Crystal structure and Hirshfeld surface analysis of new polymorph of racemic 2-phenyl­butyramide

Rigin, S.; Armijo, B.; Krivoshein, A.V.; Fonari, M.; Timofeeva, T.

doi:10.1107/S2056989019007011

research communications

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ISSN: 2056-9890

Volume 75| Part 6| June 2019| Pages 826-829

https://doi.org/10.1107/S2056989019007011

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Crystal structure and Hirshfeld surface analysis of new polymorph of racemic 2-phenylbutyramide

Sergei Rigin,^a ^* Beatrice Armijo,^a Arcadius V. Krivoshein,^b Marina Fonari ^c and Tatiana Timofeeva ^a

^aDepartment of Chemistry, New Mexico Highlands University, Las Vegas, New Mexico, 87701, USA, ^bDepartment of Physical & Applied Sciences, University of Houston – Clear Lake, 2700 Bay Area Boulevard, Houston, TX 77058, USA, and ^cInstitute of Applied Physics, Academy str., 5 MD2028, Chisinau, Moldova
^*Correspondence e-mail: rigindale@gmail.com

Edited by A. V. Yatsenko, Moscow State University, Russia (Received 29 April 2019; accepted 14 May 2019; online 21 May 2019)

A new polymorph of the title compound, C₁₀H₁₃NO, was obtained by recrystallization of the commercial product from a water/ethanol mixture (1:1 v/v). Crystals of the previously reported racemic and homochiral forms of 2-phenylbutyramide were grown from water–acetonitrile solution in 1:1 volume ratio [Khrustalev et al. (2014 ). Cryst. Growth Des. 14, 3360–3369]. While the previously reported racemic and enantiopure forms of the title compound adopt very similar supramolecular structures (hydrogen-bonded ribbons), the new racemic polymorph is stabilized by a single N—H⋯O hydrogen bond that links molecules into chains along the c-axis direction with an antiparallel (centrosymmetric) packing in the crystal. Hirshfeld molecular surface analysis was employed to compare the intermolecular interactions in the polymorphs of the title compound.

Keywords: crystal structure; racemate; 2-phenylbutyramide; hydrogen bonds; Hirshfeld surface analysis.

CCDC reference: 1916098

1. Chemical context

Many drugs exist in several polymorphic modifications (Bernstein, 2011 ; Brittain, 2009 ). For example, a second polymorph, II, was reported (Vishweshwar et al., 2005 ) in 2005 for aspirin, one of the most widely consumed medications; this was similar in structure to the original form I (Wheatley, 1964 ) and was widely discussed (Bond et al., 2007 , 2011 ). The third ambient polymorph of aspirin, crystallized from the melt, was described recently using a combination of X-ray powder diffraction analysis and crystal structure prediction algorithms (Shtukenberg et al., 2017 ). Paracetamol, one of the most frequently used antipyretic and analgesic drugs, is known in three crystal modifications: a monoclinic (form I) (Haisa et al., 1976 ), an orthorhombic (form II) (Haisa et al., 1974 ), and an unstable phase (form III), which can only be stabilized under certain conditions (Burger & Ramberger, 1979 ). The non-steroidal anti-inflammatory drug mefenamic acid is known to exist as dimorphs (I and II) and a metastable polymorph obtained during co-crystallization experiments (SeethaLekshmi & Guru Row, 2012 ). The existence of three different polymorphic forms has been reported for anhydrous carbamazepine, an anticonvulsant drug (Rustichelli et al., 2000 ). We previously reported (Khrustalev et al., 2014) two polymorphs of α-methyl-α-phenylsuccinimide (3-methyl-3-phenylpyrrolidine-2,5-dione), the N-demethylated metabolite of the anticonvulsant methsuximide. Herein, we report on the crystal structure and the Hirshfeld surface analysis of a new polymorph of the title compound, obtained by recrystallization of the commercial product (Alfa Aesar, stock No. A18501) from a water–ethanol (1:1) solution. Crystals of the previously reported racemic and homochiral forms of 2-phenylbutyramide were grown from water–acetonitrile solution in a 1:1 volume ratio (Khrustalev et al., 2014).

