The type IV polymorph of KEu(PO3)4

Abdelghani Oudahmane; Mohamed Daoud; Boumediene Tanouti; Daniel Avignant; Daniel Zambon

doi:10.1107/S1600536809048788

. 2009 Nov 21;65(Pt 12):i91–i92. doi: 10.1107/S1600536809048788

The type IV polymorph of KEu(PO₃)₄

Abdelghani Oudahmane ^a, Mohamed Daoud ^a, Boumediene Tanouti ^a, Daniel Avignant ^b, Daniel Zambon ^b,^*

PMCID: PMC2972142 PMID: 21578546

Abstract

Single crystals of KEu(PO₃)₄, potassium europium(III) polyphosphate, were obtained by solid-state reactions. This monoclinic form is the second polymorph described for this composition and belongs to type IV of long-chain polyphosphates with general formula A ^I B ^III(PO₃)₄. It is isotypic with its KEr(PO₃)₄ and KDy(PO₃)₄ homologues. The crystal structure is built of infinite helical chains of corner-sharing PO₄ tetrahedra with a repeating unit of eight tetrahedra. These chains are further linked by isolated EuO₈ square antiprisms, forming a three-dimensional framework. The K⁺ ions are located in pseudo-hexagonal channels running along [ Inline graphic 01] and are surrounded by nine O atoms in a distorted environment.

Related literature

Besides crystals of the title compound, crystals of the type III polymorph (Hu et al., 1984 ▶)) have also been obtained. For isotypic AB(PO₃)₄ structures, where A is an alkali metal, Tl or NH₄ ⁺, and B is a rare earth element, see: Palkina et al. (1977 ▶) for TlNd; Maksimova et al. (1978 ▶) for RbNd; Dago et al. (1980 ▶) for KEr; Maksimova et al. (1981 ▶) for CsNd; Maksimova et al. (1982 ▶) for RbHo; Horchani et al. (2004 ▶) for RbEr; Rekik et al. (2004 ▶) for KGd; Naïli & Mhiri (2005 ▶) for CsGd; Ben Zarkouna et al. (2006 ▶) for (NH₄)Gd; Khlissa & Férid (2006 ▶) for RbTb; Ettis et al. (2006 ▶) for RbGd; Chehimi-Moumen & Férid (2007 ▶) for KDy; Horchani-Naifer & Férid (2007 ▶) for CsPr; Zhu et al. (2009 ▶) for CsEu. For a review on the crystal chemisty of polyphosphates, see: Durif (1995 ▶). Jaouadi et al. (2003 ▶) have discussed the main crystal chemical characteristics of the seven AB(PO₃)₄ structure types. For applications of rare earth polyphosphates, see: Rashchi & Finch (2000 ▶); Barsukov et al. (2004 ▶). For general background, see: Porai-Koshits & Aslanov (1972 ▶). For ionic radii, see: Shannon (1976 ▶).

Experimental

Crystal data

KEu(PO₃)₄
M _r = 506.94
Monoclinic,
a = 10.3723 (1) Å
b = 8.9721 (1) Å
c = 10.8320 (1) Å
β = 106.053 (1)°
V = 968.73 (2) Å³
Z = 4
Mo Kα radiation
μ = 7.63 mm⁻¹
T = 296 K
0.12 × 0.11 × 0.10 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ▶) T _min = 0.466, T _max = 0.513
24299 measured reflections
6201 independent reflections
5023 reflections with I > 2σ(I)
R _int = 0.045

Refinement

R[F ² > 2σ(F ²)] = 0.030
wR(F ²) = 0.072
S = 1.04
6201 reflections
163 parameters
Δρ_max = 1.72 e Å⁻³
Δρ_min = −2.04 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT; 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: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809048788/wm2282sup1.cif

e-65-00i91-sup1.cif^{(17.4KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809048788/wm2282Isup2.hkl

e-65-00i91-Isup2.hkl^{(297.4KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

P1—O7	1.480 (2)
P1—O4ⁱ	1.483 (2)
P1—O12	1.588 (2)
P1—O3ⁱⁱ	1.5968 (19)
P2—O10ⁱⁱⁱ	1.4795 (19)
P2—O5	1.483 (2)
P2—O11ⁱⁱⁱ	1.6015 (18)
P2—O3^iv	1.602 (2)
P3—O6	1.482 (2)
P3—O2	1.4873 (19)
P3—O11	1.6005 (19)
P3—O1	1.6033 (19)
P4—O9	1.4784 (19)
P4—O8^v	1.484 (2)
P4—O1	1.601 (2)
P4—O12ⁱⁱⁱ	1.601 (2)

