The rich crystal chemistry of the AMM′(PO4)2 morphotropic series: NaZnAl(PO4)2, the first Na representative with a new structure type

Yakubovich, O.; Kiriukhina, G.; Volkov, A.; Dimitrova, O.

doi:10.1107/S2053229619004327

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The rich crystal chemistry of the AMM′(PO₄)₂ morphotropic series: NaZnAl(PO₄)₂, the first Na representative with a new structure type

O. Yakubovich, G. Kiriukhina, A. Volkov and O. Dimitrova

A novel phosphate, sodium zinc aluminium bis(phosphate), NaZnAl(PO₄)₂, was obtained under mild-temperature hydrothermal conditions at 553 K. The crystal structure has been studied using single-crystal X-ray experimental data. The pseudo-hexagonal phase NaZnAl(PO₄)₂ crystallizes in the monoclinic space group P2₁/c. Its unique crystal structure is based on a three-dimensional (3D) framework built by Zn-, Al- and P-centred tetrahedra sharing vertices. Channels parallel to the [101] and [ $\overline{1}$ 01] directions are limited by six- and eight-membered windows, and incorporate Na atoms. The new compound is discussed as a member of the morphotropic series AMM′PO₄, where A = Na, K, Rb or NH₄, M = Cu, Ni, Co, Fe, Zn or Mg and M′ = Fe, Al or Ga. The title compound is the first Na representative within the series and is characterized by a 3D architecture of tetrahedra populated in an ordered manner by Zn²⁺, Al³⁺ and P⁵⁺ ions.

Keywords: morphotropic series; phosphate; open framework; crystal structure; structure types; crystal chemistry; sodium; zinc; aluminium.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S2053229619004327/fn3303sup1.cif Contains datablocks I, global
	Structure factor file (CIF format) https://doi.org/10.1107/S2053229619004327/fn3303Isup2.hkl Contains datablock I

CCDC reference: 1906642

Computing details top

Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012); program(s) used to solve structure: SHELXT (Sheldrick, 2015a) and WinGX (Farrugia, 2012); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b) and WinGX (Farrugia, 2012); molecular graphics: DIMOND (Brandenburg, 2006).

Sodium zinc aluminium bis(phosphate) top

Crystal data top

NaZnAl(PO₄)₂	F(000) = 592
M_r = 305.28	D_x = 2.947 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.5199 (3) Å	Cell parameters from 4763 reflections
b = 8.6700 (2) Å	θ = 3.4–32.0°
c = 9.5471 (3) Å	µ = 4.24 mm⁻¹
β = 119.158 (5)°	T = 293 K
V = 688.14 (5) Å³	Plate, colorless
Z = 4	0.11 × 0.08 × 0.07 mm

Data collection top

Agilent Xcalibur Sapphire3 diffractometer	2010 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1805 reflections with I > 2σ(I)
Detector resolution: 16.0630 pixels mm^-1	R_int = 0.048
ω scans	θ_max = 30.0°, θ_min = 3.4°
Absorption correction: gaussian (CrysAlis PRO; Agilent, 2012)	h = −13→13
T_min = 0.705, T_max = 0.806	k = −12→12
12993 measured reflections	l = −13→13

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.037	Secondary atom site location: difference Fourier map
wR(F²) = 0.070	w = 1/[σ²(F_o²) + (0.019P)² + 1.P] where P = (F_o² + 2F_c²)/3
S = 1.21	(Δ/σ)_max < 0.001
2010 reflections	Δρ_max = 0.53 e Å⁻³
121 parameters	Δρ_min = −0.57 e Å⁻³

