The solid solution K3.84Ni0.78Fe3.19(PO4)5

Nataliia Yu Strutynska; Ivan V Ogorodnyk; Oksana V Livitska; Vyacheslav N Baumer; Nikolay S Slobodyanik

doi:10.1107/S1600536814013609

. 2014 Jun 14;70(Pt 7):i39–i40. doi: 10.1107/S1600536814013609

The solid solution K_3.84Ni_0.78Fe_3.19(PO₄)₅

Nataliia Yu Strutynska ^a,^*, Ivan V Ogorodnyk ^a, Oksana V Livitska ^a, Vyacheslav N Baumer ^b, Nikolay S Slobodyanik ^a

PMCID: PMC4120600 PMID: 25161510

Abstract

The title compound, tetrapotassium tetra[nickel(II)/iron(III)] pentakis(orthophosphate), K_3.84Ni_0.78Fe_3.19(PO₄)₅, has been obtained from a flux. The structure is isotypic with that of K₄MgFe₃(PO₄)₅. The three-dimensional framework is built up from (Ni/Fe)O₅ trigonal bipyramids with a mixed Fe:Ni occupancy of 0.799 (8):0.196 (10) and isolated PO₄ tetrahedra, one of which is on a general position and one of which has -4.. site symmetry. Two K⁺ cations are statistically occupied and are distributed over two positions in hexagonally shaped channels that run parallel to [001]. One K⁺ cation [occupancy 0.73 (3)] is surrounded by nine O atoms, while the other K⁺ cation [occupancy 0.23 (3)] is surrounded by eight O atoms.

Related literature

The structure of isotypic K₄MgFe₃(PO₄)₅ was determined by Hidouri et al. (2008 ▶). For applications of iron-containing phosphates, see: Barpanda et al. (2012 ▶); Fisher et al. (2008 ▶); Huang et al. (2005 ▶); Shih (2003 ▶); Trad et al. (2010 ▶). For the different coordination polyhedra of iron in the structures of these compounds, see: Hidouri et al. (2002 ▶, 2003 ▶). Lajmi et al. (2002 ▶). For crystal-space analysis using Voronoi–Dirichlet polyhedra, see Blatov et al. (1995 ▶). For related compounds, see: Strutynska et al. (2014 ▶).

Experimental

Crystal data

K_3.84Ni_0.78Fe_3.19(PO₄)₅
M _r = 848.92
Tetragonal,
a = 9.6622 (6) Å
c = 9.380 (1) Å
V = 875.70 (12) Å³
Z = 2
Mo Kα radiation
μ = 4.90 mm⁻¹
T = 293 K
0.12 × 0.10 × 0.05 mm

Data collection

Oxford Diffraction Xcalibur-3 diffractometer
Absorption correction: multi-scan (Blessing, 1995 ▶) T _min = 0.562, T _max = 0.743
14788 measured reflections
1935 independent reflections
1771 reflections with I > 2σ(I)
R _int = 0.064

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.095
S = 1.04
1935 reflections
82 parameters
1 restraint
Δρ_max = 1.02 e Å⁻³
Δρ_min = −1.00 e Å⁻³
Absolute structure: Flack (1983 ▶), 829 Friedel pairs
Absolute structure parameter: 0.02 (3)

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2006 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 1999 ▶); software used to prepare material for publication: WinGX (Farrugia, 2012 ▶) and enCIFer (Allen et al., 2004 ▶).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536814013609/wm5027sup1.cif

e-70-00i39-sup1.cif^{(28.5KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536814013609/wm5027Isup2.hkl

e-70-00i39-Isup2.hkl^{(93.4KB, hkl)}

CCDC reference: 1007841

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

Table 1. Selected bond lengths (Å).

