Self-assembly synthesis of two new cocrystals of 1,5 bis(3-pyridyl)-3,4-diaza-2,4-hexadiene: an experimental and theoretical study

Abstract

In this paper, we report the synthesis, characterization and theoretical studies of two new cocrystals of 1,5 bis(3-pyridyl)-3,4-diaza-2,4-hexadiene (3-bpdh) with two simple organic acids; oxalic and succinic with 1:1 stoichiometric ratio. These cocrystals, [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2), have been prepared by slow evaporation of saturated solutions and characterized by elemental and thermal analysis, FTIR, ¹H NMR spectroscopy, and single X-ray crystallography. X-ray crystal analyses show that these structures have been crystallized in triclinic and monoclinic space groups of $P_{\bar{1}}$ and P2₁/n, respectively. Also, the thermal behavior of compounds was investigated in an atmosphere of static air with thermal gravimetric analysis (TGA), differential thermal analysis (DTA).

These structures have been studied theoretically using RB3LYP hybrid density functional method with 6–31G(d) basis set. DFT calculations have been used to predict the geometry of the cocrystal structures. Furthermore, molecular electrostatic potential (MESP) maps of the compounds have been generated. Theoretical results show good agreement with the experimental data and these data show hydrogen bonding has played an important role in supramolecular structure formation. The cocrystal design was done based on the perfect selection of two distinct hydrogen donor and acceptor molecules.

Keywords

Co-crystal self-assembly X-ray crystallography thermal analysis DFT

1 Introduction

A cocrystal is composed of two or more different components that are generally solid at room temperature in a crystalline lattice. The cocrystal structures are formed via non-ionic and non-covalent intermolecular interactions such as van der Waals forces and hydrogen bonding. Therefore, it may be possible to fine-tune physical properties by exercising precise control over the supramolecular assembly by crystal engineering [1]. Crystal engineering strategies would be improved physicochemical properties of chemical compounds or generate new properties for utilitarian applications without altering the inherent individual properties such as pharmaceutical and electronical [2 –4], nano scale architectures [5], host–guest systems [6], topochemical reactions [7], solid-state reactivity [8] and interpenetrated network [9]. So, the cocrystal structures represent a significant synthetic challenge and a hot topic with considerable attentions in recently twenty years [10 –13] and several theoretical studies have been performed on these structural molecules [14 –19]. In this research, synthesis and characterization and theoretical studies of two novel cocrystals; [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2) have been reported. The 3-bpdh as a target is a pyridine derivative and has a unique position in the medicinal chemistry. We have used from two organic acids, oxalic and succinic, as co-former to prepare new co-crystals [20 –23]. The bond lengths and angles data derived from quantum-chemical results are comparable with experimental data in solid phase. Also, the electrostatic potential has been used for predicting sites and relative activities in studies of biological recognition, hydrogen bonding interactions and pharmaceutical ingredient (API) preparation.

2 Experimental

2.1 Reagent

All reagents and solvents used for the synthesis and analysis were commercially available, purchased from Merck and used as received without further purifications.

2.2 Methods

Infrared spectra were measured on a Perkin-Elmer 597 and Nicolet 510P spectrophotometers in the range 400–4000 cm^–1 in KBr discs technique. The microanalyses were carried out using a Heraeus CHN Rapid analyzer. The melting points were measured on an electro-thermal 9100 apparatus. ¹H-NMR spectra were measured with a BRUKER DRX-500 AVANCE spectrometer at 500 MHz. Thermal behavior was measured with PL-STA 1500 apparatus.

2.3 Preparation of [(3-bpdh)(oxalic acid)] (1)

1,5 bis(3-pyridyl)-3,4-diaza-2,4-hexadiene (3-bpdh) (0.12 g, 0.5 mmol) and oxalic acid (0.063 g, 0.5 mmol) were mixed and ground manually using a pestle and mortar then 5 mL of ethanol was added dropwise to obtain a pasty solution and stirred for 1 h at room temperature. The prepared solution was allowed to evaporate slowly for 2 days at room temperature (ca. 25°C). The yellowish crystals of the desired product precipitated, which were washed by acetone and dried in air.