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)
Zn1	0.09651 (4)	0.64275 (4)	0.76296 (4)	0.01057 (9)	0.94
Al1	0.09651 (4)	0.64275 (4)	0.76296 (4)	0.01057 (9)	0.06
P1	0.21870 (9)	0.32876 (8)	0.91619 (8)	0.00857 (14)
P2	0.28563 (9)	0.66472 (8)	0.56712 (8)	0.00920 (15)
Al2	0.41408 (9)	0.35512 (9)	0.73167 (9)	0.01034 (16)	0.94
Zn2	0.41408 (9)	0.35512 (9)	0.73167 (9)	0.01034 (16)	0.06
Na1	0.1986 (2)	0.51018 (17)	0.19444 (19)	0.0216 (3)	0.92
Na2	0.274 (2)	0.494 (2)	0.259 (2)	0.0216 (3)	0.08
O1	0.1306 (2)	0.1870 (2)	0.8206 (3)	0.0140 (4)
O2	0.1066 (2)	0.4643 (2)	0.8921 (2)	0.0140 (4)
O3	0.3807 (2)	0.8083 (2)	0.6644 (2)	0.0124 (4)
O4	0.4017 (3)	0.5256 (2)	0.6298 (2)	0.0152 (4)
O5	0.3055 (3)	0.2937 (2)	1.0978 (2)	0.0146 (4)
O6	0.2351 (3)	0.6892 (2)	0.3914 (2)	0.0151 (4)
O7	0.3458 (3)	0.3773 (3)	0.8696 (3)	0.0167 (4)
O8	0.1404 (3)	0.6420 (3)	0.5891 (3)	0.0207 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Zn1	0.01090 (17)	0.01047 (17)	0.01171 (17)	−0.00007 (13)	0.00658 (14)	0.00124 (13)
Al1	0.01090 (17)	0.01047 (17)	0.01171 (17)	−0.00007 (13)	0.00658 (14)	0.00124 (13)
P1	0.0089 (3)	0.0085 (3)	0.0087 (3)	−0.0001 (2)	0.0045 (3)	−0.0001 (2)
P2	0.0103 (3)	0.0091 (3)	0.0089 (3)	−0.0008 (3)	0.0052 (3)	−0.0004 (3)
Al2	0.0111 (4)	0.0099 (4)	0.0110 (4)	−0.0006 (3)	0.0061 (3)	−0.0003 (3)
Zn2	0.0111 (4)	0.0099 (4)	0.0110 (4)	−0.0006 (3)	0.0061 (3)	−0.0003 (3)
Na1	0.0326 (9)	0.0162 (7)	0.0244 (8)	−0.0059 (7)	0.0204 (7)	−0.0046 (6)
Na2	0.0326 (9)	0.0162 (7)	0.0244 (8)	−0.0059 (7)	0.0204 (7)	−0.0046 (6)
O1	0.0129 (10)	0.0117 (10)	0.0167 (10)	−0.0035 (8)	0.0067 (9)	−0.0058 (8)
O2	0.0153 (10)	0.0110 (10)	0.0157 (10)	0.0032 (8)	0.0074 (9)	0.0012 (8)
O3	0.0112 (10)	0.0107 (9)	0.0143 (10)	−0.0010 (7)	0.0054 (8)	−0.0024 (8)
O4	0.0179 (11)	0.0117 (10)	0.0161 (10)	0.0017 (8)	0.0084 (9)	0.0019 (8)
O5	0.0177 (11)	0.0137 (10)	0.0115 (10)	0.0019 (8)	0.0063 (9)	0.0016 (8)
O6	0.0188 (11)	0.0157 (10)	0.0103 (10)	0.0031 (8)	0.0067 (9)	0.0015 (8)
O7	0.0174 (11)	0.0212 (11)	0.0171 (10)	−0.0058 (9)	0.0127 (9)	−0.0048 (9)
O8	0.0153 (11)	0.0327 (13)	0.0179 (11)	−0.0063 (10)	0.0110 (10)	−0.0043 (10)

Geometric parameters (Å, º) top

Zn1—O8	1.899 (2)	P2—Na1ⁱⁱ	3.3303 (16)
Zn1—O1ⁱ	1.943 (2)	Al2—O7	1.740 (2)
Zn1—O6ⁱⁱ	1.947 (2)	Al2—O4	1.742 (2)
Zn1—O2	1.951 (2)	Al2—O3^vi	1.754 (2)
Zn1—Na1ⁱⁱⁱ	3.3056 (15)	Al2—O5^vii	1.754 (2)
Zn1—Na1ⁱⁱ	3.3236 (15)	Al2—Na2^viii	3.210 (19)
Zn1—Na2ⁱⁱ	3.580 (19)	Al2—Na2^v	3.372 (19)
Zn1—Na2ⁱⁱⁱ	3.625 (19)	Al2—Na1^viii	3.5951 (17)
P1—O1	1.517 (2)	Na1—Na2	0.69 (2)
P1—O2	1.528 (2)	Na1—O6	2.330 (3)
P1—O7	1.537 (2)	Na1—O1^vii	2.356 (2)
P1—O5	1.545 (2)	Na1—O3^ix	2.459 (2)
P1—Na1^iv	3.1724 (16)	Na1—O5^x	2.515 (3)
P1—Na2^v	3.334 (19)	Na1—O2^x	2.606 (3)
P1—Na2^iv	3.374 (18)	Na1—O2ⁱⁱⁱ	2.614 (3)
P2—O8	1.509 (2)	Na2—O6	2.245 (18)
P2—O6	1.518 (2)	Na2—O1^vii	2.332 (18)
P2—O4	1.546 (2)	Na2—O3^ix	2.386 (18)
P2—O3	1.553 (2)	Na2—O5^x	2.437 (18)
P2—Na2	3.243 (18)	Na2—O4^viii	2.74 (2)

