A new form of NaMnAsO4

Weil, M.; Veyer, T.

doi:10.1107/S2056989019008065

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Volume 75| Part 7| July 2019| Pages 969-971

https://doi.org/10.1107/S2056989019008065

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A new form of NaMnAsO₄

Matthias Weil ^a ^* and Théo Veyer ^b

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, TU Wien, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria, and ^bIUT Bordeaux 1, 15 Rue Naudet, 33175 Gradignan, France
^*Correspondence e-mail: matthias.weil@tuwien.ac.at

Edited by A. Van der Lee, Université de Montpellier II, France (Received 28 May 2019; accepted 5 June 2019; online 7 June 2019)

A new form of NaMnAsO₄, sodium manganese(II) orthoarsenate, has been obtained under hydrothermal conditions, and is referred to as the β-polymorph. In contrast to the previously reported orthorhombic α-polymorph that crystallizes in the olivine-type of structure and has one manganese(II) cation in a distorted octahedral coordination, the current β-polymorph contains two manganese(II) cations in [5]-coordination, intermediate between a square-pyramid and a trigonal bipyramid. In the crystal structure of β-NaMnAsO₄, four [MnO₅] polyhedra are linked through vertex- and edge-sharing into finite {Mn₄O₁₆} units strung into rows parallel to [100]. These units are linked through two distinct orthoarsenate groups into a framework structure with channels propagating parallel to the manganese oxide rows. Both unique sodium cations are situated inside the channels and exhibit coordination numbers of six and seven. β-NaMnAsO₄ is isotypic with one form of NaCoPO₄ and with NaCuAsO₄.

Keywords: crystal structure; dimorphism; structure comparison; hydrothermal synthesis.

CCDC reference: 1921163

1. Chemical context

Magnussonite is a rare manganese(II) arsenite mineral and has been described with an ideal formula of Mn^II₁₀As^III₆O₁₈(OH,Cl)₂ (Moore & Araki, 1979 ). In a recent project on hydrothermal crystal growth of phases in the system Mn^II/As^III/O (Priestner et al., 2018a ) and a precise structure refinement of magnussonite, it could be shown that the obtained synthetic material has a composition of Mn^II₃As^III₂O₆·1/3H₂O whereas naturally occurring material (type locality Långban, Sweden) is better described as Mn^II₃As^III₂O₆(Cu^II(OH,Cl)₂)_x (Priestner et al., 2018b ). Building on that knowledge, a subsequent project was started to incorporate divalent transition-metal cations under hydrothermal conditions into synthetic magnussonite for obtaining similar compositions to those in the natural material. In one of the batches, containing manganese(II) acetate, sodium hydroxide, nickel chloride and arsenic(III) oxide as the arsenic source, we observed a partial oxidation of arsenic to yield monoclinic NaMnAsO₄ as a by-product with arsenic in an oxidation state of +V. NaMnAsO₄ was reported previously, as obtained from a high-temperature synthesis in a molten salt medium (Ulutagay-Kartin et al., 2002 ). This form crystallizes in the orthorhombic system with space-group type Pnma and adopts an olivine-type of structure.

In the following, we refer to the previously reported orthorhombic polymorph (Ulutagay-Kartin et al., 2002) as the α-form, and the new monoclinic polymorph as the β-form of NaMnAsO₄.

2. Structural commentary

β-NaMnAsO₄ crystallizes isotypically with one of the three modifications of the phosphate NaCoPO₄ (Feng et al., 1997 ) and with the copper analogue NaCuAsO₄ (Ulutagay-Kartin et al., 2003 ). The asymmetric unit of β-NaMnAsO₄ comprises of two formula units, and the principal building units are two manganese(II) cations in [5]-coordination, two orthoarsenate anions AsO₄^3–, and two sodium cations in a six- and sevenfold coordination by oxygen (Fig. 1).

Figure 1
The crystal structure of β-NaMnAsO₄ in a projection along [ $[\overline{1}]$ 00]. [MnO₅] polyhedra are shown in blue, [AsO₄] tetrahedra in red, Na^I cations in green and O atoms in shaded grey. Displacement ellipsoids are drawn at the 90% probability level.

