research communications
H-chromen-2-one
of a new polymorph of 3-acetyl-8-methoxy-2aFacultad de Ciencias Químicas, Universidad de Colima, km 9 carretera, Colima-Coquimatlán, 28400, Coquimatlán, Colima, Mexico, and bLaboratorio de Quimica Supramolecular y Nanociencias, Unidad Profesional, Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, Avenida Acueducto s/n, Barrio La Laguna Ticomán, Cd. de Mexico 07340, Mexico
*Correspondence e-mail: fjmartin@ucol.mx
A new polymorphic form of the title compound, C12H10O4, is described in the orthorhombic Pbca and Z = 8, as compared to polymorph I, which crystallizes in the monoclinic C2/c and Z = 8 [Li et al. (2012). Chin. J. Struct. Chem. 31, 1003–1007.]. In polymorph II, the coumarin ring system is almost planar (r.m.s. deviation = 0.00129 Å). In the crystal, molecules are connected by Csp3—H⋯O and Car—H⋯O hydrogen bonds, forming molecular sheets linked into zigzag shaped layers along the b-axis direction. The three-dimensional lattice is assembled through stacking of the zigzag layers by π–π interactions with a centroid-to-centroid distance of 3.600 (9) Å and antiparallel C=O⋯C=O interactions with a distance of 3.1986 (17) Å, which give rise to a helical supramolecular architecture.
Keywords: crystal structure; polymorph; hydrogen bond; coumarin; 3-acetyl-8-methoxy-coumarin.
1. Chemical context
Derivatives of 2H-chromen-2-one are some of the most important heterocycles in natural and synthetic organic chemistry. These substances are bioactive compounds and have a wide range of applications in the medical field (Gaudino et al., 2016) showing, for example, anti-HIV, antimutagenic, anticancer and antitumor activities among others (Vekariya & Patel, 2014). They are synthesized using classical methodologies such as the Pechmann or Knoevenagel reactions, as well as recent methodologies such as the metathesis (Salem et al., 2018) or alkynoates (Liu et al., 2018).
The disposition of the crystalline lattices of coumarin derivatives is driven by a great variety of intermolecular interactions (Santos-Contreras et al., 2009). This working group has reported the participation of π–π stacking interactions, hydrogen-bonding and dipole–dipole interactions involving the carbonyl group (Gómez-Castro et al., 2014) in the determination of the 1D, 2D and 3D supramolecular assemblies of crystalline structures for different compounds (González-Padilla et al., 2014). This report describes the structure of a second polymorph of the title compound and the importance of C—H⋯O, C=O⋯C=O and π–π stacking intermolecular interactions in crystal packing.
2. Structural commentary
The title polymorph II (Fig. 1) crystallizes in the orthorhombic system, Pbca, with eight molecules in the whereas polymorph I (Li et al., 2012) crystallizes in the monoclinic system in C2/c, also with eight molecules in the In polymorph II, the coumarin skeleton is almost planar (r.m.s. deviation = 0.00129 Å) with dihedral angles O1—C9—C10—C5 and C8—C9—C10—C4 of 179.20 (10) and 179.87 (11)°, respectively. In contrast, in polymorph I the benzene and lactone rings deviate slightly from planarity by 2.76 (3)°. The acetyl and methoxy groups of polymorph II are almost coplanar with the coumarin ring, with torsion angles C2—C3—C11—C12 = −1.25 (18)° and C14—O13—C8—C7 = −2.70 (18)°.
3. Supramolecular features
The crystal network of the title compound (polymorph II) is assembled by zigzag shaped molecular layers that extend approximately in the (012) and (01) planes, forming an angle of 116.2°. In the flat section of the zigzag layer R33(18) motifs are formed by C6—H6⋯O2ii and C12—H12B⋯O11i hydrogen bonds (Table 1). These intermolecular interactions impart stability to the 2D sheet, while weak C14—H14A⋯O2iii interactions generate an R32(16) motif at the intersection of the planes (Fig. 2). Adjacent layers, separated by a distance of 3.4083 (5) Å, are connected by π–π stacking interactions with a centroid-to-centroid distance of 3.600 (9) Å and a slippage of 1.160 Å. In addition to the π stacking, layers are stabilized by antiparallel C=O⋯C=O interactions (Allen et al., 1998) involving the acetyl group separated by a distance of 3.1986 (17) Å.