2. Structural commentary

A view of the molecule of the new polymorph (henceforth referred to as rac-2) is illustrated in Fig. 1a. In the molecule, the rotation of the amide group around the C7—C10 bond is characterized by an N1—C10—C7—C8 torsion angle of −141.14 (9)°, thus corresponding in conformation to the previously reported polymorph (further notated as rac-1, space group C2/c), where the torsion angle is −130.06 (9)°, and one of two conformers in the R-enantiomer [space group P1, torsion angle = −144.08 (13)°; Khrustalev et al., 2014). The overlay diagram for the two racemic forms shown in Fig. 1b shows the almost perfect fit (r.m.s. deviation = 0.263 Å). The bond lengths in the molecule are in line with those of reported analogues (CSD version 5.40, last update November 2018; Groom et al., 2016 ).

Figure 1
(a) View of the molecular structure of the title rac-2 polymorph with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. (b) Superposition of the rac-1 (red) and rac-2 (green) polymorphs.

3. Supramolecular features

Molecule of the title compound contain one amino group as a potential double hydrogen-bond donor and one carbonyl group capable of acting as a multiple hydrogen-bond acceptor. Contrary to the previously reported rac-1 and two enantiomeric forms (Khrustalev et al., 2014), where the amino group acted as double hydrogen-bond donor while the carbonyl oxygen atom acted as a double hydrogen-bond acceptor being involved in two N–H⋯O hydrogen bonds leading to the formation of supramolecular ribbons, in rac-2 only one hydrogen atom of the amino group is involved in a single N—H⋯O hydrogen bond (Table 1). This hydrogen bond links molecules related by the glide plane into chains along the c-axis direction (Fig. 2). The packing of the chains obeys inversion symmetry with only van der Waals contacts between the chains (Fig. 3). In spite of the fewer number of strong directed intermolecular interactions in the crystal, the structure of rac-2 is characterized by a more effective crystal packing of the single chains, compared to the packing of ribbons in rac-1 and in the enantiomers, which follows from the higher value of the crystal density (calculated as 1.227 g cm⁻³; Table 2) compared with values of 1.160 g cm⁻³ for rac-1 and 1.188 g cm⁻³ and 1.189 g cm⁻³ for the R- and S-enantiomers (Khrustalev et al., 2014).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1B⋯O1ⁱ	0.895 (15)	2.071 (15)	2.9533 (13)	168.4 (13)
Symmetry code: (i) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ .

Table 2
Crystal lattice energies (kJ mol⁻¹) for racemic 2-phenylbutyramide polymorphs computed using AA-CLP software

Polymorph	E_{electrostatic}	E_polarization	E_dispersion	E_{exchange-repulsion}	E_total	Crystal density (g cm⁻³)
rac-1	−35.6^a	−27.6^a	−100.4^a	55.0^a	−108.6^a	1.160^b
rac-2	−33.9	−28.3	−107.9	53.8	−116.3	1.227
Notes: ^afrom Krivoshein et al. (2018 ); ^bfrom Khrustalev et al. (2014).

Figure 2
View of a hydrogen-bonded chain.

Figure 3
The crystal packing of the rac-2 polymorph.

4. Hirshfeld surface analysis and calculation of crystal lattice energies

Crystal Explorer (Wolff et al., 2012 ) was used to generate the Hirshfeld surfaces (Hirshfeld, 1977 ). The total d_norm surfaces for polymorphs rac-2 and rac-1 are shown in Figs. 4 and 5, respectively, in which the red spots correspond to the most significant N—H⋯O interactions in the crystal (Table 1). The surface diagram unambiguously shows that there are fewer active binding sites in rac-2 in comparison to rac-1. The two-dimensional fingerprint plots from the Hirshfeld surface analysis (Spackman & Jayatilaka, 2009 ) allows the intermolecular interactions to be analysed in detail and for even rather subtle differences between polymorphic systems to be quantified (Bernstein, 2011). The two-dimensional fingerprint plots for rac-2 and rac-1 are shown in Figs. 6 and 7, respectively. They clearly indicate the different distribution of interactions for a single molecule in the two structures. Decomposition of the full fingerprint plot for rac-2 shows five principle types of interactions that include H⋯H, H⋯C/C⋯H, H⋯O/O⋯H, H⋯N/N⋯H, and C⋯O/O⋯C contacts in decreasing order (Fig. 6). For the rac-1 polymorph, the set includes only four types of interactions, viz. H⋯H, H⋯C/C⋯H, H⋯O/O⋯H and H⋯N/N⋯H contacts (Fig. 7). The predominant interactions in both cases are H⋯H, constituting 65.7% in rac-2 and 67.3% in rac-1. With a significantly less contribution, the next most important interactions are H⋯C/C⋯H, contributing 19.6% in both cases, and being slightly asymmetric in shape in favour of (internal)C⋯H(external) contacts for both polymorphs. The directed H⋯O/O⋯H contacts constitute 11.4% for rac-2 and 10.8% for rac-1, with slight a asymmetry in favour of (internal)O⋯H(external) contacts for both polymorphs.