O8—Zn1—O1ⁱ	108.46 (9)	O2^x—Na1—Zn1^ix	112.54 (7)
O8—Zn1—O6ⁱⁱ	100.55 (9)	O2ⁱⁱⁱ—Na1—Zn1^ix	66.37 (6)
O1ⁱ—Zn1—O6ⁱⁱ	112.79 (9)	P1^x—Na1—Zn1^ix	139.15 (5)
O8—Zn1—O2	125.84 (10)	Zn1ⁱⁱⁱ—Na1—Zn1^ix	89.51 (4)
O1ⁱ—Zn1—O2	96.80 (9)	Na2—Na1—P2^ix	99.5 (16)
O6ⁱⁱ—Zn1—O2	112.69 (9)	O6—Na1—P2^ix	76.41 (6)
O8—Zn1—Na1ⁱⁱⁱ	131.93 (7)	O1^vii—Na1—P2^ix	168.49 (8)
O1ⁱ—Zn1—Na1ⁱⁱⁱ	44.58 (7)	O3^ix—Na1—P2^ix	25.96 (5)
O6ⁱⁱ—Zn1—Na1ⁱⁱⁱ	125.33 (7)	O5^x—Na1—P2^ix	106.30 (7)
O2—Zn1—Na1ⁱⁱⁱ	52.22 (7)	O2^x—Na1—P2^ix	74.57 (6)
O8—Zn1—Na1ⁱⁱ	67.74 (8)	O2ⁱⁱⁱ—Na1—P2^ix	104.41 (7)
O1ⁱ—Zn1—Na1ⁱⁱ	96.53 (7)	P1^x—Na1—P2^ix	89.24 (4)
O6ⁱⁱ—Zn1—Na1ⁱⁱ	43.37 (7)	Zn1ⁱⁱⁱ—Na1—P2^ix	139.63 (5)
O2—Zn1—Na1ⁱⁱ	155.94 (7)	Zn1^ix—Na1—P2^ix	56.92 (3)
Na1ⁱⁱⁱ—Zn1—Na1ⁱⁱ	137.29 (4)	Na2—Na1—Al2^viii	51.6 (16)
O8—Zn1—Na2ⁱⁱ	71.9 (3)	O6—Na1—Al2^viii	83.67 (7)
O1ⁱ—Zn1—Na2ⁱⁱ	104.9 (3)	O1^vii—Na1—Al2^viii	130.27 (8)
O6ⁱⁱ—Zn1—Na2ⁱⁱ	33.9 (3)	O3^ix—Na1—Al2^viii	25.99 (5)
O2—Zn1—Na2ⁱⁱ	145.6 (3)	O5^x—Na1—Al2^viii	75.80 (6)
Na1ⁱⁱⁱ—Zn1—Na2ⁱⁱ	141.9 (3)	O2^x—Na1—Al2^viii	91.49 (6)
Na1ⁱⁱ—Zn1—Na2ⁱⁱ	10.7 (3)	O2ⁱⁱⁱ—Na1—Al2^viii	155.55 (7)
O8—Zn1—Na2ⁱⁱⁱ	124.7 (3)	P1^x—Na1—Al2^viii	81.41 (4)
O1ⁱ—Zn1—Na2ⁱⁱⁱ	35.5 (3)	Zn1ⁱⁱⁱ—Na1—Al2^viii	163.34 (6)
O6ⁱⁱ—Zn1—Na2ⁱⁱⁱ	128.5 (3)	Zn1^ix—Na1—Al2^viii	92.15 (4)
O2—Zn1—Na2ⁱⁱⁱ	61.6 (3)	P2^ix—Na1—Al2^viii	51.89 (3)
Na1ⁱⁱⁱ—Zn1—Na2ⁱⁱⁱ	10.2 (3)	Na1—Na2—O6	88.3 (16)
Na1ⁱⁱ—Zn1—Na2ⁱⁱⁱ	130.8 (3)	Na1—Na2—O1^vii	83.5 (16)
Na2ⁱⁱ—Zn1—Na2ⁱⁱⁱ	137.4 (4)	O6—Na2—O1^vii	95.2 (7)
O1—P1—O2	113.05 (12)	Na1—Na2—O3^ix	87.8 (16)
O1—P1—O7	109.27 (12)	O6—Na2—O3^ix	83.6 (6)
O2—P1—O7	109.68 (12)	O1^vii—Na2—O3^ix	171.3 (10)
