The structure is built up from edge-sharing MgO₆ octa­hedra in chains associated with the AsO₄ arsenate groups. The three-dimensional network leads to two different tunnels occupied statistically by Na⁺ and Ca²⁺. One As and one Mg atom lie on twofold rotation axes; one Na and one Ca are disordered over two sites with occupancies of 0.7 and 0.3 and these sites lie on a twofold rotation axis and an inversion centre, respectively.

Related literature

For the alluaudite structure type, see: Moore (1971 ▶); Yakubovitch et al. (1977 ▶); Cu_1.35Fe(PO₄)₃ (Warner et al., 1993 ▶); NaFe_3.67(PO₄)₃ (Korzenski et al., 1998 ▶). For related alluaudite-like arsenates, see: NaCo₃(AsO₄)(HAsO₄)₂ (Kwang-Hwa & Pei-Fen, 1994 ▶); NaCaCdMg₂(AsO₄)₃ (Khorari et al., 1997 ▶); Ag_1.49Mn_1.49Mn₂(AsO₄)₃ (Ayed et al., 2002 ▶); Na_1.72 Mn_3.28(AsO₄)₃ (Brahim et al. 2003 ▶). For related literature, see: Leroux et al. (1995 ▶).

Experimental

Crystal data

• NaCaMg₃(AsO₄)₃

• M _r = 552.74

• Monoclinic,

• a = 11.880 (1) Å

• b = 12.817 (1) Å

• c = 6.741 (2) Å

• β = 112.45 (1)°

• V = 948.7 (3) ų

• Z = 4

• Mo Kα radiation

• μ = 11.36 mm⁻¹

• T = 293 (2) K

• 0.6 × 0.2 × 0.15 mm

Data collection

• Enraf–Nonius CAD-4 diffractometer

• Absorption correction: ψ scan (North et al., 1968 ▶) T _min = 0.110, T _max = 0.180

• 1358 measured reflections

• 1154 independent reflections

• 1133 reflections with I > 2σ(I)

• R _int = 0.021

• 2 standard reflections frequency: 120 min intensity decay: 0.4%

Refinement

• R[F ² > 2σ(F ²)] = 0.022

• wR(F ²) = 0.060

• S = 1.29

• 1154 reflections

• 100 parameters

• Δρ_max = 0.99 e Å⁻³

• Δρ_min = −1.00 e Å⁻³

Data collection: CAD-4 EXPRESS (Duisenberg, 1992 ▶; Macíček & Yordanov, 1992 ▶); cell refinement: CAD-4 EXPRESS; data reduction: MolEN (Fair, 1990 ▶); program(s) used to solve structure: SHELXS86 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 1998 ▶); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Comment