Figure 4
Hirshfeld surface for the rac-2 polymorph plotted over d_norm in the range −0.4994 to 1.0567 a.u.

Figure 5
Hirshfeld surface for the rac-1 polymorph plotted over d_norm in the range −0.5239 to 1.3882 a.u.

Figure 6
The full two-dimensional fingerprint plots for the rac-2 polymorph, showing all interactions, and delineated into H⋯H, H⋯C/C⋯H, H⋯O/O⋯H, H⋯N/N⋯H, C⋯O/O⋯C interactions. The d_i and d_e values are the closest internal and external distances (in Å) from given points on the Hirshfeld surface.

Figure 7
The full two-dimensional fingerprint plots for the rac-1 polymorph, showing all interactions, and delineated into H⋯H, H⋯C/C⋯H, H⋯O/O⋯H and H⋯N/N⋯H interactions. The d_i and d_e values are the closest internal and external distances (in Å) from given points on the Hirshfeld surface.

The Hirshfeld surface analysis confirms the decisive role of H-contacts that include hydrogen bonding and van der Waals interactions in the crystal packing. The crystal-lattice energies (Table 2) were calculated from the atomic coordinates obtained in the single-crystal X-ray diffraction experiments using the atom–atom force field with subdivision of the interaction energies into Coulombic, polarization, London dispersion, and Pauli repulsion components (AA-CLP; Gavezzotti, 2011 , 2013 ) implemented in the CLP-PIXEL computer program package (version 3.0, available from www.angelogavezzotti.it). These show that the rac-2 polymorph is more stable in terms of two criteria: total crystal energy and crystal density.

5. Database survey

The Cambridge Structural Database (CSD version 5.40, last update November 2018; Groom et al., 2016) includes crystallographic data for the R- and S-enantiomers of 2-phenylbutyramide (VOQGUF and VOQHAM, space group P1; Khrustalev et al., 2014) and the racemic form (VOQHEQ, space group C2/c; Khrustalev et al., 2014). As mentioned above, the conformations of two rac-polymorphs are quite similar, while the crystal packing differs significantly with more efficient crystal packing for the rac-2 polymorph reported here.

6. Crystallization

Crystals were obtain by the slow evaporation approach. 0.5 g of 2-phenylbutyramide (Alfa Aesar, stock No. A18501) were dissolved with extensive vortexing in 3 mL of a water/ethanol mixture (1:1 v/v) and left at room temperature (293–295 K) for six weeks. Block-shaped crystals formed on the walls of the vessel.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3.

Table 3
Experimental details

Crystal data
Chemical formula	C₁₀H₁₃NO
M_r	163.21
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	8.575 (2), 10.746 (3), 9.798 (3)
β (°)	101.811 (3)
V (Å³)	883.8 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.08
Crystal size (mm)	0.15 × 0.1 × 0.1

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2004 )
T_min, T_max	0.674, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	9961, 2240, 1914
R_int	0.038
(sin θ/λ)_max (Å⁻¹)	0.671

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.040, 0.110, 1.08
No. of reflections	2240
No. of parameters	161
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.31, −0.27
Computer programs: APEX2 and SAINT (Bruker, 2004), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b )and OLEX2 (Dolomanov et al., 2009 ).

