Crystal structure and Hirshfeld surface analysis of (C7H9N4O2)[ZnCl3(H2O)]

El Hamdani, H.; El Amane, M.; Saadi, M.; El Ammari, L.

doi:10.1107/S2056989020002753

research communications

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ISSN: 2056-9890

Volume 76| Part 4| April 2020| Pages 506-509

https://doi.org/10.1107/S2056989020002753

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Crystal structure and Hirshfeld surface analysis of (C₇H₉N₄O₂)[ZnCl₃(H₂O)]

Hicham El Hamdani,^a ^* Mohamed El Amane,^a Mohamed Saadi ^b and Lahcen El Ammari ^b

^aEquipe Metallation, Complexes Moleculaires et Applications, Université Moulay Ismail, Faculté des Sciences, BP 11201 Zitoune, 50000 Meknés, Morocco, and ^bLaboratoire de Chimie Appliquée des Matériaux, Centre des Sciences des Matériaux, Faculty of Sciences, Mohammed V University in Rabat, Avenue Ibn Batouta, BP 1014, Rabat, Morocco
^*Correspondence e-mail: elhamdanihicham40@gmail.com

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 29 January 2020; accepted 27 February 2020; online 10 March 2020)

In the title molecular salt, 1,3-dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-9-ium aquatrichloridozincate(II), (C₇H₉N₄O₂)[ZnCl₃(H₂O)], the fused ring system of the cation is close to planar, with the largest deviation from the mean plane being 0.037 (3) Å. In the complex anion, the Zn^II cation is coordinated by three chloride ions and one oxygen atom from the water ligand in a distorted tetrahedral geometry. In the crystal, inversion dimers between pairs of cations linked by pairwise N—H⋯O hydrogen bonds generate R₂²(10) rings. The anions are linked into dimers by pairs of O—H⋯Cl hydrogen bonds and the respective dimers are linked by O—H⋯O and N—H⋯Cl hydrogen bonds. Together, these generate a three-dimensional supramolecular network. Hirshfeld surfaces were generated to gain further insight into the packing.

Keywords: crystal structure; molecular salt; hydrogen bonding.

CCDC reference: 1986654

1. Chemical context

Theophylline, C₇H₈N₄O₂, is an alkaloid derivative of xanthine, containing a fused pyrimidine-imidazole ring system with conjugated double bonds. It has many biological and pharmacological properties (see, for example, Rao et al., 2005 ; Piosik et al., 2005 ). Various studies have shown that theophylline can be used as a medicine for the treatment of asthmatic bronchitis and chronic obstructive bronchitis (under several brand names), and as anticancer drugs (Nafisi et al. 2003 ; Rao et al. 2005; Piosik et al. 2005). Furthermore, theophylline complexes with transition metals can be used in anticancer drugs (David et al., 1999 ).

As part of our studies in this area, we reacted theophylline with ZnCl₂ under acid conditions to give the molecular salt (C₇H₉N₄O₂)·[ZnCl₃(H₂O)] and its crystal structure is described herein.

2. Structural commentary

The asymmetric unit of the title molecular salt (Fig. 1) comprises one theophyllinium (C₇H₉N₄O₂)⁺ cation protonated at N2 and one [ZnCl₃(H₂O)]⁻¹ anion. As expected, the [ZnCl₃(H₂O)] tetrahedron contains one short Zn—O bond distance [2.0240 (15) Å] and three longer Zn—Cl bonds distances [in the range 2.2121 (7)–2.2745 (6) Å]. These bond lengths are consistent with the values observed in analogous compounds such as [H₃N(CH₂)₈NH₃]ZnCl₄, [C₆H₅–C₂H₄–NH₃]₂ZnCl₄, (C1₂H₁₂N₂)[ZnCl₄] and (C₁₀H₂₂N₂)[ZnCl₄](El Mrabet et al., 2017 ), as are the Cl—Zn—Cl [111.45 (3)–116.99 (3)°] and Cl—Zn—O [101.36 (5)–108.19 (5)°] bond angles (Kassou et al., 2016 ; Campos-Gaxiola et al., 2015 ; Soudani et al., 2013 ).

