organic compounds
3-(2-Hydroxyethyl)-1-(4-nitrophenyl)-1H-benzo[d]imidazol-3-ium bromide
aDepartment of Chemistry, Durban University of Technology, PO Box 1334, Durban, 4000, South Africa, and bSchool of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000, South Africa
*Correspondence e-mail: zamisas@ukzn.ac.za
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.
Keywords: crystal structure; benzoimidazolium salt; tetramer.
CCDC reference: 2406833
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 (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 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 R42(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).
of (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): δp.p.m. 10.39 [s, 1H, NC(H)N], 8.67 (d, J = 8.9 Hz, 2 × 1H, CHp), 8.31 (d, J = 7.5 Hz, 1H, CHb), 8.21 (d, J = 8.9 Hz, 2 × 1H, CHp), 8.02 (d, J = 8.6 Hz, 1H, CHb), 7.87 (m, 2 × 1H, CHb), 5.29 (s, b, 1H, OHe), 4.74 (t, J = 9.8 Hz, 2H, CH2 e), 3.99 (t, J = 9.8 Hz, 2H, CH2 e): b = benzoyl, p = phenyl, e = ethanoyl. 13C NMR (100 MHz, DMSO-d6): δp.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): νO—H 3244; νaryl C—H 3081, νalkyl C—H 2997; νC=N 1566; νNitro 1512, 1328; νC—O 1255;. LCMS (ESI+): m/z (%) 284.0635 (100) [(M—Br)]+.
Refinement
Crystallographic data and structure .
details are summarized in Table 2Structural data
CCDC reference: 2406833
https://doi.org/10.1107/S2414314624011684/hb4498sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314624011684/hb4498Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2414314624011684/hb4498Isup3.cml
Acknowledgements
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.
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