3-(2-Hy­droxy­eth­yl)-1-(4-nitro­phen­yl)-1H-benzo[d]imidazol-3-ium bromide

Halliru Ibrahim; Sizwe J Zamisa; Muhammad D Bala; Pinkie Ntola; Holger B Friedrich

doi:10.1107/S2414314624011684

. 2024 Dec 10;9(Pt 12):x241168. doi: 10.1107/S2414314624011684

3-(2-Hydroxyethyl)-1-(4-nitrophenyl)-1H-benzo[d]imidazol-3-ium bromide

Halliru Ibrahim ^a,^b, Sizwe J Zamisa ^b,^*, Muhammad D Bala ^b, Pinkie Ntola ^a, Holger B Friedrich ^b

Editor: W T A Harrison^c

PMCID: PMC11701757 PMID: 39777009

In the crystal of the title salt, the bromide ions act as double acceptors for hydrogen bonds from a hydroxyl group (O—H⋯Br) and a fused imidazolium moiety (C—H⋯Br). Additionally, C—H⋯O hydrogen bonds between the phenyl group and hydroxyl oxygen atom create a two-dimensional supramolecular network extending diagonally in the crystallographic bc plane.

Keywords: crystal structure, benzoimidazolium salt, tetramer

Abstract

The cation of the title salt, C₁₅H₁₄N₃O₃⁺·Br⁻, has a dihedral angle of 24.26 (6)° between its fused imidazole and 4-nitrophenyl rings and the N—C—C—O torsion angle associated with the hydroxyethyl substituent is 60.15 (17)°. In the crystal, the bromide ions act as double acceptors for hydrogen bonds from a hydroxyl group (O—H⋯Br) and a fused imidazolium moiety (C—H⋯Br). Additionally, C—H⋯O hydrogen bonds between the phenyl group and hydroxyl oxygen atom create a two-dimensional supramolecular network extending diagonally in the crystallographic bc plane.

Structure description

The title compound is a benzimidazolylidene precursor based on the 1-(4-nitrophenyl)benzimidazol-3-yl scaffold (Lee et al., 2004 ▸; Ibrahim et al., 2022 ▸) and quaternized to form a 2-hydroxyethyl benzimidazolium bromide salt. Various works have reported the chemodosimetric potential of compounds with a fused 1H-benzo[d] backbone (Kumar et al., 2013 ▸, 2015 ▸). The bulkiness of the backbone and the steric size of the ‘wingtip’ substituents influence the properties of such compounds in the absorption of nucleophiles such as cyanide ions. Their varied structures have led to investigations into their potential medicinal uses, thereby uncovering properties such as antimicrobial and anticancer activities (Kadafour et al., 2022 ▸; Ott, 2017 ▸). Recently, we have focused on the development of imine-functionalized benzimidazolylidene compounds as potential ligands for earth-abundant metals that were utilized as homogeneous catalysts for the transfer hydrogenation of ketones (Abubakar & Bala, 2020 ▸; Kadafour & Bala, 2021 ▸). As part of our ongoing work aimed at developing new derivatives with enhanced catalytic properties, we synthesized the title compound, C₁₅H₁₄N₃O₃⁺ · Br⁻ (I), and determined its crystal structure.

The asymmetric unit of (I) consists of a cationic benzoimidazolium species and a bromide ion as depicted in Fig. 1 ▸. In comparison with the recently reported 3-(2-hydroxyethyl)-1-(4-nitrophenyl)-1H-imidazol-3-ium bromide (II) (Ibrahim et al., 2024 ▸), the presence of the benzoimidazole moiety in (I) seem to widen the dihedral angle between the imidazole and 4-nitrophenyl rings from 8.99 (14)° in (II) to 24.26 (5)° in (I) while causing the ethanolyl side chain to adopt a synclinal conformation with respect to the fused imidazole ring [C7—N3—C14—C15 torsion angle = 59.7 (2)°]. In the extended structure of (I), the bromide ion acts as a double acceptor for O3—H3A⋯Br1 and C7—H7⋯Br1 links (Table 1 ▸) and inversion symmetry generates tetramers (two cations and two anions) with an Inline graphic (16) graph-set descriptor, as shown in Fig. 2 ▸. Intermolecular C—H⋯O hydrogen bonds exist between atom H13 of the phenyl moiety and O3 of the hydroxy group (Fig. 2 ▸), which link the hydrogen-bonded 16-membered rings to form a two-dimensional supramolecular structure that extends diagonally with respect to the crystallographic bc plane (Fig. 3 ▸).