The crystal structure of NaCaMg₃(AsO₄)₃ is closely related to the common structure type of the well known mineral Alluaudite with the general formula X(1)X(2)M(1)M(2)₂(PO₄)₃ (Moore, 1971; Yakubovitch et al., 1994). It can be described by a Mg₃(AsO₄)₃ framework built up by a complex arrangement of distorted MgO₆ octahedra, and AsO₄ tetrahedra. The projection of the structure in a polyhedral representation is presented in Fig. 1. It consists of Mg1O₆ and Mg2O₆ octahedra that share edges to form staggered chains stacked parallel to the [10–1] direction. Equivalent chains are linked together through the AsO₄ tetrahedra corners. As1O₄ connects two chains and thus two of its O atoms belong of the same chain. The As2O₄ tetrahedron shares his four oxygen summits with four different MgO₆ octahedra belonging to three adjacent chains, two belong to the same chain and the two others from two different chains. The arrangement of magnesium octahedra Mg1O₆ and Mg2O₆ in chains present a distortion, with the mean Mg1—O and Mg2—O distances 2.135Å and 2.079Å respectively. The O—Mg1—O angles range from 73.28° to 112.20°, whereas the O—Mg2—O angles vary between 77.62° to 108.84°. The two crystallographic distinct As atoms are surrounded by four O atoms with the mean distance of As1—O: 1.691Å and As2—O: 1.694 Å. This structural arrangement delimits two types of hexagonal tunnels, parallel to the c axis and located at (1/2, 0, z) and (0,0,z) respectively. Sodium Na1, Na2 and calcium Ca1, Ca2 cations are located in those channels. The structure is closely related to the alluaudite structure type. In NaCaMg₃(AsO₄)₃, the X(1) site at (1/2, 0, 0) is empty. Whereas the X(2) site at (0, 0, 0) contains 0.30 Na2 and 0.70 Ca2. The site in the tunnel at (0, 0, z) shifted from the X(2) site by ± 0.25 along z is occupied by Na1 and Ca1 with respectively the occupation number 0.70 and 0.30. There are a number of possible models for the cationic distribution and it's not possible to decide which is the best solution. We retain the solution with same amount of sodium and calcium. First, the occupancies of Na1 and Ca1 in the site shifted from X(2) were refined. Second, for the site X(2), the occupancies of Na2 and Ca2 were fixed to obtain the electroneutrality. For each two cations in the same site the atomic displacement parameters were maintained the same with the instruction EADP. The bond valence sum of the Na1, Na2, Ca2, Mg1, Mg2, As1 and As2 atoms are in a good agreement with their oxidation states (Brown & Altermatt, 1985). For the calcium Ca1 which occupy partialy the tunnel the bond valence sums is different (1.33).

Experimental

Single crystals of NaCaMg₃(AsO₄)₃ were prepared by a mixture of NaNO₃, CaCO₃, MgN₂O₆(H₂O)₆ and NH₄H₂AsO₄ with molar ratio of (1:1:2:3). The powder was ground, then heated in a porcelain crucible progressively until 1223 K. This temperature was held for 3 days. Then the mixture was cooled slowly to room temperature at 10 K/h. The product was washed with hot water. Prismatic and colorless crystals of the title compound were extracted. Their qualitative analysis by electron microscope probe revealed that it contains sodium, calcium, oxygen, arsenic and magnesium atoms.

Figures

Fig. 1.

Projection of the structure of NaCaMg3(AsO4)3 along [001] direction.

Fig. 2.

A view of a sheet showing the association mode of the MgO6 in chains with AsO4 tetrahedra shown with 50% probability displacement ellipsoids.

Crystal data

NaCaMg3(AsO4)3	F000 = 1048
Mr = 552.74	Dx = 3.870 Mg m−3
Monoclinic, C2/c	Mo Kα radiation λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 25 reflections
a = 11.880 (1) Å	θ = 2.4–28º
b = 12.817 (1) Å	µ = 11.36 mm−1
c = 6.741 (2) Å	T = 293 (2) K
β = 112.45 (1)º	Prismatic, colourless
V = 948.7 (3) Å3	0.6 × 0.2 × 0.15 mm
Z = 4

Data collection

Enraf–Nonius CAD-4 diffractometer	Rint = 0.021
Radiation source: fine-focus sealed tube	θmax = 28.0º
Monochromator: graphite	θmin = 2.4º
T = 293(2) K	h = −15→14
ω/2θ scans	k = −1→16
Absorption correction: ψ scan(North et al., 1968)	l = 0→8
Tmin = 0.110, Tmax = 0.180	2 standard reflections
1358 measured reflections	every 120 min
1154 independent reflections	intensity decay: 0.4%
1133 reflections with I > 2σ(I)

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ2(Fo2) + (0.0244P)2 + 8.0874P] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.022	(Δ/σ)max < 0.001
wR(F2) = 0.060	Δρmax = 0.99 e Å−3
S = 1.29	Δρmin = −1.00 e Å−3
1154 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
100 parameters	Extinction coefficient: 0.0071 (4)
Primary atom site location: structure-invariant direct methods