Yield: 0.15 g, (89%). Mp: 195°C; FT-IR (KBr; cm^–1): 1051 (m), 1120 (w), 1183 (m), 1240 (m), 1294 (s), 1326 (w), 1367 (m), 1408 (w), 1479 (w), 1610 (s), 1709 (s), 2396 (b), 2922 (w), 3014 (w), 3069 (w), 3426 (m), 3500 (w), 3615 (w), 3660 (w). Elemental Analysis calculated for C₁₆H₁₆N₄O₄(1): C 58.54, H 4.88, N 17.07. Found: C 57.8, H 4.10, N 16.4.

2.4 Preparation of [(3-bpdh)(succinic acid)] (2)

This compound was prepared by mixing 1,5 bis(3-pyridyl)-3,4-diaza-2,4-hexadiene (3-bpdh) (0.12 g, 0.5 mmol) and succinic acid (0.059 g, 0.5 mmol). The mixture was ground with a mortar and pestle and kneaded, during which ethanol (5 mL) was added dropwise to obtain a pasty solution for 1 h at room temperature. The yellowish crystals of cocrystal 2 suitable for single crystal Xray crystallography was obtained by slow evaporation from ethanol solution at room temperature after 2 days.

Yield: 0.15 g, (87%). Mp: 157°C; ¹H NMR (500 MHz, DMSO-d6, ppm): 2.3 (s, 6 H), 2.42 (s, 4 H), 7.49–7.52 (d.q, 2 H), 8.26–8.29. (d.t, 2 H), 8.65–8.67 (d.d, 2 H), 9.1 (d, 2 H), 12.17 (s, 2 H); FT-IR (KBr; cm^–1): 1043 (m), 1078 (w), 1122 (m), 1182 (m), 1329 (s), 1368 (w), 1411 (m), 1490 (w), 1608 (s), 1704 (m), 2362 (b), 2936 (w), 3068 (w), 3183 (m), 3500 (w), 3615 (w), 3660 (w). Elemental Analysis Calculated for C₁₈H₂₀N₄O₄(2): C 60.67, H 5.62, N 15.73. Found: C 60.51, H 5.13, N 15.40.

2.5 Crystal structure determination

Crystallographic measurements were made at 293(2) K for [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2) using a Bruker APEX area-detector diffractometer using graphite monochromator Mo–Kα radiation. The structure was solved by direct methods and refined by full–matrix least–squares techniques on F2. Structure solution and refinement was accomplished using SHELXL-2014 [24 –28].

2.6 Computational

Geometrical characterization of the synthesized compounds were performed in the gas phase at the level of density functional theory (DFT) using Becke’s three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) (B3LYP) at 6–31G(d) level of theory. Starting geometries for calculation were taken from the X-ray crystal structure of the related cocrystals. To validate the optimization of the structures, frequency calculations were performed and the results showed no negative (imaginary) frequencies.

3 Results

3.1 Spectroscopic characterization

The infrared spectra of these two structures (solid in KBr pellets) show some harmonic vibrational frequencies in the range of 400–4000 cm^–1. The vibrational analysis enables the characterization of a given molecular structure. The peak of the C = N and C = O groups are observed as strong bands centered at 1610 and 1709 cm^–1 for [(3-bpdh)(oxalic acid)](1) and 1608 and 1704 cm^–1 for [(3-bpdh)(succinic acid)](2). Also, broad peak of O–H appears in 3196 and 3362 cm^–1 for cocrystal 1 and 2, respectively.

