Synthesis and crystal structure of Na₄Ni₇(AsO₄)₆

The title compound, tetra­sodium hepta­nickel hexa­arsenate, was obtained by ceramic synthesis and crystallizes in the monoclinic space group C2/m. The asymmetric unit contains seven Ni atoms of which two have site symmetry 2/m and three site symmetry 2, four As atoms of which two have site symmetry m and two site symmetry 2, three Na atoms of which two have site symmetry 2, and fifteen O atoms of which four have site symmetry m. The structure of Na₄Ni₇(AsO₄)₆ is made of layers of Ni octa­hedra and As tetra­hedra assembled in sheets parallel to the bc plane. These layers are inter­connected by corner-sharing between NiO₆ octa­hedra and AsO₄ tetra­hedra. This linkage creates tunnels running along the c axis in which the Na atoms are located. This arrangement is similar to the one observed in Na₄Ni₇(PO₄)₆, but the layers of the two compounds are slightly different because of the disorder of one of the Ni sites in the structure of the title compound.

1. Chemical context

Although the structures of transition metal phosphates have been widely investigated during the last decades, very little work has been done on comparable arsenates due to the toxicity of arsenic. The latter phases can exhibit, however, peculiar properties. BaCo₂(AsO₄)₂ is a good example of a quasi-2D system with a magnetically frustrated honeycomb lattice (Regnault et al., 1977). BaCoAs₂O₇ appears as the first example of a magnetization step promoted by a structural modulation (David et al., 2013a). LiCoAsO₄ shows reversible electrochemical activity at high potential (Satya Kishore & Varadaraju, 2006). Moreover, a recent study reveals the inter­est of arsenate groups in playing the role of efficient disconnecting units in the magnetic compound BaCo₂(As₃O₆)₂·H₂O, being the first pure inorganic compound with slow spin dynamics (David et al., 2013b). From the crystal chemistry point of view, substitution of phosphate by arsenate gives the possibility of stabilizing new phases. For example, NaNiPO₄ crystallizes with the maricite structure (Senthilkumar et al., 2014), whereas NaNiAsO₄ has a honeycomb layer structure (Range & Meister, 1984). In this study, we describe the structure of Na₄Ni₇(AsO₄)₆ and compare it with its phosphate analogue.

2. Structural commentary

The structure of the title compound Na₄Ni₇(AsO₄)₆ is quite similar to the one of the phosphate homologue Na₄Ni₇(PO₄)₆. Both are made of inter­connected Ni₇(XO₄)₆ layers with tunnels in between where the Na atoms are located, as shown in Fig. 1a. The arrangement of NiO₆ and XO₄ in the layer is, however, slightly different, as evidenced in Fig. 2. As described by Moring & Kostiner (1986), Na₄Ni₇(PO₄)₆ layers are made of parallel ribbons (called ribbon 1) containing Ni1, Ni2, P3 and P4 polyhedra. These ribbons 1 are inter­connected by another kind of ribbon (called ribbon 2) made of dimers consisting of edge-sharing NiO₆ octahedra (Ni3 and Ni4). The latter are linked to PO₄ tetrahedra (P1 and P2) by edge- and corner-sharing. The difference between the two compounds is associated with the possibility of the Ni2 atom in Na₄Ni₇(PO₄)₆ occupying two octa­hedral sites. The first site, belonging to ribbon 1, is equivalent to the Ni2a site in Na₄Ni₇(AsO₄)₆. The other, equivalent to the Ni2b and Ni5 sites in Na₄Ni₇(AsO₄)₆, belongs to ribbon 2, forming penta­mers of edge-sharing NiO₆ octa­hedra. The layers of the title compound Na₄Ni₇(AsO₄)₆ can thus be described with three kinds of ribbons, as shown in Fig. 2. The linkage between the layers is done by corner-sharing between NiO₆ and AsO₄ units of two consecutive ribbons 2 along the stacking axis (Fig. 1a). This linkage is identical to the one of the phosphorus homologue. However, since in Na₄Ni₇(AsO₄)₆ layers are made of three different kinds of ribbons, two adjacent layers are shifted to align ribbon 1 with ribbon 1′. That is why in Na₄Ni₇(AsO₄)₆ the stacking axis is roughly doubled compared to Na₄Ni₇(PO₄)₆ [c = 6.398 (2) Å versus a = 14.5383 (11) Å in the title structure]. It implies two different kinds of Na layers, as shown in Fig. 1b.

