Crystal structure of barium dinickel(II) iron(III) tris­[orthophosphate(V)], BaNi₂Fe(PO₄)₃

The orthophosphate BaNi₂Fe(PO₄)₃ crystallizes in the α-CrPO₄ type of structure, in which edge-sharing [Ni₂O₁₀] octa­hedra are linked to PO₄ tetra­hedra and [FeO₆] octa­hedra to form a three-dimensional framework delimiting channels which house disordered Ba²⁺ cations.

Abstract

The orthophosphate BaNi₂Fe(PO₄)₃ has been synthesized by a solid-state reaction route and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray spectroscopy. The crystal structure comprises (100) sheets made up of [Ni₂O₁₀] dimers that are linked to two PO₄ tetra­hedra via common edges and vertices and of linear infinite [010] chains of corner-sharing [FeO₆] octa­hedra and [PO₄] tetra­hedra. The linkage of the sheets and chains into a framework is accomplished through common vertices of PO₄ tetra­hedra and [FeO₆] octa­hedra. The framework is perforated by channels in which positionally disordered Ba²⁺ cations are located.

1. Chemical context

Phosphate-based materials have been studied extensively in the past. Among them are orthophosphates, which have gained great inter­est in recent years owing to their structural richness (Maeda, 2004 ▸) and their promising applications, for example in electrochemical catalysis (Dwibedi et al., 2020 ▸; Cheng et al., 2021 ▸; Rekha et al., 2021 ▸; Anahmadi et al., 2022 ▸). Furthermore, orthophosphates doped with rare-earth cations have shown excellent optical properties (Ci et al., 2014 ▸; Li et al., 2021 ▸; Indumathi et al., 2022 ▸), along with a wide range of applications for use in luminescence emission displays (Li et al., 2008 ▸; Wan et al., 2010 ▸; Yang et al., 2019 ▸; Santos et al., 2022 ▸).

In this context, our research inter­est is connected with tris-orthophosphate-based materials with general formula (A ₂/B)M ₂ M′(PO₄)₃, where A can be an alkali, B an alkaline earth and M and M′ transition metal cations. The crystal structures of these orthophosphates adopt the α-CrPO₄ type of structure, consisting of a three-dimensional framework made up of [MO₆] and [M′O₆] octa­hedra sharing corners and/or edges with PO₄ tetra­hedra. This framework is permeated by channels in which the A or B cations are located.

We report herein on the synthesis and structural characterization of barium dinickel(II) iron(III) tris-orthophosphate, BaNi₂Fe(PO₄)₃.

2. Structural commentary

The title compound is related to the strontium and calcium homologs MNi₂Fe(PO₄)₃ (M = Sr, Ca; Ouaatta et al., 2015 ▸, 2017 ▸), all adopting the α-CrPO₄ structure type (Attfield et al., 1986 ▸). The asymmetric unit of BaNi₂Fe(PO₄)₃ is comprised of ten sites, eight of which are on special positions, except the O3 and O4 sites on a general position (Wyckoff position 16 j). Ba1 (site occupation 0.9868) exhibits site symmetry mm2 (4 e), Ba2 (site occupation 0.0132) 2/m (4 a), Fe1 2/m (4 b), Ni1 2 (8 g), P1 mm2 (4 e), P2 2 (8 g), while O1 and O2 occupy sites with m (8 h) and m (8 i) symmetry, respectively. The framework structure of BaNi₂Fe(PO₄)₃ is composed of extended (100) sheets and linear infinite chains extending parallel to [010] (Fig. 1 ▸). The (100) sheets are made up from edge-sharing [Ni₂O₁₀] dimers linked to two P2O₄ tetra­hedra via common edges to form an [Ni₂P2₂O₁₄] unit that is linked to four neighboring units (Fig. 2 ▸). Between these sheets appear the linear infinite chains resulting from the alternating linkage of P1O₄ tetra­hedra and [FeO₆] octa­hedra, which are surrounded by a zigzag arrangement of Ba²⁺ cations (Fig. 3 ▸). The sheets and chains are linked through common vertices of PO₄ tetra­hedra and [FeO₆] octa­hedra into a framework, which delimits two types of channels parallel to [100] and [010] in which the disordered Ba²⁺ cations are located (Figs. 4 ▸, 5 ▸).

Figure 1.