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)
As1	0.26904 (3)	0.38625 (2)	0.37969 (5)	0.00207 (13)
As2	0.5000	0.21057 (3)	0.2500	0.00248 (14)
Mg1	0.5000	0.23783 (13)	0.7500	0.0043 (3)
Mg2	0.78584 (10)	0.15824 (9)	0.37643 (18)	0.0030 (2)
Na1	0.5000	0.511 (3)	0.7500	0.019 (2)	0.70
Ca1	0.5000	0.523 (3)	0.7500	0.019 (2)	0.30
Ca2	0.5000	0.0000	0.0000	0.0132 (3)	0.70
Na2	0.5000	0.0000	0.0000	0.0132 (3)	0.30
O1	0.4635 (2)	0.28350 (19)	0.0247 (4)	0.0063 (5)
O2	0.2837 (2)	0.31609 (19)	0.1792 (4)	0.0061 (5)
O3	0.3415 (2)	0.32937 (19)	0.6218 (4)	0.0053 (5)
O4	0.1175 (2)	0.39767 (19)	0.3197 (4)	0.0074 (5)
O5	0.6086 (2)	0.1221 (2)	0.2626 (4)	0.0105 (5)
O6	0.3381 (2)	0.50307 (19)	0.3963 (4)	0.0082 (5)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
As1	0.00076 (18)	0.00152 (19)	0.00403 (19)	0.00028 (10)	0.00101 (12)	0.00027 (10)
As2	0.0017 (2)	0.0013 (2)	0.0040 (2)	0.000	0.00054 (16)	0.000
Mg1	0.0020 (7)	0.0036 (7)	0.0080 (7)	0.000	0.0027 (6)	0.000
Mg2	0.0021 (5)	0.0022 (5)	0.0053 (5)	0.0000 (4)	0.0022 (4)	−0.0001 (4)
Na1	0.0091 (8)	0.035 (7)	0.0131 (8)	0.000	0.0032 (7)	0.000
Ca1	0.0091 (8)	0.035 (7)	0.0131 (8)	0.000	0.0032 (7)	0.000
Ca2	0.0161 (6)	0.0036 (5)	0.0107 (5)	−0.0026 (4)	−0.0051 (5)	−0.0003 (4)
Na2	0.0161 (6)	0.0036 (5)	0.0107 (5)	−0.0026 (4)	−0.0051 (5)	−0.0003 (4)
O1	0.0039 (11)	0.0094 (11)	0.0060 (11)	0.0020 (9)	0.0022 (9)	0.0025 (9)
O2	0.0080 (11)	0.0064 (11)	0.0045 (11)	0.0004 (9)	0.0031 (9)	−0.0010 (8)
O3	0.0050 (10)	0.0072 (11)	0.0033 (11)	0.0043 (9)	0.0010 (8)	0.0022 (8)
O4	0.0006 (10)	0.0065 (11)	0.0142 (12)	0.0005 (8)	0.0016 (9)	0.0000 (9)
O5	0.0034 (11)	0.0071 (11)	0.0169 (13)	0.0038 (9)	−0.0007 (9)	−0.0040 (9)
O6	0.0089 (11)	0.0022 (10)	0.0138 (12)	−0.0025 (9)	0.0047 (10)	−0.0007 (9)

Geometric parameters (Å, °)