Figure 1 Description of the crystal structure of Na4Ni7(AsO4)6 with (a) a view of the stacking and (b) a view of the Na layers. The dotted lines show the cell edges. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2 Description of the layers (top) and the ribbon 2 (bottom) of (a) Na4Ni7(AsO4)6 and (b) Na4Ni7(PO4)6. The dotted lines show the cell edges.

3. Synthesis and crystallization

Sodium carbonate (>99.5%), arsenic oxide (99%) and nickel sulfate hexa­hydrate (>99.9%) were purchased from Sigma–Aldrich. They were used as received without further purification. Reagents were ground together in stoichiometric ratio in an agate mortar. The obtained mixture was pelletized, placed in an alumina boat and annealed at 573 K for 1h. The obtained mixture was reground, pelletized and heated at 1073 K (5 K min⁻¹) for 48 h, after which the alumina boat was removed from the furnace and cooled to room temperature. The brown crystals of the title compound were isolated by hand.

4. Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 1. The (001) reflection, affected by the beamstop, has been removed from the refinement. Another reflection (01), flagged as potentially affected by the beamstop, was in fact not and was kept in the refinement. After positioning and refining all the atom positions except Ni2b, the difference Fourier map revealed residual density (≃8 e Å⁻³) near Ni2a (at ≃0.6 Å). It was refined introducing a second position Ni2b with complementary occupation. The occupancy ratio was refined to 0.80 (4):0.20 (4) for the Ni2a/Ni2b site, constraining the sum to be equal to 1.

Table 1
Experimental details

Crystal data
Chemical formula	Na4Ni7(AsO4)6
Mr	1336.3
Crystal system, space group	Monoclinic, C2/m
Temperature (K)	293
a, b, c (Å)	14.5383 (11), 14.5047 (11), 10.6120 (8)
β (°)	118.299 (2)
V (Å^3)	1970.3 (3)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	16.76
Crystal size (mm)	0.07 × 0.06 × 0.04
Data collection
Diffractometer	Bruker D8 Venture
Absorption correction	Multi-scan (SADABS; Bruker, 2015)
Tmin, Tmax	0.640, 0.747
No. of measured, independent and observed [I > 3σ(I)] reflections	48075, 3773, 2901
Rint	0.036
(sin θ/λ)max (Å^−1)	0.772
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.039, 0.052, 2.73
No. of reflections	3773
No. of parameters	146
Δρmax, Δρmin (e Å^−3)	3.34, −2.22
Computer programs: APEX3 and SAINT (Bruker, 2015), SUPERFLIP (Palatinus & Chapuis, 2007), JANA2006 (Petříčcek et al., 2014, DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010).

Supporting information

S1. Chemical context

Although the structures of transition metal phosphates have been widely investigated during the last decades, very little work has been done on comparable arsenates due to the toxicity of arsenic. The latter phases can exhibit, however, peculiar properties. BaCo₂(AsO₄)₂ is a good example of a quasi-2D system with a magnetically frustrated honeycomb lattice (Regnault et al., 1977). BaCoAs₂O₇ appears as the first example of a magnetization step promoted by a structural modulation (David et al., 2013a). LiCoAsO₄ shows reversible electrochemical activity at high potential (Satya Kishore & Varadaraju, 2006). Moreover, a recent study reveals the inter­est of arseniate groups in playing the role of efficient disconnecting units in the magnetic compound BaCo₂(As₃O₆)₂·H₂O, being the first pure inorganic compound with slow spin dynamics (David et al., 2013b). From the crystal chemistry point of view, substitution of phosphate by arsenate gives the possibility of stabilizing new phases. For example, NaNiPO₄ crystallizes with the maricite structure (Senthilkumar et al., 2014), whereas NaNiAsO₄ has a honeycomb layer structure (Range & Meister, 2014). In this study, we describe the structure of Na₄Ni₇(AsO₄)₆ and compare it with its phosphate analogue.