The τ₅ descriptor (Addison et al., 1984 ) was calculated as 0.59 for the polyhedron around Mn1 and 0.54 for that around Mn2, meaning that the shapes of the polyhedra are intermediate between a square pyramid (τ₅ = 0) and a trigonal bipyramid (τ₅ = 1). The Mn—O bond lengths range from 2.061 (3)–2.205 (3) Å whereby those involving Mn1 scatter in a greater range than those involving Mn2 (Table 1). Two [Mn2O₅] polyhedra are fused into a centrosymmetric dimer by sharing an edge. To each side of the dimer two [Mn1O₅] polyhedra are attached by sharing a common vertex, thus establishing a finite {Mn₄O₁₆} unit. In the crystal structure of the α-polymorph (Ulutagay-Kartin et al., 2002), the unique Mn^II site has a distorted octahedral environment with bond lengths ranging from 2.121 (2)–2.339 (2) Å. Here the [MnO₆] units are connected through sharing four of their vertices into perovskite-type sheets. The isolated {Mn₄O₁₆} units in the β-polymorph are strung into rows parallel to [100] and are connected into a three-dimensional framework structure by AsO₄^3– tetrahedra sharing common vertices. The As—O bond lengths (Table 1) are characteristic for isolated orthoarsenate groups, and their mean values of 1.692 Å (As1) and 1.676 Å (As2) conform with literature data (1.687 Å; Gagné & Hawthorne, 2018 ). This framework delimits channels parallel to [100] in which the two sodium cations are situated. They are surrounded by six (Na1) and seven (Na2) oxygen atoms, each displaying a distorted coordination polyhedron. Relevant Na—O distances are collated in Table 1. The results of bond-valence-sum calculations (Brown, 2002 ; Brese & O'Keeffe, 1991 ) are consistent with the expected oxidation states of +I for Na, +II for Mn, +V for As, and −II for O (values in valence units): Na1 = 1.03, Na2 = 0.95, Mn1 = 1.94, Mn2 = 1.98, As1 = 4.90, As2 = 5.12, O atoms = 1.83–2.16.

Table 1
Selected bond lengths (Å)

Na1—O6ⁱ	2.368 (3)	Mn1—O7	2.162 (3)
Na1—O1ⁱⁱ	2.407 (3)	Mn1—O3	2.205 (3)
Na1—O2ⁱⁱⁱ	2.411 (3)	Mn2—O2^v	2.095 (3)
Na1—O5ⁱⁱ	2.496 (3)	Mn2—O4^vii	2.124 (3)
Na1—O3ⁱ	2.526 (4)	Mn2—O1	2.139 (3)
Na1—O7^iv	2.547 (3)	Mn2—O8^v	2.150 (3)
Na2—O3	2.376 (3)	Mn2—O4^v	2.155 (3)
Na2—O2^v	2.409 (4)	As1—O2	1.683 (3)
Na2—O7ⁱ	2.539 (3)	As1—O5^vii	1.689 (3)
Na2—O5	2.540 (3)	As1—O1	1.694 (3)
Na2—O1	2.580 (4)	As1—O7	1.703 (3)
Na2—O6	2.712 (4)	As2—O6	1.647 (3)
Na2—O8	2.829 (4)	As2—O3^viii	1.676 (3)
Mn1—O6	2.061 (3)	As2—O4^ix	1.684 (3)
Mn1—O5^vi	2.144 (3)	As2—O8	1.696 (3)
Mn1—O8^vi	2.144 (3)
Symmetry codes: (i) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) -x, -y+1, -z+1; (iv) x, y+1, z; (v) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (vi) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (vii) $[-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (viii) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (ix) -x+1, -y+1, -z+1.