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The supramolecular array of polymorph II exhibits a helical conformation, like polymorph I (Li et al., 2012). However, in polymorph II the C=O⋯C=O interactions form the central axis of the helix whilst π–π interactions between the aromatic and lactone rings, aligned in a head-to-tail conformation, control the rotation of the structure. In polymorph I, the helical axis is built by hydrogen bonds and face-to-face π–π stacking interactions of the benzofused rings (Fig. 3). For polymorph I, a complete rotation of the helix is performed in 11.5 Å, while in polymorph II the displacement of the helix in a whole rotation is 12.4 Å.
4. Hirshfeld surface and 2D fingerprint plots
In order to better understand the crystal packing of both polymorphs, Hirshfeld surface analyses and 2D fingerprint plots were carried out using Crystal Explorer 17.5 (Turner et al., 2017). From the analysis of the Hirshfeld surfaces (Fig. 4), it is evident that there are differences between the chemical environments of these two identical molecules. In Fig. 4, the Hirshfeld surfaces for polymorph I show a series of strong short contacts (big red dots) corresponding to hydrogen bonds stabilizing the 2D sheets. The planar areas above and below the rings are where π–π interactions (small red dots) take place, giving rise to the 3D network. On the other hand, polymorph II is stabilized by a short directional hydrogen bond and the sum of weak interactions with longer contact distances than in polymorph I. This suggests that polymorph II may be the less stable between these two phases of the title compound. To quantitatively compare polymorphs I and II in terms of their crystal packing, 2D fingerprint plots were developed and analysed. The character of the fingerprints plots for both polymorphs is similar, with small differences in the relative contributions of each type of interaction to the Hirshfeld surface. The weak interactions include C⋯H (C—H⋯ π), C⋯O (C=O⋯C=O, C=O⋯π) and C⋯C (π–π), as well as short directional interactions such as H⋯O (Fig. 5).
Although polymorphs I and II exhibit the same type of intermolecular interactions, the way these common interactions contribute to the packing in each polymorph differs in each case. The minor differences in which weak intermolecular interactions contribute to the formation of the crystal (Fig. 6), give rise to distinct polymorphs as suggested by Hasija & Chopra (2019). As can be seen in Fig. 6, the major forces in the crystal formation of both polymorphs are H⋯H and O⋯H interactions, but C⋯O and C⋯H short contacts in polymorph I make slightly bigger contributions to build the lattice, while in polymorph II, hydrogen bonding and π–π stacking contribute in greater proportions.
5. Database survey
A search of the Cambridge Structural Database (version 5.39, February 2018; Groom et al., 2016) revealed only one of the title compound (Refcode TEBFAJ; Li et al., 2012). This structure, which we call polymorph I, is assembled by parallel flat sheets that extend along the b axis. It is worth mentioning that the acetyl coumarin without any substituent also forms at least two polymorphic forms (A and B; Munshi et al., 2004) with subtle differences in intermolecular interactions, which include weak C—H⋯O and C—H⋯ π interactions. Form A crystallizes with head-to-head stacking being favored during nucleation, while form B prefers a head-to tail-stacking. This is similar to the two polymorphs of the title compound.
6. Synthesis and crystallization
The title compound was obtained via Knoevenagel condensation. 3-Methoxysalicylaldehyde and ethyl acetoacetate in a 1:1 molar ratio were loaded in a flask with ethyl alcohol as solvent and piperidine as catalyst and left under stirring and reflux for 5 h. The product was filtered and washed with cold ethanol followed by recrystallization from ethanol to yield the title compound as colourless crystals, 88% yield, mp 444–447 K; IR νKBr (cm−1): 1727 (OC=O), 1682 (C=O), 1278, 1197 (C—O). NMR 1H (δ ppm, CDCl3): 8.42 (s, 1H, H-4); 7.25 (d, 1H, H-7, 3J = 1.1, 4J = 5.7 Hz), 7.18 (t, 1H, H-6, 3J = 5.5, 2.0 Hz) 7.14 (d, 1H, H-5, 3J = 2.0, 4J = 5.7 Hz), 3.94 (s, 3H, OCH3), 2.68 (s, 3H, H-12). NMR 13C (δ ppm, CDCl3): 195.8 (C-11), 158.9 (C-2), 147.9 (C-4), 147.2 (C-8), 145.1 (C-9), 125.0 (C-5), 124.8 (C-3), 121.5 (C-6), 118.9 (C-10), 116.0 (C-7), 56.5 (OCH3), 30.8 (C-12). EA (%) calculated for C12H10O4: 66.05 C, 4.62 H; found: 66.15 C, 4.60 H.