S2. Structural commentary

The structure of the title compound Na₄Ni₇(AsO₄)₆ is quite similar to the one of the phosphate homologue Na₄Ni₇(PO₄)₆. Both are made of inter­connected Ni₇(XO₄)₆ layers with Na tunnels in between, as shown in Fig. 1a. The arrangement of NiO₆ and XO₄ in the layer is, however, slightly different, as evidenced in Fig. 2. As described by Moring & Kostiner (1986), Na₄Ni₇(PO₄)₆ layers are made of parallel ribbons (called ribbon 1) containing Ni1, Ni2, P3 and P4 polyhedra. These ribbons 1 are inter­connected by another kind of ribbon (called ribbon 2) made of dimers edge-sharing Ni3 and Ni4 o­cta­hedra linked. The latter o­cta­hedra are linked to P1 and P2 tetra­hedra by edge- and corner-sharing. The difference between the two compounds is associated with the possibility of the Ni2 atom in Na₄Ni₇(PO₄)₆ occupying two o­cta­hedral sites. The first site, belonging to ribbon 1, is equivalent to the Ni2a site in Na₄Ni₇(AsO₄)₆. The other, equivalent to the Ni2b and Ni5 sites in Na₄Ni₇(AsO₄)₆ , belongs to ribbon 2, forming penta­mers of edge-sharing NiO₆ o­cta­hedra. The layers of the title compound Na₄Ni₇(AsO₄)₆ can thus be described with three kinds of ribbons, as shown in Fig. 2. The linkage between the layers is done by corner-sharing between NiO₆ and AsO₄ units of two consecutive ribbons 2 along the stacking axis (Fig. 1a). This linkage is identical to the one of the phospho­rous homologue. However, since in Na₄Ni₇(AsO₄)₆ layers are made of three different kinds of ribbons, two adjacent layers are shifted to align ribbon 1 with ribbon 1'. That is why in Na₄Ni₇(AsO₄)₆ the stacking axis is roughly doubled compared to Na₄Ni₇(PO₄)₆ [a =14.534 (4) vs c = 6.398 (2) Å in the title structure]. It implies two different kinds of Na layers, as shown in Fig. 1b.

S3. Synthesis and crystallization

Sodium carbonate (>99.5%), arsenic oxide (99%) and nickel sulfate hexahydrate (>99.9%) were purchased from Sigma–Aldrich. They were used as received without further purification. Reagents were ground together in stoichiometric ratio in an agate mortar. The obtained mixture was pelletized, placed in an alumina boat and annealed at 573 K for 1h. The obtained mixture was reground, pelletized and heated at 1073 K (5 K min^-1) for 48 h, after which the alumina boat was removed from the furnace and cooled to room temperature. The brown crystals of the title compound were isolated by hand.

S4. Refinement details

The (001) reflection, affected by the beamstop, was been removed from the refinement. Another reflection (2 0 1), flagged as potentially affected by the beamstop, was in fact not and was kept in the refinement. After positioning and refining all the atom positions except Ni2b, the difference Fourier map revealed residual density (≈8 e Å^-3) near Ni2a (at ≈0.6 Å). It was refined introducing a second position Ni2b with complementary occupation. The occupancy ratio was refined to 0.80 (4):0.20 (4) for the Ni2a/Ni2b site, constraining the sum to be equal to 1.

Structure description

Although the structures of transition metal phosphates have been widely investigated during the last decades, very little work has been done on comparable arsenates due to the toxicity of arsenic. The latter phases can exhibit, however, peculiar properties. BaCo₂(AsO₄)₂ is a good example of a quasi-2D system with a magnetically frustrated honeycomb lattice (Regnault et al., 1977). BaCoAs₂O₇ appears as the first example of a magnetization step promoted by a structural modulation (David et al., 2013a). LiCoAsO₄ shows reversible electrochemical activity at high potential (Satya Kishore & Varadaraju, 2006). Moreover, a recent study reveals the inter­est of arseniate groups in playing the role of efficient disconnecting units in the magnetic compound BaCo₂(As₃O₆)₂·H₂O, being the first pure inorganic compound with slow spin dynamics (David et al., 2013b). From the crystal chemistry point of view, substitution of phosphate by arsenate gives the possibility of stabilizing new phases. For example, NaNiPO₄ crystallizes with the maricite structure (Senthilkumar et al., 2014), whereas NaNiAsO₄ has a honeycomb layer structure (Range & Meister, 2014). In this study, we describe the structure of Na₄Ni₇(AsO₄)₆ and compare it with its phosphate analogue.

