Heptasodium tetra­aluminium tetra­kis­(diphosphate) orthophosphate, Na₇Al₄(P₂O₇)₄(PO₄)

Abstract

The asymmetric unit of title compound contains three Na⁺, one Al³⁺, three P⁵⁺ and eight O²⁻ atoms, with one Na⁺ atom lying on a twofold rotation axis and one Na⁺ and one P⁵⁺ atom on fourfold rotoinversion axes. The fundamental building units of the title structure are isolated PO₄ tetra­hedra, AlO₆ octa­hedra and P₂O₇ groups, which are further inter­locked by corner-sharing O atoms, forming a three-dimensional framework structure. The Na⁺ atoms are located within the cavities of the framework, showing coordination numbers of 4, 6 and 7.

Related literature

For isotypic structures, see: Rochère et al. (1985 ▶); Stus et al. (2001 ▶).

Experimental

Crystal data

• Na₇Al₄(P₂O₇)₄(PO₄)

• M _r = 1059.58

• Tetragonal,

• a = 14.054 (3) Å

• c = 6.1718 (16) Å

• V = 1219.1 (4) ų

• Z = 2

• Mo Kα radiation

• μ = 1.06 mm⁻¹

• T = 296 K

• 0.15 × 0.05 × 0.05 mm

Data collection

• Rigaku Saturn70 CCD diffractometer

• Absorption correction: multi-scan (ABSCOR; Higashi, 1995 ▶) T _min = 0.857, T _max = 0.949

• 5562 measured reflections

• 1347 independent reflections

• 1287 reflections with I > 2σ(I)

• R _int = 0.024

Refinement

• R[F ² > 2σ(F ²)] = 0.017

• wR(F ²) = 0.047

• S = 1.08

• 1347 reflections

• 118 parameters

• Δρ_max = 0.22 e Å⁻³

• Δρ_min = −0.29 e Å⁻³

• Absolute structure: Flack (1983 ▶), 540 Friedel pairs

• Flack parameter: −0.04 (9)

Data collection: CrystalClear (Rigaku, 2004 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2004 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

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

supplementary crystallographic information

Comment

Metal phosphates possessing open-framework structures with defined tunnels have been extensively investigated for their structural diversity, properties, and potential applications in shape-selective catalysis, adsorbents, ion exchangers, and molecular sieves. Among them, a series of isotypic ortho-diphosphates Na₇(MP₂O₇)₄PO₄ (M = Al, Cr, Fe) (Rochère et al., 1985) and Na₇(InP₂O₇)₄PO₄ (Stus et al., 2001) were synthesized, and their ion exchange and conductivity properties studied. However, for compound Na₇(AlP₂O₇)₄PO₄, a detailed crystal structure analysis has not been reported so far. In this work, the synthesis and results of the crystal structure refinement of this compound is reported. In comparison with the unit cell parameters reported by Rochère from X-ray powder data (a = 14.046 (3), c = 6.169 (2) Å; Rochère et al., 1985), the determined unit cell parameters from the single crystal X-ray study are slighty larger.

As shown in Figs 1 and 2, the structure of the title compound consists of a three-dimensional framework of isolated PO₄ tetrahedra, AlO₆ octahedra and P₂O₇ groups, the conformation of the latter more eclipsed than staggered. The sodium cations are located in sites within cavities in the framework, exhibiting coordination numbers of 7 (Na1), 6 (Na2) and 4 (Na3). There are three crystallography distinct P atoms in the structure of the title compound. P1 and P2 atoms are located in general positions and their corresponding P1O₄ and P2O₄ tetrahedra are connected by the bridging O5 atom to form a P₂O₇ group, which is further linked to four AlO₆ octahedra. P3 atoms are located on 4 axes, forming isolated P3O₄ tetrahedra which are further connected to four AlO₆ octahedra. The P3O₄ tetrahedra are regular with a P—O bond length of 1.5351 (18) Å, while the P–O distances in the P₂O₇ group are irregular, showing the characteristic variance of smaller P–O_terminal bonds (1.4862 (14) to 1.5199 (14) Å) and larger P–O_bridging bonds (1.6097 (14) and 1.6284 (15) Å) as typically observed for diphosphate unit. The title structure differs in their P–O–P bridging angle of the diphosphate group and the average metal–O distances from those of the isotypic congeners. For the Al compound, the interatomic distances in the MO₆ octahedron are decreasing (Fe–O₆ 1.968–2.021 Å, InO₆ 2.091–2.146 Å, AlO₆ 1.8391 (15)–1.9278 (16) Å), as expected from the smaller ionic radius of Al³⁺ comparerd to Fe³⁺ and In³⁺. With a decrease of the unit-cell parameters a trend in a likewise decreasing P–O–P bridging angle of the diphosphate groups is observed: (Na₇(FeP₂O₇)₄PO₄: 136.6 (3)°; Na₇(InP₂O₇)₄PO₄: 136.7 (3)°, Na₇(AlP₂O₇)₄PO₄: 127.92 (9)°.

