The alluaudite-like arsenate NaCaMg3(AsO4)3

Haj Abdallah, A.; Haddad, A.

doi:10.1107/S1600536808014633

inorganic compounds

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ISSN: 2056-9890

Volume 64| Part 6| June 2008| Page i36

doi:10.1107/S1600536808014633

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The alluaudite-like arsenate NaCaMg₃(AsO₄)₃

Anissa Haj Abdallah ^a ^* and Amor Haddad ^a

^aLaboratoire de Matériaux et Cristallochime, Institut Supérieur des Sciences Appliquées et Technologie de Mahdia, Avenue El Mourouj, Sidi Messoud 5111 Hiboun, Mahdia, Tunisia
^*Correspondence e-mail: haj_anissa@yahoo.fr

(Received 30 January 2008; accepted 14 May 2008; online 21 May 2008)

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, C 2/c
a = 11.880 (1) Å
b = 12.817 (1) Å
c = 6.741 (2) Å
β = 112.45 (1)°
V = 948.7 (3) Å³
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[F² > 2σ(F²)] = 0.022
wR(F²) = 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).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808014633/br2069sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808014633/br2069Isup2.hkl

checkCIF report

Comment top

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).

Related literature top

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 top

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.

Computing details top

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell refinement: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); 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).

Figures top

	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.

Sodium calcium trimagnesium tris(arsenate) top

Crystal data top

NaCaMg₃(AsO₄)₃	F(000) = 1048
M_r = 552.74	D_x = 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 = 2.4–28°
b = 12.817 (1) Å	µ = 11.36 mm⁻¹
c = 6.741 (2) Å	T = 293 K
β = 112.45 (1)°	Prismatic, colourless
V = 948.7 (3) Å³	0.6 × 0.2 × 0.15 mm
Z = 4

Data collection top

Enraf–Nonius CAD-4 diffractometer	1133 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.021
Graphite monochromator	θ_max = 28.0°, θ_min = 2.4°
ω/2θ scans	h = −15→14
Absorption correction: ψ scan (North et al., 1968)	k = −1→16
T_min = 0.110, T_max = 0.180	l = 0→8
1358 measured reflections	2 standard reflections every 120 min
1154 independent reflections	intensity decay: 0.4%

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.022	w = 1/[σ²(F_o²) + (0.0244P)² + 8.0874P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.060	(Δ/σ)_max < 0.001
S = 1.29	Δρ_max = 0.99 e Å⁻³
1154 reflections	Δρ_min = −1.00 e Å⁻³
100 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0071 (4)

Crystal data top

NaCaMg₃(AsO₄)₃	V = 948.7 (3) Å³
M_r = 552.74	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 11.880 (1) Å	µ = 11.36 mm⁻¹
b = 12.817 (1) Å	T = 293 K
c = 6.741 (2) Å	0.6 × 0.2 × 0.15 mm
β = 112.45 (1)°

Data collection top

Enraf–Nonius CAD-4 diffractometer	1133 reflections with I > 2σ(I)
Absorption correction: ψ scan (North et al., 1968)	R_int = 0.021
T_min = 0.110, T_max = 0.180	2 standard reflections every 120 min
1358 measured reflections	intensity decay: 0.4%
1154 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.022	100 parameters
wR(F²) = 0.060	0 restraints
S = 1.29	Δρ_max = 0.99 e Å⁻³
1154 reflections	Δρ_min = −1.00 e Å⁻³

Special details top

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 (Å²) top

	x	y	z	U_iso*/U_eq	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 (Å²) top

	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, º) top

As1—O2	1.687 (2)	Na1—O1^ix	2.99 (3)
As1—O6	1.690 (2)	Na1—O1^viii	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—O6^viii	2.497 (6)
As2—O1	1.693 (2)	Ca1—O6^ix	2.497 (6)
As2—O5ⁱ	1.695 (2)	Ca1—O1^ix	2.85 (4)
As2—O5	1.695 (2)	Ca1—O1^viii	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—O5^x	2.346 (3)
Mg1—O4^iv	2.164 (3)	Ca2—O4^vii	2.453 (3)
Mg1—O4^v	2.164 (3)	Ca2—O4^xi	2.453 (3)
Mg2—O5	2.001 (3)	Ca2—O4^xii	2.538 (3)
Mg2—O3^vi	2.068 (3)	Ca2—O4^vi	2.538 (3)
Mg2—O6^vii	2.072 (3)	Ca2—O5ⁱ	2.872 (3)
Mg2—O2^v	2.077 (3)	Ca2—O5^xiii	2.872 (3)
Mg2—O1^v	2.098 (3)	Na2—O5	2.346 (3)
Mg2—O2ⁱ	2.163 (3)	Na2—O5^x	2.346 (3)
Na1—O6	2.428 (3)	Na2—O4^vii	2.453 (3)
Na1—O6ⁱⁱ	2.428 (3)	Na2—O4^xi	2.453 (3)
Na1—O6^viii	2.481 (4)	Na2—O4^xii	2.538 (3)
Na1—O6^ix	2.481 (4)	Na2—O4^vi	2.538 (3)
Na1—O3	2.91 (3)	Na2—O5ⁱ	2.872 (3)
Na1—O3ⁱⁱ	2.91 (3)	Na2—O5^xiii	2.872 (3)

