An arsenate with the α-CrPO4 structure type, NaCa1–xNi3–2xAl2x(AsO4)3 (x = 0.23): crystal structure, charge-distribution and bond-valence-sum analyses

Ben Smail, R.; Zid, M.F.

doi:10.1107/S2053229617013213

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An arsenate with the α-CrPO₄ structure type, NaCa_1–xNi_3–2xAl_2x(AsO₄)₃ (x = 0.23): crystal structure, charge-distribution and bond-valence-sum analyses

R. Ben Smail and M. F. Zid

Since the discovery of electrochemically active LiFePO₄, materials with tunnel and layered structures built up of transition metals and polyanions have become the subject of much research. A new quaternary arsenate, sodium calcium trinickel aluminium triarsenate, NaCa_1–xNi_3–2xAl_2x(AsO₄)₃ (x = 0.23), was synthesized using the flux method in air at 1023 K and its crystal structure was determined from single-crystal X-ray diffraction (XRD) data. This material was also characterized by qualitative energy-dispersive X-ray spectroscopy (EDS) analysis and IR spectroscopy. The crystal structure belongs to the α-CrPO₄ type with the space group Imma. The structure is described as a three-dimensional framework built up of corner-edge-sharing NiO₆, (Ni,Al)O₆ and AsO₄ polyhedra, with channels running along the [100] and [010] directions, in which the sodium and calcium cations are located. The proposed structural model has been validated by bond-valence-sum (BVS) and charge-distribution (CHARDI) tools. The sodium ionic conduction pathways in the anionic framework were investigated by means of the bond-valence site energy (BVSE) model, which predicted that the studied material will probably be a very poor Na⁺ ion conductor (bond-valence activation energy ∼7 eV).

Keywords: arsenate; α-CrPO₄; bond valence sum (BVS); crystal structure; charge distribution (CHARDI); sodium conduction pathway simulation.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S2053229617013213/sk3667sup1.cif Contains datablock I
	Structure factor file (CIF format) https://doi.org/10.1107/S2053229617013213/sk3667Isup2.hkl Contains datablock I

CCDC reference: 1574601

Computing details top

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macícek & Yordanov, 1992); cell refinement: CAD-4 EXPRESS (Duisenberg, 1992; Macícek & Yordanov, 1992); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

Sodium calcium trinickel aluminium triarsenate top

Crystal data top

NaCa_0.77Ni_2.54Al_0.46(AsO₄)₃	D_x = 4.477 Mg m⁻³
M_r = 632.15	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Imma	Cell parameters from 25 reflections
a = 10.419 (2) Å	θ = 12.2–14.6°
b = 13.496 (2) Å	µ = 16.15 mm⁻¹
c = 6.669 (2) Å	T = 298 K
V = 937.8 (4) Å³	Prism, green-yellow
Z = 4	0.23 × 0.10 × 0.09 mm
F(000) = 1194

Data collection top

Enraf–Nonius CAD-4 diffractometer	R_int = 0.019
Radiation source: fine-focus sealed tube	θ_max = 26.9°, θ_min = 3.0°
ω/2θ scans	h = −1→13
Absorption correction: ψ scan (North et al., 1968)	k = −1→17
T_min = 0.536, T_max = 0.860	l = −8→8
1285 measured reflections	2 standard reflections every 120 reflections
566 independent reflections	intensity decay: 1%
521 reflections with I > 2σ(I)

Refinement top

Refinement on F²	1 restraint
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0313P)² + 3.2165P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.020	(Δ/σ)_max = 0.069
wR(F²) = 0.058	Δρ_max = 0.86 e Å⁻³
S = 1.13	Δρ_min = −0.93 e Å⁻³
566 reflections	Extinction correction: SHELXL-2016/4 (Sheldrick 2015), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
60 parameters	Extinction coefficient: 0.00072 (13)

