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Acta Crystallogr Sect E Struct Rep Online. 2010 July 1; 66(Pt 7): i49–i50.
Published online 2010 June 5. doi:  10.1107/S1600536810020751
PMCID: PMC3007075

Dipotassium dialuminium cyclo­octa­phosphate

Abstract

Single crystals of the title compound, K2Al2P8O24, were obtained by solid-state reaction. The monoclinic structure is isotypic with that of the GaIII analogue and is built of eight-membered phosphate ring anions P8O24 8− (2/m symmetry) isolated from each other and further linked by isolated AlO6 octa­hedra (An external file that holds a picture, illustration, etc.
Object name is e-66-00i49-efi5.jpg symmetry) by sharing corners. Each AlO6 octa­hedron is linked to four P8O24 8− rings in such a way that two rings are linked through bidentate diphosphate groups attached in the cis positions on two opposite parallel edges of the octa­hedron. The two other rings are linked via corner-sharing to the two remaining corners in the trans positions of the AlO6 octa­hedron. Each P8O24 8− ring anion is linked to eight AlO6 octa­hedra. More accurately, each ring anion is linked to four AlO6 octa­hedra through bidentate diphosphate groups attached in the cis positions to the AlO6 octa­hedron and to the four remaining octa­hedra by sharing corners. This three-dimensional linkage delimits channels running parallel to [001] in which the ten-coordinated K+ cations (2 symmetry) are distributed over two columns. These columns alternate with empty octa­gonally-shaped channels expanding through the P8O24 8− ring anions.

Related literature

The synthesis and an approximate unit cell with a slightly smaller β angle were reported for the title compound more than a quarter of a century ago (Grunze et al., 1983 [triangle]). The crystal structures of isotypic compounds determined from single-crystal data have been reported for K2Ga2P8O24 (Palkina et al., 1979 [triangle]) and K2Mn2P8O24 (Murashova & Chudinova, 1999 [triangle]). The isostructural potassium-containing cyclo­octa­phosphates K2V2P8O24 (Lavrov et al., 1981 [triangle]), K2Fe2P8O24 (Grunze et al., 1983 [triangle]) and K2Cr2P8O24 (Grunze & Chudinova, 1988 [triangle]) were reported without detailed structure analyses. For a review of the crystal chemistry of cyclo­octa­phosphates, see: Durif (1995 [triangle], 2005 [triangle]). For potential applications of aluminophosphates, see: Cheetham et al. (1999 [triangle]); Hartmann & Kevan (1999 [triangle]). For background to distortion indices, see: Momma & Izumi (2008 [triangle]).

Experimental

Crystal data

  • K2Al2P8O24
  • M r = 763.92
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-66-00i49-efi6.jpg
  • a = 16.598 (2) Å
  • b = 12.2150 (17) Å
  • c = 5.0705 (7) Å
  • β = 100.315 (4)°
  • V = 1011.4 (2) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 1.31 mm−1
  • T = 296 K
  • 0.30 × 0.10 × 0.08 mm

Data collection

  • Bruker APEXII CCD diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2008 [triangle]) T min = 0.562, T max = 0.748
  • 9643 measured reflections
  • 2844 independent reflections
  • 2252 reflections with I > 2σ(I)
  • R int = 0.047

Refinement

  • R[F 2 > 2σ(F 2)] = 0.042
  • wR(F 2) = 0.124
  • S = 1.07
  • 2844 reflections
  • 87 parameters
  • Δρmax = 1.40 e Å−3
  • Δρmin = −1.04 e Å−3

Data collection: APEX2 (Bruker, 2008 [triangle]); cell refinement: SAINT (Bruker, 2008 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: DIAMOND (Brandenburg, 1999 [triangle]), CaRine (Boudias & Monceau, 1998 [triangle]) and ORTEP-3 (Farrugia, 1997 [triangle]); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 [triangle]).

Table 1
Selected bond lengths (Å)

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810020751/wm2355sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810020751/wm2355Isup2.hkl

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

supplementary crystallographic information

Comment

The title compound, K2Al2P8O24, belongs to porous crystalline open-framework materials that gain growing interest for their potential applications as molecular sieves or catalysts (Cheetham et al. 1999; Hartmann & Kevan, 1999). The title cyclooctaphosphate is isotypic with K2Ga2P8O24 (Palkina et al., 1979) and K2Mn2P8O24 (Murashova & Chudinova, 1999). This structural family also includes K2V2P8O24 (Lavrov et al., 1981), K2Fe2P8O24 (Grunze et al., 1983) and K2Cr2P8O24 (Grunze & Chudinova, 1988), the structures of which have not yet been refined from X-ray diffraction data.

