Synergistic effects of steric constraints and non-covalent interactions in copper(ii) chloro-nitro-benzoato complexes: synthesis, structural characterization, theoretical investigations, antimicrobial studies, and molecular docking analyses

Abstract

Herein, the design and synthesis of three new copper(II) chloro-benzoato complexes (2C4NB = 2-chloro-4-nitrobenzoate; 2C5NB = 2-chloro-5-nitrobenzoate) with N-/O-donor, i.e. ethanolamine (ethmn) and N-hydroxyethyl-ethylenediamine (N-hyden), [Cu(ethmn)₂(2C4NB)₂] (1), [Cu(N-hyden)₂](2C5NB)₂ (2), and [Cu(N-hyden)₂(2C4NB)₂] (3), have been achieved for the first time under ambient conditions. All the three complexes (1–3) were structurally characterized, along with elemental and spectroscopic analyses (UV-visible, FT-IR) and other studies. Structure elucidation using single crystal X-ray diffraction clearly revealed the exact geometry and nature of bonding, i.e. covalent (1), ionic (2), and covalent (3), with distorted octahedral geometry in all cases. Deep insights into the X-ray structures of complexes 1–3 indicated that the disorientation of the nitro-group from its mean plane in 2C4NB of complexes 1 and 3 is lesser compared to that of 2C5NB of complex 2, resulting in different natures of coordination complexes. Packing analysis showed that various weak (non-covalent) interactions such as O–H⋯O, N–H⋯O, C–H⋯O, anion⋯π, and C–H⋯π play an important role in the lattice stabilization of complexes 1–3, in agreement with the Hirshfeld surface analysis revealing an interplay of non-covalent interactions in the lattice stabilization of these complexes, supporting the packing analyses. Theoretical calculations estimated the total interaction energies and band gap (i.e. HOMO–LUMO energy differences) of complexes 1–3. Antimicrobial activities of complexes 1–3 were evaluated, and the results showed that all the three complexes exhibited remarkable activities against both Gram-positive (B. cereus and S. aureus) and Gram-negative bacteria (E. coli, S. typhi, P. aeruginosa, and S. flexneri). The potential antibacterial efficacy of complexes 1 and 2 is comparable to that of chloramphenicol. In addition, molecular docking investigations of complexes 1–3 clearly showed that in silico and experimental anti-microbial studies were similar in terms of their performance. Complexes 1–3 showed docking scores of −7.6, −7.4, and −7.5 kcal mol⁻¹ against SARS-CoV-2 (PDB ID: 7Z0P), which were better than the standard drugs chloroquine and molnupiravir against SARS-CoV-2.