Poly[diaqua­[μ6-4,4′-(1,4-phenyl­ene)bis­(2,6-dimethyl­pyridine-3,5-dicarboxyl­ato)]dilead(II)]

Zhu, Y.; Zhang, M.-X.; Yang, S.-S.; Xiao, F.; Zhang, X.-P.; Gao, Y.-Y.; Li, B.-J.; Huang, K.-L.

doi:10.1107/S1600536813007733

metal-organic compounds

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ISSN: 2056-9890

Volume 69| Part 4| April 2013| Pages m232-m233

doi:10.1107/S1600536813007733

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Poly[diaqua[μ₆-4,4′-(1,4-phenylene)bis(2,6-dimethylpyridine-3,5-dicarboxylato)]dilead(II)]

Yi Zhu,^a Ming-Xing Zhang,^a Shan-Shan Yang,^a Feng Xiao,^a Xiao-Ping Zhang,^a Yuan-Yuan Gao,^a Bing-Jie Li ^a and Kun-Lin Huang ^a ^*

^aCollege of Life Science, and College of Chemistry, Chongqing Normal University, Chongqing 400047, People's Republic of China
^*Correspondence e-mail: kunlin@jlu.edu.cn

(Received 18 February 2013; accepted 20 March 2013; online 28 March 2013)

The asymmetric unit of the title Pb-based coordination polymer, [Pb₂(C₂₄H₁₆N₂O₈)(H₂O)₂]_n, consists of one Pb^II cation, half of a 4,4′-(1,4-phenylene)bis(2,6-dimethylpyridine-3,5-dicarboxylate (L⁴⁻) ligand and one coordinating water molecule. The centers of the benzene ring of the ligand and the four-membered Pb/O/Pb/O ring are located on centers of inversion. The Pb^II ion is coordinated in form of a distorted polyhedron by seven O atoms from four separate L⁴⁻ ligands and by one water O atom. The PbO₇ polyhedra share O atoms, forming infinite zigzag [PbO₄(H₂O)]_n chains along [100] that are bridged by L⁴⁻ ligands, forming a two-dimensional coordination network parallel to (001). O—H⋯O hydrogen bonds involving the water molecule are observed.

Related literature

For background to metal-organic frameworks, see: Long & Yaghi (2009 ); Zhao et al. (2003 ). For related structures, see: Liu et al. (2002 ); O'Keeffe et al. (2008 ); Zhang et al. (2011 ). For lead complexes, see: Harrowfield et al. (2004 ); Yang et al. (2007 ). For typical Pb—O distances, see: Chen et al. (2012 ); Wei et al. (2005 ). For the photoluminescent mechanism of ligand–metal charge transfer, see: Hu et al. (2010 ); Zhang et al. (2012 ).

Experimental

Crystal data

[Pb₂(C₂₄H₁₆N₂O₈)(H₂O)₂]
M_r = 910.80
Triclinic, $[P \overline 1]$
a = 7.2182 (12) Å
b = 9.0635 (14) Å
c = 9.9589 (15) Å
α = 79.202 (2)°
β = 71.683 (2)°
γ = 85.494 (3)°
V = 607.43 (17) Å³
Z = 1
Mo Kα radiation
μ = 13.90 mm⁻¹
T = 298 K
0.25 × 0.23 × 0.23 mm

Data collection

Bruker SMART APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2003 ) T_min = 0.129, T_max = 0.142
3168 measured reflections
2119 independent reflections
1932 reflections with I > 2σ(I)
R_int = 0.015

Refinement

R[F² > 2σ(F²)] = 0.022
wR(F²) = 0.055
S = 1.01
2119 reflections
174 parameters
H-atom parameters constrained
Δρ_max = 1.15 e Å⁻³
Δρ_min = −1.16 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H2⋯O4ⁱ	0.85	2.04	2.834 (6)	155
O5—H1⋯O3ⁱⁱ	0.85	2.05	2.879 (5)	165
Symmetry codes: (i) -x, -y, -z+1; (ii) -x+1, -y, -z+1.