Experimental

The finely ground reagents Na₂CO₃, Al₂O₃ and NH₄H₂PO₄ were mixed in the molar ratio Na: Al: P = 2: 1: 8, were placed in a Pt crucible, and heated at 673 K for 4 h. The mixture was then re-ground and heated at 1173 K for 20 h, then cooled to 673 K at a rate of 3 K h^-1, and finally quenched to room temperature. A few colorless crystals of the title compound with prismatic shape were obtained.

Refinement

The highest peak in the difference electron density map equals to 0.22 e/ų at the distance of 0.63 Šfrom O4 site while the deepest hole equals to -0.29 e/ų at the distance of 0.68 Šfrom the P3 site.

Figures

Fig. 1.

The expanded asymmetric unit of Na7(AlP2O7)4PO4 showing the coordination environments of the P and Al atoms. The displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (iii) -y + 1, x, -z + 1; (vii) -x + 1, -y + 1, z; (viii) -y + 1, x, -z + 2; (ix) x - 1/2, -y + 3/2, -z + 3/2; (x) y, -x + 1, -z + 1.]

Fig. 2.

View of the crystal structure of Na7(AlP2O7)4PO4. PO4 and AlO6 units are given in the polyhedral representation.

Crystal data

Na7Al4(P2O7)4(PO4)	Dx = 2.887 Mg m−3
Mr = 1059.58	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P421c	Cell parameters from 3720 reflections
Hall symbol: P -4 2n	θ = 2.9–27.5°
a = 14.054 (3) Å	µ = 1.06 mm−1
c = 6.1718 (16) Å	T = 296 K
V = 1219.1 (4) Å3	Prism, colourless
Z = 2	0.15 × 0.05 × 0.05 mm
F(000) = 1040

Data collection

Rigaku Saturn70 CCD diffractometer	1347 independent reflections
Radiation source: fine-focus sealed tube	1287 reflections with I > 2σ(I)
Graphite Monochromator	Rint = 0.024
Detector resolution: 14.6306 pixels mm-1	θmax = 27.5°, θmin = 3.2°
ω scans	h = −18→17
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −18→16
Tmin = 0.857, Tmax = 0.949	l = −7→7
5562 measured reflections

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)] = 0.017	w = 1/[σ2(Fo2) + (0.0297P)2 + 0.278P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.047	(Δ/σ)max = 0.001
S = 1.08	Δρmax = 0.22 e Å−3
1347 reflections	Δρmin = −0.29 e Å−3
118 parameters	Absolute structure: Flack (1983), 540 Friedel pairs
0 restraints	Flack parameter: −0.04 (9)

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 (Ų)

