2-O-tert-Butyl­dimethyl­silyl-4,6-O-ethyl­idene-myo-insitol 1,3,5-orthoformate

Xu, Z.; Wang, Q.; Sun, Y.

doi:10.1107/S1600536810023214

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 66| Part 7| July 2010| Page o1741

doi:10.1107/S1600536810023214

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2-O-tert-Butyldimethylsilyl-4,6-O-ethylidene-myo-insitol 1,3,5-orthoformate

Zhouqin Xu,^a Qiang Wang ^a ^* and Yanchun Sun ^b

^aThe Department of Physics-Chemistry, Henan Polytechnic University, Jiao Zuo 454000, People's Republic of China, and ^bThe Department of Medicine, Hebi College of Vocation and Technology, He Bi 458030, People's Republic of China
^*Correspondence e-mail: wangqiang@hpu.edu.cn

(Received 7 June 2010; accepted 16 June 2010; online 23 June 2010)

In the title compound, C₁₅H₂₆O₆Si, the dioxa six-membered ring bonded to the myo-inositol skeleton is in a boat conformation while the rest of the six-membered rings adopt chair conformations.

Related literature

myo-Inositol orthoesters have been used extensively for the synthesis of phosphoinositols and their derivatives, see: Das & Shashidhar (1997 ); Sureshan et al. (2003 ); Potter & Lampe (1995 ). For the synthesis of the title compound, see: Li & Vasella (1993 ). For a related structure, see: Angyal (2000 ).

Experimental

Crystal data

C₁₅H₂₆O₆Si
M_r = 330.45
Orthorhombic, P b c a
a = 12.0170 (4) Å
b = 11.2808 (3) Å
c = 25.6942 (8) Å
V = 3483.14 (18) Å³
Z = 8
Mo Kα radiation
μ = 0.16 mm⁻¹
T = 297 K
0.22 × 0.21 × 0.17 mm

Data collection

Bruker APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2003 ) T_min = 0.966, T_max = 0.973
55999 measured reflections
4060 independent reflections
2035 reflections with I > 2σ(I)
R_int = 0.102

Refinement

R[F² > 2σ(F²)] = 0.052
wR(F²) = 0.149
S = 1.00
4060 reflections
205 parameters
18 restraints
H-atom parameters constrained
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.23 e Å⁻³

Data collection: APEX2 (Bruker, 2007 ); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810023214/pv2294sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536810023214/pv2294Isup2.hkl

checkCIF report

Comment top

myo-inositol orthoesters have been used extensivedly for the synthesis of phosphoinositols (Das & Shashidhar, 1997; Sureshan et al., 2003), their derivatives and other compounds with interesting properties (Potter & Lampe, 1995). We present here the crystal structure of the title compound, which is a key intermediate for the synthesis of phosphorylated myo-inositol derivatives (Angyal, 2000).

The bond lengths and angles in the title compound (Fig. 1) are in normal range and agree well with the corresponding bond lengths and angles reported for a related structure (Angyal, 2000). In the title molecule, the six-membered ring containing O1 and O2 is in a boat conformation, the other six-membered rings are in chair conformations. The crystal packing is stabilized by van der Waals forces.

Related literature top

myo-Inositol orthoesters have been used extensivedly for the synthesis of phosphoinositols and their derivatives, see: Das & Shashidhar (1997); Sureshan et al. (2003); Potter & Lampe (1995). For the synthesis of the title compound, see: Li & Vasella (1993). For a related structure, see: Angyal (2000).

Experimental top

The title compound was prepared according to the literature (Li & Vasella, 1993). Single crystals suitable for X-ray diffraction were prepared by slow evaperation from a solution of ethyl acetate and petroleum ether (1:4).

Computing details top

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. The molecular structure of the title compound, with the atomic-numbering scheme. Displacement ellipsoids are drawn at 30% probability level.
	Fig. 2. A partial packing diagram of the title compound, viewed down the b-axis.