Data collection: APEX2 (Bruker, 2010 ); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus; 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: PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536813007733/im2422sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536813007733/im2422Isup2.hkl

checkCIF report

Comment top

In recent years, the chemistry of novel metal-organic hybrid coordination polymers has been the subject of intensive research, due to their interesting molecular structures and their potential as a new class of solid-state materials applied in catalysis, molecular recognition, gas storage, drug delivery, and so on (Liu et al., 2002; O'Keeffe et al., 2008). Generally speaking, the diversity of potential applications in the framework structures of such materials greatly depends on the selection of the metal centers and organic spacers. Recently, carboxylate groups are frequently exploited in the design, syntheses, and crystallization of coordination frameworks, because they exhibit diverse coordination modes, which can enhance the robustness of the architectures. Furthermore, the flexibility of carboxylate groups is always efficient to form fascinating structures. In this paper, we choose a new flexible and multidentate carboxylate ligand, 4,4'-(1,4-phenylene)bis(2,6-dimethylpyridine-3,5-dicarboxylic acid) (H₄L).

Up to date, research on coordination polymers has focused on transition metal ions as coordination centers, while less concentration has been given to heavy p-block metal ion, e.g. lead(II). In contrast to transiton metal ions, lead(II), with its large radius, flexible coordination environment, and variable stereochemical activity, provides unique opportunities for the formation of unusual structures with interesting properties (Harrowfield et al.., 2004; Yang et al.., 2007). In addition, the intrinsic features of lead(II), the presence of a 6 s² outer electron configuration, inspire chemists extensive interest in coordination chemistry, photophysics, and photochemistry. Herein, we report a new photoluminescent complex [Pb(L)(H₂O)]_n(1) from the flexible 4,4'-(1,4-phenylene)bis(2,6-dimethylpyridine-3,5- dicarboxylic acid) (H₄L) and lead salt.

X-ray diffraction analyses reveal that each asymmetric unit of 1 contains half deprotonated L^4- ligand, one H₂O molecule and one crystallographically independent Pb^II center(Fig 1). Pb1 center is coordinated with seven O atoms: six (O1^#1, O1^#2, O2^#2,O2^#3, O3, O4) from four H₄L ligands and one (O5) from the H₂O molecule. Of particular interest is the weak coordinative bond that exists between Pb1 and O2^#3. Pb1,O1^#1, O1^#2, O2^#2,O2^#3, O3, O4, O5 furnish a polyhydral coordination environment (PbO₇) with the Pb—O bond lengths are in agreement with those reported in other Pb(II) complexes of O-chelating ligands (Wei et al., 2005; Chen et al., 2012).

As shown in Fig.1, each H₄L ligand connects six crystallographically equivalent Pb atoms. The carboxylato group with O1 and O2 coordinates three lead atoms producing two Pb₂O₂ rings that share one common lead atom. The other carboxylate moiety with donor atoms O3 and O4 coordinates one lead atom in a chelating mode. Notably, the resulting PbO₇ polyhedra share the O1^#4, O1^#5, O2^#2, O2^#3 atoms to form infinite zigzag chains composed of [PbO₄(H₂O)]_n in which adjacent Pb atoms are coplanar and Pb···Pb distances are 4.077 Å and 4.161 Å respectively (Fig. 2). Another interesting structural feature of complex 1 is that the zigzag [PbO₄(H₂O)]_n chains are bridged by H₄L ligands to form a two-dimensional (2-D) coordination network (Fig. 3).

The photoluminescence spectrum of compound 1 was measured in the solid state at room temperature, as shown in Fig. 4. At room temperature the photoluminescent emission maximum of free H₄L was observed at 426 nm (upon λ_{Ex, max} = 208 nm). For compound 1, excitation at 380 nm leads to strong photoluminescence with an emission maximum at λ = 465 nm. The emission peak of complex 1 is red-shifted by about 40 nm compared to that of the pure H₄L ligand, which can be assigned to the ligand-metal charge transfer (LMCT) (Hu et al., 2010; Zhang et al., 2011; Zhang et al., 2012).