The principal building units in the crystal structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) −x + 1, −y +  , z − 1; (ii) x, y, z − 1; (iii) −x + 1, −y +  , z; (iv) −x +  , −y + 1, z −  ; (v) x −  , y −  , z −  ; (vi) −x +  , y −  , z −  ; (vii) x −  , −y + 1, z −  ; (viii) −x + 2, −y + 1, −z + 2; (ix) −x + 2, y, z; (x) x, −y + 1, −z + 2; (xi) −x +  , −y +  , −z +  ; (xii) −x +  , y, −z +  ; (xiii) x, −y + 1, −z + 1; (xiv) −x + 2, −y + 1, −z + 1; (xv) x +  , y, −z +  ].

Figure 2.

Projection of a (100) sheet along [100] showing the [Ni₂P(2)₂O₁₄] unit.

Figure 3.

A chain formed by sharing corners of [FeO₆] octa­hedra and P1O₄ tetra­hedra, alternating with a zigzag arrangement of barium cations (Ba1) along [010].

Figure 4.

Polyhedral representation of the crystal structure of BaNi₂Fe(PO₄)₃ showing Ba1 in the channels running along the [100] direction and a row of underoccupied Ba2 along [001].

Figure 5.

Polyhedral representation of the crystal structure of BaNi₂Fe(PO₄)₃ showing Ba1 and Ba2 in the channels.

To confirm the structure model of BaNi₂Fe(PO₄)₃, the bond-valence method (Brown, 1977 ▸; 1978 ▸; Brown & Altermatt, 1985 ▸) and charge distribution (CHARDI) concept (Hoppe et al., 1989 ▸) were employed by making use of the programs EXPO2014 (Altomare et al., 2013 ▸) and CHARDI2015 (Nespolo & Guillot, 2016 ▸), respectively. Table 1 ▸ compiles all cationic valences V(i) computed with the bond-valence method and their related charges Q(i) obtained with the CHARDI concept. The resulting Q(i) and V(i) values are all close to the corresponding charges q(i)×sof(i) [q(i) are formal oxidation numbers weighted by the site occupation factors sof(i)]. In summary, the expected oxidation states of Ba²⁺, Ni²⁺, Fe³⁺ and P⁵⁺ are predicted through the charge distribution. The inter­nal criterion q(i)/Q(i) is very near to 1 for all ionic species and the mean absolute percentage deviation (MAPD), which gives a measure for the agreement between the q(i) and Q(i) charges, is just 1.3%, thus confirming the validity of the structure model (Eon & Nespolo, 2015 ▸). The global instability index (GII; Salinas-Sanchez et al., 1992 ▸) of 0.13 is a further confirmation of the structure model.

Table 1. Bond valence and CHARDI analyses for the cations in the title compound.

q(i) = formal oxidation number; sof(i) = site occupancy; CN(i) = classical coordination number; Q(i) = calculated charge; V(i) = calculated valence; ECoN(i) = effective coordination number.

Cation	q(i)	sof(i)	CN(i)	ECoN(i)	V(i)	Q(i)	q(i)/Q(i)
Ba1	1.98	0.99	8	7.99	2.37	1.98	1.00
Ba2	0.02	0.01	8	5.43	0.02	0.99
Ni	2.00	1.00	6	5.97	2.00	1.98	1.01
Fe	3.00	1.00	4	5.96	3.01	2.99	1.00
P1	5.00	1.00	4	3.99	4.95	4.83	1.04
P2	5.00	1.00	4	3.96	4.85	5.11	0.98

3. Database survey

It is reasonable to compare the crystal structure of the title compound with that of α-CrPO₄ (Glaum et al., 1986 ▸). Both phosphates crystallize in the ortho­rhom­bic system in space group type Imma. Their unit-cell parameters are nearly the same despite the differences between their chemical formulae. In the structure of α-CrPO₄, the Cr³⁺ and P⁵⁺ cations occupy four special positions that are part of a framework is comprised of [CrO₆] octa­hedra and [PO₄] tetra­hedra. The resultant framework is permeated by vacant channels along [100] and [010]. The formula of α-CrPO₄ can be written as X1X2Cr1Cr2₂(PO₄)₃, where X1, X2 represent the empty channel sites. Accordingly, the substitution of Cr1 or Cr2 by a divalent cation requires charge compensation by cations located in the channels to result in AA’MM’₂(PO₄)₃ compounds such as BaNi₂Fe(PO₄)₃, or MNi₂Fe(PO₄)₃ (M = Sr, Ca; Ouaatta et al., 2015 ▸, 2017 ▸). The difference between BaNi₂Fe(PO₄)₃ and the closely related MNi₂Fe(PO₄)₃ structures pertains to the M site, which is split into two sites for the title compound and fully occupied for M = Ca, Sr.