Open in a new tab

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

supplementary crystallographic information

Comment

Rare earth polyphosphates are interesting materials and bear potential applications (Rashchi & Finch, 2000; Barsukov et al., 2004). The title compound is a member of a large family of polyphosphates with general formula A^IB^III(PO₃)₄ (where A^I is a monovalent cation: Li, Na, K, Rb, Cs, Tl, NH₄, Ag and B^III is a trivalent cation: Ln,Y, Bi). It is now well known that these compounds are classified into seven structural types usually labelled by roman numerals from I to VII. A short recapitulation of the main crystal chemical characteristics of these seven structural types has recently been given by Jaouadi et al. (2003). The KEu(PO₃)₄ polymorph described in this article belongs to the IV structural type.

In the crystal structure the Eu³⁺ ion is eight-coordinated by the oxygen atoms and its 8-coordination polyhedron is better described as a square antiprism than a dodecahedron according to the criteria of Porai-Koshits & Aslanov (1972) (δ₁ = 10.37°, δ₂ = 10.85°, δ₃ = 47.97°, δ₄ = 53.54°). The Eu—O distances range from 2.3199 (19) Å to 2.4827 (19) Å with an average <Eu—O> distance of 2.399 Å that is slightly shorter than the sum of the ionic radii i.e. 2.466 Å (Shannon, 1976). The structure of this type IV polymorph is built of infinite helical chains of corner-sharing PO₄ tetrahedra further linked by isolated EuO₈ square antiprisms. The (PO₃)_∞ chains exhibit a repeating unit of eight PO₄ tetrahedra (Fig. 1) and are running along the [101] direction. The three-dimensional framework resulting from the edge-sharing between the PO₄ tetrahedra and the EuO₈ square antiprisms exhibits pseudo hexagonal channels where the K⁺ ions reside. The K⁺ ion is 9-coordinated by oxygen atoms with distances ranging from 2.789 (2) Å to 3.370 (3) Å. By sharing corners, the KO₉ coordination polyhedra form corrugated chains running along the [010] direction (Fig. 2). Whereas the K atoms are separated by 6.599 (2) Å within the chain, the shortest K—K distance in the structure, 4.770 (2) Å, occurs between two adjacent (KO₉)_∞ chains. This shortest distance corresponds to the separation between two K⁺ ions within the channels of the structure running along the [201] direction. This separation distance A^I—A^I is strongly dependent on the nature of the A^I element and decreases as the size of the A^I element increases. For instance, in the A^IGd(PO₃)₄ homologue series, where A^I = K, Rb, Cs, this A^I—A^I shortest distance varies from 4.801 Å for K to 4.211 Å for Cs (4.524 Å for Rb). For CsEu(PO₃)₄ the shortest Cs—Cs distance is equal to 4.237Å (Zhu et al. 2009).

For isotypic AB(PO₃)₄ structures, where A is an alkali metal, Tl or NH₄⁺, and B is a rare earth element, see: Palkina et al. (1977) for TlNd, Maksimova et al. (1978) for RbNd, Dago et al. (1980) for KEr, Maksimova et al. (1981) for CsNd, Maksimova et al. (1982) for RbHo, Horchani et al. (2004) for RbEr, Rekik et al. (2004) for KGd, Naïli & Mhiri (2005) for CsGd, Ben Zarkouna et al. (2006) for (NH₄)Gd, Khlissa & Férid (2006) for RbTb, Ettis et al. (2006) for RbGd, Chehimi-Moumen & Férid (2007) for KDy, Horchani-Naifer & Férid (2007) for CsPr, and Zhu et al. (2009) for CsEu. For a review on the crystal chemisty of polyphosphates, see: Durif (1995).

Experimental

Crystals of the title compound were synthesized by reacting Eu₂O₃ with (NH₄)H₂PO₄ and K₂CO₃ in a platinum crucible. A mixture of these reagents in the molar ratio 34:57:9 was used for the synthesis. The mixture was heated at 473 K for 6 h, then at 573 K for 6 h and finally at 873 K for 24 h. The furnace was then cooled down first to 773 K at the rate of 2 K^.h^-1 and then to room temperature at the rate of K^.h^-1. Single crystals were extracted from the batch by washing with hot water. Besides crystals of the title compound, crystals of the type III polymorph (Hu et al., 1984)) have also been obtained.