2-Amino-4,6-dimethyl­pyrimidin-1-ium 1-oxo-2,6,7-trioxa-1λ5-phosphabicyclo­[2.2.2]octane-4-carboxyl­ate

Hou, X.-F.; Li, G.-C.; Lai, P.-Y.

doi:10.1107/S1600536810019896

organic compounds

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ISSN: 2056-9890

Volume 66| Part 7| July 2010| Page o1528

doi:10.1107/S1600536810019896

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2-Amino-4,6-dimethylpyrimidin-1-ium 1-oxo-2,6,7-trioxa-1λ⁵-phosphabicyclo[2.2.2]octane-4-carboxylate

Xu-Feng Hou,^a ^* Gong-Chun Li ^a and Peng-Yang Lai ^a

^aCollege of Chemistry and Chemical Engineering, Xuchang University, Xuchang, Henan Province 461000, People's Republic of China
^*Correspondence e-mail: hxfst@yahoo.com.cn

(Received 22 May 2010; accepted 26 May 2010; online 5 June 2010)

In the title compound, C₆H₁₀N₃⁺·C₅H₆O₆P⁻, the cation and anion are linked by pairs of N—H⋯O hydrogen bonds. There are additional intermolecular N—H⋯N hydrogen bonds, which generate centrosymmetric tetramers of two cations and two anions.

Related literature

For the applications of caged bicyclic phosphates, see: Li et al. (2000 ). For related structures, see: Meng et al. (2009 ); Guo & Zang (2008 ); Thakur & Desiraju (2008 ); Wang et al. (2007 ).

Experimental

Crystal data

C₆H₁₀N₃⁺·C₅H₆O₆P⁻
M_r = 317.24
Monoclinic, P 2₁ /c
a = 9.5080 (13) Å
b = 6.1870 (8) Å
c = 23.974 (2) Å
β = 99.611 (5)°
V = 1390.5 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.23 mm⁻¹
T = 113 K
0.24 × 0.22 × 0.14 mm

Data collection

Rigaku Saturn724 CCD diffractometer
Absorption correction: multi-scan (CrystalClear; Rigaku/MSC, 2009 ) T_min = 0.947, T_max = 0.969
23989 measured reflections
6532 independent reflections
4883 reflections with I > 2σ(I)
R_int = 0.035

Refinement

R[F² > 2σ(F²)] = 0.039
wR(F²) = 0.107
S = 1.01
6532 reflections
204 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.54 e Å⁻³
Δρ_min = −0.38 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O1	0.866 (15)	1.907 (15)	2.7719 (11)	176.4 (14)
N1—H2⋯N3ⁱ	0.900 (14)	2.113 (15)	3.0114 (12)	176.3 (12)
N2—H3⋯O2	0.988 (15)	1.738 (16)	2.7170 (10)	170.4 (15)
Symmetry code: (i) -x+1, -y, -z+1.

Data collection: CrystalClear-SM Expert (Rigaku/MSC, 2009); cell refinement: CrystalClear-SM Expert; data reduction: CrystalClear-SM Expert; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: CrystalStructure (Rigaku/MSC, 2009); software used to prepare material for publication: CrystalStructure.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810019896/fj2308sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536810019896/fj2308Isup2.hkl

checkCIF report

Comment top

Caged bicyclic phosphates are widely used as flame retardants or pesticides (Li et al. 2000). It can also serve as host–guest systems and have been studied in the context of hydrogen-bond patterns (Guo & Zang, 2008; Wang et al., 2007). Aminopyrimidine derivatives are biologically important compounds as they occur in nature as components of nucleic acids (Meng et al., 2009). The crystal structures of aminopyrimidine carboxylates have been reported (Thakur et al., 2008). We report here the crystal structure of a new bicyclic phosphate cage compound.

In the title compound, [C₆H₁₀N₃]⁺ [C₅H₆O₆P]^-, The cation and anion in the asymmetric unit are linked by N—H···O hydrogen bonds. There is also addition intermolecular N—H···N hydrogen bonds. (Fig. 2).

Related literature top

For the applications of caged bicyclic phosphates, see: Li et al. (2000). For related structures, see: Meng et al. (2009); Guo & Zang (2008); Thakur & Desiraju (2008); Wang et al. (2007).

Experimental top

The title compound was obtained by reaction of 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylic acid (0.39 g, 0.2 mmol) and 2-amino-4,6-dimethylpyrimidine(0.25 g, 0.2 mmol) in refluxing acetone (50 ml). The solvent was evaporated in vacuo. The title compound was recrystallized from ethanol and single crystals of (I) were obtained by slow evaporation.