The previously reported α-form of NaMnAsO₄ has a calculated X-ray density D_x = 4.03 g cm⁻³ and thus is denser than the current β-form (3.95 g cm⁻³). Based on the rule of thumb that the denser polymorph is (in the majority of cases) the stable form, these values point to α-NaMnAsO₄ as the thermodynamically stable polymorph. This assumption is supported by the preparation conditions of the different polymorphs. The α-polymorph was obtained under high-temperature conditions (Ulutagay-Kartin et al., 2002) whereas the β-polymorph crystallized under much milder temperature conditions. As a result of the scarcity of β-NaMnAsO₄ material, a detailed investigation of the thermal behaviour was not conducted. However, a possible β → α phase transition would be of the reconstructive type because the building units in the two structures exhibit a completely different arrangement.

For a quantitative structural comparison of β-NaMnAsO₄ with the isotypic sodium copper(II) arsenate analogue, NaCuAsO₄ (Ulutagay-Kartin et al., 2003), the program compstru (de la Flor et al., 2016 ) available at the Bilbao Crystallographic Server (Aroyo et al., 2006 ) was used. The comparison revealed a degree of lattice distortion of 0.0170, the maximum distance between the atomic positions of paired atoms of 0.1834 Å for pair Na1, the arithmetic mean of all distances of 0.1150 Å, and the measure of similarity of 0.050. All these values show a high similarity between the two crystal structures. This is supported by the similar τ₅ values of 0.57 and 0.47 for the two copper(II) cations in NaCuAsO₄.

3. Synthesis and crystallization

A stoichiometric mixture of Mn(CH₃COO)₂·4H₂O, NaOH, As₂O₃ and NiCl₂ in the ratio 1:6:1:1/6 was loaded in a Teflon container that was filled with 3 ml of water to two-thirds of its volume. Then the container was sealed with a Teflon lid and placed in a steel autoclave that was heated at 483 K for five days. After cooling to room temperature, the solid material was filtered off, washed with mother liquor, water and ethanol and air-dried. The main phase identified by single crystal and powder X-ray diffraction was synthetic magnussonite, Mn₃As₂O₆·1/3H₂O (Priestner et al., 2018b). Synthetic sarkinite, a basic manganese(II) arsenate(V) with formula Mn₂AsO₄(OH) (Stock et al., 2002 ), and the title compound were also present as minor by-products, with β-NaMnAsO₄ typically appearing in the form of needles.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. Coordinates of isotypic NaCuAsO₄ (Ulutagay-Kartin et al., 2003) were standardized using the program STRUCTURE-TIDY (Gelato & Parthé, 1987 ) and then used as starting parameters for refinement. Free refinement of the site occupation factors for the two Mn sites resulted in a value of 1.000 (3) in each case, thus revealing no incorporation of Ni at these sites.

Table 2
Experimental details

Crystal data
Chemical formula	NaMnAsO₄
M_r	216.85
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	6.0917 (6), 11.4072 (10), 10.5008 (9)
β (°)	91.517 (3)
V (Å³)	729.44 (11)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	12.60
Crystal size (mm)	0.12 × 0.02 × 0.01

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.476, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	10811, 2336, 1682
R_int	0.075
(sin θ/λ)_max (Å⁻¹)	0.726

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.035, 0.059, 1.00
No. of reflections	2336
No. of parameters	128
Δρ_max, Δρ_min (e Å⁻³)	0.93, −0.94
Computer programs: APEX3 and SAINT (Bruker, 2015 ), SHELXL2017 (Sheldrick, 2015 ), ATOMS (Dowty, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1921163

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2056989019008065/vn2148sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019008065/vn2148Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: coordinates taken from isotypic compound; program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Sodium manganese(II) orthoarsenate top

Crystal data top

NaMnAsO₄	F(000) = 808
M_r = 216.85	D_x = 3.949 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 6.0917 (6) Å	Cell parameters from 1472 reflections
b = 11.4072 (10) Å	θ = 2.6–29.1°
c = 10.5008 (9) Å	µ = 12.60 mm⁻¹
β = 91.517 (3)°	T = 296 K
V = 729.44 (11) Å³	Needle, colourless
Z = 8	0.12 × 0.02 × 0.01 mm