4. Synthesis and crystallization

BaNi₂Fe(PO₄)₃ was prepared from a mixture of Ba(NO₃)₂ (Merck, 98.5%), Ni(NO₃)₂·6H₂O (Riedel-de-Haén, 97%), Fe(NO₃)₃·9H₂O (Panreac, 98%) and H₃PO₄ (85%_wt) in the molar ratio of Ba:Ni:Fe:P = 1:2:1:3. The precursors were suspended in 50 ml of distilled water and stirred without warming for 24 h before heating to dryness at 373 K. The obtained dry residue was ground in an agate mortar until homogeneous, subsequently heated in a platinum crucible up to 673 K to remove volatile decomposition products, and then melted at 1433 K. After being kept at this temperature for one h, the melt was cooled down slowly at a rate of 5 K h⁻¹ to 1233 K and then to room temperature. Single crystals with a brown color and different forms were obtained after leaching with distilled water.

Chemical analysis of the title phosphate was performed with an energy-dispersive X-ray spectroscopy (EDS) microprobe mounted on a JEOL JSM-IT100 in TouchScope^TM scanning electron microscope. The EDS spectrum is depicted in Fig. 6 ▸ and confirms the presence of only barium, nickel, iron, phospho­rus and oxygen in approximately the correct ratios, as shown in Table 2 ▸.

Figure 6.

SEM micrograph and results of an EDS measurement of the title compound.

Table 2. Atom percentages in BaNi₂Fe(PO₄)₃ as determined by EDS.

Element	Atomic percentage	Sigma
O	56.74	0.13
P	19.60	0.16
Fe	5.63	0.17
Ni	12.25	0.27
Ba	5.78	0.30
Total	100.00

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. After assignment of the atomic sites according to the related MNi₂Fe(PO₄)₃ structures (M = Sr, Ca; Ouaatta et al., 2015 ▸, 2017 ▸), a difference-Fourier map revealed a maximum electron density of 3.61 Å⁻³ that was finally modeled as a considerably underoccupied Ba site (Ba2). For the final model, the sum of site-occupation factors for the Ba1 and Ba2 sites were constrained to be 1. The highest remaining maximum and minimum electronic densities are 0.59 Å and 0.47 Å from Ba1 and Ni1, respectively.

Table 3. Experimental details.

Crystal data
Chemical formula	BaNi2Fe(PO4)3
M r	595.52
Crystal system, space group	Orthorhombic, I m m a
Temperature (K)	296
a, b, c (Å)	10.4711 (2), 13.2007 (3), 6.6132 (1)
V (Å3)	914.12 (3)
Z	4
Radiation type	Mo Kα
μ (mm−1)	10.46
Crystal size (mm)	0.32 × 0.25 × 0.19
Data collection
Diffractometer	Bruker X8 APEX Diffractometer
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.624, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	18099, 1460, 1440
R int	0.029
(sin θ/λ)max (Å−1)	0.893
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.015, 0.036, 1.21
No. of reflections	1460
No. of parameters	58
Δρmax, Δρmin (e Å−3)	1.33, −0.78

Computer programs: APEX3 (Bruker, 2016 ▸), SAINT (Bruker, 2016 ▸), SAINT (Bruker, 2016 ▸), SHELXT2014/4 (Sheldrick, 2015a ▸), SHELXL2018/3 (Sheldrick, 2015b ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), DIAMOND (Brandenburg, 2006 ▸), publCIF (Westrip, 2010 ▸).

Supplementary Material

CCDC reference: 2172184

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

BaNi2Fe(PO4)3	Dx = 4.327 Mg m−3
Mr = 595.52	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Imma	Cell parameters from 1460 reflections
a = 10.4711 (2) Å	θ = 3.1–39.4°
b = 13.2007 (3) Å	µ = 10.46 mm−1
c = 6.6132 (1) Å	T = 296 K
V = 914.12 (3) Å3	Block, colourless
Z = 4	0.32 × 0.25 × 0.19 mm
F(000) = 1116

Data collection

Bruker X8 APEX Diffractometer	1460 independent reflections
Radiation source: fine-focus sealed tube	1440 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
φ and ω scans	θmax = 39.4°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −18→13
Tmin = 0.624, Tmax = 0.748	k = −23→23
18099 measured reflections	l = −11→11