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	Occ. (<1)
CA1	0.500000	0.750000	0.9258 (4)	0.0324 (6)	0.774
NA1	0.000000	0.500000	0.500000	0.0324 (9)
NI1	0.500000	0.000000	0.500000	0.0084 (4)	0.543 (8)
AL1	0.500000	0.000000	0.500000	0.0084 (4)	0.457 (8)
NI2	0.750000	0.36287 (5)	0.750000	0.0086 (2)
AS1	0.500000	0.250000	0.56155 (10)	0.0062 (2)
AS2	0.750000	0.57131 (4)	0.750000	0.00680 (18)
O1	0.500000	0.1487 (3)	0.4177 (6)	0.0184 (8)
O2	0.6251 (3)	0.250000	0.7227 (5)	0.0097 (7)
O3	0.6949 (3)	0.63540 (18)	0.9462 (4)	0.0146 (6)
O4	0.8679 (2)	0.48424 (18)	0.7979 (4)	0.0103 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
CA1	0.0389 (14)	0.0306 (13)	0.0277 (12)	0.000	0.000	0.000
NA1	0.0195 (17)	0.065 (3)	0.0123 (15)	0.000	0.000	0.0010 (17)
NI1	0.0069 (6)	0.0118 (7)	0.0063 (6)	0.000	0.000	−0.0014 (4)
AL1	0.0069 (6)	0.0118 (7)	0.0063 (6)	0.000	0.000	−0.0014 (4)
NI2	0.0077 (3)	0.0076 (3)	0.0105 (3)	0.000	−0.0005 (2)	0.000
AS1	0.0058 (3)	0.0069 (3)	0.0060 (3)	0.000	0.000	0.000
AS2	0.0091 (3)	0.0062 (3)	0.0051 (3)	0.000	0.00160 (16)	0.000
O1	0.0178 (18)	0.0169 (18)	0.0204 (19)	0.000	0.000	−0.0122 (15)
O2	0.0085 (16)	0.0106 (16)	0.0101 (15)	0.000	−0.0048 (14)	0.000
O3	0.0195 (13)	0.0174 (14)	0.0069 (11)	0.0060 (11)	0.0014 (10)	−0.0035 (10)
O4	0.0108 (12)	0.0089 (10)	0.0112 (10)	0.0014 (10)	0.0001 (11)	−0.0004 (9)

Geometric parameters (Å, º) top

CA1—O3	2.556 (3)	NI2—O2^xvi	2.012 (2)
CA1—O3ⁱ	2.556 (3)	NI2—O2	2.012 (2)
CA1—O3ⁱⁱ	2.556 (3)	NI2—O4^xxiii	2.072 (3)
CA1—O3ⁱⁱⁱ	2.556 (3)	NI2—O4	2.072 (3)
CA1—O1^iv	2.668 (5)	NI2—O3^xxiv	2.106 (3)
CA1—O1^v	2.668 (5)	NI2—O3^xxv	2.106 (3)
CA1—O2^vi	2.682 (4)	NI2—AS2	2.8132 (9)
CA1—O2^vii	2.682 (4)	NI2—NA1^xxvi	3.6042 (6)
CA1—AS1^v	3.250 (3)	NI2—NA1^ix	3.6042 (6)
CA1—NA1^viii	3.4102 (6)	NI2—CA1^vii	3.7123 (16)
CA1—NA1^ix	3.4102 (6)	NI2—CA1^xxii	3.7123 (16)
CA1—AS1^vii	3.419 (3)	AS1—O1	1.670 (4)
NA1—O4ⁱⁱ	2.426 (3)	AS1—O1^xxvii	1.670 (4)
NA1—O4^x	2.426 (3)	AS1—O2	1.689 (3)
NA1—O4^v	2.426 (3)	AS1—O2^xxvii	1.689 (3)
NA1—O4^xi	2.426 (3)	AS1—CA1^v	3.250 (3)
NA1—O3^xii	2.755 (3)	AS1—CA1^vii	3.419 (3)
NA1—O3^xiii	2.755 (3)	AS2—O3^xxiii	1.670 (3)
NA1—O3^xiv	2.755 (3)	AS2—O3	1.671 (2)
NA1—O3^xv	2.755 (3)	AS2—O4	1.730 (2)
NA1—AS2^xii	3.2390 (5)	AS2—O4^xxiii	1.730 (2)
NA1—AS2^xiii	3.2390 (5)	AS2—NA1^ix	3.2390 (5)
NA1—AS2^v	3.2390 (5)	AS2—NA1^xxvi	3.2390 (5)
NA1—AS2^xi	3.2390 (5)	O1—CA1^v	2.668 (5)
NI1—O4^xvi	1.938 (2)	O2—NI2^xvi	2.012 (2)
NI1—O4^xvii	1.938 (2)	O2—CA1^vii	2.682 (4)
NI1—O4^xviii	1.938 (2)	O3—NI2^xxviii	2.106 (3)
NI1—O4^xix	1.938 (2)	O3—NA1^ix	2.755 (3)
NI1—O1^xx	2.080 (4)	O4—AL1^viii	1.938 (2)
NI1—O1	2.080 (4)	O4—NI1^viii	1.938 (2)
NI1—NA1^xxi	3.3344 (10)	O4—NA1^xxvi	2.426 (3)
NI1—NA1^xxii	3.3344 (10)