7. Refinement
Crystal data, data collection and structure . H atoms were positioned geometrically and treated as riding atoms, with C—H = 0.93–0.98 Å and Uiso(H) = 1.2Ueq(C).
details are summarized in Table 2Supporting information
https://doi.org/10.1107/S2056989019015159/dx2020sup1.cif
contains datablock I. DOI:Supporting information file. DOI: https://doi.org/10.1107/S2056989019015159/dx2020Isup3.cml
Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019015159/dx2020Isup3.hkl
Data collection: APEX2 (Bruker, 2004); cell
SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2008) and WinGX2003 (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), WinGX2003 (Farrugia, 2012) and PLATON (Spek, 2009).C12H10O4 | Dx = 1.435 Mg m−3 |
Mr = 218.20 | Mo Kα radiation, λ = 0.71073 Å |
Orthorhombic, Pbca | Cell parameters from 600 reflections |
a = 9.4973 (13) Å | θ = 20–25° |
b = 7.9733 (11) Å | µ = 0.11 mm−1 |
c = 26.682 (4) Å | T = 293 K |
V = 2020.5 (5) Å3 | Prism, colorless |
Z = 8 | 0.40 × 0.35 × 0.30 × 0.15 (radius) mm |
F(000) = 912 |
Bruker APEXII area detector diffractometer | 2453 independent reflections |
Radiation source: fine-focus sealed tube | 1798 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.045 |
φ and ω scans | θmax = 28.3°, θmin = 1.5° |
Absorption correction: for a sphere [the interpolation procedure of Dwiggins (1975) was used with some modification] | h = −12→12 |
Tmin = 0.861, Tmax = 0.862 | k = −10→10 |
15317 measured reflections | l = −34→35 |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.041 | w = 1/[σ2(Fo2) + (0.0608P)2 + 0.0858P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.116 | (Δ/σ)max < 0.001 |
S = 1.10 | Δρmax = 0.20 e Å−3 |
2453 reflections | Δρmin = −0.19 e Å−3 |
148 parameters | Extinction correction: SHELXL2018 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0117 (15) |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
C2 | 0.50500 (12) | 0.47624 (16) | 0.37371 (4) | 0.0424 (3) | |
C3 | 0.44835 (12) | 0.56358 (15) | 0.41705 (4) | 0.0382 (3) | |
C4 | 0.30805 (13) | 0.57565 (15) | 0.42255 (4) | 0.0410 (3) | |
H4 | 0.272844 | 0.632762 | 0.450238 | 0.049* | |
C5 | 0.06405 (13) | 0.51543 (17) | 0.39234 (5) | 0.0503 (3) | |
H5 | 0.023660 | 0.571130 | 0.419379 | 0.060* | |
C6 | −0.01876 (14) | 0.44331 (19) | 0.35668 (6) | 0.0561 (4) | |
H6 | −0.116156 | 0.450497 | 0.359563 | 0.067* | |
C7 | 0.03947 (14) | 0.35925 (18) | 0.31610 (5) | 0.0512 (4) | |
H7 | −0.019498 | 0.311173 | 0.292263 | 0.061* | |
C8 | 0.18326 (13) | 0.34597 (15) | 0.31060 (4) | 0.0410 (3) | |
C9 | 0.26746 (12) | 0.42080 (14) | 0.34702 (4) | 0.0364 (3) | |