2-O-tert-Butyldimethylsilyl-4,6-O-ethylidene-myo- insitol 1,3,5-orthoformate top

Crystal data top

C₁₅H₂₆O₆Si	F(000) = 1424
M_r = 330.45	D_x = 1.260 Mg m⁻³
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 3612 reflections
a = 12.0170 (4) Å	θ = 2.3–18.5°
b = 11.2808 (3) Å	µ = 0.16 mm⁻¹
c = 25.6942 (8) Å	T = 297 K
V = 3483.14 (18) Å³	Block, colorless
Z = 8	0.22 × 0.21 × 0.17 mm

Data collection top

Bruker APEXII CCD area-detector diffractometer	4060 independent reflections
Radiation source: fine-focus sealed tube	2035 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.102
ϕ and ω scans	θ_max = 27.6°, θ_min = 1.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −15→15
T_min = 0.966, T_max = 0.973	k = −14→14
55999 measured reflections	l = −33→32

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)] = 0.052	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.149	H-atom parameters constrained
S = 1.00	w = 1/[σ²(F_o²) + (0.0588P)² + 1.0231P] where P = (F_o² + 2F_c²)/3
4060 reflections	(Δ/σ)_max = 0.001
205 parameters	Δρ_max = 0.24 e Å⁻³
18 restraints	Δρ_min = −0.23 e Å⁻³

Crystal data top

C₁₅H₂₆O₆Si	V = 3483.14 (18) Å³
M_r = 330.45	Z = 8
Orthorhombic, Pbca	Mo Kα radiation
a = 12.0170 (4) Å	µ = 0.16 mm⁻¹
b = 11.2808 (3) Å	T = 297 K
c = 25.6942 (8) Å	0.22 × 0.21 × 0.17 mm

Data collection top

Bruker APEXII CCD area-detector diffractometer	4060 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	2035 reflections with I > 2σ(I)
T_min = 0.966, T_max = 0.973	R_int = 0.102
55999 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.052	18 restraints
wR(F²) = 0.149	H-atom parameters constrained
S = 1.00	Δρ_max = 0.24 e Å⁻³
4060 reflections	Δρ_min = −0.23 e Å⁻³
205 parameters