Refinement

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)] = 0.015	w = 1/[σ2(Fo2) + (0.0147P)2 + 1.8221P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.036	(Δ/σ)max = 0.001
S = 1.21	Δρmax = 1.33 e Å−3
1460 reflections	Δρmin = −0.78 e Å−3
58 parameters	Extinction correction: SHELXL2018/3 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraints	Extinction coefficient: 0.00403 (16)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ba1	0.500000	0.250000	0.39902 (2)	0.00770 (4)	0.9868
Ba2	1.000000	0.500000	1.000000	0.020 (2)	0.0132
Ni1	0.750000	0.36701 (2)	0.750000	0.00501 (4)
Fe1	1.000000	0.500000	0.500000	0.00337 (5)
P1	0.500000	0.250000	0.90454 (8)	0.00317 (8)
P2	0.750000	0.57020 (3)	0.750000	0.00365 (6)
O1	0.500000	0.34524 (8)	1.03493 (17)	0.00581 (16)
O2	0.61939 (10)	0.250000	0.76536 (17)	0.00534 (15)
O3	0.78276 (8)	0.63385 (6)	0.93423 (13)	0.00771 (12)
O4	0.86254 (7)	0.49395 (6)	0.70839 (12)	0.00574 (11)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Ba1	0.00681 (5)	0.01253 (6)	0.00377 (5)	0.000	0.000	0.000
Ba2	0.014 (5)	0.041 (8)	0.006 (4)	0.000	0.000	0.000 (4)
Ni1	0.00498 (7)	0.00383 (7)	0.00621 (8)	0.000	0.00057 (5)	0.000
Fe1	0.00303 (10)	0.00352 (10)	0.00355 (10)	0.000	0.000	0.00008 (8)
P1	0.00348 (18)	0.00281 (17)	0.00322 (18)	0.000	0.000	0.000
P2	0.00380 (13)	0.00392 (13)	0.00324 (12)	0.000	0.00055 (10)	0.000
O1	0.0078 (4)	0.0033 (3)	0.0063 (4)	0.000	0.000	−0.0014 (3)
O2	0.0042 (4)	0.0063 (4)	0.0055 (4)	0.000	0.0016 (3)	0.000
O3	0.0096 (3)	0.0080 (3)	0.0055 (3)	−0.0024 (2)	0.0007 (2)	−0.0023 (2)
O4	0.0045 (3)	0.0058 (3)	0.0070 (3)	0.0009 (2)	0.0016 (2)	0.0006 (2)

Geometric parameters (Å, º)