O3—CA1—O3ⁱ	74.47 (12)	O4^xvi—NI1—O1^xx	85.55 (10)
O3—CA1—O3ⁱⁱ	105.19 (12)	O4^xvii—NI1—O1^xx	94.45 (10)
O3ⁱ—CA1—O3ⁱⁱ	173.88 (16)	O4^xviii—NI1—O1^xx	94.45 (10)
O3—CA1—O3ⁱⁱⁱ	173.88 (16)	O4^xix—NI1—O1^xx	85.55 (10)
O3ⁱ—CA1—O3ⁱⁱⁱ	105.19 (12)	O4^xvi—NI1—O1	94.45 (10)
O3ⁱⁱ—CA1—O3ⁱⁱⁱ	74.47 (12)	O4^xvii—NI1—O1	85.55 (10)
O3—CA1—O1^iv	74.67 (8)	O4^xviii—NI1—O1	85.55 (10)
O3ⁱ—CA1—O1^iv	110.85 (10)	O4^xix—NI1—O1	94.45 (10)
O3ⁱⁱ—CA1—O1^iv	74.67 (8)	O1^xx—NI1—O1	180.0
O3ⁱⁱⁱ—CA1—O1^iv	110.85 (10)	O4^xvi—NI1—NA1^xxi	45.94 (7)
O3—CA1—O1^v	110.86 (10)	O4^xvii—NI1—NA1^xxi	134.06 (7)
O3ⁱ—CA1—O1^v	74.67 (8)	O4^xviii—NI1—NA1^xxi	134.06 (7)
O3ⁱⁱ—CA1—O1^v	110.85 (10)	O4^xix—NI1—NA1^xxi	45.94 (7)
O3ⁱⁱⁱ—CA1—O1^v	74.67 (8)	O1^xx—NI1—NA1^xxi	74.71 (10)
O1^iv—CA1—O1^v	61.67 (17)	O1—NI1—NA1^xxi	105.29 (10)
O3—CA1—O2^vi	64.36 (8)	O4^xvi—NI1—NA1^xxii	134.06 (7)
O3ⁱ—CA1—O2^vi	64.36 (8)	O4^xvii—NI1—NA1^xxii	45.94 (7)
O3ⁱⁱ—CA1—O2^vi	109.83 (11)	O4^xviii—NI1—NA1^xxii	45.94 (7)
O3ⁱⁱⁱ—CA1—O2^vi	109.83 (11)	O4^xix—NI1—NA1^xxii	134.06 (7)
O1^iv—CA1—O2^vi	138.63 (7)	O1^xx—NI1—NA1^xxii	105.29 (10)
O1^v—CA1—O2^vi	138.63 (7)	O1—NI1—NA1^xxii	74.71 (10)
O3—CA1—O2^vii	109.83 (11)	NA1^xxi—NI1—NA1^xxii	180.0
O3ⁱ—CA1—O2^vii	109.83 (11)	O2^xvi—NI2—O2	81.57 (15)
O3ⁱⁱ—CA1—O2^vii	64.36 (8)	O2^xvi—NI2—O4^xxiii	174.85 (11)
O3ⁱⁱⁱ—CA1—O2^vii	64.36 (8)	O2—NI2—O4^xxiii	101.60 (10)
O1^iv—CA1—O2^vii	138.63 (7)	O2^xvi—NI2—O4	101.60 (10)
O1^v—CA1—O2^vii	138.63 (7)	O2—NI2—O4	174.85 (11)
O2^vi—CA1—O2^vii	58.14 (15)	O4^xxiii—NI2—O4	75.53 (13)
O3—CA1—AS1^v	93.06 (8)	O2^xvi—NI2—O3^xxiv	95.61 (12)
O3ⁱ—CA1—AS1^v	93.06 (8)	O2—NI2—O3^xxiv	85.36 (12)
O3ⁱⁱ—CA1—AS1^v	93.06 (8)	O4^xxiii—NI2—O3^xxiv	88.73 (10)
O3ⁱⁱⁱ—CA1—AS1^v	93.06 (8)	O4—NI2—O3^xxiv	90.27 (10)
O1^iv—CA1—AS1^v	30.84 (8)	O2^xvi—NI2—O3^xxv	85.36 (12)
O1^v—CA1—AS1^v	30.84 (8)	O2—NI2—O3^xxv	95.61 (12)
O2^vi—CA1—AS1^v	150.93 (8)	O4^xxiii—NI2—O3^xxv	90.27 (10)