Computing details top

Data collection: CrystalClear-SM Expert (Rigaku/MSC, 2009); cell refinement: CrystalClear-SM Expert (Rigaku/MSC, 2009); data reduction: CrystalClear-SM Expert (Rigaku/MSC, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: CrystalStructure (Rigaku/MSC, 2009); software used to prepare material for publication: CrystalStructure (Rigaku/MSC, 2009).

Figures top

	Fig. 1. The asymmetric unit of the title compound, (I), with displacement ellipsoids drawn at the 30% probability level.
	Fig. 2. The packing diagram of the title compound. Intermolecular hydrogen bonds are shown as dashed line.

2-Amino-4,6-dimethylpyrimidin-1-ium 1-oxo-2,6,7-trioxa-1λ⁵-phosphabicyclo[2.2.2]octane-4-carboxylate top

Crystal data top

C₆H₁₀N₃⁺·C₅H₆O₆P⁻	F(000) = 664
M_r = 317.24	D_x = 1.515 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71075 Å
Hall symbol: -P 2ybc	Cell parameters from 5985 reflections
a = 9.5080 (13) Å	θ = 2.2–36.3°
b = 6.1870 (8) Å	µ = 0.23 mm⁻¹
c = 23.974 (2) Å	T = 113 K
β = 99.611 (5)°	Prism, colorless
V = 1390.5 (3) Å³	0.24 × 0.22 × 0.14 mm
Z = 4

Data collection top

Rigaku Saturn724 CCD diffractometer	6532 independent reflections
Radiation source: rotating anode	4883 reflections with I > 2σ(I)
Multilayer monochromator	R_int = 0.035
Detector resolution: 14.222 pixels mm^-1	θ_max = 36.5°, θ_min = 1.7°
ω scans	h = −15→14
Absorption correction: multi-scan (CrystalClear; Rigaku/MSC, 2009)	k = −10→10
T_min = 0.947, T_max = 0.969	l = −36→39
23989 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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.107	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	w = 1/[σ²(F_o²) + (0.0615P)²] where P = (F_o² + 2F_c²)/3
6532 reflections	(Δ/σ)_max = 0.001
204 parameters	Δρ_max = 0.54 e Å⁻³
0 restraints	Δρ_min = −0.38 e Å⁻³

Crystal data top

C₆H₁₀N₃⁺·C₅H₆O₆P⁻	V = 1390.5 (3) Å³
M_r = 317.24	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 9.5080 (13) Å	µ = 0.23 mm⁻¹
b = 6.1870 (8) Å	T = 113 K
c = 23.974 (2) Å	0.24 × 0.22 × 0.14 mm
β = 99.611 (5)°