The structure of the title compound Na₄Ni₇(AsO₄)₆ is quite similar to the one of the phosphate homologue Na₄Ni₇(PO₄)₆. Both are made of inter­connected Ni₇(XO₄)₆ layers with Na tunnels in between, as shown in Fig. 1a. The arrangement of NiO₆ and XO₄ in the layer is, however, slightly different, as evidenced in Fig. 2. As described by Moring & Kostiner (1986), Na₄Ni₇(PO₄)₆ layers are made of parallel ribbons (called ribbon 1) containing Ni1, Ni2, P3 and P4 polyhedra. These ribbons 1 are inter­connected by another kind of ribbon (called ribbon 2) made of dimers edge-sharing Ni3 and Ni4 o­cta­hedra linked. The latter o­cta­hedra are linked to P1 and P2 tetra­hedra by edge- and corner-sharing. The difference between the two compounds is associated with the possibility of the Ni2 atom in Na₄Ni₇(PO₄)₆ occupying two o­cta­hedral sites. The first site, belonging to ribbon 1, is equivalent to the Ni2a site in Na₄Ni₇(AsO₄)₆. The other, equivalent to the Ni2b and Ni5 sites in Na₄Ni₇(AsO₄)₆ , belongs to ribbon 2, forming penta­mers of edge-sharing NiO₆ o­cta­hedra. The layers of the title compound Na₄Ni₇(AsO₄)₆ can thus be described with three kinds of ribbons, as shown in Fig. 2. The linkage between the layers is done by corner-sharing between NiO₆ and AsO₄ units of two consecutive ribbons 2 along the stacking axis (Fig. 1a). This linkage is identical to the one of the phospho­rous homologue. However, since in Na₄Ni₇(AsO₄)₆ layers are made of three different kinds of ribbons, two adjacent layers are shifted to align ribbon 1 with ribbon 1'. That is why in Na₄Ni₇(AsO₄)₆ the stacking axis is roughly doubled compared to Na₄Ni₇(PO₄)₆ [a =14.534 (4) vs c = 6.398 (2) Å in the title structure]. It implies two different kinds of Na layers, as shown in Fig. 1b.

Synthesis and crystallization

Sodium carbonate (>99.5%), arsenic oxide (99%) and nickel sulfate hexahydrate (>99.9%) were purchased from Sigma–Aldrich. They were used as received without further purification. Reagents were ground together in stoichiometric ratio in an agate mortar. The obtained mixture was pelletized, placed in an alumina boat and annealed at 573 K for 1h. The obtained mixture was reground, pelletized and heated at 1073 K (5 K min^-1) for 48 h, after which the alumina boat was removed from the furnace and cooled to room temperature. The brown crystals of the title compound were isolated by hand.

Refinement details

The (001) reflection, affected by the beamstop, was been removed from the refinement. Another reflection (2 0 1), flagged as potentially affected by the beamstop, was in fact not and was kept in the refinement. After positioning and refining all the atom positions except Ni2b, the difference Fourier map revealed residual density (≈8 e Å^-3) near Ni2a (at ≈0.6 Å). It was refined introducing a second position Ni2b with complementary occupation. The occupancy ratio was refined to 0.80 (4):0.20 (4) for the Ni2a/Ni2b site, constraining the sum to be equal to 1.

Computing details

Data collection: APEX3 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007); program(s) used to refine structure: JANA2006 (Petříčcek et al., 2014; molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. Description of the crystal structure of Na4Ni7(AsO4)6 with (a) a view of the stacking and (b) a view of the Na layers. The dotted lines show the cell edges.
	Fig. 2. Description of the layers (top) and the ribbon 2 (bottom) of (a) Na4Ni7(AsO4)6 and (b) Na4Ni7(PO4)6. The dotted lines show the cell edges.

Tetrasodium heptanickel hexaarsenate

Crystal data

Na4Ni7(AsO4)6	F(000) = 2520
Mr = 1336.3	Dx = 4.505 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2y	Cell parameters from 38754 reflections
a = 14.5383 (11) Å	θ = 2.1–33.3°
b = 14.5047 (11) Å	µ = 16.76 mm^−1
c = 10.6120 (8) Å	T = 293 K
β = 118.299 (2)°	Irregular, brown
V = 1970.3 (3) Å^3	0.07 × 0.06 × 0.04 mm
Z = 4

Data collection

Bruker D8 Venture diffractometer	2901 reflections with I > 3σ(I)
Radiation source: X-ray tube	Rint = 0.036
phi scan	θmax = 33.3°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2015)	h = −21→20
Tmin = 0.640, Tmax = 0.747	k = −22→21
48075 measured reflections	l = −16→16
3773 independent reflections