The relatively medium absorption band at 2922 cm^–1 and 2936 cm^–1 is due to the C–H modes of compounds 1 and 2 in or out of the aromatic plane. The IR spectrum of both compounds shows absorption bands resulting from the vibrations of aromatic rings in the 3068 and 3069 cm^–1.

The ¹H-NMR spectrum in DMSO-d₆ show characteristic signals at δ= 7.49, 8.26, 8.65 and 9.11 ppm for proton in the aromatic ring. Single broad peak at δ= 12.17 ppm related to O–H acid and the other signals at 2.31 and 2.42 ppm correspond to CH₃ and CH₂ groups of 3-bpdh and succinic acid, respectively.

3.2 Crystal structure

Cocrystal 1 was obtained as yellowish cubic crystals in $P_{\bar{1}}$ space group. Crystallographic data were collected in (Table 1). Each unit cell consists of two molecules of 3-bpdh and oxalic acid. An ORTEP view of the asymmetric unit of the cocrystal 1 can be found in (Fig. 1a). The key structural feature of cocrystal 1 is involved in simultaneous hydrogen bonding (N4 ... HO) between (N4) pyridyl ring of 3-bpdh molecules and hydrogen atoms of the oxalic acid. This assembly formed an infinite one-dimensional zigzag structure along more hydrogen bonds (Fig. 1b).

Fig.1

a) ORTEP plot b) a perspective view of hydrogen bonded 1D assembly c) 2D view assembly of [(3-bpdh)(oxalic acid)] (1).

Table 1

Crystal data and structure refinement for compounds [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2)

Identification code	[(3-bpdh)(oxalic)]^{( 1 )}	[(3-bpdh)(Succinic)]^{( 2 )}
Empirical formula	C₁₆H₁₅N₄O₄	C₁₈H₂₀N₄O₄
Formula weight	327.32	342
Temperature	293(2) K	293(2) K
Wavelength	0.71073 Å	0.71073 Å
Crystal system	trilinic	monoclinic
Space group	$P_{\bar{1}}$	P2_1/n
Unit cell dimensions	a = 7.4179(2) Å	a = 4.8205(2)Å
	b = 9.2423(2)Å	b = 14.4637(7)Å
	c = 12.2745(3) Å	c = 13.0214(6)Å
	α= 78.6140(10)°	α= 90.00°
	β= 72.7300(10)°	β= 93.176(2) °
	γ= 81.1450(10)°	γ= 90.00°
Volume	783.67(3) Å³	905.86(7)Å³
Z	2	4
Density (calculated)	1.387 gcm^-3	1.430 g cm^-3
Absorption coefficient	0.103 mm^-1	0.148 mm^-1
F(000)	342	396
Theta range for data collection	2.632 to 25.997°	3.438 to 25.999°
Reflections collected	2984	1767
Absorption correctioncoeffi	0.103	0.148
Refinement method	Shelxl	Shelxl
Data/restraints/parameters	2984/0/228	1767/0/132
Goodness-of-fit-ref	1.028	0.900
Final R indices [I > 2σ (I)]	R1 = 0.0388	R1 = 0.0389
	wR2 = 0.1125	wR2 = 0.1135
R Indices (all data)	R1 = 0.0537	R1 = 0.0468
	wR2 = 0.1265	wR2 = 0.1266

Weak hydrogen bonding between hydrogen atoms of aryl rings and oxygen atoms of oxalic acid (C_(Aryl)–H ... O) form a two dimensional (2D) structure (Fig. 1c). As (Fig. 2a) shows; two other weak hydrogen bonding between hydrogen atoms of methyl groups and oxygen atoms of oxalic acid from adjacent layers (C_(Me)–H(12) ... O(4)) and (C_(Me)–H(6) ... O(3)) form a 3D structure of cocrystal 1.

Fig.2

3D views of the cocrystal assemblies of cocrystal a) [(3-bpdh)(oxalic acid)] (1) and b) [(3-bpdh)(succinic acid)] (2).