Supporting information

CCDC reference: 1916098

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989019007011/yk2123sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019007011/yk2123Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989019007011/yk2123Isup3.cml

checkCIF report

Computing details top

Data collection: SAINT (Bruker, 2004); cell refinement: APEX2 (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

2-Phenylbutyramide top

Crystal data top

C₁₀H₁₃NO	F(000) = 352
M_r = 163.21	D_x = 1.227 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.575 (2) Å	Cell parameters from 3598 reflections
b = 10.746 (3) Å	θ = 2.4–30.1°
c = 9.798 (3) Å	µ = 0.08 mm⁻¹
β = 101.811 (3)°	T = 100 K
V = 883.8 (4) Å³	Block, colourless
Z = 4	0.15 × 0.1 × 0.1 mm

Data collection top

Bruker APEXII CCD diffractometer	1914 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.038
Absorption correction: multi-scan (SADABS; Bruker, 2004)	θ_max = 28.5°, θ_min = 2.4°
T_min = 0.674, T_max = 0.746	h = −11→10
9961 measured reflections	k = −14→14
2240 independent reflections	l = −13→13

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.040	All H-atom parameters refined
wR(F²) = 0.110	w = 1/[σ²(F_o²) + (0.0614P)² + 0.1474P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max < 0.001
2240 reflections	Δρ_max = 0.31 e Å⁻³
161 parameters	Δρ_min = −0.27 e Å⁻³
0 restraints

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.32919 (9)	0.23775 (7)	0.06137 (7)	0.0216 (2)
N1	0.27946 (11)	0.17768 (8)	0.26886 (9)	0.0192 (2)
H1A	0.2469 (17)	0.1033 (15)	0.2342 (15)	0.031 (4)*
H1B	0.2895 (17)	0.1927 (14)	0.3601 (15)	0.028 (3)*
C1	0.68011 (12)	0.34374 (9)	0.20614 (10)	0.0179 (2)
H1	0.6296 (16)	0.3276 (12)	0.1099 (14)	0.021 (3)*
C2	0.84492 (13)	0.33963 (10)	0.24848 (11)	0.0206 (2)
H2	0.9097 (17)	0.3192 (13)	0.1809 (14)	0.027 (3)*
C3	0.91672 (13)	0.36033 (10)	0.38704 (11)	0.0217 (2)
H3	1.0322 (19)	0.3568 (14)	0.4177 (15)	0.035 (4)*
C4	0.82161 (13)	0.38440 (10)	0.48320 (11)	0.0219 (2)
H4	0.8698 (17)	0.3979 (13)	0.5822 (15)	0.027 (3)*
C5	0.65680 (13)	0.38737 (9)	0.44137 (10)	0.0184 (2)
H5	0.5908 (15)	0.4038 (12)	0.5099 (13)	0.017 (3)*
C6	0.58384 (12)	0.36770 (8)	0.30233 (10)	0.0151 (2)
C7	0.40388 (12)	0.37876 (9)	0.25694 (10)	0.0150 (2)
H7	0.3586 (15)	0.3913 (12)	0.3424 (13)	0.019 (3)*
C8	0.35882 (12)	0.49138 (9)	0.16087 (11)	0.0189 (2)
H8A	0.4084 (18)	0.5661 (13)	0.2142 (15)	0.030 (4)*
H8B	0.4098 (16)	0.4803 (12)	0.0771 (14)	0.024 (3)*
C9	0.18019 (13)	0.50974 (11)	0.11476 (12)	0.0226 (2)
H9A	0.1318 (18)	0.4394 (14)	0.0522 (15)	0.033 (4)*
H9B	0.1575 (19)	0.5862 (15)	0.0573 (16)	0.039 (4)*
H9C	0.1253 (18)	0.5153 (14)	0.1957 (16)	0.034 (4)*
C10	0.33405 (11)	0.25883 (9)	0.18573 (10)	0.0148 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0261 (4)	0.0250 (4)	0.0141 (4)	−0.0021 (3)	0.0046 (3)	−0.0035 (3)
N1	0.0241 (5)	0.0158 (4)	0.0184 (4)	−0.0028 (3)	0.0060 (3)	−0.0006 (3)
C1	0.0198 (5)	0.0181 (5)	0.0155 (4)	−0.0020 (4)	0.0026 (4)	−0.0003 (3)
C2	0.0202 (5)	0.0185 (5)	0.0244 (5)	−0.0016 (4)	0.0073 (4)	−0.0004 (4)
C3	0.0168 (5)	0.0182 (5)	0.0279 (5)	−0.0025 (4)	−0.0004 (4)	0.0011 (4)
C4	0.0259 (6)	0.0191 (5)	0.0177 (5)	−0.0025 (4)	−0.0025 (4)	−0.0003 (4)
C5	0.0227 (5)	0.0160 (5)	0.0162 (5)	−0.0006 (4)	0.0034 (4)	−0.0003 (3)
C6	0.0167 (5)	0.0118 (4)	0.0163 (4)	−0.0012 (3)	0.0022 (3)	0.0010 (3)
C7	0.0163 (5)	0.0159 (5)	0.0129 (4)	−0.0007 (3)	0.0035 (3)	−0.0002 (3)
C8	0.0187 (5)	0.0176 (5)	0.0202 (5)	−0.0003 (4)	0.0036 (4)	0.0036 (4)
C9	0.0196 (5)	0.0231 (5)	0.0244 (5)	0.0031 (4)	0.0028 (4)	0.0036 (4)
C10	0.0131 (4)	0.0158 (4)	0.0150 (4)	0.0012 (3)	0.0020 (3)	−0.0003 (3)

