supplementary materials


HTML versionpdf versioncif file3d viewstructure factorssupplementary materialsCIF check reportsimilar papers Open access

er2051 scheme

Acta Cryst. (2008). E64, o845    [ doi:10.1107/S1600536808009744 ]

5-Butylamino-6-(4-fluorophenyl)-7-oxo-1-p-tolyl-6,7-dihydro-1H-pyrazolo[4,3-d]pyrimidine-3-carbonitrile

J.-H. Hu and M.-H. Wu

Abstract top

In the title compound, C23H21FN6O, the dihedral angle between the fluorophenyl and pyrimidinone rings is 75.9 (1)°, and the dihedral angle between the methylphenyl and pyrazole rings is 40.3 (1)°. In the crystal structure, weak C-H...[pi](arene) and C-N...[pi](arene) interactions and intermolecular C-H...N and N-H...O hydrogen-bonding interactions are present.

Comment top

Pyrazolo[4,3-d]pyrimidin-7-ones have been reported as potent and selective inhibitors of PDE5 (Bell et al., 1991; Zhao et al., 2006). Sildenafil citrate, a pyrazolo[4,3-d]pyrimidin-7-one derivative, is the first orally effective PDE5 inhibitor approved for the treatment of erectile dysfunction. Its advent has spurred significant interest in the development of additional PDE5 inhibitors (Allerton et al., 2006). Herein, the title compound as Sildenafil analog was synthesized and determined by X-ray crystal diffraction in order to find new potent PDE5 inhibitors.

In the molecule (Fig. 1), the dihedral angle between the fluorophenyl and pyrimidinon ring is 75.9 (1)°, and the dihedral angle between the methylphenyl and pyrazole ring is 40.3 (1)°. The atoms O1, N1–N6, C5, C8–C14 and C20 are nearly coplanar, and N6, C21–C23 formed a plane.

In the crystal structure, molecules are linked by weak C—H···π (arene) interactions, which connected H6 to the centroid of atoms C14–19, Cg1, (symmetry code: -x,1/2 + y,1/2 - z). In addition, the crystal structure is stablized by intermolecular N—H···O and intramolecular C—H···N hydrogen-bonding interactions (Fig. 2).

Related literature top

For background information, see: Bell et al. (1991); Zhao et al. (2006); Allerton et al. (2006).

Experimental top

To a solution of 4-(3-cyano-5-ethoxycarbonyl-p-tolyl-1H-pyrazolyl) iminophosphorane (1.59 g, 3 mmol) in absolute anhydrous CH2Cl2, 4-fluorophenylisocyanate (3 mmol) was added at room temperature. The reaction mixture was left unstirred for 6 h at 273–278 K, whereafter a slight excess of butylamine (3.1 mmol) was added. After that, the reaction mixture was stirred for 6 h, the solution was cooled and the reaction product was recrystallized from EtOH and CH2Cl2 to give colorless crystals of the title compound in yield 93%, suitable for X-ray analysis.

Refinement top

All H atoms bound to C atoms were placed in calculated positions (C—H = 0.93–0.97 Å) and included in the riding model approximation, with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(methyl C).

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: PLATON (Spek, 2003).