Cocrystal (2), [(3-bpdh)(succinic acid)] obtained from ethanolic solution and crystallizes in _P21/n space group (Table 1). Figure 3a shows an ORTEP diagram of the cocrystal 2 asymmetric unit. The hydrogen bonding (N₁ ... HO) between nitrogen atom (N₁) of pyridyl rings and hydrogen atoms of succinic acid leads to one-dimensional zigzag assembly (Fig. 3b). The weak hydrogen bonding (C_(Aryl)–H ... O) have been observed between aryl groups of 3-bpdh and oxygen atoms of succinic acid. These weak interaction leads to form two-dimensional structures (Fig. 3c).

Fig.3

a) ORTEP plot b) a perspective view of hydrogen bonded 1D assembly c) 2D assembly view of [(3-bpdh)(succinic acid)] (2).

As (Fig. 2b) shows, some weak hydrogen bonding is observed between methyl group and oxygen atom of two adjacent layers (C_(Me)–H ... O). These interactions lead to form three dimensional (3D) supramolecular structure of cocrystal 1 and 2. All hydrogen bond distances and angles for two cocrystals 1 and 2 are set out in Table 2.

Table 2

Hydrogen bond length (Å)/angel (°) in the structure of [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2)

Cocrystal No.	D–H ... A	d(D ... H)	d(H ... A)	d(D ... A)	< (DHA)
(1)	O(2)–H(10) ... N(3)	1.007	1.596	2.606	170.99
(2)	O(6)–H(10) ... N(1)	0.907	1.763	2.673	177.72

The comparison between X-ray powder diffraction (XRD) patterns of the simulated X-ray crystallography and experimental XRD pattern was done and good matches were observed (Fig. 4a, b).

Fig.4

XRD Pattern of a₁) simulated pattern based on single crystal data, a₂) synthesized powder of [(3-bpdh)(oxalic acid)] (1); b₁) simulated pattern based on single crystal data, b₂) synthesized powder of [(3-bpdh)(succinic acid)] (2).

3.3 DFT calculations

The theoretical studies enable the characterization of these molecular cocrystal structures 1 and 2 as a true minimum on the molecular potential energy surface, respectively (Fig. 5a, b). Geometrical calculated parameters of two new cocrystals and experimental results are gathered in Table 3. Good agreement between structural parameters from DFT calculation and experimental results has been observed. A little difference between theoretical and experimental values may originate from the fact that the experimental data was obtained in the solid state, while the calculated values describe single molecules in the gaseous state without considering lattice interactions.

Fig.5

Optimized structure of cocrystal structures a)[(3-bpdh)(oxalic acid)] (1) and b)[(3-bpdh)(succinic acid)] (2).

Table 3

Experimental (X-ray) and calculated [RB3LYP/6–31 ... G(d)] selected bond lengths (Å), angles (°) and torsion angels (°) for [(DABTZ)(bpo)] (1) and [(DABTZ)(bpa)] (2)