The crystal structure of K2M2P8O24 is built up of 8-membered phosphate ring anions P8O248- (symmetry 2/m) (Fig. 1), further linked by isolated MIIIO6 octahedra to form the three-dimensional skeleton. Each MO6 octahedron is linked to four ring anions P8O248-. Two ring anions are linked by corner-sharing in trans positions whereas the two others are connected in a bidentate fashion in cis positions on two opposite edges of the equatorial plane of the octahedron. This three-dimensional framework of K2Al2P8O24 delimits two kinds of channels expanding along the [001] direction (Fig. 2). The first channel is octagonally shaped since passing through the ring anions and is empty despite a size of ≈ 5.2 Å in diameter. The second channel, cross shaped, accommodates the K+ ions in a [6 + 4] coordination. The K+ ions are located over two columns shifted of about c/2 with respect to each other along the c axis. Thus they form two distinct K—K pairs with common square faces involving only O(5) oxygen atoms. In the first pair, corresponding to the shortest K—K distance (3.634 (9) Å) (Fig. 3), the four O(5) atoms delimit a pseudo-square face with O—O separations of 2.995 (2) and 3.064 (6) Å and O(5)—O(5)—O(5) angles of 90°. This pair corresponds to the two shortest K—O distances, viz. 2.7559 (15) and 2.8612 (15) Å. In the second pair with a K—K distance of 4.365 (7) Å, the four O(5) atoms at the vertices of the pseudo-square face (O—O separation 2.995 (2) and 3.139 (7) Å with O(5)—O(5)—O(5) angles of 90°), the respective K—O bonds lengths are 2.8612 (15) and 3.2790 (17) Å. The polyhedra surrounding three potassium cations engaged in two successive pairs (one long and one short) form a cluster within they share a common O(5)—O(5) edge with a contact distance of 2.995 (2) Å. This potassium-oxygen polyhedra packing also prevails in the Ga and Mn cyclooctaphosphate analogues but the K—O distances spread over larger ranges, viz. from 2.754 (28) Å to 3.359 (28) Å and from 2.738 (2) to 3.506 (2) Å, respectively. Thus the respective coordinations of the potassium cations can be regarded as being [6 + 4] and [8 + 2] for Ga and Mn cyclooctaphosphate.

A careful examination of the geometry of the MIIIO6 octahedra in this structural type shows that the distortion index (bond length) (Momma & Izumi, 2008) increases from Al to Mn (0.0117 for Al, 0.0202 for Ga and 0.0574 for Mn). The AlO6 octahedron is only very slightly distorted with two shorter Al—O distances of 1.8523 (12) Å and four others very close to 1.90 Å (1.9013 (12) (× 2) and 1.9021 (11) (× 2) Å). The significant larger distortion of the MnO6 octahedron is probably due to the Jahn-Teller effect associated with the d4 electronic configuration of MnIII (Murashova & Chudinova, 1999).

Besides the structural family to which the title compound belongs, only another sodium and silver- containing cyclooctaphosphate, Ag9NaP8O24(NO3)2.4H2O, exhibits a ring anion with internal 2/m symmetry among the presently known cyclooctaphosphates (Durif, 1995, 2005). However, despite the common internal symmetry, the shape of the 8-membered ring anion present in this structure is very different from that of the title compound as shown in Fig. 4.

Experimental

Single-crystals of the title compound were obtained by solid state reaction, from the reagents K2CO3, Al2O3 and (NH4)H2PO4 in the molar ratio K / P / Al = 57 / 34 / 9. The mixture has progressively been heated up to 873 K over a period of 12 h. Then the temperature was slowly decreased down to 723 K at the rate of 5 K h-1 and maintained at this value for 12 h. Then a new cooling step down to 573 K at the rate of 5 K h-1 was carried out before the furnace was switched off. Single-crystals of K2Al2P8O24 were extracted from the batch by washing with hot water in order to remove the excess of P2O5. A translucent colorless needle of the title compound was used for the structure refinement.

Refinement

The highest residual peak in the final difference Fourier map was located 0.74 Å from atom P2 and the deepest hole was located 0.69 Å from atom P1.

Figures

Fig. 1.
ORTEP-3 view (Farrugia, 1997) of the centrosymmetric (P8O24)8- ring anion. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) -x, -y + 1, -z + 1; (iv) -x, y, -z; (v) -x, -y + 1, -z; (vi) x - 1/2, -y + 1/2, z; (ix) -x + ...
Fig. 2.
Projections of the 8-membered ring anions P8O248- along [010] (left) and [001] (right).
Fig. 3.
Partial view showing the packing of the K—O polyhedra along the c axis in the ball and stick (left) and polyhedral (right) representation.
Fig. 4.
Comparison of the 8-membered ring anions P8O248- (both with internal 2/m symmetry) in K2Al2P8O24 (top) and Ag9NaP8O24(NO3)2.4H2O (bottom).