Data collection top

Bruker APEXII CCD diffractometer	1682 reflections with I > 2σ(I)
ω– and φ–scans	R_int = 0.075
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 31.1°, θ_min = 3.4°
T_min = 0.476, T_max = 0.746	h = −8→8
10811 measured reflections	k = −16→16
2336 independent reflections	l = −15→15

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0138P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.035	(Δ/σ)_max < 0.001
wR(F²) = 0.059	Δρ_max = 0.93 e Å⁻³
S = 1.00	Δρ_min = −0.94 e Å⁻³
2336 reflections	Extinction correction: SHELXL2017 (Sheldrick, 2015), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
128 parameters	Extinction coefficient: 0.00083 (19)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
As1	0.12080 (7)	0.11305 (3)	0.33114 (4)	0.00717 (10)
As2	0.62792 (7)	0.35882 (3)	0.41290 (4)	0.00749 (10)
Mn1	0.61290 (11)	0.09632 (5)	0.23084 (6)	0.00943 (14)
Mn2	0.14942 (11)	0.12113 (5)	0.00555 (6)	0.00920 (14)
Na1	0.1190 (3)	0.84466 (15)	0.36519 (18)	0.0193 (4)
Na2	0.3740 (3)	0.36374 (17)	0.1217 (2)	0.0294 (5)
O1	0.1342 (5)	0.1909 (2)	0.1942 (3)	0.0135 (7)
O2	0.1143 (5)	0.2010 (2)	0.4596 (3)	0.0117 (6)
O3	0.5901 (5)	0.2026 (3)	0.0556 (3)	0.0148 (7)
O4	0.1471 (5)	0.5556 (2)	0.5782 (3)	0.0111 (6)
O5	0.1034 (5)	0.5259 (2)	0.1712 (3)	0.0123 (6)
O6	0.6572 (5)	0.2657 (2)	0.2946 (3)	0.0145 (7)
O7	0.3513 (5)	0.0291 (2)	0.3453 (3)	0.0117 (6)
O8	0.3980 (5)	0.4378 (2)	0.3788 (3)	0.0117 (6)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
As1	0.0078 (2)	0.0068 (2)	0.0069 (2)	−0.00017 (16)	−0.00021 (16)	−0.00042 (16)
As2	0.0079 (2)	0.0072 (2)	0.0073 (2)	−0.00031 (16)	−0.00027 (16)	0.00011 (16)
Mn1	0.0117 (3)	0.0073 (3)	0.0093 (3)	−0.0010 (2)	−0.0009 (2)	−0.0003 (2)
Mn2	0.0104 (3)	0.0079 (3)	0.0094 (3)	0.0007 (2)	0.0008 (2)	0.0000 (2)
Na1	0.0179 (10)	0.0133 (9)	0.0271 (11)	0.0000 (8)	0.0083 (8)	−0.0007 (8)
Na2	0.0195 (10)	0.0250 (11)	0.0432 (13)	0.0032 (8)	−0.0086 (9)	−0.0179 (9)
O1	0.0214 (17)	0.0099 (14)	0.0094 (17)	0.0012 (13)	0.0032 (13)	0.0014 (11)
O2	0.0176 (17)	0.0121 (14)	0.0055 (15)	0.0001 (13)	0.0038 (12)	−0.0022 (11)
O3	0.0245 (18)	0.0115 (15)	0.0082 (16)	0.0030 (13)	0.0001 (13)	0.0001 (12)
O4	0.0068 (15)	0.0102 (14)	0.0161 (17)	−0.0040 (12)	−0.0019 (12)	−0.0019 (12)
O5	0.0088 (16)	0.0123 (15)	0.0157 (17)	0.0025 (12)	−0.0002 (12)	−0.0013 (12)
O6	0.0217 (18)	0.0104 (15)	0.0115 (17)	−0.0022 (12)	0.0028 (13)	−0.0064 (12)
O7	0.0083 (15)	0.0127 (15)	0.0141 (16)	0.0028 (12)	0.0005 (12)	0.0015 (12)
O8	0.0075 (15)	0.0114 (15)	0.0161 (17)	0.0024 (12)	0.0005 (12)	0.0039 (12)