Cocrystal No.	Bond	Bond length(Å)		Angle (ex.)	Angel(°)		Torsion angel	Torsion angel(°)
		Exp¹.	Theo².		Exp.	Theo.		Exp.	Theo.
(1)	C(1)–N(4)	1.325	1.33	C(11)N(3)C(12)	119.28	117.32	C(8)N(2)N(1)C(6)	151.50	141.52
	C(5)–N(4)	1.340	1.341	C(8)N(2)N(1)	143.91	117.44	C(5)N(4)HO(1)	162.13	159.55
	C(6)–N(1)	1.284	1.292	C(6)N(1)N(2)	114.43	117.34	C(15)O(1)HN(4)	157.13	159.89
	C(8)–N(2)	1.284	1.293	C(1)N(4)C(5)	120.07	118.97	HC(1)N(4)C(5)	179.63	179.76
	C(11)–N(3)	1.340	1.338	O(1)C(15)O(3)	126.12	127.04	C(16)C(15)O(1)H	178.11	179.92
	C(12)–N(3)	1.326	1.336	O(2)C(16)O(4)	125.37	124.36
	C(15)–O(1)	1.285	1.314
	C(15)–O(3)	1.214	1.217
	C(16)–O(2)	1.292	1.345
	C(16)–O(4)	1.204	1.207
	N(1)–N(2)	1.400	1.369
	O(2)–H(10)	1.007	1.028
	H(10)N(3)	1.608	1.661
	O(2)N(3)	2.609	2.681
(2)	C(1F)–N(1)	1.333	1.336	C(1F)N(1)C(1G	118.17	118.89	C(1 G)N(1)HO(6)	129.40	114.385
	C(1 G)–N(1)	1.330	1.338	C(1)N(2)N(2)	113.86	117.33	C(3)O(6)HN(1)	111.54	109.83
	C(1)–N(2)	1.287	1.292	O(6)C(3)O(8)	123.26	124.43	HO(6)C(3)C(1K)	–176.04	–166.36
	N(2)–N(2)	1.404	1.370	C–C(1)N(2)	114.72	116.14
	C(3)–O(6)	1.313	1.328	O(8)C(3)C(1K)	124.08	123.47
	C(3)O(8)	1.209	1.223
	C(6)H(10)	0.901	1.012
	H(10)N(1)	1.762	1.728
	O(6)N(1)	2,672	2,734

3.4 Molecular electrostatic potential maps

MESP displays three-dimensional visual regions for the electrophilic attack of charged point-like reagents on molecules and chemical reactivity of them [29].

The MESP diagrams (Fig. 6a, b) for these cocrystals were obtained based on the DFT optimized results. As these diagrams show the electrophilic sites (negative electrostatic potential in red color) such as carboxylic groups make hydrogen bond acceptor while electron deficient groups (positive electrostatic potential in blue color) such as nitrogen atoms in 3-bpdh makes hydrogen bond donor regions.

Fig.6

Molecular electrostatic potential map of cocrystals a)[(3-bpdh)(oxalic acid)] (1) and b)[(3-bpdh)(succinic acid)] (2).

Effectually, MEP contour map provides a simple way to predict how these cocrystals could interact, geometrically. The binding of an attacking molecule such as drug to a target depends on the variation in electrostatic potential of them. As depicted in (Fig. 6) the negative regions are partial on the C = O double bonds of acids and nitrogen atoms of pyridine rings in 3-bpdh ligand, and positive ones on O–H bond of carboxylic groups.

3.5 Thermogravimetric analysis

The thermal decomposition behavior of these two new cocrystals [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2) were investigated in static air atmosphere from ambient temperature to 700°C. Cocrystal 1 is stable up until 200C and the release of an oxalic acid molecule was started at this temperature until 280°C (observed 29.8%, calc. 27.4%). This fragment exits by an endothermic process. The weight loss of 68 % from 280 to 460°C is equivalent to the loss of 3-bpdh molecule [cacl: 72.6% ] with an exothermic event at 400°C (Fig. 7a).

Fig.7

TGA and DTA diagrams of two cocrystals a) [(3-bpdh)(oxalic acid)] (1) and b) [(3-bpdh)(succinic acid)] (2).

Thermal decomposition of cocrystal 2 takes place from 100°C. At this temperature, the 3-bpdh molecule exit by an endothermic process with the mass loss of 65% that is consistent with the calculated value of 66.8%. In the final step, the elimination of succinic acid molecule (observed 25%, calc. 33.15%) with an exothermic feature follows from 300 to 450°C (Fig. 7b).

All of the DTA curves were merged into one picture and illustrated in (Fig. 8). DTA diagram of oxalic acid shows two endothermic process at 102 and 200C (Fig. 8a₁). These peaks and another endothermic peak of 3-bpdh ligand at 97°C (Fig. 8a₂) were removed after co-crystallization. Results revealed that the peaks of cocrystal 1 (100 and 210C) were distinct from individual co-formers (Fig. 8a₃).

