Synthesis, crystallography, and DFT calculations of the ion-association complex formed by neostigmine and tetraphenylborate

• Synthesis of a new crystal of the neostigmine-tetraphenylborate (NSG-TPB) complex. • Validation of structure using single crystal X-ray diffraction. • Intermolecular interaction is validated by theoretical and experimental research. • Computational insights highlighted the critical roles that [NSG]+ and [TPB]-play in the activity and antioxidant capacity of the molecule. An anion exchange process was employed to synthesize a neostigmine-tetraphenylborate (NSG-TPB) complex with a yield of 81%. The resulting white crystalline complex was obtained in acetonitrile and characterized using various spectroscopic and analytical techniques, including ultraviolet, mass, elemental, and nuclear magnetic resonance (NMR) spectroscopy, alongside X-ray crystallography. This study elucidated the structural formation of a 1:1 charge transfer (CT) complex with intermolecular interactions further analyzed via Hirshfeld surface analysis. Additionally, a comprehensive theoretical study employing Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) methods explored the molecules`s reactivity profile. This analysis encompassed frontier molecular orbitals (FMO), HOMO-LUMO energies, molecular electrostatic potential (MEP), and global chemical reactivity descriptors. Computational insights underscored the pivotal roles of both [NSG] + and [TPB] − in the molecule's activity and antioxidant capacity.