Refinement

Refinement on F	0 restraints
R[F^2 > 2σ(F^2)] = 0.039	0 constraints
wR(F^2) = 0.052	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 2.73	(Δ/σ)max = 0.015
3773 reflections	Δρmax = 3.34 e Å^−3
146 parameters	Δρmin = −2.22 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ni1	0.5	0	0	0.0068 (4)
Ni2a	0.5	0.1306 (6)	0.5	0.0078 (8)	0.80 (4)
Ni2b	0.5	0.166 (5)	0.5	0.027 (7)	0.20 (4)
Ni3	0.91312 (4)	0.18257 (3)	0.23065 (6)	0.00542 (19)
Ni4	0.59336 (4)	0.18693 (3)	0.26615 (6)	0.00530 (19)
Ni5	0.5	0.32688 (6)	0	0.0112 (3)
Ni6	0	0	0.5	0.0061 (4)
As1	0.85957 (3)	0.18473 (3)	0.45674 (4)	0.00503 (16)
As2	0.65106 (3)	0.18354 (3)	0.05278 (4)	0.00470 (15)
As3	0.47038 (5)	0	0.28662 (6)	0.0062 (2)
As4	0.45990 (5)	0.5	−0.20991 (6)	0.0056 (2)
Na1	0.2934 (2)	0.5	−0.0189 (3)	0.0304 (13)
Na2	0.25173 (16)	0.11586 (14)	0.3367 (2)	0.0305 (9)
Na3	0.7399 (2)	0	0.3103 (4)	0.0435 (15)
O1	0.6079 (2)	0.09855 (19)	0.1237 (3)	0.0067 (5)*
O2	0.8783 (2)	0.2776 (2)	0.3717 (3)	0.0125 (6)*
O3	0.4137 (3)	0	0.1101 (4)	0.0104 (8)*
O4	0.4391 (2)	0.21767 (19)	0.1132 (3)	0.0090 (6)*
O5	0.7665 (2)	0.1552 (2)	0.0682 (3)	0.0097 (6)*
O6	0.5380 (2)	0.4081 (2)	−0.1240 (3)	0.0096 (6)*
O8	0.3535 (3)	0.5	−0.1899 (5)	0.0140 (9)*
O9	0.3901 (4)	0	0.3581 (5)	0.0232 (11)*
O10	0.9333 (2)	0.20454 (19)	0.6329 (3)	0.0089 (6)*
O11	0.5468 (2)	0.0939 (2)	0.3604 (3)	0.0115 (6)*
O12	0.7395 (2)	0.1588 (2)	0.4274 (3)	0.0096 (6)*
O13	0.6448 (2)	0.27433 (19)	0.1522 (3)	0.0092 (6)*
O14	0.4220 (3)	0.5	−0.3841 (4)	0.0108 (9)*
O15	0.8965 (2)	0.10027 (18)	0.3788 (3)	0.0062 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.0070 (5)	0.0067 (5)	0.0068 (5)	0	0.0032 (4)	0
Ni2a	0.0102 (7)	0.006 (2)	0.0096 (7)	0	0.0068 (5)	0
Ni2b	0.021 (3)	0.04 (2)	0.019 (3)	0	0.010 (2)	0
Ni3	0.0047 (2)	0.0062 (3)	0.0048 (3)	−0.00029 (18)	0.0018 (2)	0.00088 (18)
Ni4	0.0050 (2)	0.0057 (3)	0.0048 (3)	0.00053 (18)	0.0020 (2)	−0.00048 (18)
Ni5	0.0097 (4)	0.0149 (4)	0.0084 (4)	0	0.0039 (3)	0
Ni6	0.0070 (5)	0.0048 (5)	0.0066 (5)	0	0.0033 (4)	0
As1	0.0049 (2)	0.0058 (2)	0.0047 (2)	0.00044 (14)	0.00248 (16)	0.00007 (14)
As2	0.00360 (19)	0.0057 (2)	0.0046 (2)	0.00079 (14)	0.00184 (16)	0.00099 (14)
As3	0.0082 (3)	0.0051 (3)	0.0054 (3)	0	0.0032 (2)	0
As4	0.0061 (3)	0.0044 (3)	0.0058 (3)	0	0.0024 (2)	0
Na1	0.0270 (17)	0.0353 (17)	0.0297 (17)	0	0.0141 (14)	0
Na2	0.0251 (11)	0.0240 (11)	0.0399 (14)	−0.0090 (9)	0.0134 (10)	−0.0080 (10)
Na3	0.0236 (17)	0.0179 (15)	0.061 (2)	0	−0.0026 (16)	0

Geometric parameters (Å, º)