O2^vii—CA1—AS1^v	150.93 (8)	O4—NI2—O3^xxv	88.73 (10)
O3—CA1—NA1^viii	126.22 (6)	O3^xxiv—NI2—O3^xxv	178.73 (14)
O3ⁱ—CA1—NA1^viii	52.67 (6)	O2^xvi—NI2—AS2	139.22 (8)
O3ⁱⁱ—CA1—NA1^viii	126.22 (6)	O2—NI2—AS2	139.21 (7)
O3ⁱⁱⁱ—CA1—NA1^viii	52.67 (6)	O4^xxiii—NI2—AS2	37.77 (7)
O1^iv—CA1—NA1^viii	129.18 (11)	O4—NI2—AS2	37.77 (7)
O1^v—CA1—NA1^viii	67.51 (8)	O3^xxiv—NI2—AS2	89.37 (7)
O2^vi—CA1—NA1^viii	82.71 (4)	O3^xxv—NI2—AS2	89.37 (7)
O2^vii—CA1—NA1^viii	82.71 (4)	O2^xvi—NI2—NA1^xxvi	87.89 (8)
AS1^v—CA1—NA1^viii	98.35 (4)	O2—NI2—NA1^xxvi	144.53 (9)
O3—CA1—NA1^ix	52.67 (6)	O4^xxiii—NI2—NA1^xxvi	87.20 (7)
O3ⁱ—CA1—NA1^ix	126.22 (6)	O4—NI2—NA1^xxvi	40.27 (7)
O3ⁱⁱ—CA1—NA1^ix	52.67 (6)	O3^xxiv—NI2—NA1^xxvi	129.53 (7)
O3ⁱⁱⁱ—CA1—NA1^ix	126.22 (6)	O3^xxv—NI2—NA1^xxvi	49.62 (7)
O1^iv—CA1—NA1^ix	67.51 (8)	AS2—NI2—NA1^xxvi	59.103 (10)
O1^v—CA1—NA1^ix	129.18 (11)	O2^xvi—NI2—NA1^ix	144.53 (9)
O2^vi—CA1—NA1^ix	82.71 (4)	O2—NI2—NA1^ix	87.89 (8)
O2^vii—CA1—NA1^ix	82.71 (4)	O4^xxiii—NI2—NA1^ix	40.27 (7)
AS1^v—CA1—NA1^ix	98.35 (4)	O4—NI2—NA1^ix	87.20 (7)
NA1^viii—CA1—NA1^ix	163.31 (9)	O3^xxiv—NI2—NA1^ix	49.62 (7)
O3—CA1—AS1^vii	86.94 (8)	O3^xxv—NI2—NA1^ix	129.53 (7)
O3ⁱ—CA1—AS1^vii	86.94 (8)	AS2—NI2—NA1^ix	59.103 (10)
O3ⁱⁱ—CA1—AS1^vii	86.94 (8)	NA1^xxvi—NI2—NA1^ix	118.21 (2)
O3ⁱⁱⁱ—CA1—AS1^vii	86.94 (8)	O2^xvi—NI2—CA1^vii	95.19 (9)
O1^iv—CA1—AS1^vii	149.16 (8)	O2—NI2—CA1^vii	44.61 (10)
O1^v—CA1—AS1^vii	149.16 (8)	O4^xxiii—NI2—CA1^vii	89.90 (7)
O2^vi—CA1—AS1^vii	29.07 (8)	O4—NI2—CA1^vii	130.58 (8)
O2^vii—CA1—AS1^vii	29.07 (8)	O3^xxiv—NI2—CA1^vii	41.65 (8)
AS1^v—CA1—AS1^vii	180.0	O3^xxv—NI2—CA1^vii	139.14 (8)
NA1^viii—CA1—AS1^vii	81.65 (4)	AS2—NI2—CA1^vii	114.227 (14)
NA1^ix—CA1—AS1^vii	81.65 (4)	NA1^xxvi—NI2—CA1^vii	170.85 (3)
O4ⁱⁱ—NA1—O4^x	180.0	NA1^ix—NI2—CA1^vii	55.539 (12)
O4ⁱⁱ—NA1—O4^v	110.86 (12)	O2^xvi—NI2—CA1^xxii	44.61 (10)
O4^x—NA1—O4^v	69.14 (12)	O2—NI2—CA1^xxii	95.19 (9)
O4ⁱⁱ—NA1—O4^xi	69.14 (12)	O4^xxiii—NI2—CA1^xxii	130.58 (8)