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
C1	1.0701 (3)	0.6537 (3)	0.59939 (13)	0.0839 (10)
H1A	1.1352	0.6900	0.5848	0.126*
H1B	1.0112	0.7110	0.6013	0.126*
H1C	1.0473	0.5886	0.5778	0.126*
C2	1.0960 (2)	0.6094 (2)	0.65278 (12)	0.0623 (8)
H2	1.1226	0.6746	0.6747	0.075*
C3	1.2002 (2)	0.4541 (3)	0.69423 (11)	0.0606 (8)
H3	1.2794	0.4578	0.7032	0.073*
C4	1.0113 (2)	0.4980 (2)	0.72188 (10)	0.0525 (6)
H4	0.9641	0.5327	0.7490	0.063*
C5	1.1318 (2)	0.4988 (3)	0.73907 (11)	0.0615 (7)
H5	1.1545	0.5797	0.7481	0.074*
C6	1.1663 (2)	0.3251 (2)	0.68424 (10)	0.0565 (7)
H6	1.2134	0.2913	0.6569	0.068*
C7	0.9784 (2)	0.3686 (2)	0.71229 (10)	0.0475 (6)
H7	0.8989	0.3641	0.7041	0.057*
C8	1.0450 (2)	0.3186 (2)	0.66778 (10)	0.0477 (6)
H8	1.0333	0.3668	0.6365	0.057*
C9	1.1140 (3)	0.3057 (3)	0.77096 (12)	0.0663 (8)
H9	1.1255	0.2570	0.8021	0.080*
C10	1.0905 (3)	0.2103 (4)	0.55151 (14)	0.1063 (13)
H10A	1.0859	0.2952	0.5534	0.160*
H10B	1.0710	0.1847	0.5171	0.160*
H10C	1.1651	0.1856	0.5593	0.160*
C11	1.0206 (3)	−0.0159 (3)	0.60583 (12)	0.0748 (9)
H11A	1.0988	−0.0286	0.6111	0.112*
H11B	0.9973	−0.0561	0.5748	0.112*
H11C	0.9800	−0.0465	0.6351	0.112*
C12	0.8465 (3)	0.1719 (3)	0.57919 (11)	0.0673 (8)
C13	0.8201 (3)	0.1084 (3)	0.52793 (12)	0.0919 (11)
H13A	0.7429	0.1190	0.5196	0.138*
H13B	0.8359	0.0254	0.5315	0.138*
H13C	0.8651	0.1411	0.5006	0.138*
C14	0.7693 (3)	0.1210 (4)	0.62207 (15)	0.1046 (12)
H14A	0.7834	0.1612	0.6543	0.157*
H14B	0.7837	0.0378	0.6262	0.157*
H14C	0.6930	0.1324	0.6122	0.157*
C15	0.8231 (4)	0.3032 (3)	0.57262 (19)	0.141 (2)
H15A	0.7474	0.3141	0.5618	0.212*
H15B	0.8722	0.3354	0.5468	0.212*
H15C	0.8351	0.3431	0.6052	0.212*
O1	0.99714 (14)	0.56100 (14)	0.67385 (7)	0.0554 (5)
O2	1.18006 (14)	0.52151 (17)	0.64779 (7)	0.0621 (5)
O3	1.14699 (17)	0.42203 (18)	0.78300 (7)	0.0728 (6)
O4	1.00096 (16)	0.30181 (15)	0.75876 (7)	0.0584 (5)
O5	1.18069 (15)	0.25908 (18)	0.73137 (8)	0.0689 (6)
O6	1.01461 (16)	0.19916 (15)	0.65769 (7)	0.0610 (5)
Si1	0.99324 (6)	0.14381 (6)	0.59918 (3)	0.0530 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.081 (2)	0.074 (2)	0.096 (3)	0.0003 (17)	0.0099 (19)	0.032 (2)
C2	0.0583 (17)	0.0506 (16)	0.078 (2)	−0.0097 (14)	0.0084 (15)	0.0002 (15)
C3	0.0401 (15)	0.077 (2)	0.0650 (18)	−0.0088 (14)	−0.0059 (13)	0.0029 (16)
C4	0.0549 (16)	0.0477 (14)	0.0550 (17)	−0.0024 (12)	0.0088 (13)	−0.0084 (13)
C5	0.0650 (18)	0.0632 (18)	0.0563 (18)	−0.0168 (15)	−0.0026 (14)	−0.0060 (15)
C6	0.0492 (15)	0.0673 (18)	0.0531 (17)	0.0093 (14)	0.0019 (13)	−0.0007 (14)
C7	0.0458 (15)	0.0451 (14)	0.0515 (16)	−0.0045 (11)	−0.0005 (12)	−0.0021 (12)
C8	0.0507 (15)	0.0432 (14)	0.0491 (16)	−0.0002 (11)	−0.0029 (12)	−0.0048 (12)
C9	0.072 (2)	0.070 (2)	0.0565 (18)	−0.0023 (16)	−0.0084 (16)	0.0069 (16)
C10	0.121 (3)	0.112 (3)	0.086 (3)	−0.040 (2)	0.038 (2)	−0.020 (2)
C11	0.093 (2)	0.0545 (17)	0.077 (2)	0.0151 (16)	−0.0045 (17)	−0.0142 (15)
C12	0.0784 (19)	0.0668 (17)	0.0567 (17)	0.0118 (15)	−0.0106 (15)	−0.0052 (14)
C13	0.104 (2)	0.096 (2)	0.076 (2)	0.0068 (19)	−0.0219 (18)	−0.0122 (18)
C14	0.072 (2)	0.142 (3)	0.100 (2)	0.008 (2)	0.0024 (19)	−0.005 (2)
C15	0.178 (5)	0.084 (3)	0.162 (4)	0.060 (3)	−0.091 (4)	−0.026 (3)
O1	0.0522 (10)	0.0465 (10)	0.0677 (12)	−0.0015 (8)	0.0059 (9)	0.0021 (9)
O2	0.0495 (11)	0.0730 (12)	0.0639 (12)	−0.0066 (9)	0.0089 (9)	0.0042 (11)
O3	0.0812 (14)	0.0844 (15)	0.0527 (12)	−0.0182 (11)	−0.0141 (10)	−0.0024 (11)
O4	0.0626 (12)	0.0582 (11)	0.0544 (12)	−0.0061 (9)	0.0037 (9)	0.0049 (9)
O5	0.0637 (12)	0.0759 (13)	0.0671 (14)	0.0167 (10)	−0.0079 (10)	0.0074 (11)
O6	0.0870 (14)	0.0419 (10)	0.0543 (11)	−0.0050 (9)	−0.0042 (10)	−0.0059 (8)
Si1	0.0636 (5)	0.0452 (4)	0.0502 (5)	−0.0004 (4)	0.0056 (4)	−0.0067 (3)