As1—O2	1.687 (2)	Na1—O1ix	2.99 (3)
As1—O6	1.690 (2)	Na1—O1viii	2.99 (3)
As1—O3	1.692 (2)	Ca1—O6	2.439 (5)
As1—O4	1.694 (2)	Ca1—O6ii	2.439 (5)
As2—O1i	1.693 (2)	Ca1—O6viii	2.497 (6)
As2—O1	1.693 (2)	Ca1—O6ix	2.497 (6)
As2—O5i	1.695 (2)	Ca1—O1ix	2.85 (4)
As2—O5	1.695 (2)	Ca1—O1viii	2.85 (4)
Mg1—O3ii	2.104 (2)	Ca1—O3	3.04 (4)
Mg1—O3	2.104 (2)	Ca1—O3ii	3.04 (4)
Mg1—O1iii	2.139 (2)	Ca2—O5	2.346 (3)
Mg1—O1i	2.139 (2)	Ca2—O5x	2.346 (3)
Mg1—O4iv	2.164 (3)	Ca2—O4vii	2.453 (3)
Mg1—O4v	2.164 (3)	Ca2—O4xi	2.453 (3)
Mg2—O5	2.001 (3)	Ca2—O4xii	2.538 (3)
Mg2—O3vi	2.068 (3)	Ca2—O4vi	2.538 (3)
Mg2—O6vii	2.072 (3)	Ca2—O5i	2.872 (3)
Mg2—O2v	2.077 (3)	Ca2—O5xiii	2.872 (3)
Mg2—O1v	2.098 (3)	Na2—O5	2.346 (3)
Mg2—O2i	2.163 (3)	Na2—O5x	2.346 (3)
Na1—O6	2.428 (3)	Na2—O4vii	2.453 (3)
Na1—O6ii	2.428 (3)	Na2—O4xi	2.453 (3)
Na1—O6viii	2.481 (4)	Na2—O4xii	2.538 (3)
Na1—O6ix	2.481 (4)	Na2—O4vi	2.538 (3)
Na1—O3	2.91 (3)	Na2—O5i	2.872 (3)
Na1—O3ii	2.91 (3)	Na2—O5xiii	2.872 (3)
O2—As1—O6	109.24 (12)	O6—Ca1—O6ix	92.2 (3)
O2—As1—O3	111.91 (11)	O6ii—Ca1—O6ix	86.1 (2)
O6—As1—O3	105.22 (12)	O6—Ca1—O1ix	121.1 (13)
O2—As1—O4	106.26 (12)	O6ii—Ca1—O1ix	70.7 (6)
O6—As1—O4	112.57 (12)	O6viii—Ca1—O1ix	83.7 (7)
O3—As1—O4	111.73 (12)	O6ix—Ca1—O1ix	110.2 (10)
O1i—As2—O1	112.96 (17)	O6—Ca1—O1viii	70.7 (6)
O1i—As2—O5i	110.10 (13)	O6ii—Ca1—O1viii	121.1 (13)
O1—As2—O5i	113.27 (12)	O6viii—Ca1—O1viii	110.2 (10)
O1i—As2—O5	113.27 (12)	O6ix—Ca1—O1viii	83.7 (7)
O1—As2—O5	110.10 (13)	O6ii—Ca1—O3	111.3 (13)
O5i—As2—O5	96.04 (18)	O6viii—Ca1—O3	60.9 (6)
O3ii—Mg1—O3	112.20 (15)	O6ix—Ca1—O3	105.3 (12)
O3ii—Mg1—O1iii	86.41 (10)	O6—Ca1—O3ii	111.3 (13)
O3—Mg1—O1iii	75.96 (9)	O6viii—Ca1—O3ii	105.3 (12)
O3ii—Mg1—O1i	75.96 (9)	O6ix—Ca1—O3ii	60.9 (6)
O3—Mg1—O1i	86.41 (10)	O3—Ca1—O3ii	70.2 (9)
O3—Mg1—O4iv	87.51 (9)	O5—Ca2—O4vii	74.30 (9)
O1iii—Mg1—O4iv	94.61 (10)	O5x—Ca2—O4vii	105.70 (9)
O1i—Mg1—O4iv	111.02 (10)	O5—Ca2—O4xi	105.70 (9)
O3ii—Mg1—O4v	87.51 (9)	O5x—Ca2—O4xi	74.30 (9)