Geometric parameters (Å, º) top

O1—C10	1.2316 (12)	C5—H5	0.979 (12)
N1—H1A	0.890 (16)	C5—C6	1.3940 (14)
N1—H1B	0.895 (15)	C6—C7	1.5206 (14)
N1—C10	1.3414 (13)	C7—H7	1.002 (12)
C1—H1	0.970 (13)	C7—C8	1.5333 (14)
C1—C2	1.3898 (15)	C7—C10	1.5282 (13)
C1—C6	1.3982 (14)	C8—H8A	1.004 (14)
C2—H2	0.973 (14)	C8—H8B	1.013 (13)
C2—C3	1.3891 (15)	C8—C9	1.5187 (15)
C3—H3	0.975 (16)	C9—H9A	1.007 (15)
C3—C4	1.3909 (16)	C9—H9B	0.992 (16)
C4—H4	0.984 (14)	C9—H9C	1.004 (15)
C4—C5	1.3890 (15)

H1A—N1—H1B	120.1 (13)	C6—C7—H7	108.0 (7)
C10—N1—H1A	118.2 (9)	C6—C7—C8	110.76 (8)
C10—N1—H1B	121.0 (9)	C6—C7—C10	110.30 (8)
C2—C1—H1	120.6 (8)	C8—C7—H7	108.4 (7)
C2—C1—C6	120.62 (9)	C10—C7—H7	108.2 (7)
C6—C1—H1	118.8 (8)	C10—C7—C8	111.06 (8)
C1—C2—H2	119.4 (8)	C7—C8—H8A	106.5 (8)
C3—C2—C1	120.46 (10)	C7—C8—H8B	107.9 (8)
C3—C2—H2	120.1 (8)	H8A—C8—H8B	108.0 (11)
C2—C3—H3	120.9 (9)	C9—C8—C7	113.41 (8)
C2—C3—C4	119.20 (10)	C9—C8—H8A	110.2 (8)
C4—C3—H3	119.9 (9)	C9—C8—H8B	110.5 (8)
C3—C4—H4	120.6 (8)	C8—C9—H9A	110.4 (8)
C5—C4—C3	120.45 (9)	C8—C9—H9B	110.2 (9)
C5—C4—H4	119.0 (8)	C8—C9—H9C	112.4 (9)
C4—C5—H5	119.9 (7)	H9A—C9—H9B	105.6 (12)
C4—C5—C6	120.73 (9)	H9A—C9—H9C	108.9 (12)
C6—C5—H5	119.4 (7)	H9B—C9—H9C	109.2 (12)
C1—C6—C7	121.41 (9)	O1—C10—N1	122.40 (9)
C5—C6—C1	118.55 (9)	O1—C10—C7	122.52 (9)
C5—C6—C7	119.98 (9)	N1—C10—C7	115.07 (8)

C1—C2—C3—C4	0.44 (16)	C5—C6—C7—C8	112.46 (10)
C1—C6—C7—C8	−64.48 (12)	C5—C6—C7—C10	−124.17 (9)
C1—C6—C7—C10	58.89 (11)	C6—C1—C2—C3	−0.55 (16)
C2—C1—C6—C5	0.03 (15)	C6—C7—C8—C9	−178.47 (8)
C2—C1—C6—C7	177.01 (9)	C6—C7—C10—O1	−83.85 (11)
C2—C3—C4—C5	0.18 (15)	C6—C7—C10—N1	95.67 (10)
C3—C4—C5—C6	−0.70 (15)	C8—C7—C10—O1	39.34 (13)
C4—C5—C6—C1	0.59 (15)	C8—C7—C10—N1	−141.14 (9)
C4—C5—C6—C7	−176.43 (9)	C10—C7—C8—C9	58.60 (11)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1B···O1ⁱ	0.895 (15)	2.071 (15)	2.9533 (13)	168.4 (13)

Symmetry code: (i) x, −y+1/2, z+1/2.