O4^x—NA1—O4^xi	110.86 (12)	O4—NI2—CA1^xxii	89.90 (7)
O4^v—NA1—O4^xi	180.0	O3^xxiv—NI2—CA1^xxii	139.14 (8)
O4ⁱⁱ—NA1—O3^xii	62.19 (8)	O3^xxv—NI2—CA1^xxii	41.65 (8)
O4^x—NA1—O3^xii	117.81 (8)	AS2—NI2—CA1^xxii	114.227 (14)
O4^v—NA1—O3^xii	68.30 (8)	NA1^xxvi—NI2—CA1^xxii	55.539 (12)
O4^xi—NA1—O3^xii	111.70 (8)	NA1^ix—NI2—CA1^xxii	170.85 (3)
O4ⁱⁱ—NA1—O3^xiii	117.81 (8)	CA1^vii—NI2—CA1^xxii	131.55 (3)
O4^x—NA1—O3^xiii	62.19 (8)	O1—AS1—O1^xxvii	109.9 (3)
O4^v—NA1—O3^xiii	111.70 (8)	O1—AS1—O2	111.42 (10)
O4^xi—NA1—O3^xiii	68.30 (8)	O1^xxvii—AS1—O2	111.42 (10)
O3^xii—NA1—O3^xiii	180.0	O1—AS1—O2^xxvii	111.42 (10)
O4ⁱⁱ—NA1—O3^xiv	68.30 (8)	O1^xxvii—AS1—O2^xxvii	111.42 (10)
O4^x—NA1—O3^xiv	111.70 (8)	O2—AS1—O2^xxvii	101.0 (2)
O4^v—NA1—O3^xiv	62.19 (8)	O1—AS1—CA1^v	54.96 (14)
O4^xi—NA1—O3^xiv	117.81 (8)	O1^xxvii—AS1—CA1^v	54.96 (14)
O3^xii—NA1—O3^xiv	85.05 (11)	O2—AS1—CA1^v	129.51 (12)
O3^xiii—NA1—O3^xiv	94.95 (11)	O2^xxvii—AS1—CA1^v	129.50 (12)
O4ⁱⁱ—NA1—O3^xv	111.70 (8)	O1—AS1—CA1^vii	125.04 (14)
O4^x—NA1—O3^xv	68.30 (8)	O1^xxvii—AS1—CA1^vii	125.04 (14)
O4^v—NA1—O3^xv	117.81 (8)	O2—AS1—CA1^vii	50.49 (12)
O4^xi—NA1—O3^xv	62.19 (8)	O2^xxvii—AS1—CA1^vii	50.50 (12)
O3^xii—NA1—O3^xv	94.95 (11)	CA1^v—AS1—CA1^vii	180.0
O3^xiii—NA1—O3^xv	85.05 (11)	O3^xxiii—AS2—O3	117.63 (18)
O3^xiv—NA1—O3^xv	180.0	O3^xxiii—AS2—O4	104.61 (13)
O4ⁱⁱ—NA1—AS2^xii	31.60 (6)	O3—AS2—O4	116.83 (12)
O4^x—NA1—AS2^xii	148.40 (6)	O3^xxiii—AS2—O4^xxiii	116.83 (12)
O4^v—NA1—AS2^xii	86.51 (6)	O3—AS2—O4^xxiii	104.61 (13)
O4^xi—NA1—AS2^xii	93.49 (6)	O4—AS2—O4^xxiii	94.40 (17)
O3^xii—NA1—AS2^xii	31.04 (5)	O3^xxiii—AS2—NI2	121.18 (9)
O3^xiii—NA1—AS2^xii	148.96 (5)	O3—AS2—NI2	121.18 (9)
O3^xiv—NA1—AS2^xii	70.82 (6)	O4—AS2—NI2	47.20 (8)
O3^xv—NA1—AS2^xii	109.18 (6)	O4^xxiii—AS2—NI2	47.20 (8)
O4ⁱⁱ—NA1—AS2^xiii	148.40 (6)	O3^xxiii—AS2—NA1^ix	146.47 (9)
O4^x—NA1—AS2^xiii	31.60 (6)	O3—AS2—NA1^ix	58.27 (9)
