Exploring the interaction of alkali metal cations with the tetramethylborate anion

Understanding the interactions between metallic cations and anions is crucial for elucidating the structure and reactivity of ionic systems. In this work, we investigate the binding modes and energetic characteristics of a series of alkali metal cations (Li+, Na+, K+, Rb+, Cs+) with the tetramethylborate anion using density functional theory. Molecular electrostatic potential analysis reveals three preferential binding regions corresponding to distinct local minima on the tetramethylborate surface. Geometry optimizations and penetration index analysis confirm the formation of ion pairs with site-specific interaction modes: κ¹C, κ²C, and κ¹B. Energy decomposition analysis shows that electrostatics dominates the interaction energy, with polarisation playing a significant secondary role. Correlations between penetration indices and interaction energies provide insight into the nature of cation–anion interactions, including the role of collective stabilisation effects. These findings contribute to a deeper understanding of ion pairing phenomena in organoborate-based systems and the broader field of supramolecular chemistry.