O1—P1—O5	110.65 (12)	Na1—Na2—O5^x	88.4 (16)
O2—P1—O5	105.83 (12)	O6—Na2—O5^x	175.8 (10)
O7—P1—O5	108.22 (12)	O1^vii—Na2—O5^x	86.9 (6)
O1—P1—Na1^iv	131.63 (9)	O3^ix—Na2—O5^x	93.7 (6)
O2—P1—Na1^iv	54.68 (9)	Na1—Na2—O4^viii	146.5 (19)
O7—P1—Na1^iv	118.93 (9)	O6—Na2—O4^viii	107.0 (7)
O5—P1—Na1^iv	51.32 (9)	O1^vii—Na2—O4^viii	123.2 (8)
O1—P1—Na2^v	37.9 (4)	O3^ix—Na2—O4^viii	65.3 (5)
O2—P1—Na2^v	146.0 (4)	O5^x—Na2—O4^viii	74.7 (5)
O7—P1—Na2^v	77.4 (3)	Na1—Na2—Al2^viii	118.7 (17)
O5—P1—Na2^v	103.0 (3)	O6—Na2—Al2^viii	94.6 (6)
Na1^iv—P1—Na2^v	151.6 (3)	O1^vii—Na2—Al2^viii	156.0 (8)
O1—P1—Na2^iv	135.0 (3)	O3^ix—Na2—Al2^viii	32.5 (3)
O2—P1—Na2^iv	65.5 (4)	O5^x—Na2—Al2^viii	84.7 (5)
O7—P1—Na2^iv	113.1 (3)	O4^viii—Na2—Al2^viii	32.8 (2)
O5—P1—Na2^iv	41.3 (3)	Na1—Na2—P2	106.4 (17)
Na1^iv—P1—Na2^iv	11.6 (3)	O6—Na2—P2	24.5 (2)
Na2^v—P1—Na2^iv	144.0 (5)	O1^vii—Na2—P2	81.2 (5)
O8—P2—O6	110.69 (13)	O3^ix—Na2—P2	100.6 (6)
O8—P2—O4	112.01 (13)	O5^x—Na2—P2	159.7 (8)
O6—P2—O4	108.58 (12)	O4^viii—Na2—P2	98.2 (6)
O8—P2—O3	109.14 (12)	Al2^viii—Na2—P2	99.6 (5)
O6—P2—O3	109.13 (12)	Na1—Na2—P1^vii	104.5 (17)
O4—P2—O3	107.19 (12)	O6—Na2—P1^vii	106.0 (6)
O8—P2—Na2	115.9 (4)	O1^vii—Na2—P1^vii	23.6 (2)
O6—P2—Na2	37.8 (4)	O3^ix—Na2—P1^vii	164.3 (8)
O4—P2—Na2	72.4 (4)	O5^x—Na2—P1^vii	77.3 (5)
O3—P2—Na2	131.4 (3)	O4^viii—Na2—P1^vii	99.7 (6)
O8—P2—Na1ⁱⁱ	69.64 (10)	Al2^viii—Na2—P1^vii	132.5 (7)
O6—P2—Na1ⁱⁱ	106.49 (9)	P2—Na2—P1^vii	85.4 (4)
O4—P2—Na1ⁱⁱ	141.00 (9)	Na1—Na2—Al2^vii	112.7 (17)
O3—P2—Na1ⁱⁱ	43.89 (8)	O6—Na2—Al2^vii	154.2 (8)
Na2—P2—Na1ⁱⁱ	144.3 (4)	O1^vii—Na2—Al2^vii	73.6 (5)