O4^v—NA1—AS2^xiii	93.49 (6)	O4—AS2—NA1^ix	105.91 (9)
O4^xi—NA1—AS2^xiii	86.51 (6)	O4^xxiii—AS2—NA1^ix	47.31 (8)
O3^xii—NA1—AS2^xiii	148.96 (5)	NI2—AS2—NA1^ix	72.713 (9)
O3^xiii—NA1—AS2^xiii	31.04 (5)	O3^xxiii—AS2—NA1^xxvi	58.27 (9)
O3^xiv—NA1—AS2^xiii	109.18 (6)	O3—AS2—NA1^xxvi	146.47 (9)
O3^xv—NA1—AS2^xiii	70.82 (6)	O4—AS2—NA1^xxvi	47.31 (8)
AS2^xii—NA1—AS2^xiii	180.0	O4^xxiii—AS2—NA1^xxvi	105.91 (9)
O4ⁱⁱ—NA1—AS2^v	86.51 (6)	NI2—AS2—NA1^xxvi	72.713 (9)
O4^x—NA1—AS2^v	93.49 (6)	NA1^ix—AS2—NA1^xxvi	145.426 (18)
O4^v—NA1—AS2^v	31.60 (6)	AS1—O1—NI1	129.7 (2)
O4^xi—NA1—AS2^v	148.40 (6)	AS1—O1—CA1^v	94.21 (17)
O3^xii—NA1—AS2^v	70.82 (6)	NI1—O1—CA1^v	136.13 (17)
O3^xiii—NA1—AS2^v	109.18 (6)	AS1—O2—NI2^xvi	123.83 (10)
O3^xiv—NA1—AS2^v	31.04 (5)	AS1—O2—NI2	123.83 (10)
O3^xv—NA1—AS2^v	148.96 (5)	NI2^xvi—O2—NI2	98.43 (15)
AS2^xii—NA1—AS2^v	72.931 (18)	AS1—O2—CA1^vii	100.44 (15)
AS2^xiii—NA1—AS2^v	107.069 (18)	NI2^xvi—O2—CA1^vii	103.60 (11)
O4ⁱⁱ—NA1—AS2^xi	93.49 (6)	NI2—O2—CA1^vii	103.60 (11)
O4^x—NA1—AS2^xi	86.51 (6)	AS2—O3—NI2^xxviii	131.73 (15)
O4^v—NA1—AS2^xi	148.40 (6)	AS2—O3—CA1	123.00 (14)
O4^xi—NA1—AS2^xi	31.60 (6)	NI2^xxviii—O3—CA1	105.15 (11)
O3^xii—NA1—AS2^xi	109.18 (6)	AS2—O3—NA1^ix	90.68 (10)
O3^xiii—NA1—AS2^xi	70.82 (6)	NI2^xxviii—O3—NA1^ix	94.77 (9)
O3^xiv—NA1—AS2^xi	148.96 (5)	CA1—O3—NA1^ix	79.80 (8)
O3^xv—NA1—AS2^xi	31.04 (5)	AS2—O4—AL1^viii	123.93 (14)
AS2^xii—NA1—AS2^xi	107.069 (18)	AS2—O4—NI1^viii	123.93 (14)
AS2^xiii—NA1—AS2^xi	72.931 (18)	AL1^viii—O4—NI1^viii	0.0
AS2^v—NA1—AS2^xi	180.0	AS2—O4—NI2	95.03 (11)
O4^xvi—NI1—O4^xvii	180.0	AL1^viii—O4—NI2	127.94 (12)
O4^xvi—NI1—O4^xviii	89.50 (15)	NI1^viii—O4—NI2	127.94 (12)
O4^xvii—NI1—O4^xviii	90.50 (15)	AS2—O4—NA1^xxvi	101.08 (11)
O4^xvi—NI1—O4^xix	90.50 (15)	AL1^viii—O4—NA1^xxvi	99.02 (10)
O4^xvii—NI1—O4^xix	89.50 (15)	NI1^viii—O4—NA1^xxvi	99.02 (10)
O4^xviii—NI1—O4^xix	180.00 (10)	NI2—O4—NA1^xxvi	106.23 (10)