Related literature top

For background to metal-organic frameworks, see: Long & Yaghi (2009); Zhao et al. (2003). For related structures, see: Liu et al. (2002); O'Keeffe et al. (2008); Zhang et al. (2011). For lead complexes, see: Harrowfield et al. (2004); Yang et al. (2007). For typical Pb—O distances, see: Chen et al. (2012); Wei et al. (2005). For photoluminescent mechanism of ligand–metal charge transfer, see: Hu et al. (2010); Zhang et al. (2012).

Experimental top

A mixture of Pb(NO₃)₂ × 6 H₂O (66 mg), H₄L (40 mg) and DMF (6 ml) was sealed in a 25 ml Teflon-lined stainless steel reactor. The mixture was heated to 373 K for 3 days and then cooled to room temperature. The crystal samples were washed with methanol to yield 18 mg of compound 1.

Computing details top

Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus (Bruker, 2008); 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: PLATON (Spek, 2009).

Figures top

	Fig. 1. Part of crystal structure of the L^4- ligand and Pb^II centres in 1. All H atoms have been omitted for clarity. [symmetry code: (#1) -x, y+1, -z+1; (#2) x, y - 1,z; (#3) -x + 1, -y + 1, -z + 1; (#4) x + 1, y-1, z; (#5) -x + 1, -y + 1, -z + 1.]
	Fig. 2. Sectional crystal structure of zigzag chain [PbO₄(H₂O)]_n. Pb, green; O, red; H, white
	Fig. 3. View along c axis of two-dimensional coordination polymer from Pb ions and L^4- ligands. PbO₇, polyhedron: green; O: red; N: blue; C: grey.
	Fig. 4. Photoluminescent spectra of 1 (λ_em at 465 nm, upon λ_ex at 380 nm). I = relative intensity, em = emission, and ex = excitation.

Poly[diaqua[µ₆-4,4'-(1,4-phenylene)bis(2,6-dimethylpyridine-3,5-dicarboxylato)]dilead(II)] top

Crystal data top

[Pb₂(C₂₄H₁₆N₂O₈)(H₂O)₂]	Z = 1
M_r = 910.80	F(000) = 422
Triclinic, P1	D_x = 2.490 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.2182 (12) Å	Cell parameters from 1580 reflections
b = 9.0635 (14) Å	θ = 2.7–23.1°
c = 9.9589 (15) Å	µ = 13.90 mm⁻¹
α = 79.202 (2)°	T = 298 K
β = 71.683 (2)°	Block, colorless
γ = 85.494 (3)°	0.25 × 0.23 × 0.23 mm
V = 607.43 (17) Å³

Data collection top

Bruker SMART APEXII CCD diffractometer	2119 independent reflections
Radiation source: fine-focus sealed tube	1932 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.015
phi and ω scans	θ_max = 25.0°, θ_min = 2.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −8→8
T_min = 0.129, T_max = 0.142	k = −10→10
3168 measured reflections	l = −10→11

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)] = 0.022	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.055	H-atom parameters constrained
S = 1.01	w = 1/[σ²(F_o²) + (0.0347P)²] where P = (F_o² + 2F_c²)/3
2119 reflections	(Δ/σ)_max < 0.001
174 parameters	Δρ_max = 1.15 e Å⁻³
0 restraints	Δρ_min = −1.16 e Å⁻³

Crystal data top

[Pb₂(C₂₄H₁₆N₂O₈)(H₂O)₂]	γ = 85.494 (3)°
M_r = 910.80	V = 607.43 (17) Å³
Triclinic, P1	Z = 1
a = 7.2182 (12) Å	Mo Kα radiation
b = 9.0635 (14) Å	µ = 13.90 mm⁻¹
c = 9.9589 (15) Å	T = 298 K
α = 79.202 (2)°	0.25 × 0.23 × 0.23 mm
β = 71.683 (2)°