Crystal data

K2Al2P8O24F(000) = 752
Mr = 763.92Dx = 2.508 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yCell parameters from 3017 reflections
a = 16.598 (2) Åθ = 3.3–37.7°
b = 12.2150 (17) ŵ = 1.31 mm1
c = 5.0705 (7) ÅT = 296 K
β = 100.315 (4)°Needle, colourless
V = 1011.4 (2) Å30.30 × 0.10 × 0.08 mm
Z = 2

Data collection

Bruker APEXII CCD diffractometer2844 independent reflections
Radiation source: fine-focus sealed tube2252 reflections with I > 2σ(I)
graphiteRint = 0.047
Detector resolution: 8.3333 pixels mm-1θmax = 38.7°, θmin = 4.1°
ω and [var phi] scansh = −29→28
Absorption correction: multi-scan (SADABS; Bruker, 2008)k = −18→20
Tmin = 0.562, Tmax = 0.748l = −8→8
9643 measured reflections

Refinement

Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.042Secondary atom site location: difference Fourier map
wR(F2) = 0.124w = 1/[σ2(Fo2) + (0.0738P)2 + 0.0398P] where P = (Fo2 + 2Fc2)/3
S = 1.07(Δ/σ)max < 0.001
2844 reflectionsΔρmax = 1.40 e Å3
87 parametersΔρmin = −1.04 e Å3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/Ueq
K−0.09371 (4)0.50000.25194 (13)0.02290 (13)
Al0.25000.25000.00000.00771 (13)
P10.19023 (2)0.12098 (3)0.46962 (8)0.00720 (9)
P20.07782 (2)0.27631 (3)0.16477 (8)0.00835 (9)
O10.28060 (8)0.36965 (10)0.2366 (2)0.0118 (2)
O20.14059 (7)0.28394 (11)−0.0132 (2)0.0132 (2)
O30.24968 (7)0.15349 (10)0.2942 (2)0.0105 (2)
O40.10711 (7)0.18408 (11)0.3873 (2)0.0122 (2)
O50.05469 (9)0.37739 (12)0.2866 (3)0.0184 (3)
O60.00000.21471 (15)0.00000.0140 (3)
O70.16028 (11)0.00000.3993 (3)0.0125 (3)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
K0.0299 (3)0.0147 (3)0.0240 (3)0.0000.0046 (2)0.000
Al0.0085 (3)0.0083 (3)0.0064 (3)0.0001 (2)0.0016 (2)0.0006 (2)
P10.00956 (16)0.00518 (17)0.00672 (15)0.00032 (12)0.00110 (11)0.00033 (11)
P20.00850 (17)0.00632 (18)0.01023 (16)0.00094 (12)0.00164 (12)0.00031 (12)
O10.0186 (5)0.0084 (5)0.0078 (4)−0.0009 (4)0.0006 (4)−0.0006 (3)
O20.0095 (5)0.0177 (6)0.0130 (5)0.0020 (4)0.0033 (4)0.0049 (4)
O30.0104 (5)0.0111 (5)0.0105 (5)0.0011 (4)0.0037 (3)0.0033 (4)
O40.0108 (5)0.0125 (6)0.0138 (5)0.0033 (4)0.0034 (4)0.0051 (4)
O50.0247 (6)0.0105 (6)0.0198 (6)0.0053 (5)0.0030 (5)−0.0045 (5)
O60.0096 (7)0.0092 (8)0.0217 (8)0.000−0.0011 (6)0.000
O70.0177 (7)0.0051 (7)0.0129 (7)0.000−0.0021 (5)0.000

Geometric parameters (Å, °)