Data collection top

Rigaku Saturn724 CCD diffractometer	6532 independent reflections
Absorption correction: multi-scan (CrystalClear; Rigaku/MSC, 2009)	4883 reflections with I > 2σ(I)
T_min = 0.947, T_max = 0.969	R_int = 0.035
23989 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.039	0 restraints
wR(F²) = 0.107	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	Δρ_max = 0.54 e Å⁻³
6532 reflections	Δρ_min = −0.38 e Å⁻³
204 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
P1	0.14090 (2)	0.74372 (4)	0.157866 (9)	0.01584 (6)
O1	0.32415 (8)	0.33013 (12)	0.32735 (3)	0.02813 (17)
O2	0.46621 (8)	0.62093 (12)	0.33500 (3)	0.02544 (16)
O3	0.29862 (7)	0.67033 (12)	0.15596 (3)	0.02097 (14)
O4	0.15812 (7)	0.91396 (11)	0.20765 (3)	0.02023 (13)
O5	0.06923 (7)	0.54214 (12)	0.18168 (3)	0.02421 (15)
O6	0.06557 (8)	0.82445 (13)	0.10419 (3)	0.02619 (16)
N1	0.45629 (9)	0.17785 (15)	0.43177 (4)	0.02312 (17)
N2	0.61028 (8)	0.46847 (12)	0.43466 (3)	0.01702 (14)
N3	0.63811 (8)	0.21010 (14)	0.50821 (3)	0.01949 (15)
C1	0.36366 (9)	0.50774 (14)	0.31115 (4)	0.01674 (15)
C2	0.27993 (8)	0.59650 (13)	0.25498 (3)	0.01332 (14)
C3	0.37600 (9)	0.58891 (16)	0.20974 (4)	0.01990 (17)
H3A	0.4621	0.6782	0.2219	0.024*
H3B	0.4070	0.4383	0.2049	0.024*
C4	0.23414 (10)	0.83103 (15)	0.26188 (4)	0.02018 (17)
H4A	0.1711	0.8386	0.2908	0.024*
H4B	0.3193	0.9214	0.2749	0.024*
C5	0.14789 (10)	0.45860 (16)	0.23533 (4)	0.02254 (19)
H5A	0.1769	0.3072	0.2302	0.027*
H5B	0.0854	0.4605	0.2645	0.027*
C6	0.56840 (9)	0.28450 (15)	0.45830 (4)	0.01698 (15)
C7	0.72567 (10)	0.58213 (15)	0.45997 (4)	0.01896 (16)
C8	0.79892 (10)	0.51036 (16)	0.51086 (4)	0.02109 (17)
H8	0.8792	0.5871	0.5300	0.025*
C9	0.75166 (10)	0.32090 (16)	0.53356 (4)	0.01951 (17)
C10	0.76334 (12)	0.77807 (16)	0.42947 (5)	0.0264 (2)
H10A	0.8040	0.7342	0.3962	0.032*
H10B	0.8334	0.8642	0.4547	0.032*
H10C	0.6774	0.8647	0.4173	0.032*
C11	0.82793 (13)	0.22887 (19)	0.58813 (4)	0.0295 (2)
H11A	0.7581	0.1869	0.6120	0.035*
H11B	0.8927	0.3379	0.6079	0.035*
H11C	0.8828	0.1016	0.5803	0.035*
H1	0.4144 (16)	0.231 (2)	0.3998 (7)	0.033 (4)*
H2	0.4287 (15)	0.065 (2)	0.4512 (6)	0.039 (4)*
H3	0.5623 (16)	0.511 (3)	0.3965 (6)	0.052 (4)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
P1	0.01665 (11)	0.01722 (10)	0.01235 (10)	0.00168 (8)	−0.00133 (7)	0.00215 (7)
O1	0.0314 (4)	0.0245 (3)	0.0237 (3)	−0.0074 (3)	−0.0093 (3)	0.0116 (3)
O2	0.0232 (3)	0.0255 (3)	0.0229 (3)	−0.0060 (3)	−0.0101 (3)	0.0070 (3)
O3	0.0215 (3)	0.0277 (3)	0.0142 (3)	0.0069 (3)	0.0043 (2)	0.0034 (2)
O4	0.0265 (3)	0.0171 (3)	0.0155 (3)	0.0085 (2)	−0.0013 (2)	0.0013 (2)
O5	0.0211 (3)	0.0261 (3)	0.0213 (3)	−0.0082 (3)	−0.0087 (2)	0.0080 (3)
O6	0.0282 (4)	0.0310 (4)	0.0167 (3)	0.0031 (3)	−0.0042 (3)	0.0060 (3)
N1	0.0190 (4)	0.0305 (4)	0.0177 (4)	−0.0039 (3)	−0.0029 (3)	0.0094 (3)
N2	0.0183 (3)	0.0190 (3)	0.0127 (3)	0.0026 (3)	−0.0005 (2)	0.0021 (2)
N3	0.0171 (3)	0.0277 (4)	0.0127 (3)	0.0015 (3)	−0.0002 (3)	0.0054 (3)
C1	0.0161 (4)	0.0180 (4)	0.0149 (4)	0.0020 (3)	−0.0012 (3)	0.0028 (3)
C2	0.0126 (3)	0.0130 (3)	0.0134 (3)	0.0002 (3)	−0.0007 (3)	0.0011 (3)
C3	0.0157 (4)	0.0266 (4)	0.0171 (4)	0.0057 (3)	0.0018 (3)	0.0032 (3)
C4	0.0240 (4)	0.0190 (4)	0.0151 (4)	0.0073 (3)	−0.0040 (3)	−0.0018 (3)
C5	0.0200 (4)	0.0239 (4)	0.0203 (4)	−0.0077 (3)	−0.0065 (3)	0.0090 (3)
C6	0.0151 (4)	0.0231 (4)	0.0125 (3)	0.0028 (3)	0.0016 (3)	0.0034 (3)
C7	0.0219 (4)	0.0185 (4)	0.0157 (4)	0.0021 (3)	0.0009 (3)	−0.0016 (3)
C8	0.0231 (4)	0.0231 (4)	0.0154 (4)	0.0002 (3)	−0.0018 (3)	−0.0015 (3)
C9	0.0187 (4)	0.0273 (4)	0.0116 (3)	0.0031 (3)	−0.0002 (3)	0.0010 (3)
C10	0.0334 (5)	0.0182 (4)	0.0247 (5)	−0.0026 (4)	−0.0033 (4)	0.0018 (3)
C11	0.0280 (5)	0.0417 (6)	0.0151 (4)	−0.0023 (4)	−0.0070 (4)	0.0075 (4)