Figures top
[Figure 1] Fig. 1. View of the molecule with the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. The packing viewed down the b axis. Intermolecular hydrogen bonds are shown as dashed lines.
5-Butylamino-6-(4-fluorophenyl)-7-oxo-1-p-tolyl-6,7-dihydro- 1H-pyrazolo[4,3-d]pyrimidine-3-carbonitrile top
Crystal data top
C23H21FN6OF000 = 872
Mr = 416.46Dx = 1.309 Mg m−3
Monoclinic, P21/cMo Kα radiation
λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3510 reflections
a = 11.8800 (5) Åθ = 2.4–23.9º
b = 9.36020 (4) ŵ = 0.09 mm−1
c = 19.0053 (8) ÅT = 295 (2) K
β = 91.1780 (10)ºBlock, colourless
V = 2112.93 (13) Å30.30 × 0.20 × 0.20 mm
Z = 4
Data collection top
Bruker SMART APEX CCD
diffractometer		3704 independent reflections
Radiation source: fine-focus sealed tube3085 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.031
T = 295(2) Kθmax = 25.0º
φ and ω scansθmin = 2.1º
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)		h = −14→14
Tmin = 0.973, Tmax = 0.982k = −11→11
12013 measured reflectionsl = −16→22
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.055H atoms treated by a mixture of
independent and constrained refinement
wR(F2) = 0.154  w = 1/[σ2(Fo2) + (0.0811P)2 + 0.4221P]
where P = (Fo2 + 2Fc2)/3
S = 1.11(Δ/σ)max < 0.001
3704 reflectionsΔρmax = 0.23 e Å−3
285 parametersΔρmin = −0.26 e Å−3
1 restraintExtinction correction: none
Primary atom site location: structure-invariant direct methods
Crystal data top
C23H21FN6OV = 2112.93 (13) Å3
Mr = 416.46Z = 4
Monoclinic, P21/cMo Kα
a = 11.8800 (5) ŵ = 0.09 mm−1
b = 9.36020 (4) ÅT = 295 (2) K
c = 19.0053 (8) Å0.30 × 0.20 × 0.20 mm
β = 91.1780 (10)º
Data collection top
Bruker SMART APEX CCD
diffractometer		3704 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)		3085 reflections with I > 2σ(I)
Tmin = 0.973, Tmax = 0.982Rint = 0.031
12013 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0551 restraint
wR(F2) = 0.154H atoms treated by a mixture of
independent and constrained refinement
S = 1.11Δρmax = 0.23 e Å−3
3704 reflectionsΔρmin = −0.26 e Å−3
285 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
xyzUiso*/Ueq
C10.6274 (2)0.3875 (3)0.22154 (16)0.0778 (9)
H1A0.64290.35280.26830.117*
H1B0.60680.48650.22360.117*
H1C0.69340.37690.19370.117*
C20.53165 (19)0.3027 (3)0.18861 (12)0.0517 (6)
C30.55219 (19)0.1809 (3)0.15018 (14)0.0614 (7)
H30.62610.15120.14430.074*