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

CHARDI and BVS calculations of cation polyhedra in three different structural models: (a) NaCa_0.77Ni_2.54Al_0.46(AsO₄)₃ (I); (b) NaCaNi₃(AsO₄)₃ and (c) NaCaNi_2.58Al_0.42(AsO₄)₃. (Structure described as built on cation-centered polyhedra). top

Cation(i)	CN(i)		ECoN(i)			q(i).sof(i)			V(i).sof(i)			Q(i)			q(i)/Q(i)
		a	b	c	a	b	c	a	b	c	a	b	c	a	b	c
Ca1	8	7.85	7.86	7.86	1.54	2.00	2.00	1.54	1.53	1.53	1.58	2.00	1.99	0.97	1.00	1.00
Na1	8	6.82	6.81	6.81	1.00	1.00	1.00	1.11	1.11	1.11	0.97	1.00	0.97	1.03	1.00	1.03
M1	6	5.77	5.81	5.79	2.46	2.00	2.46	2.45	2.43	2.46	2.46	2.09	2.42	1.00	0.96	1.00
Ni2	6	5.92	5.93	5.93	2.00	2.00	2.00	2.02	2.02	2.02	1.93	1.92	1.90	1.03	1.04	1.05
As1	4	4.00	4.00	4.00	5.00	5.00	5.00	5.09	5.02	5.07	5.21	5.16	5.08	0.96	0.97	0.98
As2	4	3.96	3.95	3.96	5.00	5.00	5.00	4.93	4.92	4.93	4.95	4.96	4.87	1.01	1.01	1.03

Notes: CN is coordination number; sof(Ca) in (a) = 0.77; M1 = Ni in (b), Ni_0.54Al_0.46 in (a) and Ni_0.58Al_0.42 in (c); V(M1 = Ni1/Al1) = 2.40/2.51 in (a) and 2.41/2.52 in (c).

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