	x	y	z	Uiso*/Ueq
Na1	0.42251 (6)	0.75865 (7)	0.09314 (15)	0.0200 (2)
Na2	0.5000	1.0000	0.3156 (2)	0.0268 (3)
Na3	0.5000	0.5000	1.0000	0.0411 (6)
Al1	0.32097 (4)	0.62225 (4)	0.63747 (9)	0.00558 (13)
P1	0.62752 (3)	0.74207 (3)	0.84990 (8)	0.00573 (11)
P2	0.46166 (3)	0.79988 (3)	0.60041 (8)	0.00656 (11)
P3	0.5000	0.5000	0.5000	0.00535 (19)
O1	0.42717 (10)	0.89936 (10)	0.5600 (2)	0.0117 (3)
O2	0.54197 (10)	0.81323 (10)	0.7882 (2)	0.0109 (3)
O3	0.38751 (10)	0.73621 (10)	0.7038 (2)	0.0128 (3)
O4	0.51085 (9)	0.75581 (10)	0.4067 (2)	0.0104 (3)
O5	0.71136 (9)	0.80522 (10)	0.8791 (2)	0.0129 (3)
O6	0.59683 (10)	0.69263 (10)	1.0575 (2)	0.0113 (3)
O7	0.63718 (10)	0.66852 (9)	0.6721 (2)	0.0087 (3)
O8	0.43148 (9)	0.55247 (10)	0.6522 (2)	0.0100 (3)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Na1	0.0224 (4)	0.0242 (5)	0.0133 (4)	−0.0060 (3)	−0.0034 (4)	0.0031 (4)
Na2	0.0280 (7)	0.0405 (9)	0.0118 (6)	−0.0216 (6)	0.000	0.000
Na3	0.0561 (9)	0.0561 (9)	0.0111 (9)	0.000	0.000	0.000
Al1	0.0049 (2)	0.0063 (3)	0.0055 (3)	0.0010 (2)	0.0002 (2)	0.0000 (2)
P1	0.0056 (2)	0.0069 (2)	0.0047 (2)	−0.00024 (16)	0.00004 (17)	0.00036 (18)
P2	0.0064 (2)	0.0068 (2)	0.0064 (2)	0.00048 (16)	−0.00085 (19)	−0.00024 (18)
P3	0.0053 (3)	0.0053 (3)	0.0054 (4)	0.000	0.000	0.000
O1	0.0133 (7)	0.0101 (6)	0.0117 (8)	0.0030 (6)	−0.0018 (6)	0.0007 (6)
O2	0.0106 (7)	0.0123 (7)	0.0097 (7)	0.0043 (5)	−0.0043 (6)	−0.0034 (6)
O3	0.0139 (7)	0.0127 (7)	0.0118 (7)	−0.0066 (6)	0.0023 (6)	−0.0033 (6)
O4	0.0086 (6)	0.0138 (7)	0.0088 (6)	0.0027 (5)	0.0000 (5)	−0.0019 (6)
O5	0.0101 (7)	0.0166 (7)	0.0121 (8)	−0.0056 (5)	−0.0004 (6)	−0.0012 (6)
O6	0.0149 (7)	0.0134 (7)	0.0055 (7)	−0.0024 (5)	0.0008 (6)	0.0021 (5)
O7	0.0119 (7)	0.0076 (7)	0.0065 (7)	0.0015 (5)	−0.0005 (5)	0.0007 (5)
O8	0.0081 (6)	0.0135 (7)	0.0084 (6)	0.0039 (5)	0.0000 (6)	−0.0014 (5)

Geometric parameters (Å, °)