C10 | 0.21098 (12) | 0.50478 (14) | 0.38783 (4) | 0.0389 (3) | |
C11 | 0.54296 (14) | 0.64209 (16) | 0.45541 (4) | 0.0457 (3) | |
C12 | 0.69794 (15) | 0.6292 (2) | 0.45047 (6) | 0.0645 (4) | |
H12A | 0.724728 | 0.513243 | 0.449103 | 0.097* | |
H12B | 0.742035 | 0.681599 | 0.478819 | 0.097* | |
H12C | 0.727490 | 0.684582 | 0.420301 | 0.097* | |
C14 | 0.17018 (17) | 0.1828 (2) | 0.23613 (5) | 0.0637 (4) | |
H14A | 0.111460 | 0.262506 | 0.219101 | 0.096* | |
H14B | 0.112261 | 0.099779 | 0.252075 | 0.096* | |
H14C | 0.231370 | 0.129280 | 0.212366 | 0.096* | |
O1 | 0.40976 (8) | 0.40859 (11) | 0.34056 (3) | 0.0415 (2) | |
O2 | 0.62587 (9) | 0.45659 (16) | 0.36291 (4) | 0.0728 (4) | |
O11 | 0.49013 (11) | 0.71394 (14) | 0.49062 (4) | 0.0688 (3) | |
O13 | 0.25265 (9) | 0.26717 (11) | 0.27307 (3) | 0.0524 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C2 | 0.0323 (6) | 0.0528 (8) | 0.0422 (6) | −0.0022 (5) | −0.0010 (5) | −0.0078 (5) |
C3 | 0.0384 (6) | 0.0398 (7) | 0.0366 (6) | −0.0002 (5) | 0.0004 (5) | −0.0005 (5) |
C4 | 0.0432 (7) | 0.0407 (7) | 0.0391 (6) | 0.0040 (5) | 0.0075 (5) | 0.0005 (5) |
C5 | 0.0355 (7) | 0.0548 (8) | 0.0608 (8) | 0.0073 (6) | 0.0079 (6) | 0.0094 (6) |
C6 | 0.0287 (6) | 0.0638 (9) | 0.0756 (9) | 0.0034 (6) | −0.0017 (6) | 0.0203 (8) |
C7 | 0.0383 (7) | 0.0542 (8) | 0.0612 (8) | −0.0070 (6) | −0.0140 (6) | 0.0146 (7) |
C8 | 0.0377 (7) | 0.0424 (7) | 0.0428 (6) | −0.0039 (5) | −0.0060 (5) | 0.0087 (5) |
C9 | 0.0290 (6) | 0.0389 (6) | 0.0413 (6) | −0.0007 (5) | −0.0014 (4) | 0.0072 (5) |
C10 | 0.0341 (6) | 0.0387 (7) | 0.0439 (6) | 0.0031 (5) | 0.0041 (5) | 0.0075 (5) |
C11 | 0.0530 (8) | 0.0441 (7) | 0.0400 (6) | −0.0015 (6) | −0.0030 (5) | −0.0030 (5) |
C12 | 0.0495 (8) | 0.0822 (11) | 0.0619 (8) | −0.0103 (7) | −0.0129 (7) | −0.0193 (8) |
C14 | 0.0738 (10) | 0.0702 (10) | 0.0472 (8) | −0.0148 (8) | −0.0223 (7) | −0.0020 (7) |
O1 | 0.0292 (4) | 0.0548 (5) | 0.0406 (4) | −0.0015 (4) | −0.0003 (3) | −0.0094 (4) |
O2 | 0.0288 (5) | 0.1185 (10) | 0.0710 (7) | −0.0005 (5) | 0.0019 (4) | −0.0424 (7) |
O11 | 0.0716 (7) | 0.0821 (8) | 0.0527 (6) | 0.0059 (6) | −0.0036 (5) | −0.0262 (5) |
O13 | 0.0503 (6) | 0.0613 (6) | 0.0455 (5) | −0.0085 (4) | −0.0092 (4) | −0.0084 (4) |
C2—O2 | 1.1940 (14) | C8—O13 | 1.3535 (15) |
C2—O1 | 1.3753 (14) | C8—C9 | 1.3929 (16) |
C2—C3 | 1.4530 (16) | C9—O1 | 1.3659 (14) |
C3—C4 | 1.3440 (16) | C9—C10 | 1.3863 (16) |
C3—C11 | 1.4991 (17) | C11—O11 | 1.2094 (15) |
C4—C10 | 1.4238 (17) | C11—C12 | 1.481 (2) |
C4—H4 | 0.9300 | C12—H12A | 0.9600 |
C5—C6 | 1.362 (2) | C12—H12B | 0.9600 |
C5—C10 | 1.4032 (17) | C12—H12C | 0.9600 |