Geometric parameters (Å, º) top

Na1—O6ⁱ	2.368 (3)	Mn1—O7	2.162 (3)
Na1—O1ⁱⁱ	2.407 (3)	Mn1—O3	2.205 (3)
Na1—O2ⁱⁱⁱ	2.411 (3)	Mn2—O2^v	2.095 (3)
Na1—O5ⁱⁱ	2.496 (3)	Mn2—O4^vii	2.124 (3)
Na1—O3ⁱ	2.526 (4)	Mn2—O1	2.139 (3)
Na1—O7^iv	2.547 (3)	Mn2—O8^v	2.150 (3)
Na2—O3	2.376 (3)	Mn2—O4^v	2.155 (3)
Na2—O2^v	2.409 (4)	As1—O2	1.683 (3)
Na2—O7ⁱ	2.539 (3)	As1—O5^vii	1.689 (3)
Na2—O5	2.540 (3)	As1—O1	1.694 (3)
Na2—O1	2.580 (4)	As1—O7	1.703 (3)
Na2—O6	2.712 (4)	As2—O6	1.647 (3)
Na2—O8	2.829 (4)	As2—O3^viii	1.676 (3)
Mn1—O6	2.061 (3)	As2—O4^ix	1.684 (3)
Mn1—O5^vi	2.144 (3)	As2—O8	1.696 (3)
Mn1—O8^vi	2.144 (3)