Figure 1
Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

3. Supramolecular features

The packing is consolidated by a network of hydrogen bonds (Table 1, Fig. 2). The cations are linked into inversion dimers by pairs of N1—H1⋯O2 hydrogen bonds, which generate R₂²(10) rings. The anions also form inversion dimers, being linked by pairwise O3—H3A⋯Cl3 hydrogen bonds. The anions are linked to the cations via O3—H3B⋯O1 hydrogen bonds from the water molecule to a carbonyl group of the pyrimidine ring. Finally, the cations are linked to the anions via N2—H2⋯Cl2 hydrogen bonds. Taken together, these hydrogen bonds generate a three-dimensional supramolecular network (Fig. 3), which also features short Cl⋯π contacts [Cl⋯centroid distances in the range of 3.533 (2)–3.620 (2) Å].

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O2ⁱ	0.86	1.87	2.7067 (18)	163
N2—H2⋯Cl2ⁱⁱ	0.86	2.21	3.0652 (15)	174
C6—H6C⋯O2ⁱⁱⁱ	0.96	2.65	3.431 (3)	139
O3—H3A⋯Cl3^iv	0.77	2.43	3.1915 (17)	176
O3—H3B⋯O1	0.82	1.90	2.718 (2)	173
Symmetry codes: (i) -x, -y+2, -z+1; (ii) x-1, y, z; (iii) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ ; (iv) -x+2, -y+1, -z+1.

Figure 2
Molecules linked by O–H⋯O and O–H⋯Cl strong hydrogen bonds.

Figure 3
Perspective view of the crystal structure along the c axis showing the layered organization.

4. Database survey

A search of the Cambridge Structural Database (CSD, Version 5.40, May 2019; Groom et al., 2016 ) for organic–inorganic compounds containing theophilinium in the cation revealed three similar structures: theophyllinium trichlorotheophyllineplatinum(II), bis(theophyllinium) tetrachloroplatinum(II) (Griffith et al., 1979 ) and bis(theophyllinium) tetrabromopalladium(II) (Salas et al., 1989 ). In each of the three complexes, the metal cation is surrounded by four ligands in a planar geometry. The crystal structures of these compounds are different from that of the title compound; however, the organic–inorganic moities are linked through hydrogen bonds in all of these structures.

5. Hirshfeld surface analysis

In order to gain further insight into the intermolecular interactions in the title compound, we used the program Crystal Explorer (Spackman & Jayatilaka, 2009 ), to consider separately the (C₇H₉N₄O₂)⁺ organic cation and the [ZnCl₃(H₂O)]⁻ inorganic anion.

The Hirshfeld d_norm surface of the cation is depicted in Fig. 4. The most significant interactions are H⋯H (29.6%) contacts and the second largest percentage (25.8%) can be attributed to H⋯O interactions, which are responsible for the appearance of deep-red spots and correlate with the O—H⋯O and N—H⋯O hydrogen bonds. H⋯Cl (21.9%), C⋯Cl (8.1%), N⋯Cl (5.5%) and C⋯H (3.6%) interactions are also observed, with other contact types making a negligible contribution.

Figure 4
Hirshfeld d_norm surface of the (C₇H₉N₄O₂)⁺ cation in the title compound.

The Hirshfeld surface of the [ZnCl₃(H₂O)] anion is depicted in Fig. 5 and shows red spots that correspond to the strong N—H⋯Cl and O—H⋯Cl hydrogen bonds: Cl⋯H contacts are the most abundant contributor to the surface at 54.7%. Other significant contributions include Cl⋯C (10.3%), H⋯H (9.6%), Cl⋯N (7.3%), H⋯O (5.6%) and H⋯Cl (4.7%). It is notable that the Cl⋯Cl contact percentage is 0%, i.e. the chloride anions avoid each other in the crystal.

Figure 5
Hirshfeld d_norm surface of the [ZnCl₃(H₂O)]⁻ anion in the title compound.

6. Synthesis and crystallization

ZnCl₂·6H₂O (0.244 g, 1 mmol) was dissolved in 5 ml of water. Then, theophylline [C₇H₈N₄O₂] (0.180 g, 1 mmol) was dissolved in 3 ml of ethanol/water (1:1 v:v) with a few drops of conc. HCl (37%). The two solutions were mixed and after two weeks, colourless crystals of the title molecular salt were obtained.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were all located in a difference map, but those attached to C and N atoms were repositioned geometrically (C—H = 0.93–0.96, N—H = 0.86 Å). The water H atoms were located in a difference map and refined as riding atoms in their as-found relative positions. The constraint U_iso(H) = 1.2U_eq(carrier) or 1.5U_eq(C-methyl) was applied in all cases.

