Unveiling the supramolecular assembly of a novel antimony(iii)-based co-crystal: integrating multi-spectroscopic analyses, DFT calculations, and advanced biological evaluations

Abstract

An antimony(III) co-crystal [SbCl₃(C₄H₃N₂ClO)]₂·(C₄H₃N₂ClO)₂ (abbreviated as PdzSb) was successfully prepared under hydrothermal reaction conditions at 140 °C and comprehensively analyzed through a variety of physicochemical techniques. The asymmetric unit comprises four distinct neutral species: two free ligands of 6-chloro-3(2H)-pyridazinone (6,3Pdz) and two discrete antimony-based complexes, each coordinated by three chloride ions and one aromatic ligand (C₄H₃N₂OCl) (6,3Pdz–O) through the oxygen donor atom. Notably, the Sb(III) center adopts a seesaw geometry, which is relatively uncommon and highlights the influence of the stereochemically active lone pair on the coordination environment. The main novelty of this work lies in establishing a clear correlation between the stereochemically active lone pair of Sb(III), the resulting structural organization, and the associated physicochemical properties, rather than focusing on the optimization of a single specific application. Single-crystal X-ray analysis reveals that an extensive network of diverse non-covalent interactions plays a key role in stabilizing the three-dimensional supramolecular architecture, thereby governing the cohesion and properties of the co-crystal. Comprehensive spectroscopic and thermal analyses validated both the structural integrity and the chemical composition of the material. Hirshfeld surface and reduced density gradient (RDG) analyses emphasize the importance of non-covalent interactions, including hydrogen and halogen bonding, which are quantitatively evaluated using two-dimensional fingerprint plots. In addition, molecular electrostatic potential (MEP), electron localization function (ELF), and localized orbital locator (LOL) confirm the relevance of this interaction in the self-assembly process. To elucidate this unexpected observation and to further understand the intricate balance of the supramolecular interactions governing the crystal packing, a high-level density functional theory (DFT) study was conducted. Furthermore, optical studies indicate an indirect band gap of 3.42 eV, suggesting semiconducting behavior. Beyond its electronic functionality, the title compound exhibits significant antibacterial activity against clinically relevant human pathogens, with efficiencies comparable to those of standard antibiotics, and demonstrates promising larval biocontrol activity against lepidopteran species. Therefore, these findings clearly establish structure–property–activity relationships and highlight the multifunctional nature of the Sb(III) co-crystal that combines optical and biological functionalities in a single material.