Na1—O4	2.2998 (17)	P1—O7	1.5136 (14)
Na1—O1i	2.3993 (17)	P1—O6	1.5199 (14)
Na1—O3ii	2.4730 (18)	P1—O2	1.6097 (14)
Na1—O7iii	2.5789 (17)	P2—O1	1.5006 (14)
Na1—O6ii	2.6291 (18)	P2—O4	1.5134 (14)
Na1—O2ii	2.6363 (18)	P2—O3	1.5145 (15)
Na1—O6iii	2.9419 (18)	P2—O2	1.6284 (15)
Na2—O1iv	2.3072 (16)	P3—O8iii	1.5341 (14)
Na2—O1	2.3072 (17)	P3—O8x	1.5341 (14)
Na2—O1i	2.3532 (17)	P3—O8	1.5341 (14)
Na2—O1v	2.3532 (17)	P3—O8vii	1.5341 (14)
Na2—O2i	2.6957 (15)	O1—Na2xi	2.3532 (17)
Na2—O2v	2.6957 (15)	O1—Na1xii	2.3993 (17)
Na3—O8vi	2.4655 (16)	O2—Na1xiii	2.6363 (18)
Na3—O8	2.4655 (16)	O2—Na2xi	2.6957 (15)
Na3—O8vii	2.4655 (16)	O3—Na1xiii	2.4730 (18)
Na3—O8viii	2.4655 (16)	O4—Al1x	1.9210 (15)
Al1—O8	1.8391 (15)	O5—Al1xiv	1.8500 (15)
Al1—O5ix	1.8500 (15)	O6—Al1vi	1.9258 (16)
Al1—O3	1.8993 (16)	O6—Na1xiii	2.6291 (18)
Al1—O4iii	1.9210 (15)	O6—Na1x	2.9419 (18)
Al1—O6viii	1.9258 (16)	O7—Al1x	1.9278 (16)
Al1—O7iii	1.9278 (16)	O7—Na1x	2.5789 (17)
P1—O5	1.4862 (14)
O4—Na1—O1i	99.33 (6)	O3—Al1—O6viii	89.69 (7)
O4—Na1—O3ii	157.36 (7)	O4iii—Al1—O6viii	86.10 (7)
O1i—Na1—O3ii	90.92 (6)	O8—Al1—O7iii	92.43 (7)
O4—Na1—O7iii	77.49 (5)	O5ix—Al1—O7iii	87.07 (6)
O1i—Na1—O7iii	129.35 (6)	O3—Al1—O7iii	94.82 (7)
O3ii—Na1—O7iii	111.27 (6)	O4iii—Al1—O7iii	89.49 (6)
O4—Na1—O6ii	63.97 (5)	O6viii—Al1—O7iii	175.36 (7)
O1i—Na1—O6ii	117.88 (6)	O5—P1—O7	115.13 (8)
O3ii—Na1—O6ii	93.38 (6)	O5—P1—O6	113.31 (8)
O7iii—Na1—O6ii	106.00 (5)	O7—P1—O6	108.92 (9)
O4—Na1—O2ii	105.20 (6)	O5—P1—O2	104.47 (8)
O1i—Na1—O2ii	74.83 (5)	O7—P1—O2	108.65 (8)
O3ii—Na1—O2ii	58.00 (5)	O6—P1—O2	105.76 (8)
O7iii—Na1—O2ii	155.46 (6)	O1—P2—O4	113.43 (9)
O6ii—Na1—O2ii	56.60 (5)	O1—P2—O3	113.46 (8)
O4—Na1—O6iii	123.33 (6)	O4—P2—O3	113.91 (8)
O1i—Na1—O6iii	131.42 (6)	O1—P2—O2	103.58 (8)
O3ii—Na1—O6iii	59.00 (5)	O4—P2—O2	107.01 (8)
O7iii—Na1—O6iii	52.62 (5)	O3—P2—O2	104.19 (8)
O6ii—Na1—O6iii	102.31 (6)	O8iii—P3—O8x	104.48 (11)
O2ii—Na1—O6iii	110.46 (5)	O8iii—P3—O8	112.02 (6)
O1iv—Na2—O1	98.36 (9)	O8x—P3—O8	112.02 (6)
O1iv—Na2—O1i	166.32 (7)	O8iii—P3—O8vii	112.02 (6)
O1—Na2—O1i	84.54 (5)	O8x—P3—O8vii	112.02 (6)
O1iv—Na2—O1v	84.54 (5)	O8—P3—O8vii	104.48 (11)
O1—Na2—O1v	166.32 (7)	P1—O2—P2	127.92 (9)
O1i—Na2—O1v	95.80 (8)	P1—O2—Na1xiii	97.23 (7)
O1iv—Na2—O2i	109.82 (5)	P2—O2—Na1xiii	91.90 (7)
O1—Na2—O2i	75.12 (5)	P1—O2—Na2xi	138.90 (8)
O1i—Na2—O2i	57.84 (5)	P2—O2—Na2xi	90.30 (6)
O1v—Na2—O2i	116.61 (6)	Na1xiii—O2—Na2xi	95.69 (5)
O1iv—Na2—O2v	75.12 (5)	P2—O3—Al1	138.27 (10)
O1—Na2—O2v	109.82 (5)	P2—O3—Na1xiii	101.37 (7)
O1i—Na2—O2v	116.61 (6)	Al1—O3—Na1xiii	114.51 (7)
O1v—Na2—O2v	57.84 (5)	P2—O4—Al1x	135.59 (9)
O2i—Na2—O2v	172.79 (8)	P2—O4—Na1	114.27 (8)
O8vi—Na3—O8	139.29 (4)	Al1x—O4—Na1	109.28 (7)
O8vi—Na3—O8vii	139.29 (4)	P1—O5—Al1xiv	169.27 (10)
O8—Na3—O8vii	58.94 (7)	P1—O6—Al1vi	144.77 (10)
O8vi—Na3—O8viii	58.94 (7)	P1—O6—Na1xiii	100.00 (7)
O8—Na3—O8viii	139.29 (4)	Al1vi—O6—Na1xiii	97.24 (6)
O8vii—Na3—O8viii	139.29 (4)	P1—O6—Na1x	76.46 (6)
O8—Al1—O5ix	178.73 (7)	Al1vi—O6—Na1x	96.37 (6)
O8—Al1—O3	91.33 (7)	Na1xiii—O6—Na1x	160.22 (7)
O5ix—Al1—O3	87.55 (7)	P1—O7—Al1x	131.02 (9)
O8—Al1—O4iii	92.68 (6)	P1—O7—Na1x	89.48 (7)
O5ix—Al1—O4iii	88.48 (6)	Al1x—O7—Na1x	131.83 (7)
O3—Al1—O4iii	173.98 (7)	P3—O8—Al1	139.13 (10)
O8—Al1—O6viii	86.36 (7)	P3—O8—Na3	98.29 (7)
O5ix—Al1—O6viii	94.23 (6)	Al1—O8—Na3	122.17 (7)

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