Aluminium cyclo­hexa­phosphate

Abdelghani Oudahmane; Aïcha Mbarek; Malika El-Ghozzi; Daniel Avignant

doi:10.1107/S1600536810005374

. 2010 Feb 13;66(Pt 3):i17. doi: 10.1107/S1600536810005374

Aluminium cyclohexaphosphate

Abdelghani Oudahmane ^a, Aïcha Mbarek ^b, Malika El-Ghozzi ^c, Daniel Avignant ^c,^*

PMCID: PMC2983707 PMID: 21580196

Abstract

Single crystals of the title compound, Al₂P₆O₁₈, were obtained by solid-state reaction. The monoclinic structure is isotypic with its Cr^III, Ga^III and Ru^III analogues and is built up of six-membered phosphate ring anions, P₆O₁₈ ⁶⁻, isolated from each other and further linked by isolated AlO₆ octahedra by sharing corners. Each AlO₆ octahedron is linked to four P₆O₁₈ ⁶⁻ rings. More accurately, two rings are linked through bidentate diphosphate groups attached in the cis-positions to the AlO₆ octahedron. The other two rings are linked to the two remaining corners, also in cis-positions of the AlO₆ octahedron.

Related literature

The title compound was first synthesized by Kanene et al. (1985 ▶) and its unit cell determined from Weissenberg photographs. Isotypic compounds have been reported: Ga₂P₆O₁₈ (Chudinova et al., 1987 ▶); Cr₂P₆O₁₈ (Bagieu-Beucher & Guitel, 1977 ▶) and Ru₂P₆O₁₈ (Fukuoka et al., 1995 ▶). For a review of the crystal chemistry of cyclohexaphosphates, see: Durif (1995 ▶, 2005 ▶). For applications of aluminium phosphate, see: Vippola et al. (2000 ▶). For the structures of other cyclohexaphosphates with the P₆O₁₈ ⁶⁻ anion, see: Averbuch-Pouchot & Durif (1991a ▶,b ▶,c ▶).

Experimental

Crystal data

Al₂P₆O₁₈
M _r = 527.79
Monoclinic,
a = 6.0931 (2) Å
b = 15.0676 (4) Å
c = 8.2016 (3) Å
β = 105.166 (1)°
V = 726.75 (4) Å³
Z = 2
Mo Kα radiation
μ = 0.96 mm⁻¹
T = 296 K
0.16 × 0.07 × 0.06 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ▶) T _min = 0.860, T _max = 0.945
6548 measured reflections
1674 independent reflections
1398 reflections with I > 2σ(I)
R _int = 0.035

Refinement

R[F ² > 2σ(F ²)] = 0.032
wR(F ²) = 0.130
S = 1.16
1674 reflections
118 parameters
Δρ_max = 0.56 e Å⁻³
Δρ_min = −0.71 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: CaRine (Boudias & Monceau, 1998 ▶) and ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810005374/wm2303sup1.cif

e-66-00i17-sup1.cif^{(13.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810005374/wm2303Isup2.hkl

e-66-00i17-Isup2.hkl^{(82.5KB, hkl)}

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

Table 1. Selected geometric parameters (Å, °).

P1—O3	1.471 (2)
P1—O5	1.478 (2)
P1—O7	1.587 (2)
P1—O9	1.594 (3)
P2—O4	1.482 (2)
P2—O6	1.487 (2)
P2—O7ⁱ	1.579 (2)
P2—O8	1.593 (2)
P3—O1	1.476 (2)
P3—O2	1.479 (3)
P3—O9ⁱⁱ	1.594 (2)
P3—O8ⁱⁱⁱ	1.597 (2)
Al—O3	1.852 (2)
Al—O2^iv	1.873 (3)
Al—O1	1.877 (3)
Al—O4	1.887 (3)
Al—O5^v	1.889 (3)
Al—O6ⁱⁱⁱ	1.904 (2)

Open in a new tab

P2^v—O7—P1	139.91 (16)
P2—O8—P3ⁱⁱⁱ	130.56 (16)
P1—O9—P3^vi	129.42 (16)

Open in a new tab

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

supplementary crystallographic information

Comment

Although the Al₂P₆0₁₈ cyclohexaphosphate is known since twenty five years (Kanene et al., 1985), its crystal structure has never been refined from single crystal X-ray diffraction data. This paper deals with this purpose.