Fig.8

DTA diagrams of a₁) oxalic acid; b₁) succinic acid; a₂ and b₂) 3-bpdh; a₃) [(3-bpdh)(oxalic acid)] (1); b₃) [(3-bpdh)(succinic acid)] (2).

The succinic acid (Fig. 8b₁) and 3-bpdh ligand (Fig. 8b₂) exhibited endothermic peaks at 190, 250 and 97°C, respectively.

The new peaks in the DTA curves of cocrystal 2 and the marked changes in the thermograms confirmed the emergence of new solid phase of this cocrystal. It is evident that both DTA peaks at 185 and 310°C corresponded to removal of oxalic acid and 3-bpdh ligand from cocrystal 2 structure (Fig. 8b₃).

4 Conclusions

Herein, we report the synthesize of two new 1:1 stoichiometry ratio cocrystals of 3-bpdh as hydrogen acceptor with two distinct simple acids. Hydrogen bonding controls the packing of these two cocrystals. They are characterized and formulated as [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2) according to the obtained results from theoretical and experimental studies (DFT, elemental, thermal, ¹H-NMR, FTIR spectroscopies, and single X-ray crystallography). It is gratifying to see that there is good agreement between experimental and theoretical results.

Footnotes

Acknowledgments

Support of this investigation by the Iran National Science Foundation is gratefully acknowledged.

CCDC 1437628 and 1437645 contain the supplementary crystallographic data for [(3-bpdh)(oxalic acid)] (1) and [(3-bpdh)(succinic acid)] (2), respectively and check-cif files were added as S1 and S2. A copy of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, Cb2 1EZ, UK (fax: C441223 336 033). Web page: .

References

Aakeroy

C.B.

, Forbes

, Desper

, Using Cocrystals to Systematically Modulate Aqueous Solubility and Melting Behavior of an Anticancer Drug, J Am Chem Soc 131 (2009), 17048–17049.

Nauha

, Kolehmainen

, Nissinen

, Packing incentives and a reliable N–H…N–pyridine synthon in co-crystallization of bipyridines with two agrochemical actives, Cryst Eng Comm 13 (2011), 6531–6537.

Luo

Y.H.

, Wu

G.G.

, Mao

S.L.

, Sun

B.W.

, Complexation of different metals with a novel N-donor bridging receptor and Hirshfeld surfaces analysis, Inorg Chim Acta 397 (2013), 1–9.

Desiraju

G.R.

, Hydrogen Bridges in Crystal Engineering: Interactions without Borders, Acc Chem Res 35 (2002), 565–573.

Springuel

, Norberg

, Robeyns

, Wouters

, Leyssens

, Advances in Pharmaceutical Co-Crystal Screening: Effective Co-crystal Screening through Structural Resemblance, Cryst Growth Des 12 (2011), 475–484.

Ebenezer

, Muthiah

P.T.

, Design of Co-crystals/Salts of Aminopyrimidines and Carboxylic Acids through Recurrently Occurring Synthons, Cryst Growth Des 12 (2012), 3766–3785.

Luo

Y.H.

, Zhou

, Sun

B.W.

, Synthesis, crystal structure and DNA binding properties of a new member of the [Mn₃Zn₂] ¹³⁺ complex family, J Chem Res 36 (2012), 506–509.

Luo

Y.H.

, Xu

, Sun

B.W.

, Antisolvent Crystallization of Biapenem: Estimation of Growth and Nucleation Kinetics, J Chem Res 369 (2012), 697–700.

Lyssenko

K.A.

, Analysis of supramolecular architectures: Beyond molecular packing diagrams, Mendeleev Commun 22 (2012), 1–7.

10.

Yan

D.P.

, Delori

, Lloyd

G.O.