C5—H5 | 0.9300 | C14—O13 | 1.4275 (15) |
C6—C7 | 1.388 (2) | C14—H14A | 0.9600 |
C6—H6 | 0.9300 | C14—H14B | 0.9600 |
C7—C8 | 1.3776 (17) | C14—H14C | 0.9600 |
C7—H7 | 0.9300 | ||
O2—C2—O1 | 115.19 (11) | O1—C9—C8 | 116.70 (10) |
O2—C2—C3 | 127.66 (11) | C10—C9—C8 | 122.20 (11) |
O1—C2—C3 | 117.15 (10) | C9—C10—C5 | 118.77 (11) |
C4—C3—C2 | 119.23 (10) | C9—C10—C4 | 116.89 (11) |
C4—C3—C11 | 119.32 (11) | C5—C10—C4 | 124.34 (11) |
C2—C3—C11 | 121.44 (10) | O11—C11—C12 | 120.94 (12) |
C3—C4—C10 | 122.85 (11) | O11—C11—C3 | 118.66 (12) |
C3—C4—H4 | 118.6 | C12—C11—C3 | 120.40 (11) |
C10—C4—H4 | 118.6 | C11—C12—H12A | 109.5 |
C6—C5—C10 | 119.27 (13) | C11—C12—H12B | 109.5 |
C6—C5—H5 | 120.4 | H12A—C12—H12B | 109.5 |
C10—C5—H5 | 120.4 | C11—C12—H12C | 109.5 |
C5—C6—C7 | 121.25 (12) | H12A—C12—H12C | 109.5 |
C5—C6—H6 | 119.4 | H12B—C12—H12C | 109.5 |
C7—C6—H6 | 119.4 | O13—C14—H14A | 109.5 |
C8—C7—C6 | 121.00 (12) | O13—C14—H14B | 109.5 |
C8—C7—H7 | 119.5 | H14A—C14—H14B | 109.5 |
C6—C7—H7 | 119.5 | O13—C14—H14C | 109.5 |
O13—C8—C7 | 126.67 (11) | H14A—C14—H14C | 109.5 |
O13—C8—C9 | 115.82 (11) | H14B—C14—H14C | 109.5 |
C7—C8—C9 | 117.51 (12) | C9—O1—C2 | 122.79 (9) |
O1—C9—C10 | 121.09 (10) | C8—O13—C14 | 117.55 (11) |
O2—C2—C3—C4 | 178.80 (14) | O1—C9—C10—C4 | −0.53 (16) |
O1—C2—C3—C4 | −0.59 (17) | C8—C9—C10—C4 | 179.87 (11) |
O2—C2—C3—C11 | −0.5 (2) | C6—C5—C10—C9 | 0.02 (18) |
O1—C2—C3—C11 | −179.90 (10) | C6—C5—C10—C4 | 179.73 (12) |
C2—C3—C4—C10 | 0.63 (18) | C3—C4—C10—C9 | −0.08 (17) |
C11—C3—C4—C10 | 179.96 (11) | C3—C4—C10—C5 | −179.79 (11) |
C10—C5—C6—C7 | 0.2 (2) | C4—C3—C11—O11 | 0.34 (18) |
C5—C6—C7—C8 | 0.0 (2) | C2—C3—C11—O11 | 179.66 (12) |
C6—C7—C8—O13 | 179.70 (11) | C4—C3—C11—C12 | 179.43 (12) |
C6—C7—C8—C9 | −0.40 (18) | C2—C3—C11—C12 | −1.25 (18) |
O13—C8—C9—O1 | 0.88 (15) | C10—C9—O1—C2 | 0.57 (16) |
C7—C8—C9—O1 | −179.03 (10) | C8—C9—O1—C2 | −179.80 (11) |
O13—C8—C9—C10 | −179.50 (10) | O2—C2—O1—C9 | −179.47 (12) |
C7—C8—C9—C10 | 0.58 (17) | C3—C2—O1—C9 | 0.00 (16) |
O1—C9—C10—C5 | 179.20 (10) | C7—C8—O13—C14 | −2.70 (18) |
C8—C9—C10—C5 | −0.40 (17) | C9—C8—O13—C14 | 177.40 (11) |
D—H···A | D—H | H···A | D···A | D—H···A |
C12—H12B···O11i | 0.96 | 2.63 | 3.4255 (17) | 141 |
C6—H6···O2ii | 0.93 | 2.45 | 3.3808 (16) | 176 |
C14—H14A···O2iii | 0.96 | 2.68 | 3.4535 (18) | 138 |
C4—H4···O11 | 0.93 | 2.42 | 2.7395 (16) | 100 |
C12—H12A···O2 | 0.96 | 2.52 | 2.797 (2) | 97 |
Symmetry codes: (i) x+1/2, −y+3/2, −z+1; (ii) x−1, y, z; (iii) x−1/2, y, −z+1/2. |
Acknowledgements
The authors thank Juan Pablo Mojica Sánchez for his contribution to the Hirshfeld surfaces calculation.