O2—As1—O5^vii	109.07 (14)	O3—Na2—O6	61.90 (10)
O2—As1—O1	111.74 (14)	O2^v—Na2—O6	137.80 (12)
O5^vii—As1—O1	110.68 (15)	O7ⁱ—Na2—O6	79.02 (11)
O2—As1—O7	107.60 (15)	O5—Na2—O6	124.60 (12)
O5^vii—As1—O7	109.56 (14)	O1—Na2—O6	80.96 (11)
O1—As1—O7	108.11 (14)	O3—Na2—O8	119.67 (12)
O6—As2—O3^viii	115.17 (14)	O2^v—Na2—O8	141.48 (13)
O6—As2—O4^ix	108.13 (15)	O7ⁱ—Na2—O8	68.33 (10)
O3^viii—As2—O4^ix	108.90 (15)	O5—Na2—O8	66.72 (10)
O6—As2—O8	106.78 (15)	O1—Na2—O8	87.83 (11)
O3^viii—As2—O8	106.17 (15)	O6—Na2—O8	57.89 (9)
O4^ix—As2—O8	111.73 (14)	As1—O1—Mn2	126.51 (15)
O6—Mn1—O5^vi	95.67 (12)	As1—O1—Na1^vii	123.87 (15)
O6—Mn1—O8^vi	165.34 (12)	Mn2—O1—Na1^vii	94.27 (12)
O5^vi—Mn1—O8^vi	87.40 (11)	As1—O1—Na2	133.73 (16)
O6—Mn1—O7	104.14 (12)	Mn2—O1—Na2	88.43 (11)
O5^vi—Mn1—O7	101.37 (11)	Na1^vii—O1—Na2	74.38 (10)
O8^vi—Mn1—O7	89.23 (11)	As1—O2—Mn2^viii	139.26 (16)
O6—Mn1—O3	76.13 (11)	As1—O2—Na2^viii	110.78 (15)
O5^vi—Mn1—O3	129.69 (11)	Mn2^viii—O2—Na2^viii	94.20 (12)
O8^vi—Mn1—O3	90.86 (11)	As1—O2—Na1ⁱⁱⁱ	120.64 (15)
O7—Mn1—O3	128.90 (12)	Mn2^viii—O2—Na1ⁱⁱⁱ	95.30 (11)
O2^v—Mn2—O4^vii	99.50 (12)	Na2^viii—O2—Na1ⁱⁱⁱ	77.51 (11)
O2^v—Mn2—O1	81.14 (11)	As2^v—O3—Mn1	120.63 (15)
O4^vii—Mn2—O1	117.21 (12)	As2^v—O3—Na2	132.47 (17)
O2^v—Mn2—O8^v	103.27 (11)	Mn1—O3—Na2	101.81 (12)
O4^vii—Mn2—O8^v	103.81 (11)	As2^v—O3—Na1^vi	116.79 (15)
O1—Mn2—O8^v	137.57 (12)	Mn1—O3—Na1^vi	92.86 (12)
O2^v—Mn2—O4^v	170.23 (11)	Na2—O3—Na1^vi	78.27 (11)
O4^vii—Mn2—O4^v	78.69 (12)	As2^ix—O4—Mn2ⁱⁱ	120.06 (15)
O1—Mn2—O4^v	91.11 (11)	As2^ix—O4—Mn2^viii	123.30 (15)
O8^v—Mn2—O4^v	86.45 (11)	Mn2ⁱⁱ—O4—Mn2^viii	101.31 (12)
O6ⁱ—Na1—O1ⁱⁱ	85.20 (12)	As1ⁱⁱ—O5—Mn1ⁱ	115.32 (14)
O6ⁱ—Na1—O2ⁱⁱⁱ	145.14 (12)	As1ⁱⁱ—O5—Na1^vii	92.86 (13)
O1ⁱⁱ—Na1—O2ⁱⁱⁱ	69.73 (11)	Mn1ⁱ—O5—Na1^vii	144.25 (14)
O6ⁱ—Na1—O5ⁱⁱ	121.79 (12)	As1ⁱⁱ—O5—Na2	162.63 (17)
O1ⁱⁱ—Na1—O5ⁱⁱ	102.84 (12)	Mn1ⁱ—O5—Na2	81.48 (10)
O2ⁱⁱⁱ—Na1—O5ⁱⁱ	88.13 (11)	Na1^vii—O5—Na2	73.62 (10)
O6ⁱ—Na1—O3ⁱ	64.99 (11)	As2—O6—Mn1	146.46 (18)
O1ⁱⁱ—Na1—O3ⁱ	93.26 (11)	As2—O6—Na1^vi	111.42 (15)
O2ⁱⁱⁱ—Na1—O3ⁱ	91.88 (11)	Mn1—O6—Na1^vi	101.49 (12)
O5ⁱⁱ—Na1—O3ⁱ	162.80 (13)	As2—O6—Na2	99.17 (13)
O6ⁱ—Na1—O7^iv	85.65 (11)	Mn1—O6—Na2	95.37 (12)
O1ⁱⁱ—Na1—O7^iv	159.09 (13)	Na1^vi—O6—Na2	74.75 (11)
O2ⁱⁱⁱ—Na1—O7^iv	125.53 (12)	As1—O7—Mn1	111.73 (14)
O5ⁱⁱ—Na1—O7^iv	66.66 (10)	As1—O7—Na2^vi	165.60 (16)
O3ⁱ—Na1—O7^iv	99.82 (11)	Mn1—O7—Na2^vi	81.17 (10)
O3—Na2—O2^v	85.11 (12)	As1—O7—Na1^x	90.74 (12)
O3—Na2—O7ⁱ	104.26 (12)	Mn1—O7—Na1^x	139.29 (14)
O2^v—Na2—O7ⁱ	137.92 (14)	Na2^vi—O7—Na1^x	74.98 (10)
O3—Na2—O5	172.25 (14)	As2—O8—Mn1ⁱ	125.11 (15)
O2^v—Na2—O5	87.16 (12)	As2—O8—Mn2^viii	107.14 (14)
O7ⁱ—Na2—O5	81.95 (11)	Mn1ⁱ—O8—Mn2^viii	125.73 (13)
O3—Na2—O1	79.48 (11)	As2—O8—Na2	93.68 (12)
O2^v—Na2—O1	66.91 (11)	Mn1ⁱ—O8—Na2	74.88 (10)
O7ⁱ—Na2—O1	154.63 (13)	Mn2^viii—O8—Na2	118.54 (13)
O5—Na2—O1	96.92 (11)

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

Acknowledgements

The X-ray centre of the TU Wien is acknowledged for financial support and for providing access to the single-crystal and powder X-ray diffractometers. TV acknowledges the Erasmus + program for a grant during a student exchange programme.

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