O7—Al2—O4	112.36 (11)	O3^ix—Na2—Al2^vii	110.9 (6)
O7—Al2—O3^vi	108.74 (11)	O5^x—Na2—Al2^vii	30.0 (2)
O4—Al2—O3^vi	105.42 (10)	O4^viii—Na2—Al2^vii	63.8 (4)
O7—Al2—O5^vii	109.12 (11)	Al2^viii—Na2—Al2^vii	88.3 (5)
O4—Al2—O5^vii	111.21 (11)	P2—Na2—Al2^vii	129.8 (6)
O3^vi—Al2—O5^vii	109.90 (10)	P1^vii—Na2—Al2^vii	55.7 (3)
O7—Al2—Na2^viii	128.1 (3)	Na1—Na2—P1^x	67.4 (15)
O4—Al2—Na2^viii	58.6 (4)	O6—Na2—P1^x	151.1 (8)
O3^vi—Al2—Na2^viii	46.9 (4)	O1^vii—Na2—P1^x	97.1 (6)
O5^vii—Al2—Na2^viii	121.9 (3)	O3^ix—Na2—P1^x	80.2 (5)
O7—Al2—Na2^v	74.4 (3)	O5^x—Na2—P1^x	24.7 (2)
O4—Al2—Na2^v	152.2 (4)	O4^viii—Na2—P1^x	87.8 (5)
O3^vi—Al2—Na2^v	97.1 (3)	Al2^viii—Na2—P1^x	84.4 (4)
O5^vii—Al2—Na2^v	44.0 (3)	P2—Na2—P1^x	173.8 (7)
Na2^viii—Al2—Na2^v	139.5 (5)	P1^vii—Na2—P1^x	95.5 (5)
O7—Al2—Na1^viii	122.77 (8)	Al2^vii—Na2—P1^x	54.7 (3)
O4—Al2—Na1^viii	67.52 (8)	Na1—Na2—Zn1^ix	63.1 (15)
O3^vi—Al2—Na1^viii	37.90 (7)	O6—Na2—Zn1^ix	29.0 (3)
O5^vii—Al2—Na1^viii	124.46 (8)	O1^vii—Na2—Zn1^ix	104.7 (6)
Na2^viii—Al2—Na1^viii	9.7 (4)	O3^ix—Na2—Zn1^ix	70.3 (5)
Na2^v—Al2—Na1^viii	133.2 (3)	O5^x—Na2—Zn1^ix	146.9 (8)
Na2—Na1—O6	74.4 (16)	O4^viii—Na2—Zn1^ix	119.9 (6)
Na2—Na1—O1^vii	79.5 (16)	Al2^viii—Na2—Zn1^ix	94.4 (5)
O6—Na1—O1^vii	92.35 (9)	P2—Na2—Zn1^ix	53.0 (3)
Na2—Na1—O3^ix	75.8 (16)	P1^vii—Na2—Zn1^ix	123.8 (5)
O6—Na1—O3^ix	80.28 (8)	Al2^vii—Na2—Zn1^ix	175.7 (7)
O1^vii—Na1—O3^ix	155.32 (11)	P1^x—Na2—Zn1^ix	122.2 (6)
Na2—Na1—O5^x	75.6 (16)	P1—O1—Zn1^xi	125.84 (12)
O6—Na1—O5^x	149.91 (11)	P1—O1—Na2^v	118.5 (5)
O1^vii—Na1—O5^x	84.65 (8)	Zn1^xi—O1—Na2^v	115.6 (5)
O3^ix—Na1—O5^x	90.04 (8)	P1—O1—Na1^v	133.34 (13)