Data collection top

Bruker SMART APEXII CCD diffractometer	2119 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	1932 reflections with I > 2σ(I)
T_min = 0.129, T_max = 0.142	R_int = 0.015
3168 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.022	0 restraints
wR(F²) = 0.055	H-atom parameters constrained
S = 1.01	Δρ_max = 1.15 e Å⁻³
2119 reflections	Δρ_min = −1.16 e Å⁻³
174 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
Pb1	0.24557 (3)	0.11141 (2)	0.47717 (2)	0.02892 (9)
O1	0.0452 (5)	0.9117 (4)	0.6086 (4)	0.0281 (8)
O2	0.3224 (5)	0.8538 (4)	0.6568 (5)	0.0365 (9)
O3	0.2253 (5)	0.1995 (4)	0.7194 (4)	0.0343 (9)
O4	−0.0248 (6)	0.2448 (5)	0.6332 (5)	0.0382 (10)
O5	0.3782 (6)	−0.0957 (5)	0.3132 (5)	0.0441 (11)
H1	0.4881	−0.1412	0.3019	0.066*
H2	0.2924	−0.1629	0.3379	0.066*
N1	−0.2153 (6)	0.5547 (5)	0.9379 (5)	0.0275 (10)
C1	−0.1131 (7)	0.6798 (6)	0.8704 (6)	0.0245 (11)
C2	0.0591 (7)	0.6774 (5)	0.7553 (5)	0.0220 (11)
C3	0.1282 (7)	0.5404 (6)	0.7125 (5)	0.0213 (10)
C4	0.0148 (7)	0.4140 (6)	0.7758 (5)	0.0233 (11)
C5	−0.1579 (7)	0.4255 (6)	0.8888 (6)	0.0271 (12)
C6	−0.1922 (8)	0.8214 (6)	0.9291 (6)	0.0341 (13)
H6A	−0.2907	0.8662	0.8872	0.051*
H6B	−0.0882	0.8906	0.9060	0.051*
H6C	−0.2481	0.7975	1.0315	0.051*
C7	0.1542 (7)	0.8222 (6)	0.6705 (6)	0.0242 (11)
C8	0.0752 (7)	0.2736 (6)	0.7103 (6)	0.0243 (11)
C9	−0.2867 (8)	0.2946 (7)	0.9630 (7)	0.0379 (14)
H9A	−0.2869	0.2692	1.0611	0.057*
H9B	−0.2388	0.2102	0.9154	0.057*
H9C	−0.4172	0.3203	0.9603	0.057*
C10	0.3206 (7)	0.5253 (5)	0.5999 (5)	0.0192 (10)
C11	0.3313 (7)	0.5098 (6)	0.4608 (5)	0.0249 (11)
H11	0.2177	0.5160	0.4347	0.030*
C12	0.5090 (7)	0.4854 (6)	0.3615 (5)	0.0241 (11)
H12	0.5146	0.4761	0.2689	0.029*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Pb1	0.02297 (13)	0.02526 (13)	0.03649 (14)	−0.00185 (8)	−0.00454 (9)	−0.00765 (9)
O1	0.0269 (19)	0.0225 (19)	0.037 (2)	−0.0014 (15)	−0.0143 (17)	−0.0010 (16)
O2	0.024 (2)	0.029 (2)	0.054 (3)	−0.0052 (16)	−0.0106 (19)	−0.0020 (18)
O3	0.034 (2)	0.029 (2)	0.044 (2)	0.0113 (17)	−0.0165 (19)	−0.0119 (18)
O4	0.030 (2)	0.036 (2)	0.056 (3)	0.0017 (17)	−0.017 (2)	−0.022 (2)
O5	0.029 (2)	0.048 (3)	0.059 (3)	0.0011 (19)	−0.013 (2)	−0.021 (2)
N1	0.021 (2)	0.031 (3)	0.026 (2)	0.0005 (19)	0.0000 (19)	−0.008 (2)
C1	0.020 (3)	0.027 (3)	0.026 (3)	0.002 (2)	−0.006 (2)	−0.008 (2)
C2	0.021 (2)	0.018 (3)	0.027 (3)	0.002 (2)	−0.009 (2)	−0.004 (2)
C3	0.020 (2)	0.026 (3)	0.018 (2)	0.002 (2)	−0.006 (2)	−0.005 (2)
C4	0.023 (3)	0.022 (3)	0.024 (3)	0.001 (2)	−0.007 (2)	−0.005 (2)
C5	0.021 (3)	0.033 (3)	0.027 (3)	−0.001 (2)	−0.009 (2)	−0.002 (2)
C6	0.031 (3)	0.029 (3)	0.037 (3)	0.006 (2)	0.000 (3)	−0.014 (2)
C7	0.024 (3)	0.019 (3)	0.027 (3)	0.001 (2)	−0.001 (2)	−0.007 (2)
C8	0.020 (3)	0.021 (3)	0.027 (3)	0.002 (2)	−0.002 (2)	−0.003 (2)
C9	0.030 (3)	0.034 (3)	0.041 (4)	−0.006 (3)	0.001 (3)	−0.003 (3)
C10	0.018 (2)	0.017 (2)	0.020 (2)	0.0026 (19)	−0.003 (2)	−0.0028 (19)
C11	0.020 (2)	0.028 (3)	0.029 (3)	0.001 (2)	−0.011 (2)	−0.005 (2)
C12	0.023 (3)	0.030 (3)	0.019 (3)	0.001 (2)	−0.005 (2)	−0.004 (2)