Geometric parameters (Å, º) top

P1—O6	1.4529 (7)	C2—C3	1.5310 (12)
P1—O5	1.5734 (7)	C2—C4	1.5318 (12)
P1—O3	1.5748 (7)	C3—H3A	0.9900
P1—O4	1.5798 (7)	C3—H3B	0.9900
O1—C1	1.2443 (11)	C4—H4A	0.9900
O2—C1	1.2578 (11)	C4—H4B	0.9900
O3—C3	1.4631 (11)	C5—H5A	0.9900
O4—C4	1.4703 (10)	C5—H5B	0.9900
O5—C5	1.4694 (11)	C7—C8	1.3737 (12)
N1—C6	1.3227 (12)	C7—C10	1.4901 (14)
N1—H1	0.866 (15)	C8—C9	1.3977 (14)
N1—H2	0.900 (14)	C8—H8	0.9500
N2—C7	1.3580 (12)	C9—C11	1.4983 (13)
N2—C6	1.3603 (12)	C10—H10A	0.9800
N2—H3	0.988 (15)	C10—H10B	0.9800
N3—C9	1.3363 (12)	C10—H10C	0.9800
N3—C6	1.3484 (11)	C11—H11A	0.9800
C1—C2	1.5460 (11)	C11—H11B	0.9800
C2—C5	1.5260 (12)	C11—H11C	0.9800

O6—P1—O5	114.50 (4)	O4—C4—H4B	109.7
O6—P1—O3	113.86 (4)	C2—C4—H4B	109.7
O5—P1—O3	104.73 (4)	H4A—C4—H4B	108.2
O6—P1—O4	114.43 (4)	O5—C5—C2	110.24 (7)
O5—P1—O4	104.52 (4)	O5—C5—H5A	109.6
O3—P1—O4	103.59 (4)	C2—C5—H5A	109.6
C3—O3—P1	114.52 (5)	O5—C5—H5B	109.6
C4—O4—P1	114.14 (5)	C2—C5—H5B	109.6
C5—O5—P1	114.11 (5)	H5A—C5—H5B	108.1
C6—N1—H1	116.8 (10)	N1—C6—N3	119.58 (8)
C6—N1—H2	114.7 (9)	N1—C6—N2	119.05 (8)
H1—N1—H2	128.2 (13)	N3—C6—N2	121.37 (8)
C7—N2—C6	121.20 (7)	N2—C7—C8	118.78 (8)
C7—N2—H3	119.3 (10)	N2—C7—C10	116.39 (8)
C6—N2—H3	119.1 (10)	C8—C7—C10	124.83 (9)
C9—N3—C6	117.95 (8)	C7—C8—C9	117.94 (8)
O1—C1—O2	126.96 (8)	C7—C8—H8	121.0
O1—C1—C2	116.56 (7)	C9—C8—H8	121.0
O2—C1—C2	116.46 (7)	N3—C9—C8	122.75 (8)
C5—C2—C3	108.75 (7)	N3—C9—C11	116.02 (9)
C5—C2—C4	109.20 (7)	C8—C9—C11	121.23 (9)
C3—C2—C4	108.63 (7)	C7—C10—H10A	109.5
C5—C2—C1	110.36 (7)	C7—C10—H10B	109.5
C3—C2—C1	108.95 (7)	H10A—C10—H10B	109.5
C4—C2—C1	110.90 (7)	C7—C10—H10C	109.5
O3—C3—C2	110.00 (7)	H10A—C10—H10C	109.5
O3—C3—H3A	109.7	H10B—C10—H10C	109.5
C2—C3—H3A	109.7	C9—C11—H11A	109.5
O3—C3—H3B	109.7	C9—C11—H11B	109.5
C2—C3—H3B	109.7	H11A—C11—H11B	109.5
H3A—C3—H3B	108.2	C9—C11—H11C	109.5
O4—C4—C2	109.99 (7)	H11A—C11—H11C	109.5
O4—C4—H4A	109.7	H11B—C11—H11C	109.5
C2—C4—H4A	109.7