Na2—Na1—O2^x	126.9 (16)	Zn1^xi—O1—Na1^v	100.05 (9)
O6—Na1—O2^x	146.40 (10)	Na2^v—O1—Na1^v	17.0 (5)
O1^vii—Na1—O2^x	115.31 (9)	P1—O2—Zn1	121.37 (12)
O3^ix—Na1—O2^x	81.04 (8)	P1—O2—Na1^iv	96.75 (10)
O5^x—Na1—O2^x	57.16 (7)	Zn1—O2—Na1^iv	117.73 (10)
Na2—Na1—O2ⁱⁱⁱ	143.3 (16)	P1—O2—Na1ⁱⁱⁱ	134.43 (12)
O6—Na1—O2ⁱⁱⁱ	84.53 (8)	Zn1—O2—Na1ⁱⁱⁱ	91.62 (8)
O1^vii—Na1—O2ⁱⁱⁱ	71.53 (8)	Na1^iv—O2—Na1ⁱⁱⁱ	93.39 (8)
O3^ix—Na1—O2ⁱⁱⁱ	130.31 (9)	P2—O3—Al2^xii	133.43 (13)
O5^x—Na1—O2ⁱⁱⁱ	122.23 (9)	P2—O3—Na2ⁱⁱ	124.8 (5)
O2^x—Na1—O2ⁱⁱⁱ	86.61 (8)	Al2^xii—O3—Na2ⁱⁱ	100.6 (5)
Na2—Na1—P1^x	101.0 (15)	P2—O3—Na1ⁱⁱ	110.14 (11)
O6—Na1—P1^x	163.73 (8)	Al2^xii—O3—Na1ⁱⁱ	116.11 (10)
O1^vii—Na1—P1^x	102.23 (7)	Na2ⁱⁱ—O3—Na1ⁱⁱ	16.4 (5)
O3^ix—Na1—P1^x	83.46 (6)	P2—O4—Al2	136.01 (14)
O5^x—Na1—P1^x	28.65 (5)	P2—O4—Na2^viii	131.1 (4)
O2^x—Na1—P1^x	28.57 (5)	Al2—O4—Na2^viii	88.5 (4)
O2ⁱⁱⁱ—Na1—P1^x	106.77 (7)	P1—O5—Al2^v	139.94 (14)
Na2—Na1—Zn1ⁱⁱⁱ	112.2 (16)	P1—O5—Na2^iv	113.9 (5)
O6—Na1—Zn1ⁱⁱⁱ	88.25 (7)	Al2^v—O5—Na2^iv	105.9 (5)
O1^vii—Na1—Zn1ⁱⁱⁱ	35.37 (5)	P1—O5—Na1^iv	100.02 (11)
O3^ix—Na1—Zn1ⁱⁱⁱ	163.84 (8)	Al2^v—O5—Na1^iv	118.81 (10)
O5^x—Na1—Zn1ⁱⁱⁱ	105.41 (7)	Na2^iv—O5—Na1^iv	16.0 (5)
O2^x—Na1—Zn1ⁱⁱⁱ	103.17 (7)	P2—O6—Zn1^ix	123.60 (12)
O2ⁱⁱⁱ—Na1—Zn1ⁱⁱⁱ	36.16 (5)	P2—O6—Na2	117.7 (5)
P1^x—Na1—Zn1ⁱⁱⁱ	107.81 (5)	Zn1^ix—O6—Na2	117.1 (5)
Na2—Na1—Zn1^ix	106.2 (16)	P2—O6—Na1	129.88 (13)
O6—Na1—Zn1^ix	35.02 (6)	Zn1^ix—O6—Na1	101.61 (10)
O1^vii—Na1—Zn1^ix	112.15 (7)	Na2—O6—Na1	17.3 (5)
O3^ix—Na1—Zn1^ix	74.56 (6)	P1—O7—Al2	145.65 (15)
O5^x—Na1—Zn1^ix	163.20 (7)	P2—O8—Zn1	136.70 (14)