Geometric parameters (Å, º) top

Pb1—O1ⁱ	2.327 (4)	C2—C3	1.393 (7)
Pb1—O4	2.472 (4)	C2—C7	1.507 (7)
Pb1—O1ⁱⁱ	2.538 (3)	C3—C4	1.390 (7)
Pb1—O3	2.638 (4)	C3—C10	1.501 (7)
Pb1—O5	2.644 (4)	C4—C5	1.405 (7)
O3—C8	1.248 (6)	C5—C9	1.494 (8)
O4—C8	1.277 (7)	C6—H6A	0.9600
C8—C4	1.510 (7)	C6—H6B	0.9600
O1—C7	1.294 (6)	C6—H6C	0.9600
O1—Pb1ⁱⁱⁱ	2.327 (4)	C9—H9A	0.9600
O1—Pb1ⁱⁱ	2.538 (3)	C9—H9B	0.9600
N1—C5	1.338 (7)	C9—H9C	0.9600
N1—C1	1.348 (7)	C10—C12^iv	1.391 (7)
O2—C7	1.230 (6)	C10—C11	1.395 (7)
O5—H1	0.8500	C11—C12	1.383 (7)
O5—H2	0.8500	C11—H11	0.9300
C1—C2	1.403 (7)	C12—C10^iv	1.391 (7)
C1—C6	1.507 (7)	C12—H12	0.9300

