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

Zhao, D.

doi:10.1107/S1600536811041729

inorganic compounds

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Volume 67| Part 11| November 2011| Page i64

doi:10.1107/S1600536811041729

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

Dan Zhao ^a ^*

^aDepartment of Physics and Chemistry, Henan Polytechnic University, Jiaozuo, Henan 454000, People's Republic of China
^*Correspondence e-mail: iamzd@hpu.edu.cn

(Received 3 September 2011; accepted 10 October 2011; online 22 October 2011)

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, $[P \overline 42_1 c ]$
a = 14.054 (3) Å
c = 6.1718 (16) Å
V = 1219.1 (4) Å³
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[F² > 2σ(F²)] = 0.017
wR(F²) = 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).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811041729/wm2530sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811041729/wm2530Isup2.hkl

checkCIF report

Comment top

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)°.

Related literature top

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

Experimental top

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.

Computing details top

Data collection: CrystalClear (Rigaku, 2004); cell refinement: CrystalClear (Rigaku, 2004); data reduction: CrystalClear (Rigaku, 2004); 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).

Figures top

	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.

Heptasodium tetraaluminium tetrakis(diphosphate) orthophosphate top

Crystal data top

Na₇Al₄(P₂O₇)₄(PO₄)	D_x = 2.887 Mg m⁻³
M_r = 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 top

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

Refinement top

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(F_o²) + (0.0297P)² + 0.278P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.047	(Δ/σ)_max = 0.001
S = 1.08	Δρ_max = 0.22 e Å⁻³
1347 reflections	Δρ_min = −0.29 e Å⁻³
118 parameters	Absolute structure: Flack (1983), 540 Friedel pairs
0 restraints	Absolute structure parameter: −0.04 (9)

Crystal data top

Na₇Al₄(P₂O₇)₄(PO₄)	Z = 2
M_r = 1059.58	Mo Kα radiation
Tetragonal, P42₁c	µ = 1.06 mm⁻¹
a = 14.054 (3) Å	T = 296 K
c = 6.1718 (16) Å	0.15 × 0.05 × 0.05 mm
V = 1219.1 (4) Å³

Data collection top

Rigaku Saturn70 CCD diffractometer	1347 independent reflections
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	1287 reflections with I > 2σ(I)
T_min = 0.857, T_max = 0.949	R_int = 0.024
5562 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.017	0 restraints
wR(F²) = 0.047	Δρ_max = 0.22 e Å⁻³
S = 1.08	Δρ_min = −0.29 e Å⁻³
1347 reflections	Absolute structure: Flack (1983), 540 Friedel pairs
118 parameters	Absolute structure parameter: −0.04 (9)

Special details top

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) top

	x	y	z	U_iso*/U_eq
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 (Å²) top

	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, º) top

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—O1^iv	2.3072 (16)	P3—O8ⁱⁱⁱ	1.5341 (14)
Na2—O1	2.3072 (17)	P3—O8^x	1.5341 (14)
Na2—O1ⁱ	2.3532 (17)	P3—O8	1.5341 (14)
Na2—O1^v	2.3532 (17)	P3—O8^vii	1.5341 (14)
Na2—O2ⁱ	2.6957 (15)	O1—Na2^xi	2.3532 (17)
Na2—O2^v	2.6957 (15)	O1—Na1^xii	2.3993 (17)
Na3—O8^vi	2.4655 (16)	O2—Na1^xiii	2.6363 (18)
Na3—O8	2.4655 (16)	O2—Na2^xi	2.6957 (15)
Na3—O8^vii	2.4655 (16)	O3—Na1^xiii	2.4730 (18)
Na3—O8^viii	2.4655 (16)	O4—Al1^x	1.9210 (15)
Al1—O8	1.8391 (15)	O5—Al1^xiv	1.8500 (15)
Al1—O5^ix	1.8500 (15)	O6—Al1^vi	1.9258 (16)
Al1—O3	1.8993 (16)	O6—Na1^xiii	2.6291 (18)
Al1—O4ⁱⁱⁱ	1.9210 (15)	O6—Na1^x	2.9419 (18)
Al1—O6^viii	1.9258 (16)	O7—Al1^x	1.9278 (16)
Al1—O7ⁱⁱⁱ	1.9278 (16)	O7—Na1^x	2.5789 (17)
P1—O5	1.4862 (14)