Funding information
GGC thanks CONACYT (Mexico) for PhD scholarship No. 364826.
References
Allen, F. H., Baalham, C. A., Lommerse, J. P. M. & Raithby, P. R. (1998). Acta Cryst. B54, 320–329. Web of Science CrossRef CAS IUCr Journals Google Scholar
Bruker (2004). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Dwiggins, C. W. (1975). Acta Cryst. A31, 146–148. CrossRef IUCr Journals Web of Science Google Scholar
Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Web of Science CrossRef CAS IUCr Journals Google Scholar
Gaudino, E. C., Tagliapietra, S., Martina, K., Palmisano, G. & Cravotto, G. (2016). RSC Adv. 6, 46394–46405. Google Scholar
Gómez-Castro, C. Z., Padilla-Martínez, I. I., García-Báez, E. V., Castrejón-Flores, J. L., Peraza-Campos, A. L. & Martínez-Martínez, F. J. (2014). Molecules, 19, 14446–14460. Web of Science PubMed Google Scholar
González-Padilla, J. E., Rosales-Hernández, M. C., Padilla-Martínez, I. I., García-Báez, E. V., Rojas-Lima, S. & Salazar-Pereda, V. (2014). Acta Cryst. C70, 55–59. Web of Science CSD CrossRef IUCr Journals Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CrossRef IUCr Journals Google Scholar
Hasija, A. & Chopra, D. (2019). Acta Cryst. C75, 451–461. Web of Science CSD CrossRef IUCr Journals Google Scholar
Li, J., Li, X. & Wang, S. (2012). Chin. J. Struct. Chem. 31, 1003–1007. Web of Science CrossRef CAS Google Scholar
Liu, Y., Wang, Q. L., Zhou, C. S., Xiong, B. Q., Zhang, P. L., Kang, S. J., Yang, C. A. & Tang, K. W. (2018). Tetrahedron Lett. 59, 2038–2041. Web of Science CrossRef CAS Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CrossRef CAS IUCr Journals Google Scholar
Munshi, P., Venugopala, K. N., Jayashree, B. S. & Guru Row, T. N. (2004). Cryst. Growth Des. 4, 1105–1107. Web of Science CSD CrossRef CAS Google Scholar
Salem, M. A., Helal, M. H., Gouda, M. A., Ammar, Y. A., El-Gaby, M. S. A. & Abbas, S. Y. (2018). Synth. Commun. 48, 1534–1550. Web of Science CrossRef CAS Google Scholar
Santos-Contreras, R. J., Martínez-Martínez, F. J., Mancilla-Margalli, N. A., Peraza-Campos, A. L., Morín-Sánchez, L. M., García-Báez, E. V. & Padilla-Martínez, I. I. (2009). CrystEngComm, 11, 1451–1461. CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Turner, M. J., McKinnon, J. J., Wolff, S. K., Grimwood, D. J., Spackman, P. R., Jayatilaka, D. & Spackman, M. A. (2017). CrystalExplorer17. University of Western Australia. https://hirshfeldsurface.net. Google Scholar
Vekariya, R. H. & Patel, H. D. (2014). Synth. Commun. 44, 2756–2788. Web of Science CrossRef CAS Google Scholar
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