Crystal lattice energies (kJ mol^-1) for racemic 2-phenylbutyramide polymorphs computed using AA-CLP software top

Polymorph	E_{electrostatic}	E_polarization	E_dispersion	E_{exchange-repulsion}	E_total	Crystal density (g cm^-3)
rac-1	-35.6^a	-27.6^a	-100.4^a	55.0^a	-108.6^a	1.160^b
rac-2	-33.9	-28.3	-107.9	53.8	-116.3	1.227

Notes: ^afrom Krivoshein et al. (2018); ^bfrom Khrustalev et al. (2014).

Funding information

Funding for this research was provided by: NSF DMR 1523611 (PREM) and Welch Foundation (Departmental Grant; award No. BC-0022) .

References

Bernstein, J. (2011). Cryst. Growth Des. 11, 632–650. Web of Science CrossRef CAS Google Scholar
Bond, A. D., Boese, R. & Desiraju, G. R. (2007). Angew. Chem. Int. Ed. 46, 618–622. Web of Science CSD CrossRef CAS Google Scholar
Bond, A. D., Solanko, K. A., Parsons, S., Redder, S. & Boese, R. (2011). CrystEngComm, 13, 399–401. Web of Science CrossRef CAS Google Scholar
Brittain, H. G. (2009). Polymorphism in pharmaceutical solids. Informa, Healthcare. NY. Google Scholar
Bruker (2004). SAINT, APEX2 and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Burger, A. & Ramberger, R. (1979). Mikrochim. Acta, 72, 273–316. CrossRef Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Gavezzotti, A. (2011). New J. Chem. 35, 1360–1368. Web of Science CrossRef CAS Google Scholar
Gavezzotti, A. (2013). New J. Chem. 37, 2110–2119. CrossRef CAS 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
Haisa, M., Kashino, S., Kawai, R. & Maeda, H. (1976). Acta Cryst. B32, 1283–1285. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Haisa, M., Kashino, S. & Maeda, H. (1974). Acta Cryst. B30, 2510–2512. CSD CrossRef IUCr Journals Web of Science Google Scholar
Hirshfeld, F. L. (1977). Theor. Chim. Acta, 44, 129–138. CrossRef CAS Web of Science Google Scholar
Khrustalev, V. N., Sandhu, B., Bentum, S., Fonari, A., Krivoshein, A. V. & Timofeeva, T. V. (2014). Cryst. Growth Des. 14, 3360–3369. CSD CrossRef CAS PubMed Google Scholar
Krivoshein, A. V., Lindeman, S. V., Bentum, S., Averkiev, B. B., Sena, V. & Timofeeva, T. V. (2018). Z. Kristallogr. Cryst. Mat. 233, 781–793. CSD CrossRef CAS Google Scholar
Rustichelli, C., Gamberini, G., Ferioli, V., Gamberini, M. C., Ficarra, R. & Tommasini, S. (2000). J. Pharm. Biomed. Anal. 23, 41–54. Web of Science CrossRef PubMed CAS Google Scholar
SeethaLekshmi, S. & Guru Row, T. N. (2012). Cryst. Growth Des. 12, 4283–4289. Web of Science CSD CrossRef CAS Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Shtukenberg, A. G., Hu, C. T., Zhu, Q., Schmidt, M. U., Xu, W., Tan, M. & Kahr, B. (2017). Cryst. Growth Des. 17, 3562–3566. CSD CrossRef CAS Google Scholar
Spackman, M. A. & Jayatilaka, D. (2009). CrystEngComm, 11, 19–32. Web of Science CrossRef CAS Google Scholar
Vishweshwar, P., McMahon, J. A., Oliveira, M., Peterson, M. L. & Zaworotko, M. J. (2005). J. Am. Chem. Soc. 127, 16802–16803. Web of Science CSD CrossRef PubMed CAS Google Scholar
Wheatley, P. J. (1964). J. Chem. Soc. pp. 6036–6048. CSD CrossRef Google Scholar
Wolff, S. K., Grimwood, D. J., McKinnon, J. J., Turner, M. J., Jayatilaka, D. & Spackman, M. A. (2012). Crystal Explorer. University of Western Australia, Australia. Google Scholar

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