Geometric parameters (Å, º) top

C1—C2	1.493 (4)	C9—O5	1.397 (3)
C1—H1A	0.9600	C9—O3	1.406 (3)
C1—H1B	0.9600	C9—H9	0.9800
C1—H1C	0.9600	C10—Si1	1.852 (3)
C2—O1	1.415 (3)	C10—H10A	0.9600
C2—O2	1.421 (3)	C10—H10B	0.9600
C2—H2	0.9800	C10—H10C	0.9600
C3—O2	1.436 (3)	C11—Si1	1.840 (3)
C3—C5	1.502 (4)	C11—H11A	0.9600
C3—C6	1.533 (4)	C11—H11B	0.9600
C3—H3	0.9800	C11—H11C	0.9600
C4—O1	1.434 (3)	C12—C15	1.516 (4)
C4—C5	1.513 (4)	C12—C13	1.532 (4)
C4—C7	1.533 (3)	C12—C14	1.550 (5)
C4—H4	0.9800	C12—Si1	1.864 (3)
C5—O3	1.434 (3)	C13—H13A	0.9600
C5—H5	0.9800	C13—H13B	0.9600
C6—O5	1.432 (3)	C13—H13C	0.9600
C6—C8	1.520 (3)	C14—H14A	0.9600
C6—H6	0.9800	C14—H14B	0.9600
C7—O4	1.437 (3)	C14—H14C	0.9600
C7—C8	1.505 (3)	C15—H15A	0.9600
C7—H7	0.9800	C15—H15B	0.9600
C8—O6	1.420 (3)	C15—H15C	0.9600
C8—H8	0.9800	O6—Si1	1.6480 (18)
C9—O4	1.395 (3)

C2—C1—H1A	109.5	O4—C9—H9	107.7
C2—C1—H1B	109.5	O5—C9—H9	107.7
H1A—C1—H1B	109.5	O3—C9—H9	107.7
C2—C1—H1C	109.5	Si1—C10—H10A	109.5
H1A—C1—H1C	109.5	Si1—C10—H10B	109.5
H1B—C1—H1C	109.5	H10A—C10—H10B	109.5
O1—C2—O2	111.3 (2)	Si1—C10—H10C	109.5
O1—C2—C1	107.8 (2)	H10A—C10—H10C	109.5
O2—C2—C1	107.4 (2)	H10B—C10—H10C	109.5
O1—C2—H2	110.1	Si1—C11—H11A	109.5
O2—C2—H2	110.1	Si1—C11—H11B	109.5
C1—C2—H2	110.1	H11A—C11—H11B	109.5
O2—C3—C5	111.6 (2)	Si1—C11—H11C	109.5
O2—C3—C6	108.6 (2)	H11A—C11—H11C	109.5
C5—C3—C6	107.5 (2)	H11B—C11—H11C	109.5
O2—C3—H3	109.7	C15—C12—C13	108.8 (3)
C5—C3—H3	109.7	C15—C12—C14	109.3 (3)
C6—C3—H3	109.7	C13—C12—C14	108.3 (3)
O1—C4—C5	111.2 (2)	C15—C12—Si1	111.8 (3)
O1—C4—C7	107.6 (2)	C13—C12—Si1	110.7 (2)
C5—C4—C7	107.4 (2)	C14—C12—Si1	107.9 (2)
O1—C4—H4	110.2	C12—C13—H13A	109.5
C5—C4—H4	110.2	C12—C13—H13B	109.5
C7—C4—H4	110.2	H13A—C13—H13B	109.5
O3—C5—C3	109.3 (2)	C12—C13—H13C	109.5
O3—C5—C4	110.4 (2)	H13A—C13—H13C	109.5
C3—C5—C4	107.3 (2)	H13B—C13—H13C	109.5
O3—C5—H5	109.9	C12—C14—H14A	109.5
C3—C5—H5	109.9	C12—C14—H14B	109.5
C4—C5—H5	109.9	H14A—C14—H14B	109.5
O5—C6—C8	109.0 (2)	C12—C14—H14C	109.5
O5—C6—C3	108.7 (2)	H14A—C14—H14C	109.5
C8—C6—C3	110.3 (2)	H14B—C14—H14C	109.5
O5—C6—H6	109.6	C12—C15—H15A	109.5
C8—C6—H6	109.6	C12—C15—H15B	109.5
C3—C6—H6	109.6	H15A—C15—H15B	109.5
O4—C7—C8	109.6 (2)	C12—C15—H15C	109.5
O4—C7—C4	108.5 (2)	H15A—C15—H15C	109.5
C8—C7—C4	109.9 (2)	H15B—C15—H15C	109.5
O4—C7—H7	109.6	C2—O1—C4	114.9 (2)
C8—C7—H7	109.6	C2—O2—C3	114.5 (2)
C4—C7—H7	109.6	C9—O3—C5	110.8 (2)
O6—C8—C7	110.9 (2)	C9—O4—C7	110.8 (2)
O6—C8—C6	110.0 (2)	C9—O5—C6	110.5 (2)
C7—C8—C6	106.3 (2)	C8—O6—Si1	124.48 (16)
O6—C8—H8	109.8	O6—Si1—C11	104.99 (12)
C7—C8—H8	109.8	O6—Si1—C10	110.57 (14)
C6—C8—H8	109.8	C11—Si1—C10	110.20 (17)
O4—C9—O5	112.5 (2)	O6—Si1—C12	109.54 (12)
O4—C9—O3	110.7 (2)	C11—Si1—C12	111.17 (15)
O5—C9—O3	110.5 (2)	C10—Si1—C12	110.25 (17)