The molecular structure of (I) showing displacement ellipsoids drawn at the 50% probability level.

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3A⋯Br1	0.84 (1)	2.39 (1)	3.2316 (11)	175
C7—H7⋯Br1ⁱ	0.95	2.68	3.5881 (16)	161
C13—H13⋯O3ⁱⁱ	0.95	2.39	3.3052 (19)	161

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Symmetry codes: (i) Inline graphic ; (ii) .

Representation of C7—H7⋯Br1, O3—H3A⋯Br1 and C13—H13⋯O3 hydrogen bonds (dotted bonds) in the packing of (I).

Representation of the propagation of the two-dimensional supramolecular structure in (I).

Synthesis and crystallization

The title compound was synthesized using a modified literature protocol (Ibrahim & Bala, 2016 ▸). To a Schlenk tube initially charged with N-para nitrophenyl benzimidazole (0.50 g, 0.0021 mol) and an excess of 2-bromoethanol (0.78 g, 0.0063 mol) was added dry acetonitrile (20 ml). The mixture was stirred and refluxed under nitrogen for 16 h. Removal of all volatiles from the greenish grey mixture and subsequent washing with batches of dry ethyl acetate (30 ml × 5) until the washing became colourless gave a grey solid, which was shown to be pure with TLC. The grey precipitate was then dried under vacuum to yield a greyish solid of the title compound. Colourless, block-shaped crystals of (I) suitable for crystal-structure determination were grown by the slow diffusion of diethyl ether into a methanolic solution of the title compound. Yield: 0.42 g, 55.3%. m.p. 226–228°C. ¹H NMR (400 MHz, DMSO-d₆): δ_p.p.m. 10.39 [s, 1H, NC(H)N], 8.67 (d, J = 8.9 Hz, 2 × 1H, CH_p), 8.31 (d, J = 7.5 Hz, 1H, CH_b), 8.21 (d, J = 8.9 Hz, 2 × 1H, CH_p), 8.02 (d, J = 8.6 Hz, 1H, CH_b), 7.87 (m, 2 × 1H, CH_b), 5.29 (s, b, 1H, OH_e), 4.74 (t, J = 9.8 Hz, 2H, CH_2 e), 3.99 (t, J = 9.8 Hz, 2H, CH_2 e): b = benzoyl, p = phenyl, e = ethanoyl. ¹³C NMR (100 MHz, DMSO-d₆): δ_p.p.m. 148.1 (NCN), 143.2, 138.1, 131.5, 130.7, 127.6, 127.1, 126.6, 114.5, 113.4, 58.6 (CH₂), 50.1 (CH₂). FTIR (cm⁻¹): ν_O—H 3244; ν_{aryl C—H} 3081, ν_{alkyl C—H} 2997; ν_C=N 1566; ν_Nitro 1512, 1328; ν_C—O 1255;. LCMS (ESI⁺): m/z (%) 284.0635 (100) [(M—Br)]⁺.

Refinement

Crystallographic data and structure refinement details are summarized in Table 2 ▸.

Table 2. Experimental details.

Crystal data
Chemical formula	C₁₅H₁₄N₃O₃⁺·Br⁻
M _r	364.20
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	100
a, b, c (Å)	6.7708 (1), 17.2107 (2), 12.3465 (2)
β (°)	98.184 (1)
V (Å³)	1424.09 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	2.90
Crystal size (mm)	0.32 × 0.19 × 0.13

Data collection
Diffractometer	Bruker SMARTAPEX2 CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T_min, T_max	0.628, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	32857, 3555, 3006
R _int	0.029
(sin θ/λ)_max (Å⁻¹)	0.669

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.057, 1.04
No. of reflections	3555
No. of parameters	202
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.38, −0.31

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Computer programs: APEX2 (Bruker, 2010 ▸), SHELXT2013 (Sheldrick, 2015a ▸), SHELXL2018/3 (Sheldrick, 2015b ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2414314624011684/hb4498sup1.cif

x-09-x241168-sup1.cif^{(976.4KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S2414314624011684/hb4498Isup2.hkl

x-09-x241168-Isup2.hkl^{(283.7KB, hkl)}

x-09-x241168-Isup3.cml^{(5.7KB, cml)}

Supporting information file. DOI: 10.1107/S2414314624011684/hb4498Isup3.cml

CCDC reference: 2406833

Additional supporting information: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors would like to thank the University of KwaZulu-Natal for the research facilities. DUT/HANT is acknowledged for funding the postdoctoral fellowship of HI.

full crystallographic data