C40.46540 (18)0.1021 (3)0.12017 (14)0.0552 (6)
H40.48090.02040.09420.066*
C50.35615 (17)0.1450 (2)0.12887 (11)0.0399 (5)
C60.33266 (18)0.2674 (2)0.16595 (12)0.0473 (6)
H60.25870.29780.17080.057*
C70.4207 (2)0.3443 (2)0.19588 (13)0.0525 (6)
H70.40490.42620.22160.063*
C80.18880 (17)−0.0696 (2)0.01909 (11)0.0406 (5)
C90.11084 (16)−0.0625 (2)0.07421 (10)0.0362 (5)
C100.16433 (16)0.0224 (2)0.12452 (11)0.0361 (5)
C110.17644 (18)−0.1440 (3)−0.04584 (12)0.0468 (6)
C12−0.03810 (16)−0.1084 (2)0.14132 (11)0.0371 (5)
C130.11533 (16)0.0439 (2)0.19173 (11)0.0368 (5)
C14−0.04608 (16)−0.0095 (2)0.26283 (10)0.0378 (5)
C15−0.13358 (18)0.0858 (2)0.26853 (12)0.0465 (5)
H15−0.16060.13470.22910.056*
C16−0.1812 (2)0.1083 (3)0.33376 (13)0.0533 (6)
H16−0.24130.17090.33840.064*
C17−0.1383 (2)0.0369 (3)0.39086 (12)0.0544 (6)
C18−0.0514 (2)−0.0580 (3)0.38634 (12)0.0555 (6)
H18−0.0241−0.10560.42610.067*
C19−0.00515 (19)−0.0814 (2)0.32127 (12)0.0481 (6)
H190.0538−0.14590.31680.058*
C20−0.19690 (18)−0.2591 (2)0.10305 (12)0.0466 (5)
H20A−0.1732−0.35700.11130.056*
H20B−0.1764−0.23290.05560.056*
C21−0.32235 (19)−0.2480 (3)0.11024 (13)0.0523 (6)
H21A−0.3451−0.14990.10170.063*
H21B−0.3416−0.27190.15820.063*
C22−0.3878 (2)−0.3448 (3)0.06021 (15)0.0654 (7)
H22A−0.3655−0.44300.06890.078*
H22B−0.3684−0.32140.01230.078*
C23−0.5142 (2)−0.3322 (4)0.0676 (2)0.1029 (13)
H23A−0.5328−0.33850.11640.154*
H23B−0.5507−0.40810.04200.154*
H23C−0.5392−0.24190.04910.154*
F1−0.18395 (16)0.0621 (2)0.45430 (8)0.0869 (6)
N10.26695 (13)0.06138 (18)0.09789 (9)0.0396 (4)
N20.28234 (14)0.0051 (2)0.03381 (9)0.0437 (5)
N30.16543 (19)−0.2048 (3)−0.09756 (11)0.0671 (6)
N40.00947 (14)−0.12733 (18)0.08064 (9)0.0386 (4)
N50.01053 (13)−0.02716 (18)0.19646 (8)0.0373 (4)
N6−0.13968 (15)−0.1649 (2)0.15346 (9)0.0452 (5)
H6A−0.1566 (19)−0.175 (3)0.1970 (6)0.054*
O10.15378 (12)0.11047 (17)0.24170 (8)0.0502 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0649 (18)0.080 (2)0.087 (2)−0.0194 (15)−0.0151 (16)−0.0128 (16)
C20.0469 (13)0.0553 (14)0.0527 (14)−0.0113 (11)−0.0035 (10)0.0014 (11)
C30.0333 (12)0.0704 (17)0.0807 (19)−0.0020 (11)0.0045 (12)−0.0152 (14)
C40.0386 (12)0.0573 (15)0.0698 (17)−0.0003 (10)0.0073 (11)−0.0186 (12)
C50.0375 (11)0.0428 (12)0.0395 (12)−0.0042 (9)0.0018 (9)0.0025 (9)
C60.0379 (11)0.0435 (12)0.0605 (14)0.0020 (9)0.0013 (10)0.0014 (11)
C70.0520 (14)0.0427 (13)0.0628 (15)−0.0041 (10)0.0031 (11)−0.0073 (11)