O2—C3—C5—O3	174.7 (2)	C1—C2—O2—C3	−169.0 (2)
C6—C3—C5—O3	55.7 (3)	C5—C3—O2—C2	−4.0 (3)
O2—C3—C5—C4	54.9 (3)	C6—C3—O2—C2	114.4 (2)
C6—C3—C5—C4	−64.1 (3)	O4—C9—O3—C5	−62.2 (3)
O1—C4—C5—O3	−172.03 (19)	O5—C9—O3—C5	63.1 (3)
C7—C4—C5—O3	−54.5 (3)	C3—C5—O3—C9	−59.7 (3)
O1—C4—C5—C3	−52.9 (3)	C4—C5—O3—C9	58.1 (3)
C7—C4—C5—C3	64.6 (3)	O5—C9—O4—C7	−59.7 (3)
O2—C3—C6—O5	−176.93 (19)	O3—C9—O4—C7	64.4 (3)
C5—C3—C6—O5	−56.1 (3)	C8—C7—O4—C9	59.0 (3)
O2—C3—C6—C8	−57.5 (3)	C4—C7—O4—C9	−61.0 (3)
C5—C3—C6—C8	63.4 (3)	O4—C9—O5—C6	60.5 (3)
O1—C4—C7—O4	175.20 (18)	O3—C9—O5—C6	−63.7 (3)
C5—C4—C7—O4	55.3 (3)	C8—C6—O5—C9	−59.9 (3)
O1—C4—C7—C8	55.4 (3)	C3—C6—O5—C9	60.3 (3)
C5—C4—C7—C8	−64.5 (3)	C7—C8—O6—Si1	135.56 (19)
O4—C7—C8—O6	61.8 (3)	C6—C8—O6—Si1	−107.1 (2)
C4—C7—C8—O6	−179.1 (2)	C8—O6—Si1—C11	154.8 (2)
O4—C7—C8—C6	−57.9 (3)	C8—O6—Si1—C10	35.9 (2)
C4—C7—C8—C6	61.2 (3)	C8—O6—Si1—C12	−85.8 (2)
O5—C6—C8—O6	−61.8 (3)	C15—C12—Si1—O6	65.4 (3)
C3—C6—C8—O6	179.0 (2)	C13—C12—Si1—O6	−173.1 (2)
O5—C6—C8—C7	58.4 (3)	C14—C12—Si1—O6	−54.8 (2)
C3—C6—C8—C7	−60.8 (3)	C15—C12—Si1—C11	−179.0 (3)
O2—C2—O1—C4	53.3 (3)	C13—C12—Si1—C11	−57.5 (3)
C1—C2—O1—C4	170.8 (2)	C14—C12—Si1—C11	60.8 (3)
C5—C4—O1—C2	0.2 (3)	C15—C12—Si1—C10	−56.5 (3)
C7—C4—O1—C2	−117.2 (2)	C13—C12—Si1—C10	65.0 (3)
O1—C2—O2—C3	−51.2 (3)	C14—C12—Si1—C10	−176.7 (2)

Experimental details

Crystal data
Chemical formula	C₁₅H₂₆O₆Si
M_r	330.45
Crystal system, space group	Orthorhombic, Pbca
Temperature (K)	297
a, b, c (Å)	12.0170 (4), 11.2808 (3), 25.6942 (8)
V (Å³)	3483.14 (18)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	0.16
Crystal size (mm)	0.22 × 0.21 × 0.17

Data collection
Diffractometer	Bruker APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2003)
T_min, T_max	0.966, 0.973
No. of measured, independent and observed [I > 2σ(I)] reflections	55999, 4060, 2035
R_int	0.102
(sin θ/λ)_max (Å⁻¹)	0.653

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.052, 0.149, 1.00
No. of reflections	4060
No. of parameters	205
No. of restraints	18
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.24, −0.23

Computer programs: APEX2 (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Acknowledgements

This work was supported by the Henan Polytechnic University Foundation for Doctor Teachers (B2010–65) and the Henan Polytechnic University Foundation for the Youth (P051102). The authors thank Drs L. Yang, D. Zhao and Z. Z. Zhang for their assistance with the data collection and analysis.

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