Table 2
Experimental details

Crystal data
Chemical formula	(C₇H₉N₄O₂)[ZnCl₃(H₂O)]
M_r	370.92
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	8.0932 (14), 13.744 (3), 12.429 (2)
β (°)	92.290 (6)
V (Å³)	1381.4 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	2.36
Crystal size (mm)	0.32 × 0.25 × 0.11

Data collection
Diffractometer	Bruker D8 VENTURE Super DUO
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.587, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	29522, 3046, 2753
R_int	0.035

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.025, 0.070, 1.04
No. of reflections	3046
No. of parameters	166
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.42, −0.26
Computer programs: APEX3 and SAINT (Bruker, 2016 ), SHELXT2014/5 (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick 2015b ), Mercury (Macrae et al., 2020 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1986654

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989020002753/hb7891sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989020002753/hb7891Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: publCIF (Westrip, 2010).

1,3-Dimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-9-ium aquatrichloridozincate(II) top

Crystal data top

(C₇H₉N₄O₂)[ZnCl₃(H₂O)]	F(000) = 744
M_r = 370.92	D_x = 1.783 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.0932 (14) Å	Cell parameters from 3046 reflections
b = 13.744 (3) Å	θ = 2.2–27.1°
c = 12.429 (2) Å	µ = 2.36 mm⁻¹
β = 92.290 (6)°	T = 296 K
V = 1381.4 (4) Å³	Plate, colorless
Z = 4	0.32 × 0.25 × 0.11 mm

Data collection top

Bruker D8 VENTURE Super DUO diffractometer	3046 independent reflections
Radiation source: INCOATEC IµS micro-focus source	2753 reflections with I > 2σ(I)
HELIOS mirror optics monochromator	R_int = 0.035
Detector resolution: 10.4167 pixels mm^-1	θ_max = 27.1°, θ_min = 2.2°
φ and ω scans	h = −10→10
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −17→17
T_min = 0.587, T_max = 0.746	l = −15→15
29522 measured reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.025	w = 1/[σ²(F_o²) + (0.0361P)² + 0.7104P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.070	(Δ/σ)_max = 0.001
S = 1.04	Δρ_max = 0.42 e Å⁻³
3046 reflections	Δρ_min = −0.26 e Å⁻³
166 parameters	Extinction correction: SHELXL2018/3 (Sheldrick 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0116 (9)
Primary atom site location: dual