O3—Mg1—O4v	159.81 (11)	O5—Ca2—O4xii	103.17 (9)
O1iii—Mg1—O4v	111.02 (10)	O5x—Ca2—O4xii	76.83 (9)
O1i—Mg1—O4v	94.61 (10)	O4vii—Ca2—O4xii	62.31 (10)
O4iv—Mg1—O4v	73.28 (14)	O4xi—Ca2—O4xii	117.69 (10)
O5—Mg2—O3vi	108.84 (12)	O5—Ca2—O4vi	76.83 (9)
O5—Mg2—O6vii	92.76 (11)	O5x—Ca2—O4vi	103.17 (9)
O3vi—Mg2—O6vii	86.82 (11)	O4vii—Ca2—O4vi	117.69 (10)
O5—Mg2—O2v	90.41 (11)	O4xi—Ca2—O4vi	62.31 (10)
O6vii—Mg2—O2v	101.79 (11)	O5—Ca2—O5i	56.66 (10)
O3vi—Mg2—O1v	77.62 (10)	O4vii—Ca2—O5i	91.59 (8)
O6vii—Mg2—O1v	95.10 (11)	O4xi—Ca2—O5i	88.41 (8)
O2v—Mg2—O1v	82.14 (10)	O4xii—Ca2—O5i	64.46 (7)
O5—Mg2—O2i	82.74 (10)	O4vi—Ca2—O5i	115.54 (7)
O3vi—Mg2—O2i	90.36 (10)	O5x—Ca2—O5xiii	56.66 (10)
O2v—Mg2—O2i	82.81 (10)	O4vii—Ca2—O5xiii	88.41 (8)
O1v—Mg2—O2i	89.86 (10)	O4xi—Ca2—O5xiii	91.59 (8)
O6—Na1—O6viii	86.76 (12)	O4xii—Ca2—O5xiii	115.54 (7)
O6ii—Na1—O6viii	92.89 (13)	O4vi—Ca2—O5xiii	64.46 (7)
O6—Na1—O6ix	92.89 (13)	O5—Na2—O4vii	74.30 (9)
O6ii—Na1—O6ix	86.76 (12)	O5x—Na2—O4vii	105.70 (9)
O6—Na1—O3	59.6 (5)	O5—Na2—O4xi	105.70 (9)
O6ii—Na1—O3	116.0 (11)	O5x—Na2—O4xi	74.30 (9)
O6viii—Na1—O3	63.1 (5)	O5—Na2—O4xii	103.17 (9)
O6ix—Na1—O3	109.6 (10)	O5x—Na2—O4xii	76.83 (9)
O6—Na1—O3ii	116.0 (11)	O4vii—Na2—O4xii	62.31 (10)
O6viii—Na1—O3ii	109.6 (10)	O4xi—Na2—O4xii	117.69 (10)
O6ix—Na1—O3ii	63.1 (5)	O5—Na2—O4vi	76.83 (9)
O3—Na1—O3ii	73.7 (8)	O5x—Na2—O4vi	103.17 (9)
O6—Na1—O1ix	116.3 (11)	O4vii—Na2—O4vi	117.69 (10)
O6ii—Na1—O1ix	68.4 (5)	O4xi—Na2—O4vi	62.31 (10)
O6viii—Na1—O1ix	81.2 (6)	O4vii—Na2—O5i	91.59 (8)
O6ix—Na1—O1ix	106.4 (9)	O4xi—Na2—O5i	88.41 (8)
O6—Na1—O1viii	68.4 (5)	O4xii—Na2—O5i	64.46 (7)
O6ii—Na1—O1viii	116.3 (11)	O4vi—Na2—O5i	115.54 (7)
O6viii—Na1—O1viii	106.4 (9)	O4vii—Na2—O5xiii	88.41 (8)
O6ix—Na1—O1viii	81.2 (6)	O4xi—Na2—O5xiii	91.59 (8)
O6—Ca1—O6viii	86.1 (2)	O4xii—Na2—O5xiii	115.54 (7)
O6ii—Ca1—O6viii	92.2 (3)	O4vi—Na2—O5xiii	64.46 (7)

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