C80.0373 (11)0.0505 (12)0.0340 (11)−0.0020 (9)0.0000 (9)0.0006 (9)
C90.0353 (10)0.0389 (11)0.0344 (11)0.0006 (8)−0.0018 (8)0.0031 (9)
C100.0330 (10)0.0376 (11)0.0377 (11)0.0011 (8)0.0004 (8)0.0013 (9)
C110.0417 (12)0.0613 (14)0.0375 (13)−0.0070 (10)0.0064 (9)0.0005 (11)
C120.0357 (11)0.0395 (11)0.0359 (12)−0.0004 (8)−0.0031 (9)0.0030 (9)
C130.0337 (10)0.0394 (11)0.0372 (11)0.0023 (8)−0.0025 (8)−0.0008 (9)
C140.0347 (10)0.0422 (11)0.0365 (11)−0.0046 (9)0.0012 (8)−0.0023 (9)
C150.0422 (12)0.0484 (13)0.0490 (14)−0.0015 (10)0.0025 (10)0.0043 (10)
C160.0468 (13)0.0523 (14)0.0615 (16)0.0020 (10)0.0162 (11)−0.0049 (12)
C170.0598 (15)0.0617 (15)0.0423 (14)−0.0120 (12)0.0157 (11)−0.0092 (12)
C180.0569 (15)0.0720 (16)0.0376 (13)−0.0013 (12)0.0001 (10)0.0037 (12)
C190.0466 (12)0.0561 (14)0.0418 (13)0.0063 (10)0.0014 (10)0.0032 (10)
C200.0452 (12)0.0517 (13)0.0430 (13)−0.0091 (10)−0.0007 (10)−0.0018 (10)
C210.0459 (13)0.0547 (14)0.0561 (15)−0.0105 (11)0.0009 (11)−0.0026 (11)
C220.0543 (15)0.0717 (18)0.0700 (17)−0.0164 (13)−0.0053 (13)−0.0101 (14)
C230.0517 (17)0.104 (3)0.152 (3)−0.0189 (17)−0.0184 (19)−0.032 (2)
F10.0979 (12)0.1106 (14)0.0536 (10)0.0002 (10)0.0339 (9)−0.0121 (9)
N10.0336 (9)0.0448 (10)0.0405 (10)−0.0028 (7)0.0036 (7)−0.0026 (8)
N20.0391 (10)0.0533 (11)0.0390 (10)−0.0034 (8)0.0039 (8)−0.0027 (8)
N30.0729 (15)0.0862 (16)0.0425 (12)−0.0188 (12)0.0066 (10)−0.0109 (12)
N40.0366 (9)0.0445 (10)0.0346 (10)−0.0043 (7)−0.0011 (7)0.0006 (7)
N50.0342 (9)0.0461 (10)0.0316 (9)−0.0027 (7)0.0016 (7)−0.0008 (7)
N60.0430 (10)0.0552 (11)0.0374 (10)−0.0145 (8)0.0036 (8)−0.0004 (9)
O10.0453 (9)0.0611 (10)0.0442 (9)−0.0109 (7)0.0015 (7)−0.0139 (7)
Geometric parameters (Å, °) top
C1—C21.512 (3)C14—C151.375 (3)
C1—H1A0.9600C14—C191.379 (3)
C1—H1B0.9600C14—N51.451 (3)
C1—H1C0.9600C15—C161.389 (3)
C2—C31.379 (3)C15—H150.9300
C2—C71.384 (3)C16—C171.364 (3)
C3—C41.382 (3)C16—H160.9300
C3—H30.9300C17—F11.353 (3)
C4—C51.372 (3)C17—C181.366 (3)
C4—H40.9300C18—C191.381 (3)
C5—C61.376 (3)C18—H180.9300
C5—N11.434 (3)C19—H190.9300
C6—C71.382 (3)C20—N61.460 (3)
C6—H60.9300C20—C211.503 (3)
C7—H70.9300C20—H20A0.9700
C8—N21.338 (3)C20—H20B0.9700
C8—C91.414 (3)C21—C221.516 (3)
C8—C111.422 (3)C21—H21A0.9700
C9—N41.356 (3)C21—H21B0.9700
C9—C101.387 (3)C22—C231.516 (4)
C10—N11.379 (2)C22—H22A0.9700
C10—C131.429 (3)C22—H22B0.9700
C11—N31.141 (3)C23—H23A0.9600