O1ⁱ—Pb1—O4	79.28 (13)	C3—C4—C5	119.1 (5)
O1ⁱ—Pb1—O1ⁱⁱ	66.21 (14)	C3—C4—C8	117.7 (4)
O4—Pb1—O1ⁱⁱ	75.30 (12)	C5—C4—C8	122.9 (5)
O1ⁱ—Pb1—O3	89.30 (13)	N1—C5—C4	121.7 (5)
O4—Pb1—O3	51.16 (12)	N1—C5—C9	116.0 (5)
O1ⁱⁱ—Pb1—O3	124.84 (11)	C4—C5—C9	122.3 (5)
O1ⁱ—Pb1—O5	78.92 (13)	C1—C6—H6A	109.5
O4—Pb1—O5	151.48 (13)	C1—C6—H6B	109.5
O1ⁱⁱ—Pb1—O5	79.19 (12)	H6A—C6—H6B	109.5
O3—Pb1—O5	146.08 (13)	C1—C6—H6C	109.5
C8—O3—Pb1	87.8 (3)	H6A—C6—H6C	109.5
C8—O4—Pb1	94.7 (3)	H6B—C6—H6C	109.5
O3—C8—O4	122.3 (5)	O2—C7—O1	121.6 (5)
O3—C8—C4	121.6 (5)	O2—C7—C2	124.0 (5)
O4—C8—C4	115.8 (4)	O1—C7—C2	114.4 (4)
C7—O1—Pb1ⁱⁱⁱ	104.5 (3)	C5—C9—H9A	109.5
C7—O1—Pb1ⁱⁱ	136.9 (3)	C5—C9—H9B	109.5
Pb1ⁱⁱⁱ—O1—Pb1ⁱⁱ	113.79 (14)	H9A—C9—H9B	109.5
C5—N1—C1	119.3 (4)	C5—C9—H9C	109.5
Pb1—O5—H1	125.1	H9A—C9—H9C	109.5
Pb1—O5—H2	107.8	H9B—C9—H9C	109.5
H1—O5—H2	106.8	C12^iv—C10—C11	119.3 (4)
N1—C1—C2	122.0 (5)	C12^iv—C10—C3	118.9 (4)
N1—C1—C6	115.8 (5)	C11—C10—C3	121.6 (4)
C2—C1—C6	122.2 (5)	C12—C11—C10	120.7 (5)
C3—C2—C1	118.6 (5)	C12—C11—H11	119.7
C3—C2—C7	120.8 (5)	C10—C11—H11	119.7
C1—C2—C7	120.2 (4)	C11—C12—C10^iv	120.0 (5)
C4—C3—C2	118.8 (5)	C11—C12—H12	120.0
C4—C3—C10	119.1 (4)	C10^iv—C12—H12	120.0
C2—C3—C10	122.1 (5)

Symmetry codes: (i) x, y−1, z; (ii) −x, −y+1, −z+1; (iii) x, y+1, z; (iv) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H2···O4^v	0.85	2.04	2.834 (6)	155
O5—H1···O3^vi	0.85	2.05	2.879 (5)	165

Symmetry codes: (v) −x, −y, −z+1; (vi) −x+1, −y, −z+1.

Experimental details

Crystal data
Chemical formula	[Pb₂(C₂₄H₁₆N₂O₈)(H₂O)₂]
M_r	910.80
Crystal system, space group	Triclinic, P1
Temperature (K)	298
a, b, c (Å)	7.2182 (12), 9.0635 (14), 9.9589 (15)
α, β, γ (°)	79.202 (2), 71.683 (2), 85.494 (3)
V (Å³)	607.43 (17)
Z	1
Radiation type	Mo Kα
µ (mm⁻¹)	13.90
Crystal size (mm)	0.25 × 0.23 × 0.23

Data collection
Diffractometer	Bruker SMART APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2003)
T_min, T_max	0.129, 0.142
No. of measured, independent and observed [I > 2σ(I)] reflections	3168, 2119, 1932
R_int	0.015
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.055, 1.01
No. of reflections	2119
No. of parameters	174
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	1.15, −1.16

Computer programs: APEX2 (Bruker, 2010), SAINT-Plus (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008), PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H2···O4ⁱ	0.85	2.04	2.834 (6)	155.3
O5—H1···O3ⁱⁱ	0.85	2.05	2.879 (5)	165.4

Symmetry codes: (i) −x, −y, −z+1; (ii) −x+1, −y, −z+1.

Acknowledgements

This work was supported by the Science and Technology Projects of Chongqing Municipal Education Commission (grant No. KJ120632) and Chongqing Normal University Scientific Research Foundation Project (grant No. 2011XLS30).

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