The crystal structure of Al₂P₆0₁₈ is isotypic with Cr₂P₆O₁₈ (Bagieu-Beucher & Guitel, 1977), Ga₂P₆O₁₈ (Chudinova et al., 1987) and Ru₂P₆O₁₈ (Fukuoka et al., 1995). It is built up of six-membered phosphate ring anions (P₆O₁₈)^6- isolated from each others and further linked by AlO₆ octahedra by sharing corners. These centrosymmetric ring anions (P₆O₁₈)^6- are located around inversion centers at 0 0 1/2 and 0 1/2 0 (Fig. 1a). Their mean planes are parallel to either (121) or (121 ) planes (Fig. 1 b). Each AlO₆ octahedron is linked to four P₆O₁₈ rings. More accurately, two rings are linked through bidentate diphosphate groups attached in cis-positions to the AlO₆ octahedron. The two other rings are linked to the two remaining corners of the AlO₆ octahedron (Fig. 2). Each (P₆O₁₈)^6- ring anion is connected to eight AlO₆ octahedra by corner-sharing. Four diphosphate groups of the ring anion including P(3)O₄ and either P(1)O₄ or P(2)O₄ tetrahedra are bidentate whereas the P(1)O₄—P(2)O₄ couple does not bind in a bidentate fashion. This may be correlated with the value of the P(1)—O—P(2) angle (139.91 (16)°) which is greater than P(2)—O—P(3) (130.56 (16)°) and P(1)—O—P(3) (129.42 (16) °) ones and also to the P(1)—P(2) distance (2.9741 (12) Å) slightly greater than P(2)—P(3) = 2.8970 (11) Å and P(1)—P(3) = 2.8826 (12) Å ones.

A survey of the internal symmetry of the (P₆O₁₈)^6- ring anions shows that most of them are centrosymmetric with P—P—P angles spreading from 87.8° to 142.8° (Averbuch-Pouchot & Durif, 1991a), i.e. with large deviations from the ideal value of 120°. When the (P₆O₁₈)^6- ring anion has internal 1 symmetry, it is built up of three independent P atoms and hence there are three characteristic α_i = P—P—P angles in the ring (α₁ = P₁—P₂—P₃, α₂ = P₂—P₃—P₁, α₃ = P₃—P₁—P₂). When taking the δ = Σ_i|120-α_i| parameter as a rough measure of the ring distorsion, Al₂P₆O₁₈ exhibits the third lowest δ = 15.28° value after its homologous congeners Ru₂P₆O₁₈ (δ = 13.78°) and Cr₂P₆O₁₈ (δ = 14.39°). It should be noted that the characteristic P—P—P angles for both isotypic Ga₂P₆O₁₈ and Fe₂P₆O₁₈ structures have not been reported. The highest δ values calculated from data for other cyclohexaphosphates reported up to date are related to Cu₂(NH₄)₂P₆O₁₈^.8H₂O (δ = 65.98°) (Averbuch-Pouchot & Durif, 1991b) and Ag₄Li₂P₆O₁₈.2H₂O (δ = 67.29°) (Averbuch-Pouchot & Durif, 1991c).

For applications of aluminium phosphate, see: Vippola et al. (2000). For general reviews on the crystal chemistry of cyclohexaphosphates, see: Durif (1995) and Durif (2005).

Experimental

Single crystals of the title compound have been obtained by reacting Al₂O₃ with (NH₄)H₂PO₄ in an alumina boat. A mixture of these reagents in the molar ratio 1:6 was used for the synthesis. The mixture was first heated at 473 K for 24 h. Afterwards the temperature was successively raised to 573 K for 12 h, then to 673 K for 12 additional hours and finally to 923 K. After a heating period of 48 h at this temperature, the sample was cooled to room temperature by switching the furnace off. Translucent rhombs of Al₂P₆O₁₈ were extracted from the batch.