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
C1	0.3890 (2)	0.73981 (12)	0.43314 (14)	0.0328 (4)
C2	0.23025 (19)	0.88256 (11)	0.49620 (13)	0.0270 (3)
C3	0.09587 (19)	0.84313 (11)	0.43243 (13)	0.0275 (3)
C4	−0.1427 (2)	0.81114 (13)	0.35170 (15)	0.0347 (4)
H4	−0.252141	0.816209	0.326593	0.042*
C5	0.10920 (19)	0.75700 (12)	0.37968 (13)	0.0279 (3)
C6	0.2625 (3)	0.61496 (16)	0.3140 (2)	0.0534 (6)
H6A	0.175032	0.571204	0.331328	0.080*
H6B	0.367334	0.584272	0.329585	0.080*
H6C	0.253138	0.631212	0.238896	0.080*
C7	0.5201 (2)	0.85870 (15)	0.55359 (17)	0.0427 (4)
H7A	0.593033	0.889908	0.505244	0.064*
H7B	0.575456	0.804184	0.587203	0.064*
H7C	0.489054	0.904175	0.607817	0.064*
N1	−0.06417 (17)	0.87524 (10)	0.41341 (12)	0.0314 (3)
H1	−0.105499	0.928117	0.437743	0.038*
N2	−0.04038 (17)	0.73720 (10)	0.33052 (12)	0.0317 (3)
H2	−0.064969	0.686459	0.292687	0.038*
N3	0.25046 (17)	0.70379 (10)	0.37848 (12)	0.0316 (3)
N4	0.37091 (16)	0.82468 (10)	0.49296 (12)	0.0307 (3)
O1	0.52249 (16)	0.69911 (11)	0.42937 (12)	0.0463 (3)
O2	0.22824 (15)	0.95718 (8)	0.54976 (10)	0.0348 (3)
O3	0.7194 (2)	0.54071 (11)	0.46116 (13)	0.0567 (4)
H3A	0.791444	0.560052	0.496924	0.085*
H3B	0.653875	0.586278	0.454444	0.085*
Cl1	0.53785 (8)	0.37606 (5)	0.28558 (6)	0.06943 (19)
Cl2	0.84322 (7)	0.55879 (3)	0.20036 (4)	0.04325 (13)
Cl3	0.98173 (7)	0.36721 (4)	0.39782 (4)	0.05047 (15)
Zn1	0.76669 (3)	0.45595 (2)	0.33282 (2)	0.03798 (10)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0309 (8)	0.0313 (8)	0.0364 (9)	0.0047 (7)	0.0020 (7)	0.0003 (7)
C2	0.0268 (7)	0.0248 (7)	0.0293 (7)	0.0002 (6)	0.0002 (6)	0.0013 (6)
C3	0.0244 (7)	0.0245 (7)	0.0333 (8)	0.0023 (6)	−0.0005 (6)	−0.0009 (6)
C4	0.0276 (8)	0.0346 (9)	0.0414 (9)	−0.0006 (7)	−0.0030 (7)	−0.0028 (7)
C5	0.0289 (8)	0.0250 (7)	0.0299 (8)	−0.0004 (6)	0.0014 (6)	0.0003 (6)
C6	0.0538 (13)	0.0432 (11)	0.0627 (13)	0.0120 (9)	−0.0033 (10)	−0.0252 (10)
C7	0.0269 (8)	0.0451 (10)	0.0551 (12)	0.0004 (7)	−0.0089 (8)	−0.0086 (9)
N1	0.0257 (7)	0.0273 (7)	0.0411 (8)	0.0027 (5)	−0.0018 (6)	−0.0044 (6)
N2	0.0307 (7)	0.0281 (7)	0.0359 (7)	−0.0026 (5)	−0.0021 (6)	−0.0055 (6)
N3	0.0316 (7)	0.0269 (7)	0.0364 (7)	0.0046 (5)	0.0013 (6)	−0.0055 (6)
N4	0.0246 (6)	0.0305 (7)	0.0366 (7)	0.0018 (5)	−0.0027 (5)	−0.0025 (6)
O1	0.0334 (7)	0.0440 (8)	0.0612 (9)	0.0146 (6)	−0.0020 (6)	−0.0063 (6)
O2	0.0335 (6)	0.0302 (6)	0.0401 (7)	0.0031 (5)	−0.0052 (5)	−0.0086 (5)
O3	0.0556 (9)	0.0577 (9)	0.0556 (9)	0.0250 (7)	−0.0129 (7)	−0.0217 (7)
Cl1	0.0508 (3)	0.0742 (4)	0.0829 (4)	−0.0221 (3)	−0.0032 (3)	−0.0209 (3)
Cl2	0.0543 (3)	0.0337 (2)	0.0405 (2)	−0.00102 (19)	−0.0130 (2)	−0.00533 (17)
Cl3	0.0538 (3)	0.0503 (3)	0.0467 (3)	0.0195 (2)	−0.0059 (2)	0.0006 (2)
Zn1	0.03676 (14)	0.03346 (14)	0.04306 (15)	0.00315 (8)	−0.00657 (9)	−0.00676 (8)

Geometric parameters (Å, º) top

C1—O1	1.219 (2)	C6—H6B	0.9600
C1—N3	1.379 (2)	C6—H6C	0.9600
C1—N4	1.394 (2)	C7—N4	1.474 (2)
C2—O2	1.223 (2)	C7—H7A	0.9600
C2—N4	1.391 (2)	C7—H7B	0.9600
C2—C3	1.427 (2)	C7—H7C	0.9600
C3—C5	1.360 (2)	N1—H1	0.8600
C3—N1	1.380 (2)	N2—H2	0.8600
C4—N1	1.315 (2)	O3—H3A	0.7665
C4—N2	1.343 (2)	O3—H3B	0.8227
C4—H4	0.9300	Zn1—O3	2.0240 (15)
C5—N3	1.358 (2)	Zn1—Cl1	2.2121 (7)
C5—N2	1.362 (2)	Zn1—Cl2	2.2745 (6)
C6—N3	1.466 (2)	Zn1—Cl3	2.2487 (6)
C6—H6A	0.9600