Ni1—O1	2.068 (2)	Ni6—O15^iv	2.049 (2)
Ni1—O1^i	2.068 (2)	Ni6—O15^xiii	2.049 (2)
Ni1—O1^ii	2.068 (2)	Ni6—O15^xiv	2.049 (2)
Ni1—O1^iii	2.068 (2)	As1—Na2^vii	3.249 (2)
Ni1—O3	2.081 (6)	As1—Na3	3.1713 (16)
Ni1—O3^i	2.081 (6)	As1—O2	1.714 (3)
Ni2a—Ni2b	0.51 (7)	As1—O10	1.681 (3)
Ni2a—Na2	3.185 (2)	As1—O12	1.664 (3)
Ni2a—Na2^iv	3.185 (2)	As1—O15	1.702 (3)
Ni2a—O11	1.974 (4)	As2—O1	1.711 (3)
Ni2a—O11^iv	1.974 (4)	As2—O4^i	1.696 (3)
Ni2b—Na2	3.260 (17)	As2—O5	1.659 (3)
Ni2b—Na2^iv	3.260 (17)	As2—O13	1.716 (3)
Ni2b—O2^v	1.83 (3)	As3—O3	1.650 (4)
Ni2b—O2^vi	1.83 (3)	As3—O9	1.667 (7)
Ni3—O4^vii	2.058 (3)	As3—O11	1.697 (3)
Ni3—O5	2.047 (3)	As3—O11^iii	1.697 (3)
Ni3—O6^viii	2.069 (3)	As4—Na1^i	3.240 (3)
Ni3—O10^ix	2.029 (3)	As4—Na2^xv	3.190 (2)
Ni3—O15	2.077 (3)	As4—Na2^xvi	3.190 (2)
Ni4—O1	2.068 (3)	As4—O6	1.707 (3)
Ni4—O4	2.101 (3)	As4—O6^xvii	1.707 (3)
Ni4—O10^v	2.042 (3)	As4—O8	1.658 (6)
Ni4—O11	1.980 (4)	As4—O14	1.660 (5)
Ni4—O12	2.041 (3)	Na1—Na2^xv	3.540 (4)
Ni5—O6	2.029 (3)	Na1—Na2^xvi	3.540 (4)
Ni5—O6^i	2.029 (3)	Na1—Na3^xviii	3.923 (6)
Ni5—O13	2.097 (3)	Na1—O8	2.358 (7)
Ni5—O13^i	2.097 (3)	Na2—Na2^iii	3.361 (3)
Ni6—O14^x	2.030 (6)	Na2—O2^vi	2.294 (4)
Ni6—O14^xi	2.030 (6)	Na2—O8^xi	2.309 (3)
Ni6—O15^xii	2.049 (2)	Na2—O13^vi	2.429 (3)
O1—Ni1—O1^i	92.53 (10)	Na1^i—As4—Na2^xvi	145.04 (5)
O1—Ni1—O1^ii	180.0 (5)	Na1^i—As4—O6	51.71 (9)
O1—Ni1—O1^iii	87.47 (10)	Na1^i—As4—O6^xvii	51.71 (9)
O1—Ni1—O3	96.97 (12)	Na1^i—As4—O8	132.24 (16)
O1—Ni1—O3^i	83.03 (12)	Na1^i—As4—O14	119.95 (18)
O1^i—Ni1—O1^ii	87.47 (10)	Na2^xv—As4—Na2^xvi	63.58 (5)
O1^i—Ni1—O1^iii	180.0 (5)	Na2^xv—As4—O6	154.25 (13)
O1^i—Ni1—O3	83.03 (12)	Na2^xv—As4—O6^xvii	94.48 (10)
O1^i—Ni1—O3^i	96.97 (12)	Na2^xv—As4—O8	44.13 (10)
O1^ii—Ni1—O1^iii	92.53 (10)	Na2^xv—As4—O14	77.65 (15)
O1^ii—Ni1—O3	83.03 (12)	Na2^xvi—As4—O6	94.48 (10)
O1^ii—Ni1—O3^i	96.97 (12)	Na2^xvi—As4—O6^xvii	154.25 (13)
O1^iii—Ni1—O3	96.97 (12)	Na2^xvi—As4—O8	44.13 (10)
O1^iii—Ni1—O3^i	83.03 (12)	Na2^xvi—As4—O14	77.65 (15)
O3—Ni1—O3^i	180.0 (5)	O6—As4—O6^xvii	102.64 (12)
Ni2b—Ni2a—Na2	93.85 (16)	O6—As4—O8	110.86 (15)
Ni2b—Ni2a—Na2^iv	93.85 (16)	O6—As4—O14	112.34 (14)
Ni2b—Ni2a—O11	105.6 (3)	O6^xvii—As4—O8	110.86 (15)
Ni2b—Ni2a—O11^iv	105.6 (3)	O6^xvii—As4—O14	112.34 (14)