O2—As1—O6	109.24 (12)	O6—Ca1—O6^ix	92.2 (3)
O2—As1—O3	111.91 (11)	O6ⁱⁱ—Ca1—O6^ix	86.1 (2)
O6—As1—O3	105.22 (12)	O6—Ca1—O1^ix	121.1 (13)
O2—As1—O4	106.26 (12)	O6ⁱⁱ—Ca1—O1^ix	70.7 (6)
O6—As1—O4	112.57 (12)	O6^viii—Ca1—O1^ix	83.7 (7)
O3—As1—O4	111.73 (12)	O6^ix—Ca1—O1^ix	110.2 (10)
O1ⁱ—As2—O1	112.96 (17)	O6—Ca1—O1^viii	70.7 (6)
O1ⁱ—As2—O5ⁱ	110.10 (13)	O6ⁱⁱ—Ca1—O1^viii	121.1 (13)
O1—As2—O5ⁱ	113.27 (12)	O6^viii—Ca1—O1^viii	110.2 (10)
O1ⁱ—As2—O5	113.27 (12)	O6^ix—Ca1—O1^viii	83.7 (7)
O1—As2—O5	110.10 (13)	O6ⁱⁱ—Ca1—O3	111.3 (13)
O5ⁱ—As2—O5	96.04 (18)	O6^viii—Ca1—O3	60.9 (6)
O3ⁱⁱ—Mg1—O3	112.20 (15)	O6^ix—Ca1—O3	105.3 (12)
O3ⁱⁱ—Mg1—O1ⁱⁱⁱ	86.41 (10)	O6—Ca1—O3ⁱⁱ	111.3 (13)
O3—Mg1—O1ⁱⁱⁱ	75.96 (9)	O6^viii—Ca1—O3ⁱⁱ	105.3 (12)
O3ⁱⁱ—Mg1—O1ⁱ	75.96 (9)	O6^ix—Ca1—O3ⁱⁱ	60.9 (6)
O3—Mg1—O1ⁱ	86.41 (10)	O3—Ca1—O3ⁱⁱ	70.2 (9)
O3—Mg1—O4^iv	87.51 (9)	O5—Ca2—O4^vii	74.30 (9)
O1ⁱⁱⁱ—Mg1—O4^iv	94.61 (10)	O5^x—Ca2—O4^vii	105.70 (9)
O1ⁱ—Mg1—O4^iv	111.02 (10)	O5—Ca2—O4^xi	105.70 (9)
O3ⁱⁱ—Mg1—O4^v	87.51 (9)	O5^x—Ca2—O4^xi	74.30 (9)
O3—Mg1—O4^v	159.81 (11)	O5—Ca2—O4^xii	103.17 (9)
O1ⁱⁱⁱ—Mg1—O4^v	111.02 (10)	O5^x—Ca2—O4^xii	76.83 (9)
O1ⁱ—Mg1—O4^v	94.61 (10)	O4^vii—Ca2—O4^xii	62.31 (10)
O4^iv—Mg1—O4^v	73.28 (14)	O4^xi—Ca2—O4^xii	117.69 (10)
O5—Mg2—O3^vi	108.84 (12)	O5—Ca2—O4^vi	76.83 (9)
O5—Mg2—O6^vii	92.76 (11)	O5^x—Ca2—O4^vi	103.17 (9)
O3^vi—Mg2—O6^vii	86.82 (11)	O4^vii—Ca2—O4^vi	117.69 (10)
O5—Mg2—O2^v	90.41 (11)	O4^xi—Ca2—O4^vi	62.31 (10)
O6^vii—Mg2—O2^v	101.79 (11)	O5—Ca2—O5ⁱ	56.66 (10)
O3^vi—Mg2—O1^v	77.62 (10)	O4^vii—Ca2—O5ⁱ	91.59 (8)
O6^vii—Mg2—O1^v	95.10 (11)	O4^xi—Ca2—O5ⁱ	88.41 (8)
O2^v—Mg2—O1^v	82.14 (10)	O4^xii—Ca2—O5ⁱ	64.46 (7)
O5—Mg2—O2ⁱ	82.74 (10)	O4^vi—Ca2—O5ⁱ	115.54 (7)
O3^vi—Mg2—O2ⁱ	90.36 (10)	O5^x—Ca2—O5^xiii	56.66 (10)
O2^v—Mg2—O2ⁱ	82.81 (10)	O4^vii—Ca2—O5^xiii	88.41 (8)
O1^v—Mg2—O2ⁱ	89.86 (10)	O4^xi—Ca2—O5^xiii	91.59 (8)
O6—Na1—O6^viii	86.76 (12)	O4^xii—Ca2—O5^xiii	115.54 (7)
O6ⁱⁱ—Na1—O6^viii	92.89 (13)	O4^vi—Ca2—O5^xiii	64.46 (7)
O6—Na1—O6^ix	92.89 (13)	O5—Na2—O4^vii	74.30 (9)