O6—P1—O3—C3	179.91 (6)	C5—C2—C4—O4	−59.68 (9)
O5—P1—O3—C3	−54.29 (7)	C3—C2—C4—O4	58.79 (9)
O4—P1—O3—C3	55.00 (7)	C1—C2—C4—O4	178.50 (7)
O6—P1—O4—C4	179.86 (6)	P1—O5—C5—C2	1.39 (11)
O5—P1—O4—C4	53.84 (7)	C3—C2—C5—O5	−60.03 (10)
O3—P1—O4—C4	−55.60 (7)	C4—C2—C5—O5	58.35 (10)
O6—P1—O5—C5	178.68 (7)	C1—C2—C5—O5	−179.49 (7)
O3—P1—O5—C5	53.28 (8)	C9—N3—C6—N1	179.42 (9)
O4—P1—O5—C5	−55.34 (8)	C9—N3—C6—N2	−1.06 (13)
O1—C1—C2—C5	8.87 (11)	C7—N2—C6—N1	−179.24 (9)
O2—C1—C2—C5	−172.46 (9)	C7—N2—C6—N3	1.24 (13)
O1—C1—C2—C3	−110.46 (9)	C6—N2—C7—C8	−1.19 (13)
O2—C1—C2—C3	68.20 (10)	C6—N2—C7—C10	178.60 (8)
O1—C1—C2—C4	130.02 (9)	N2—C7—C8—C9	0.99 (13)
O2—C1—C2—C4	−51.31 (11)	C10—C7—C8—C9	−178.78 (9)
P1—O3—C3—C2	0.12 (9)	C6—N3—C9—C8	0.90 (14)
C5—C2—C3—O3	59.14 (9)	C6—N3—C9—C11	−178.44 (9)
C4—C2—C3—O3	−59.61 (9)	C7—C8—C9—N3	−0.89 (14)
C1—C2—C3—O3	179.47 (7)	C7—C8—C9—C11	178.42 (9)
P1—O4—C4—C2	1.10 (9)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1	0.866 (15)	1.907 (15)	2.7719 (11)	176.4 (14)
N1—H2···N3ⁱ	0.900 (14)	2.113 (15)	3.0114 (12)	176.3 (12)
N2—H3···O2	0.988 (15)	1.738 (16)	2.7170 (10)	170.4 (15)

Symmetry code: (i) −x+1, −y, −z+1.

Experimental details

Crystal data
Chemical formula	C₆H₁₀N₃⁺·C₅H₆O₆P⁻
M_r	317.24
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	113
a, b, c (Å)	9.5080 (13), 6.1870 (8), 23.974 (2)
β (°)	99.611 (5)
V (Å³)	1390.5 (3)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.23
Crystal size (mm)	0.24 × 0.22 × 0.14

Data collection
Diffractometer	Rigaku Saturn724 CCD diffractometer
Absorption correction	Multi-scan (CrystalClear; Rigaku/MSC, 2009)
T_min, T_max	0.947, 0.969
No. of measured, independent and observed [I > 2σ(I)] reflections	23989, 6532, 4883
R_int	0.035
(sin θ/λ)_max (Å⁻¹)	0.836

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.039, 0.107, 1.01
No. of reflections	6532
No. of parameters	204
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.54, −0.38

Computer programs: CrystalClear-SM Expert (Rigaku/MSC, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), CrystalStructure (Rigaku/MSC, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1	0.866 (15)	1.907 (15)	2.7719 (11)	176.4 (14)
N1—H2···N3ⁱ	0.900 (14)	2.113 (15)	3.0114 (12)	176.3 (12)
N2—H3···O2	0.988 (15)	1.738 (16)	2.7170 (10)	170.4 (15)

Symmetry code: (i) −x+1, −y, −z+1.

Acknowledgements

This work was supported by the Natural Science Foundation of Henan Province, China (grant No. 082300420110) and the Natural Science Foundation of Henan Province Education Department, China (grant No. 2007150036).

References

Guo, M.-L. & Zang, H.-J. (2008). Acta Cryst. C64, m173–m175. Web of Science CSD CrossRef IUCr Journals Google Scholar
Li, X., Ou, Y.-X., Zhang, Y.-H. & Lian, D.-J. (2000). Chin. Chem. Lett. 11, 887–890. CAS Google Scholar
Meng, A.-L., Huang, J.-E., Zheng, B. & Li, Z.-J. (2009). Acta Cryst. E65, o1595. Web of Science CSD CrossRef IUCr Journals Google Scholar
Rigaku/MSC (2009). CrystalClear-SM Expert and CrystalStructure. Rigaku/MSC, The Woodlands, Texas, USA. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Thakur, T. S. & Desiraju, G. R. (2008). Cryst. Growth Des. 8, 4031–4044. Web of Science CSD CrossRef CAS Google Scholar
Wang, Z., Zang, H.-J. & Guo, M.-L. (2007). Acta Cryst. E63, o3418. Web of Science CSD CrossRef IUCr Journals Google Scholar

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