Na2—Ni2a—Na2^iv	172.3 (3)	O8—As4—O14	107.8 (2)
Na2—Ni2a—O11	106.17 (12)	As4^i—Na1—Na2^xv	110.70 (11)
Na2—Ni2a—O11^iv	71.66 (9)	As4^i—Na1—Na2^xvi	110.70 (11)
Na2^iv—Ni2a—O11	71.66 (9)	As4^i—Na1—Na3^xviii	87.08 (8)
Na2^iv—Ni2a—O11^iv	106.17 (12)	As4^i—Na1—O8	83.94 (14)
O11—Ni2a—O11^iv	148.7 (5)	Na2^xv—Na1—Na2^xvi	56.69 (7)
Ni2a—Ni2b—Na2	77.1 (13)	Na2^xv—Na1—Na3^xviii	145.38 (8)
Ni2a—Ni2b—Na2^iv	77.1 (13)	Na2^xv—Na1—O8	40.16 (9)
Ni2a—Ni2b—O2^v	116 (2)	Na2^xvi—Na1—Na3^xviii	145.38 (8)
Ni2a—Ni2b—O2^vi	116 (2)	Na2^xvi—Na1—O8	40.16 (9)
Na2—Ni2b—Na2^iv	154 (3)	Na3^xviii—Na1—O8	171.02 (14)
Na2—Ni2b—O2^v	158 (2)	Ni2a—Na2—Ni2b	9.1 (13)
Na2—Ni2b—O2^vi	43.1 (7)	Ni2a—Na2—As1^vi	61.00 (16)
Na2^iv—Ni2b—O2^v	43.1 (7)	Ni2a—Na2—As4^xi	151.93 (17)
Na2^iv—Ni2b—O2^vi	158 (2)	Ni2a—Na2—Na1^xi	101.59 (12)
O2^v—Ni2b—O2^vi	127 (4)	Ni2a—Na2—Na2^iii	93.85 (17)
O4^vii—Ni3—O5	92.46 (12)	Ni2a—Na2—O2^vi	41.55 (17)
O4^vii—Ni3—O6^viii	84.64 (13)	Ni2a—Na2—O8^xi	129.3 (2)
O4^vii—Ni3—O10^ix	82.32 (12)	Ni2a—Na2—O13^vi	121.44 (17)
O4^vii—Ni3—O15	169.39 (11)	Ni2b—Na2—As1^vi	52.1 (12)
O5—Ni3—O6^viii	84.66 (12)	Ni2b—Na2—As4^xi	160.9 (13)
O5—Ni3—O10^ix	170.33 (16)	Ni2b—Na2—Na1^xi	105.7 (6)
O5—Ni3—O15	94.46 (12)	Ni2b—Na2—Na2^iii	102.9 (13)
O6^viii—Ni3—O10^ix	86.74 (12)	Ni2b—Na2—O2^vi	33.1 (12)
O6^viii—Ni3—O15	103.99 (12)	Ni2b—Na2—O8^xi	137.2 (11)
O10^ix—Ni3—O15	91.91 (12)	Ni2b—Na2—O13^vi	114.0 (11)
O1—Ni4—O4	90.49 (11)	As1^vi—Na2—As4^xi	145.50 (8)
O1—Ni4—O10^v	166.43 (12)	As1^vi—Na2—Na1^xi	129.31 (10)
O1—Ni4—O11	97.17 (13)	As1^vi—Na2—Na2^iii	152.92 (7)
O1—Ni4—O12	93.57 (12)	As1^vi—Na2—O2^vi	30.22 (10)
O4—Ni4—O10^v	80.96 (11)	As1^vi—Na2—O8^xi	162.71 (11)
O4—Ni4—O11	92.27 (12)	As1^vi—Na2—O13^vi	74.79 (8)
O4—Ni4—O12	175.26 (15)	As4^xi—Na2—Na1^xi	69.02 (7)
O10^v—Ni4—O11	93.70 (14)	As4^xi—Na2—Na2^iii	58.21 (5)
O10^v—Ni4—O12	95.48 (12)	As4^xi—Na2—O2^vi	164.23 (11)
O11—Ni4—O12	84.81 (12)	As4^xi—Na2—O8^xi	30.00 (15)
O6—Ni5—O6^i	108.95 (13)	As4^xi—Na2—O13^vi	83.39 (9)
O6—Ni5—O13	103.20 (12)	Na1^xi—Na2—Na2^iii	61.65 (6)
O6—Ni5—O13^i	101.19 (12)	Na1^xi—Na2—O2^vi	104.27 (14)
O6^i—Ni5—O13	101.19 (12)	Na1^xi—Na2—O8^xi	41.18 (16)
O6^i—Ni5—O13^i	103.20 (12)	Na1^xi—Na2—O13^vi	77.57 (10)
O13—Ni5—O13^i	137.37 (11)	Na2^iii—Na2—O2^vi	132.33 (13)