O6ⁱⁱ—Na1—O6^ix	86.76 (12)	O5^x—Na2—O4^vii	105.70 (9)
O6—Na1—O3	59.6 (5)	O5—Na2—O4^xi	105.70 (9)
O6ⁱⁱ—Na1—O3	116.0 (11)	O5^x—Na2—O4^xi	74.30 (9)
O6^viii—Na1—O3	63.1 (5)	O5—Na2—O4^xii	103.17 (9)
O6^ix—Na1—O3	109.6 (10)	O5^x—Na2—O4^xii	76.83 (9)
O6—Na1—O3ⁱⁱ	116.0 (11)	O4^vii—Na2—O4^xii	62.31 (10)
O6^viii—Na1—O3ⁱⁱ	109.6 (10)	O4^xi—Na2—O4^xii	117.69 (10)
O6^ix—Na1—O3ⁱⁱ	63.1 (5)	O5—Na2—O4^vi	76.83 (9)
O3—Na1—O3ⁱⁱ	73.7 (8)	O5^x—Na2—O4^vi	103.17 (9)
O6—Na1—O1^ix	116.3 (11)	O4^vii—Na2—O4^vi	117.69 (10)
O6ⁱⁱ—Na1—O1^ix	68.4 (5)	O4^xi—Na2—O4^vi	62.31 (10)
O6^viii—Na1—O1^ix	81.2 (6)	O4^vii—Na2—O5ⁱ	91.59 (8)
O6^ix—Na1—O1^ix	106.4 (9)	O4^xi—Na2—O5ⁱ	88.41 (8)
O6—Na1—O1^viii	68.4 (5)	O4^xii—Na2—O5ⁱ	64.46 (7)
O6ⁱⁱ—Na1—O1^viii	116.3 (11)	O4^vi—Na2—O5ⁱ	115.54 (7)
O6^viii—Na1—O1^viii	106.4 (9)	O4^vii—Na2—O5^xiii	88.41 (8)
O6^ix—Na1—O1^viii	81.2 (6)	O4^xi—Na2—O5^xiii	91.59 (8)
O6—Ca1—O6^viii	86.1 (2)	O4^xii—Na2—O5^xiii	115.54 (7)
O6ⁱⁱ—Ca1—O6^viii	92.2 (3)	O4^vi—Na2—O5^xiii	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.

Experimental details

Crystal data
Chemical formula	NaCaMg₃(AsO₄)₃
M_r	552.74
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	293
a, b, c (Å)	11.880 (1), 12.817 (1), 6.741 (2)
β (°)	112.45 (1)
V (Å³)	948.7 (3)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	11.36
Crystal size (mm)	0.6 × 0.2 × 0.15

Data collection
Diffractometer	Enraf–Nonius CAD-4 diffractometer
Absorption correction	ψ scan (North et al., 1968)
T_min, T_max	0.110, 0.180
No. of measured, independent and observed [I > 2σ(I)] reflections	1358, 1154, 1133
R_int	0.021
(sin θ/λ)_max (Å⁻¹)	0.660

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.060, 1.29
No. of reflections	1154
No. of parameters	100
Δρ_max, Δρ_min (e Å⁻³)	0.99, −1.00

Computer programs: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992), MolEN (Fair, 1990), SHELXS86 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1998).

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