K—O5i2.7559 (15)Al—O31.9021 (11)
K—O5ii2.7559 (15)P1—O1ix1.4861 (12)
K—O52.8612 (15)P1—O31.4956 (12)
K—O5iii2.8612 (15)P1—O41.5701 (13)
K—O2iv2.9493 (14)P1—O71.5794 (8)
K—O2v2.9493 (13)P2—O51.4622 (14)
K—O3vi3.2431 (13)P2—O21.4983 (12)
K—O3vii3.2431 (13)P2—O61.5957 (10)
K—O5iv3.2790 (17)P2—O41.6070 (13)
K—O5v3.2790 (17)P2—Kv3.4928 (7)
K—P2iv3.4927 (7)O1—P1ix1.4861 (12)
K—P2v3.4927 (7)O2—Kv2.9494 (13)
Al—O2viii1.8523 (12)O3—Kx3.2431 (13)
Al—O21.8523 (12)O5—Ki2.7559 (15)
Al—O1viii1.9013 (12)O5—Kv3.2790 (17)
Al—O11.9013 (12)O6—P2iv1.5957 (10)
Al—O3viii1.9021 (11)O7—P1xi1.5793 (8)
O5i—K—O5ii65.84 (6)O5—K—P2v106.81 (4)
O5i—K—O599.41 (4)O5iii—K—P2v58.01 (3)
O5ii—K—O566.08 (6)O2iv—K—P2v119.65 (3)
O5i—K—O5iii66.08 (6)O2v—K—P2v25.13 (2)
O5ii—K—O5iii99.41 (4)O3vi—K—P2v129.83 (3)
O5—K—O5iii63.13 (6)O3vii—K—P2v74.69 (2)
O5i—K—O2iv147.08 (5)O5iv—K—P2v78.81 (3)
O5ii—K—O2iv82.35 (4)O5v—K—P2v24.68 (2)
O5—K—O2iv73.61 (4)P2iv—K—P2v102.94 (2)
O5iii—K—O2iv130.89 (4)O2viii—Al—O2180.0
O5i—K—O2v82.35 (4)O2viii—Al—O1viii90.00 (6)
O5ii—K—O2v147.08 (5)O2—Al—O1viii89.99 (6)
O5—K—O2v130.89 (4)O2viii—Al—O189.99 (6)
O5iii—K—O2v73.61 (4)O2—Al—O190.01 (6)
O2iv—K—O2v126.97 (6)O1viii—Al—O1180.00 (5)
O5i—K—O3vi109.11 (4)O2viii—Al—O3viii91.53 (5)
O5ii—K—O3vi72.48 (4)O2—Al—O3viii88.47 (5)
O5—K—O3vi112.63 (4)O1viii—Al—O3viii91.12 (5)
O5iii—K—O3vi171.88 (4)O1—Al—O3viii88.88 (5)
O2iv—K—O3vi49.77 (3)O2viii—Al—O388.47 (5)
O2v—K—O3vi112.88 (4)O2—Al—O391.52 (5)
O5i—K—O3vii72.48 (4)O1viii—Al—O388.88 (5)
O5ii—K—O3vii109.11 (4)O1—Al—O391.12 (5)
O5—K—O3vii171.88 (4)O3viii—Al—O3180.0
O5iii—K—O3vii112.63 (4)O1ix—P1—O3116.38 (7)
O2iv—K—O3vii112.88 (4)O1ix—P1—O4109.98 (7)
O2v—K—O3vii49.77 (3)O3—P1—O4110.70 (7)
O3vi—K—O3vii70.64 (5)O1ix—P1—O7109.34 (8)
O5i—K—O5iv154.67 (6)O3—P1—O7109.20 (8)
O5ii—K—O5iv114.04 (5)O4—P1—O799.98 (8)
O5—K—O5iv61.04 (5)O5—P2—O2117.73 (9)
O5iii—K—O5iv89.66 (4)O5—P2—O6111.73 (8)
O2iv—K—O5iv47.65 (3)O2—P2—O6107.39 (6)
O2v—K—O5iv98.27 (4)O5—P2—O4111.39 (8)
O3vi—K—O5iv94.08 (3)O2—P2—O4108.11 (7)
O3vii—K—O5iv126.82 (4)O6—P2—O498.73 (7)
O5i—K—O5v114.04 (5)O5—P2—Kv69.45 (6)
O5ii—K—O5v154.67 (6)O2—P2—Kv56.71 (5)
O5—K—O5v89.66 (4)O6—P2—Kv101.18 (5)
O5iii—K—O5v61.04 (5)O4—P2—Kv157.99 (5)
O2iv—K—O5v98.27 (4)P1ix—O1—Al133.95 (8)
O2v—K—O5v47.65 (3)P2—O2—Al138.36 (8)
O3vi—K—O5v126.82 (4)P2—O2—Kv98.17 (6)
O3vii—K—O5v94.08 (3)Al—O2—Kv113.58 (5)
O5iv—K—O5v54.36 (5)P1—O3—Al136.54 (8)
O5i—K—P2iv155.10 (4)P1—O3—Kx120.51 (6)
O5ii—K—P2iv93.25 (3)Al—O3—Kx101.05 (4)
O5—K—P2iv58.01 (3)P1—O4—P2132.20 (8)
O5iii—K—P2iv106.81 (4)P2—O5—Ki141.08 (8)
O2iv—K—P2iv25.13 (2)P2—O5—K134.77 (8)
O2v—K—P2iv119.65 (3)Ki—O5—K80.59 (4)
O3vi—K—P2iv74.69 (2)P2—O5—Kv85.87 (6)
O3vii—K—P2iv129.83 (3)Ki—O5—Kv114.04 (5)
O5iv—K—P2iv24.68 (2)K—O5—Kv90.34 (4)
O5v—K—P2iv78.81 (3)P2—O6—P2iv123.73 (12)
O5i—K—P2v93.25 (3)P1xi—O7—P1138.66 (12)
O5ii—K—P2v155.10 (4)

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

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2355).

References

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