C12—N41.307 (3)C23—H23B0.9600
C12—N61.342 (3)C23—H23C0.9600
C12—N51.409 (3)N1—N21.343 (2)
C13—O11.217 (2)N6—H6A0.861 (10)
C13—N51.416 (3)
C2—C1—H1A109.5C17—C16—H16120.5
C2—C1—H1B109.5C15—C16—H16120.5
H1A—C1—H1B109.5F1—C17—C16118.2 (2)
C2—C1—H1C109.5F1—C17—C18119.1 (2)
H1A—C1—H1C109.5C16—C17—C18122.6 (2)
H1B—C1—H1C109.5C17—C18—C19118.3 (2)
C3—C2—C7117.7 (2)C17—C18—H18120.8
C3—C2—C1120.9 (2)C19—C18—H18120.8
C7—C2—C1121.4 (2)C14—C19—C18120.2 (2)
C2—C3—C4121.5 (2)C14—C19—H19119.9
C2—C3—H3119.3C18—C19—H19119.9
C4—C3—H3119.3N6—C20—C21110.36 (18)
C5—C4—C3119.6 (2)N6—C20—H20A109.6
C5—C4—H4120.2C21—C20—H20A109.6
C3—C4—H4120.2N6—C20—H20B109.6
C4—C5—C6120.5 (2)C21—C20—H20B109.6
C4—C5—N1118.90 (19)H20A—C20—H20B108.1
C6—C5—N1120.57 (18)C20—C21—C22113.5 (2)
C5—C6—C7119.0 (2)C20—C21—H21A108.9
C5—C6—H6120.5C22—C21—H21A108.9
C7—C6—H6120.5C20—C21—H21B108.9
C6—C7—C2121.8 (2)C22—C21—H21B108.9
C6—C7—H7119.1H21A—C21—H21B107.7
C2—C7—H7119.1C21—C22—C23113.0 (2)
N2—C8—C9111.97 (18)C21—C22—H22A109.0
N2—C8—C11120.53 (19)C23—C22—H22A109.0
C9—C8—C11127.50 (19)C21—C22—H22B109.0
N4—C9—C10126.10 (19)C23—C22—H22B109.0
N4—C9—C8129.92 (18)H22A—C22—H22B107.8
C10—C9—C8103.89 (17)C22—C23—H23A109.5
N1—C10—C9107.14 (17)C22—C23—H23B109.5
N1—C10—C13132.08 (18)H23A—C23—H23B109.5
C9—C10—C13120.51 (18)C22—C23—H23C109.5
N3—C11—C8179.1 (3)H23A—C23—H23C109.5
N4—C12—N6120.35 (18)H23B—C23—H23C109.5
N4—C12—N5123.46 (17)N2—N1—C10111.51 (16)
N6—C12—N5116.17 (18)N2—N1—C5118.25 (16)
O1—C13—N5120.49 (18)C10—N1—C5130.19 (17)
O1—C13—C10128.07 (19)C8—N2—N1105.48 (16)
N5—C13—C10111.42 (16)C12—N4—C9114.82 (17)
C15—C14—C19120.5 (2)C12—N5—C13123.64 (16)
C15—C14—N5120.46 (18)C12—N5—C14121.19 (16)
C19—C14—N5118.84 (18)C13—N5—C14115.17 (15)
C14—C15—C16119.4 (2)C12—N6—C20122.23 (18)
C14—C15—H15120.3C12—N6—H6A116.0 (16)
C16—C15—H15120.3C20—N6—H6A116.6 (16)
C17—C16—C15118.9 (2)
C7—C2—C3—C4−0.4 (4)N6—C20—C21—C22−179.1 (2)
C1—C2—C3—C4179.6 (3)C20—C21—C22—C23−179.7 (3)
C2—C3—C4—C5−0.3 (4)C9—C10—N1—N2−0.6 (2)
C3—C4—C5—C61.3 (4)C13—C10—N1—N2173.4 (2)
C3—C4—C5—N1−179.5 (2)C9—C10—N1—C5−178.14 (19)
C4—C5—C6—C7−1.7 (3)C13—C10—N1—C5−4.2 (4)
N1—C5—C6—C7179.2 (2)C4—C5—N1—N2−38.9 (3)
C5—C6—C7—C21.0 (4)C6—C5—N1—N2140.2 (2)
C3—C2—C7—C60.0 (4)C4—C5—N1—C10138.4 (2)
C1—C2—C7—C6−180.0 (2)C6—C5—N1—C10−42.4 (3)
N2—C8—C9—N4−177.1 (2)C9—C8—N2—N10.0 (2)
C11—C8—C9—N43.1 (4)C11—C8—N2—N1179.83 (19)
N2—C8—C9—C10−0.3 (2)C10—N1—N2—C80.4 (2)