O1—C1—N3	121.36 (16)	N4—C7—H7C	109.5
O1—C1—N4	121.10 (16)	H7A—C7—H7C	109.5
N3—C1—N4	117.55 (14)	H7B—C7—H7C	109.5
O2—C2—N4	121.61 (15)	C4—N1—C3	108.30 (14)
O2—C2—C3	126.47 (15)	C4—N1—H1	125.8
N4—C2—C3	111.92 (14)	C3—N1—H1	125.8
C5—C3—N1	106.73 (14)	C4—N2—C5	107.74 (14)
C5—C3—C2	121.68 (15)	C4—N2—H2	126.1
N1—C3—C2	131.54 (15)	C5—N2—H2	126.1
N1—C4—N2	109.50 (15)	C5—N3—C1	117.99 (14)
N1—C4—H4	125.2	C5—N3—C6	121.95 (15)
N2—C4—H4	125.2	C1—N3—C6	119.84 (15)
N3—C5—C3	123.88 (15)	C2—N4—C1	126.70 (14)
N3—C5—N2	128.42 (15)	C2—N4—C7	117.30 (14)
C3—C5—N2	107.71 (14)	C1—N4—C7	115.90 (14)
N3—C6—H6A	109.5	Zn1—O3—H3A	119.6
N3—C6—H6B	109.5	Zn1—O3—H3B	120.0
H6A—C6—H6B	109.5	H3A—O3—H3B	105.5
N3—C6—H6C	109.5	O3—Zn1—Cl3	101.36 (5)
H6A—C6—H6C	109.5	O3—Zn1—Cl2	106.16 (6)
H6B—C6—H6C	109.5	O3—Zn1—Cl1	108.19 (5)
N4—C7—H7A	109.5	Cl1—Zn1—Cl2	111.45 (3)
N4—C7—H7B	109.5	Cl3—Zn1—Cl2	111.58 (2)
H7A—C7—H7B	109.5	Cl1—Zn1—Cl3	116.99 (3)

O2—C2—C3—C5	−176.95 (16)	N2—C5—N3—C1	178.75 (17)
N4—C2—C3—C5	2.2 (2)	C3—C5—N3—C6	−175.40 (18)
O2—C2—C3—N1	0.2 (3)	N2—C5—N3—C6	4.0 (3)
N4—C2—C3—N1	179.38 (17)	O1—C1—N3—C5	−175.01 (17)
N1—C3—C5—N3	179.06 (15)	N4—C1—N3—C5	5.0 (2)
C2—C3—C5—N3	−3.2 (3)	O1—C1—N3—C6	−0.2 (3)
N1—C3—C5—N2	−0.48 (18)	N4—C1—N3—C6	179.78 (18)
C2—C3—C5—N2	177.31 (15)	O2—C2—N4—C1	−178.35 (16)
N2—C4—N1—C3	0.8 (2)	C3—C2—N4—C1	2.4 (2)
C5—C3—N1—C4	−0.18 (19)	O2—C2—N4—C7	−2.2 (2)
C2—C3—N1—C4	−177.67 (18)	C3—C2—N4—C7	178.56 (15)
N1—C4—N2—C5	−1.1 (2)	O1—C1—N4—C2	173.82 (17)
N3—C5—N2—C4	−178.56 (16)	N3—C1—N4—C2	−6.1 (3)
C3—C5—N2—C4	0.95 (19)	O1—C1—N4—C7	−2.3 (3)
C3—C5—N3—C1	−0.7 (2)	N3—C1—N4—C7	177.68 (16)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2ⁱ	0.86	1.87	2.7067 (18)	163
N2—H2···Cl2ⁱⁱ	0.86	2.21	3.0652 (15)	174
C6—H6C···O2ⁱⁱⁱ	0.96	2.65	3.431 (3)	139
O3—H3A···Cl3^iv	0.77	2.43	3.1915 (17)	176
O3—H3B···O1	0.82	1.90	2.718 (2)	173

Symmetry codes: (i) −x, −y+2, −z+1; (ii) x−1, y, z; (iii) x, −y+3/2, z−1/2; (iv) −x+2, −y+1, −z+1.

Acknowledgements

The authors thank the Faculty of Science, Mohammed V University in Rabat, Morocco for the X-ray data collection.

References

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