Influence of pseudohalide anions on non-covalent supramolecular synthons in Hg(ii) complexes with an 8-aminoquinoline ligand: DFT approach and biological implications

Abstract

In this work, we report the synthesis, structural characterization, DFT calculations, and antimicrobial/anticancer properties of two identical X-ray structures of Hg(II) complexes (1 and 2). The complexes crystallized in the monoclinic space group P2₁/c. Hg(II) ions in two complexes exhibit four-coordinated geometries. The complex crystal network flourishes with hydrogen bonds and π⋯π interactions. In the crystal networks, supramolecular features have been explained by Hirshfeld surface and 2D fingerprint plots. The HOMO–LUMO energy gap of Hg(II) complexes enables conducting behaviour. NLO examines complex 2, which is a promising candidate for optoelectronic applications. The NLO findings are in accordance with the calculated hyperpolarizability (β₀) values. Further, X-ray structure reveals the existence of spodium (SpB) and chalcogen bonds (ChB) in the crystal networks of the complexes. QTAIM, NCI-RDG plots, NBO, and MEP studies successfully ensure the existence of these bonds. Also, energy decomposition analysis (EDA) rationalizes the role of electrostatics in all cases. Here, it is highlighted that dispersion plays a vital role in dimers showing LP⋯π interactions. However, in the case of hydrogen-bonding, the orbital effects are equally significant. Meanwhile, the as-prepared compounds' antimicrobial activities were investigated against Gram-positive and Gram-negative microbial strains. These studies include S. aureus (ATCC 25923) and B. subtilis (ATCC 6633), E. coli (ATCC 25922) and S. typhimurium (ATCC 14028), the fungus A. fumigatus, and the yeast C. albicans (ATCC 10231). The MIC value compares the antimicrobial results. Additionally, cytotoxicity was assessed in DLA, HepG2, and human H9c2 cancer cell lines, revealing that Hg(II) complexes exhibit low cytotoxicity in human H9c2 cells. The structure–activity relationship (SAR) rationalized the core biological findings.