C11—C8—C9—C10179.8 (2)C5—N1—N2—C8178.24 (17)
N4—C9—C10—N1177.48 (18)N6—C12—N4—C9178.61 (18)
C8—C9—C10—N10.6 (2)N5—C12—N4—C90.1 (3)
N4—C9—C10—C132.7 (3)C10—C9—N4—C12−1.8 (3)
C8—C9—C10—C13−174.26 (18)C8—C9—N4—C12174.3 (2)
N2—C8—C11—N3159 (18)N4—C12—N5—C130.7 (3)
C9—C8—C11—N3−21 (18)N6—C12—N5—C13−177.79 (18)
N1—C10—C13—O13.8 (4)N4—C12—N5—C14179.94 (18)
C9—C10—C13—O1177.1 (2)N6—C12—N5—C141.4 (3)
N1—C10—C13—N5−174.8 (2)O1—C13—N5—C12−178.73 (18)
C9—C10—C13—N5−1.5 (3)C10—C13—N5—C120.0 (3)
C19—C14—C15—C16−0.5 (3)O1—C13—N5—C142.0 (3)
N5—C14—C15—C16−175.46 (19)C10—C13—N5—C14−179.23 (16)
C14—C15—C16—C171.2 (3)C15—C14—N5—C12−78.0 (2)
C15—C16—C17—F1178.7 (2)C19—C14—N5—C12106.9 (2)
C15—C16—C17—C18−1.2 (4)C15—C14—N5—C13101.2 (2)
F1—C17—C18—C19−179.4 (2)C19—C14—N5—C13−73.8 (2)
C16—C17—C18—C190.4 (4)N4—C12—N6—C205.5 (3)
C15—C14—C19—C18−0.3 (3)N5—C12—N6—C20−175.88 (18)
N5—C14—C19—C18174.8 (2)C21—C20—N6—C12−152.0 (2)
C17—C18—C19—C140.3 (4)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N6—H6A···O1i0.861 (10)2.32 (2)2.904 (2)125 (2)
C15—H15···N3ii0.932.583.449 (3)155
C19—H19···N3iii0.932.503.219 (3)134
C6—H6···Cg1iv0.932.823.671 (2)152
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) −x, −y, −z; (iii) x, −y−1/2, z+1/2; (iv) −x, y+1/2, −z+1/2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N6—H6A···O1i0.861 (10)2.32 (2)2.904 (2)125 (2)
C15—H15···N3ii0.932.583.449 (3)155
C19—H19···N3iii0.932.503.219 (3)134
C6—H6···Cg1iv0.932.823.671 (2)152
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) −x, −y, −z; (iii) x, −y−1/2, z+1/2; (iv) −x, y+1/2, −z+1/2.
Acknowledgements top

The authors gratefully acknowledge financial support of this work as a project of the Natural Science Foundation of Hubei Province under grant No. 2006ABA334.

references
References top

Allerton, C. M. N., Barber, C. G., Beaumont, K. C., Brown, D. G., Cole, S. M., Ellis, D., Lane, C. A. L., Maw, G. N., Mount, N. M., Rawson, D. J., Robinson, C. M., Street, S. D. A. & Summerhill, N. W. (2006). J. Med. Chem. 49, 3581–3594.

Bell, A. S., Brown, D. & Terrett, N. K. (1991). Eur. Patent 463756.

Bruker (2001). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.

Sheldrick, G. M. (2001). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Spek, A. L. (2003). J. Appl. Cryst. 36, 7–13.

Zhao, Y., Zhai, X., Chen, J., Guo, S. & GONG, P. (2006). Chem. Res. Chin. Univ. 22, 468–473.