Ba1—O1i	2.7163 (11)	Ni1—O4	2.0670 (8)
Ba1—O1ii	2.7163 (11)	Ni1—O4xii	2.0670 (8)
Ba1—O2iii	2.7262 (11)	Ni1—O3x	2.1163 (8)
Ba1—O2	2.7262 (11)	Ni1—O3iv	2.1163 (8)
Ba1—O3iv	2.7530 (8)	Fe1—O4	1.9944 (8)
Ba1—O3v	2.7530 (8)	Fe1—O4ix	1.9944 (8)
Ba1—O3vi	2.7530 (8)	Fe1—O4xiii	1.9944 (8)
Ba1—O3vii	2.7530 (8)	Fe1—O4xiv	1.9944 (8)
Ba2—O4	2.4077 (8)	Fe1—O1iv	2.0559 (11)
Ba2—O4viii	2.4078 (8)	Fe1—O1xv	2.0559 (11)
Ba2—O4ix	2.4078 (8)	P1—O1	1.5246 (11)
Ba2—O4x	2.4078 (8)	P1—O1iii	1.5246 (11)
Ba2—O3ix	2.9129 (9)	P1—O2	1.5524 (11)
Ba2—O3x	2.9129 (9)	P1—O2iii	1.5524 (11)
Ba2—O3viii	2.9129 (9)	P2—O3	1.5192 (8)
Ba2—O3	2.9129 (9)	P2—O3xii	1.5193 (8)
Ni1—O2xi	2.0655 (7)	P2—O4xii	1.5739 (8)
Ni1—O2	2.0655 (7)	P2—O4	1.5739 (8)
O1i—Ba1—O1ii	55.14 (4)	O4viii—Ba2—O3	124.49 (2)
O1i—Ba1—O2iii	141.97 (2)	O4ix—Ba2—O3	111.55 (2)
O1ii—Ba1—O2iii	141.97 (2)	O4x—Ba2—O3	68.45 (2)
O1i—Ba1—O2	141.97 (2)	O3ix—Ba2—O3	102.68 (3)
O1ii—Ba1—O2	141.97 (2)	O3x—Ba2—O3	77.32 (3)
O2iii—Ba1—O2	54.59 (5)	O3viii—Ba2—O3	180.0
O1i—Ba1—O3iv	109.44 (2)	O2xi—Ni1—O2	83.20 (5)
O1ii—Ba1—O3iv	79.47 (2)	O2xi—Ni1—O4	102.84 (3)
O2iii—Ba1—O3iv	107.68 (3)	O2—Ni1—O4	172.00 (3)
O2—Ba1—O3iv	63.00 (2)	O2xi—Ni1—O4xii	172.00 (4)
O1i—Ba1—O3v	79.47 (2)	O2—Ni1—O4xii	102.84 (3)
O1ii—Ba1—O3v	109.44 (2)	O4—Ni1—O4xii	71.66 (4)
O2iii—Ba1—O3v	63.00 (2)	O2xi—Ni1—O3x	86.40 (4)
O2—Ba1—O3v	107.68 (3)	O2—Ni1—O3x	93.14 (4)
O3iv—Ba1—O3v	170.30 (4)	O4—Ni1—O3x	92.48 (3)
O1i—Ba1—O3vi	79.47 (2)	O4xii—Ni1—O3x	88.02 (3)
O1ii—Ba1—O3vi	109.44 (2)	O2xi—Ni1—O3iv	93.14 (4)
O2iii—Ba1—O3vi	107.68 (3)	O2—Ni1—O3iv	86.40 (4)
O2—Ba1—O3vi	63.00 (2)	O4—Ni1—O3iv	88.02 (3)
O3iv—Ba1—O3vi	67.69 (4)	O4xii—Ni1—O3iv	92.48 (3)
O3v—Ba1—O3vi	111.43 (4)	O3x—Ni1—O3iv	179.39 (5)
O1i—Ba1—O3vii	109.44 (2)	O2xi—Ni1—P2	138.40 (2)
O1ii—Ba1—O3vii	79.47 (2)	O2—Ni1—P2	138.40 (2)
O2iii—Ba1—O3vii	63.00 (2)	O4—Fe1—O4ix	92.40 (5)
O2—Ba1—O3vii	107.68 (3)	O4—Fe1—O4xiii	87.60 (5)
O3iv—Ba1—O3vii	111.43 (4)	O4ix—Fe1—O4xiii	180.0
O3v—Ba1—O3vii	67.69 (4)	O4—Fe1—O4xiv	180.0
O3vi—Ba1—O3vii	170.30 (4)	O4ix—Fe1—O4xiv	87.60 (5)
O4—Ba2—O4viii	180.0	O4xiii—Fe1—O4xiv	92.40 (5)
O4—Ba2—O4ix	73.43 (4)	O4—Fe1—O1iv	87.83 (3)
O4viii—Ba2—O4ix	106.57 (4)	O4ix—Fe1—O1iv	87.83 (3)
O4—Ba2—O4x	106.57 (4)	O4xiii—Fe1—O1iv	92.17 (3)
O4viii—Ba2—O4x	73.43 (4)	O4xiv—Fe1—O1iv	92.17 (3)
O4ix—Ba2—O4x	180.0	O4—Fe1—O1xv	92.17 (3)
O4—Ba2—O3ix	111.55 (2)	O4ix—Fe1—O1xv	92.17 (3)
O4viii—Ba2—O3ix	68.45 (2)	O4xiii—Fe1—O1xv	87.83 (3)
O4ix—Ba2—O3ix	55.51 (2)	O4xiv—Fe1—O1xv	87.83 (3)
O4x—Ba2—O3ix	124.49 (2)	O1iv—Fe1—O1xv	180.0
O4—Ba2—O3x	68.45 (2)	O1—P1—O1iii	111.11 (9)
O4viii—Ba2—O3x	111.55 (2)	O1—P1—O2	109.59 (3)
O4ix—Ba2—O3x	124.49 (2)	O1iii—P1—O2	109.59 (3)
O4x—Ba2—O3x	55.51 (2)	O1—P1—O2iii	109.59 (3)
O3ix—Ba2—O3x	180.0	O1iii—P1—O2iii	109.59 (3)
O4—Ba2—O3viii	124.49 (2)	O2—P1—O2iii	107.28 (9)
O4viii—Ba2—O3viii	55.51 (2)	O3—P2—O3xii	112.84 (7)
O4ix—Ba2—O3viii	68.45 (2)	O3—P2—O4xii	112.49 (4)
O4x—Ba2—O3viii	111.55 (2)	O3xii—P2—O4xii	108.95 (5)
O3ix—Ba2—O3viii	77.32 (3)	O3—P2—O4	108.95 (5)
O3x—Ba2—O3viii	102.68 (3)	O3xii—P2—O4	112.49 (4)
O4—Ba2—O3	55.51 (2)	O4xii—P2—O4	100.50 (6)

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