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

Bond valence data for KZnAl(PO₄)₂ top

Atom	Na	Zn	Al	P1	P2	Σ
O1	0.224	0.524		1.310		2.06
O2	0.114 0.112	0.513		1.272		2.01
O3	0.179		0.757		1.189	2.12
O4			0.782		1.212	1.99
O5	0.146		0.757	1.215		2.12
O6	0.241	0.519			1.307	2.07
O7			0.786	1.241		2.03
O8		0.590			1.339	1.93
Σ	1.01	2.15	3.08	5.04	5.05

The calculation is made without considering the splitting of the Na position and `dilution' of the positions of Zn and Al.

Composition, crystal characteristics, selected distances and physical properties of members of the AMM'(PO₄)₂ morphotropic series (A⁺ = Rb, K, NH₄ or Na; M²⁺ = Cu, Ni, Co, Fe, Zn or Mg; M'³⁺ = Fe, Al or Ga) top

Formula	Unit-cell parameters a, b, c (Å) and β (°)	V (Å³), ρ (Mg m^-3) and V/Z (Å³)	<M—O> (Å) <M'–O> (Å)	Physical properties	Reference
1. The KNiFe(PO₄)₂ structure type, space group P2₁/c, Z = 4
3D framework built by M'³⁺O₅ bipyramids and PO₄ tetrahedra sharing oxygen vertices. Channels in the [100] and [001] directions accommodate A⁺ cations and chains of M²⁺O₆ octahedra sharing edges
K(Ni,Fe)Fe(PO₄)₂	5.102 (1)	658.4	2.090 (1) (M = Ni²⁺, Fe²⁺)	No information available	Strutynska et al. (2014)
	14.464 (3)	3.46	1.937 (1) (M' = Fe³⁺)
	9.226 (2)	164.6
	104.74 (3)
KNiFe(PO₄)₂	5.101 (2)	657.3	2.090 (2) (M = Ni²⁺)	The thermal study showed a congruent melting of the compound at 941 °C	Badri et al. (2015)
	14.456 (2)	3.47
	9.216 (1)	164.3
	104.73 (2)
KMgFe(PO₄)₂-LT	5.171 (3)	665.9	2.105 (2) (M = Mg²⁺)	The DTA analysis demonstrated an irreversible phase transition from the low- to the high-temperature stable phases at 778 °C	Badri et al. (2015)
	14.479 (2)	3.08	1.939 (1) (M' = Fe³⁺)
	9.209 (2)	166.5
	105.02 (1)
KCoFe(PO₄)₂-LT	5.148 (1)	663.3	2.122 (2) (M = Co²⁺)	An irreversible phase transition from the low- to the high-temperature stable phases at 840 °C	Badri et al. (2015)
	14.403 (2)	3.44	1.934 (1) (M' = Fe³⁺)
	9.256 (1)	165.8
	104.87 (2)
RbCuAl(PO₄)₂	5.0723 (8)	656.4	2.136 (2) (M = Cu²⁺)	The compound orders antiferromagnetically at TN = 10.5 K and exhibits spontaneous magnetization in the magnetically ordered state	Yakubovich et al. (2016)
	14.070 (2)	3.70	1.837 (2) (M' = Al³⁺)
	9.352 (1)	164.1
	100.41 (1)

2. The KFe²⁺Fe³⁺(PO₄)₂ structure type, space group P2₁/c, Z = 4
3D framework built by MO₅ bipyramids, M'O₆ octahedra and PO₄ tetrahedra sharing oxygen edges and vertices. Channels along the [001] direction accommodate A+ cations
KFe²⁺Fe³⁺(PO₄)₂	7.846 (3)	646.4	2.024 (5) (M = Fe²⁺)	No information available	Yakubovich et al. (1986)
	10.032 (3)	3.50	2.021 (4) (M' = Fe³⁺)
	9.127 (4)	161.6
	115.87 (3)
K(Fe²⁺,Fe³⁺)(Fe³⁺,Fe²⁺,Mg)(PO₄)₂	7.8444 (3)	643.5	2.006 (3) (M = Fe²⁺,Fe³⁺)	No information available	Yatskin et al. (2012)
	10.0033 (3)	3.49	2.014 (3) (M' = Fe³⁺,Fe²⁺,Mg)
	9.1459 (4)	160.9
	116.272 (5)
KCuFe(PO₄)₂	7.958 (3)	644.3	2.005 (2) (M = Cu²⁺)	The compound is antiferromagnetic. Electrical measurements revealed the activation energy (1.22 eV) and the conductivity evaluation suggested the potassium cations as the charge carriers	Badri et al. (2011)
	9.931 (2)	3.59	2.015 (2) (M' = Fe³⁺)
	9.105 (2)	161.1
	116.44 (3)

3. The (NH₄)Fe²⁺Fe³⁺(PO₄)₂ structure type, space group C2/c, Z = 16
Chains of edge-sharing Fe²⁺O₆ octahedra, chains of corner-sharing Fe³⁺O₆ octahedra and PO₄ tetrahedra form 3D framework with tunnels in the [221], [221] and [001] directions, in which NH₄⁺ cations are located
(NH₄)Fe²⁺Fe³⁺(PO₄)₂	20.007 (1)	2585.7	2.014 (2) (M' = Fe³⁺)	No information available	Boudin & Lii (1998)
	14.832 (1)	3.29	2.145 (2) (M = Fe²⁺)
	9.990 (1)	161.6
	119.28 (1)