Fe1—O1	1.908 (3)
Fe1—O4ⁱ	1.908 (3)
Fe1—O3ⁱⁱ	1.918 (3)
Fe1—O5	1.975 (2)
Fe1—O2ⁱⁱⁱ	1.979 (3)
P1—O5^iv	1.531 (3)
P1—O5	1.531 (2)
P1—O5^v	1.531 (3)
P1—O5^vi	1.531 (2)
P2—O2	1.510 (3)
P2—O4	1.514 (3)
P2—O3	1.520 (3)
P2—O1	1.542 (3)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

supplementary crystallographic information

S1. Comment

Complex iron-containing phosphates have different applications, for example as ionic conductors (Fisher et al., 2008), cathode materials (Barpanda et al., 2012; Trad et al., 2010) and matrices for storage of nuclear waste (Huang et al., 2005; Shih, 2003). In the crystal structures of these compounds the iron cations can adopt different coordination numbers and hence different oxygen polyhedra: FeO₄ (Hidouri et al., 2002), FeO₅ (Hidouri et al., 2003) or FeO₆ (Lajmi et al., 2002). Herein, the structure of the solid solution K_3.84Ni_0.78Fe_3.19(PO₄)₅, tetrapotassium tetra(nickel(II)/iron(III)) pentakis(orthophosphate), (I), is reported. The crystal structure of (I) is isotypic with K₄MgFe₃(PO₄)₅ (Hidouri et al., 2008).

The asymmetric unit of (I) consists of one mixed-occupied (Ni^II/Fe^III) site, two P sites (one of which is located on a fourfold rotoinversion axis), five oxygen sites and two K⁺ sites which are partly occupied and distributed over two positions (K1A and K1B) (Fig. 1). The main building blocks are one [(Ni/Fe^III)O₅] trigonal bipyramid and two [PO₄] tetrahedra. The [(Ni/Fe^III)O₅] polyhedron is linked with [P1O₄] tetrahedra into chains along [001] which additionally are aggregated by the linkage with [P2O₄] tetrahedra into a three-dimensional framework with composition [Ni_0.78Fe_3.19(PO₄)₅]^3.84- (Fig. 2).

The environment of the mixed (Ni^II/Fe^III) site is defined by five oxygen atoms from four [P2O₄] tetrahedra and one [P1O₄] tetrahedron. The distances (Ni/Fe)—O vary between 1.908 (3) and 1.979 (3) Å. The average distance ((Ni/Fe)—O) = 1.937 Å is slightly less than that in K₄MgFe₃(PO₄)₅ (d((Mg/Fe)—O) = 1.952 Å) (Hidouri et al., 2008). The tetrahedral orthophosphate anions deviate only slightly from ideal values with P—O bond lengths ranging from 1.510 (3) to 1.542 (3) Å.

The disordered K⁺ cations are located in hexagonally-shaped channels running along [001], with occupancies of 0.73 (3) (K1A) and 0.23 (3) (K1B). The results of the construction of Voronoi-Dirichlet polyhedra (Blatov et al., 1995) show the K1A being surrounded by nine O atoms while K1B is surrounded by eight O atoms. The K—O distances in the [K1AO₉]-polyhedron are in the range 2.719 (5)–3.072 (6) Å, while in the [K1BO₈]-polyhedron they are in the range 2.636 (13)–3.065 (15) Å.

The main difference between the obtained solid solution and the phosphate K₄MgFe₃(PO₄)₅ (Hidouri et al., 2008) is the splitting of the K⁺ site in two positions. The occupation of the K1B site (0.23 (3)) correlates with the increase of the iron content (from 3 to 3.19) in the starting matrix [M^IIFe^III₃(PO₄)₅]^4-. It seems that a partial substitution of Ni by Fe in [M^IIFe^III₃(PO₄)₅]^4- causes the formation of vacancies in the cationic K⁺ lattice and a splitting of the respective K⁺ site. A similar influence of an heterovalent substitution on the splitting of alkaline metal sites was found for KNi_0.93Fe^II_0.07Fe^III(PO₄)₂ (Strutynska et al., 2014).

S2. Experimental

The title compound was obtained during investigation of the melting system K₂O–P₂O₅–Fe₂O₃–NiO–MoO₃. A mixture of KPO₃ (14.16 g), NiO (2.70 g), Fe₂O₃ (2.88 g) and K₂Mo₂O₇ (4 g) was ground in an agate mortar, placed in a platinum crucible and heated up to 1273 K. The melt was kept at this temperature for 3 h. After that, the temperature was cooled down to 873 K at a rate of 10 K/h. The crystals of (I) were separated from the remaining flux by boiling with water. The chemical composition of selected single-crystal was verified by EDX analysis. Analysis found (calculated) for K_3.84Ni_0.78Fe_3.19 (PO₄)₅ in atomic percentage: K 17.62 (17.69), Ni 5.34 (5.39), Fe 20.83 (20.99), P 18.44 (18.24) and O 37.77 (37.69).