O14^x—Ni6—O14^xi	180.0 (5)	Na2^iii—Na2—O8^xi	43.30 (8)
O14^x—Ni6—O15^xii	85.74 (12)	Na2^iii—Na2—O13^vi	130.98 (10)
O14^x—Ni6—O15^iv	94.26 (12)	O2^vi—Na2—O8^xi	145.4 (2)
O14^x—Ni6—O15^xiii	94.26 (12)	O2^vi—Na2—O13^vi	81.18 (12)
O14^x—Ni6—O15^xiv	85.74 (12)	O8^xi—Na2—O13^vi	88.13 (11)
O14^xi—Ni6—O15^xii	94.26 (12)	As1—Na3—As1^iii	115.32 (9)
O14^xi—Ni6—O15^iv	85.74 (12)	As1—Na3—Na1^xix	98.15 (10)
O14^xi—Ni6—O15^xiii	85.74 (12)	As1^iii—Na3—Na1^xix	98.15 (10)
O14^xi—Ni6—O15^xiv	94.26 (12)	Ni1—O1—Ni4	125.67 (17)
O15^xii—Ni6—O15^iv	89.57 (10)	Ni1—O1—As2	123.00 (15)
O15^xii—Ni6—O15^xiii	180.0 (5)	Ni4—O1—As2	93.49 (12)
O15^xii—Ni6—O15^xiv	90.43 (10)	Ni2b^v—O2—As1	107.3 (16)
O15^iv—Ni6—O15^xiii	90.43 (10)	Ni2b^v—O2—Na2^vii	103.8 (19)
O15^iv—Ni6—O15^xiv	180.0 (5)	As1—O2—Na2^vii	107.4 (2)
O15^xiii—Ni6—O15^xiv	89.57 (10)	Ni1—O3—As3	121.8 (2)
Na2^vii—As1—Na3	120.62 (5)	Ni3^vi—O4—Ni4	96.68 (11)
Na2^vii—As1—O2	42.36 (13)	Ni3^vi—O4—As2^i	124.13 (16)
Na2^vii—As1—O10	102.64 (10)	Ni4—O4—As2^i	139.19 (19)
Na2^vii—As1—O12	81.93 (11)	Ni3—O5—As2	129.51 (19)
Na2^vii—As1—O15	130.93 (11)	Ni3^viii—O6—Ni5	104.78 (13)
Na3—As1—O2	126.42 (12)	Ni3^viii—O6—As4	121.23 (17)
Na3—As1—O10	127.00 (12)	Ni5—O6—As4	118.91 (19)
Na3—As1—O12	55.54 (13)	As4—O8—Na1	143.8 (2)
Na3—As1—O15	51.68 (13)	As4—O8—Na2^xv	105.9 (2)
O2—As1—O10	105.90 (14)	As4—O8—Na2^xvi	105.9 (2)
O2—As1—O12	119.59 (14)	Na1—O8—Na2^xv	98.65 (19)
O2—As1—O15	98.30 (17)	Na1—O8—Na2^xvi	98.65 (19)
O10—As1—O12	107.84 (17)	Na2^xv—O8—Na2^xvi	93.40 (14)
O10—As1—O15	118.79 (13)	Ni3^ix—O10—Ni4^v	99.49 (11)
O12—As1—O15	106.93 (14)	Ni3^ix—O10—As1	132.3 (2)
O1—As2—O4^i	113.78 (13)	Ni4^v—O10—As1	122.37 (14)
O1—As2—O5	110.07 (15)	Ni2a—O11—Ni4	121.2 (3)
O1—As2—O13	98.34 (16)	Ni2a—O11—As3	100.3 (3)
O4^i—As2—O5	114.98 (17)	Ni4—O11—As3	128.29 (18)
O4^i—As2—O13	100.05 (14)	Ni4—O12—As1	134.0 (2)
O5—As2—O13	118.36 (14)	Ni5—O13—As2	97.57 (12)
O3—As3—O9	115.8 (2)	Ni5—O13—Na2^vii	114.05 (13)
O3—As3—O11	112.91 (14)	As2—O13—Na2^vii	142.98 (18)
O3—As3—O11^iii	112.91 (14)	Ni6^xx—O14—As4	133.6 (2)
O9—As3—O11	103.68 (16)	Ni3—O15—Ni6^xxi	124.68 (17)
O9—As3—O11^iii	103.68 (16)	Ni3—O15—As1	97.52 (13)
O11—As3—O11^iii	106.83 (13)	Ni6^xxi—O15—As1	120.85 (15)
Na1^i—As4—Na2^xv	145.04 (5)

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