4. The celsian, BaAl₂[SiO₄]₂ structure type, space group C2/c, Z = 8
3D framework built by corner-sharing (M/M')O₄ and PO₄ tetrahedra with the A⁺ ions in the framework tunnels
K(Co,Al)₂(PO₄)₂	13.318 (2)	1496.9	1.826 (19) (M = 0.5Co²⁺,0.5Al³⁺)	No information available	Chen et al. (1997)
	13.152 (1)	2.80	1.829 (13) (M' = 0.5Co²⁺,0.5Al³⁺)
	8.683 (1)	187.1
	100.19 (1)
K(Zn,Fe)₂(PO₄)₂	13.514 (4)	1543.9	1.884 (2) (M = 0.5Zn²⁺,0.5Fe³⁺)	The magnetic measuring revealed an antiferromagnetic behaviour with TN = 8.5 K	Badri et al. (2014)
	13.273 (6)	3.01	1.891 (3) (M' = 0.5Zn²⁺,0.5Fe³⁺)
	8.742 (3)	193.0
	100.07 (2)
(NH₄)(Co,Al)₂(PO₄)₂	13.474 (1)	1571.4	1.839 (4) (M = 0.5Co²⁺,0.5Al³⁺)	The framework density is 20.4	Bu et al. (1998)
	13.257 (1)	2.48	1.854 (4) (M' = 0.5Co²⁺,0.5Al³⁺)
	8.960 (1)	196.4
	100.92 (1)
(NH₄)(Zn,Ga)₂(PO₄)₂	13.370 (3)	1560.4	1.863 (2) (M = 0.5Zn²⁺,0.5Ga³⁺)	No information available	Mrak et al. (2002)
	13.190 (3)	2.92	1.870 (2) (M' = 0.5Zn²⁺,0.5Ga³⁺)
	8.998 (2)	195.1
	100.46 (3)
(NH₄)_0.83(Zn_0.83Al_1.17)(PO₄)₂	13.533 (8)	1617.2	1.846 (5) (M = Zn²⁺,Al³⁺)	The compound has a potential usage as adsorbent or catalytic material at low temperature	Ma et al. (2006)
	13.392 (8)	2.39	1.862 (5) (M' = Zn²⁺,Al³⁺)
	9.072 (5)	202.1
	100.87 (8)

*5. The paracelsian, BaAl₂[SiO₄]₂ structure type, space group P2₁/a, Z = 4**
3D framework built from alternating corner-sharing MO₄ and TO₄ tetrahedra with eight-membered ring channels with the A⁺ions incorporated
(NH₄)(Zn,Ga)₂(PO₄)₂	9.406 (1)	800.4	1.872 (2) (M = 0.5Zn²⁺,0.5Ga³⁺)	The compound has a potential for high ion-exchange capacity	Logar et al. (2001)
	9.881 (1)	2.85	1.877 (2) (M' = 0.5Zn²⁺,0.5Ga³⁺)
	8.612 (1)	200.1
	90.58 (1)

6. The KMgFe(PO₄)₂ structure type, space group C2/c, Z = 4
2D layers built by corner-sharing (M/M')O₄ and PO₄ tetrahedra with the K atoms in the interlayer space
K(Mg,Fe)₂(PO₄)₂-HT	18.529 (7)	807.3	1.878 (2) (M = 0.5Mg²⁺,0.5Fe³⁺)	This material behaves as a 2D ionic conductor with low activation energy of 0.51 eV	Badri et al. (2009)
	5.402 (3)	3.49
	9.374 (9)	201.8
	120.64 (5)

7. The NaZnAl(PO₄)₂ structure type, space group P2₁/c, Z = 4
3D framework built by M²⁺O₄, M'³⁺O₄ and PO₄ tetrahedra sharing oxygen vertices. The Na atoms are statistically distributed in two sites in the structure tunnels
NaZnAl(PO₄)₂	9.520 (1)	688.1	1.935 (2) (M = Zn²⁺)	The compound presents a possible candidate for the ionic conductivity	Present work
	8.670 (1)	2.95	1.748 (2) (M' = Al³⁺)
	9.547 (1)	172.0
	119.16 (1)

Note: (*) crystal characteristics are given in nonstandard setting of the space group C₂_h⁵ = P2₁/c for consistency of data.

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