O4—Na1—O1ⁱ	99.33 (6)	O3—Al1—O6^viii	89.69 (7)
O4—Na1—O3ⁱⁱ	157.36 (7)	O4ⁱⁱⁱ—Al1—O6^viii	86.10 (7)
O1ⁱ—Na1—O3ⁱⁱ	90.92 (6)	O8—Al1—O7ⁱⁱⁱ	92.43 (7)
O4—Na1—O7ⁱⁱⁱ	77.49 (5)	O5^ix—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)	O6^viii—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—O8^x	104.48 (11)
O2ⁱⁱ—Na1—O6ⁱⁱⁱ	110.46 (5)	O8ⁱⁱⁱ—P3—O8	112.02 (6)
O1^iv—Na2—O1	98.36 (9)	O8^x—P3—O8	112.02 (6)
O1^iv—Na2—O1ⁱ	166.32 (7)	O8ⁱⁱⁱ—P3—O8^vii	112.02 (6)
O1—Na2—O1ⁱ	84.54 (5)	O8^x—P3—O8^vii	112.02 (6)
O1^iv—Na2—O1^v	84.54 (5)	O8—P3—O8^vii	104.48 (11)
O1—Na2—O1^v	166.32 (7)	P1—O2—P2	127.92 (9)
O1ⁱ—Na2—O1^v	95.80 (8)	P1—O2—Na1^xiii	97.23 (7)
O1^iv—Na2—O2ⁱ	109.82 (5)	P2—O2—Na1^xiii	91.90 (7)
O1—Na2—O2ⁱ	75.12 (5)	P1—O2—Na2^xi	138.90 (8)
O1ⁱ—Na2—O2ⁱ	57.84 (5)	P2—O2—Na2^xi	90.30 (6)
O1^v—Na2—O2ⁱ	116.61 (6)	Na1^xiii—O2—Na2^xi	95.69 (5)
O1^iv—Na2—O2^v	75.12 (5)	P2—O3—Al1	138.27 (10)
O1—Na2—O2^v	109.82 (5)	P2—O3—Na1^xiii	101.37 (7)
O1ⁱ—Na2—O2^v	116.61 (6)	Al1—O3—Na1^xiii	114.51 (7)
O1^v—Na2—O2^v	57.84 (5)	P2—O4—Al1^x	135.59 (9)
O2ⁱ—Na2—O2^v	172.79 (8)	P2—O4—Na1	114.27 (8)
O8^vi—Na3—O8	139.29 (4)	Al1^x—O4—Na1	109.28 (7)
O8^vi—Na3—O8^vii	139.29 (4)	P1—O5—Al1^xiv	169.27 (10)
O8—Na3—O8^vii	58.94 (7)	P1—O6—Al1^vi	144.77 (10)
O8^vi—Na3—O8^viii	58.94 (7)	P1—O6—Na1^xiii	100.00 (7)
O8—Na3—O8^viii	139.29 (4)	Al1^vi—O6—Na1^xiii	97.24 (6)
O8^vii—Na3—O8^viii	139.29 (4)	P1—O6—Na1^x	76.46 (6)
O8—Al1—O5^ix	178.73 (7)	Al1^vi—O6—Na1^x	96.37 (6)
O8—Al1—O3	91.33 (7)	Na1^xiii—O6—Na1^x	160.22 (7)
O5^ix—Al1—O3	87.55 (7)	P1—O7—Al1^x	131.02 (9)
O8—Al1—O4ⁱⁱⁱ	92.68 (6)	P1—O7—Na1^x	89.48 (7)
O5^ix—Al1—O4ⁱⁱⁱ	88.48 (6)	Al1^x—O7—Na1^x	131.83 (7)
O3—Al1—O4ⁱⁱⁱ	173.98 (7)	P3—O8—Al1	139.13 (10)
O8—Al1—O6^viii	86.36 (7)	P3—O8—Na3	98.29 (7)
O5^ix—Al1—O6^viii	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.

Experimental details

Crystal data
Chemical formula	Na₇Al₄(P₂O₇)₄(PO₄)
M_r	1059.58
Crystal system, space group	Tetragonal, P42₁c
Temperature (K)	296
a, c (Å)	14.054 (3), 6.1718 (16)
V (Å³)	1219.1 (4)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	1.06
Crystal size (mm)	0.15 × 0.05 × 0.05

Data collection
Diffractometer	Rigaku Saturn70 CCD diffractometer
Absorption correction	Multi-scan (ABSCOR; Higashi, 1995)
T_min, T_max	0.857, 0.949
No. of measured, independent and observed [I > 2σ(I)] reflections	5562, 1347, 1287
R_int	0.024
(sin θ/λ)_max (Å⁻¹)	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.017, 0.047, 1.08
No. of reflections	1347
No. of parameters	118
Δρ_max, Δρ_min (e Å⁻³)	0.22, −0.29
Absolute structure	Flack (1983), 540 Friedel pairs
Absolute structure parameter	−0.04 (9)

Computer programs: CrystalClear (Rigaku, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2004), SHELXTL (Sheldrick, 2008).

Acknowledgements

The author acknowledges the Doctoral Foundation of Henan Polytechnic University (B2010–92, 648483).

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