, Friscic

, Day

G.M.

, Jones

, Lu

, Wei

, Evans

D.G.

, The role of mechanochemistry and supramolecular design in the development of pharmaceutical materials, Chem Int Ed 52 (2011), 12483–12486.

11.

Metrangolo

, Meyer

, Pilati

, Resnati

, Terraneo

, Halogen

Angew.

, Bonding in Supramolecular Chemistry, Chem Int Ed 47 (2008), 6114–6127.

12.

Wuest

J.D.

, Molecular solids: Co-crystals give light a tune-up, Nat Chem 4 (2012), 74–75.

13.

Friscic

, Supramolecular concepts and new techniques in mechanochemistry: Cocrystals, cages, rotaxanes, open metal–organic frameworks, Chem Soc Rev 41 (2012), 3493–3510.

14.

Luo

Y.H.

, Sun

B.W.

, Pharmaceutical Co-Crystals of Pyrazinecarboxamide (PZA) with Various Carboxylic Acids: Crystallography, Hirshfeld Surfaces, and Dissolution Study, Cryst Growth Des 13 (2013), 2098–2106.

15.

Luo

Y.H.

, Xu

, Sun

B.W.

, Investigation of supramolecular synthons of p-hydroxybenzoic acid (PHBA): Comparison of its hydrate, co-crystal and salt, J Cryst Growth 374 (2013), 88–98.

16.

Trask

A.V.

, An Overview of Pharmaceutical Cocrystals as Intellectual Property, Mol Pharm 4 (2007), 301–309.

17.

Schneider

H.J.

, Binding Mechanisms in Supramolecular Complexes, Angew Chem Int Ed 48 (2009), 3924–3977.

18.

Luo

Y.H.

, Wu

G.G.

, Sun

B.W.

, Anti-solvent crystallization of biapenem: Estimation nucleation kinetics, J Chem Eng Data 58 (2013), 588–597.

19.

Lara-Ocha

, Espinosa-Perez

, Crystals and Patents, Cryst Growth Des 7 (2007), 1213–1215.

20.

Zhang

, Yu

, Li

, Ma

, Preparation of 2:1 urea-succinic acid cocrystals by sublimation, J Cryst Growth 469 (2017), 114–118.

21.

Jang

, Kim

I.W.

, Poly(acrylic acid) to induce competitive crystallization of a theophylline/oxalic acid cocrystal and a theophylline polymorph, J Cryst Growth 434 (2016), 104–109.

22.

Sangeetha

, Mathammal

, Establishment of the structural and enhanced physicochemical properties of the cocrystal-2-benzyl amino pyridine with oxalic acid, J Mol Struct 1143 (2017), 192–203.

23.

da Silva Filho

J.G.

, Freire

V.N.

, Caetano

E.W.S.

, Ladeira

L.O.

, Fulco

U.L.

and Albuquerque

E.L.

, A comparative density functional theory study of electronic structure and optical properties of c-aminobutyric acid and its cocrystals with oxalic and benzoic acid, Chem Phys Lett 587 (2013), 20–24.

24.

COSMO, version 1.60. Bruker AXS Inc., Madison, WI, 2005.

25.

SAINT, version 7.06A. Bruker AXS Inc., Madison, WI, 2005.

26.

SADABS, version 2.10. Bruker AXS Inc., Madison, WI, 2005.

27.

Burla

M.C.

, Caliandro

, Camalli

, Carrozzini

, Cascarano

G.L.

, De Caro

, Giacovazzo

, Polidori

and Spagna

, An improved tool for crystal structure determination and refinement, J Appl Crystallogr 38 (2005), 381–388.

28.

Sheldrick

G.M.

, SHELXL97. University of Gottingen, Germany, 1997.

29.

Politzer

, Truhlar

D.G.

, (Eds.), Chemical Application of Atomic and Molecular Electrostatic Potentials, Plenum, New York, 1981.