Molecular simulation of B-N systems: insights into the interactions and properties of borospherene-pyridine hybrids

Borospherene (B₄₀), an all-boron fullerene analogue, exhibits Lewis acidity at its boron sites, while pyridine, a common organic ligand, acts as a Lewis base. Despite extensive research on B₄₀ interactions with metals and small inorganic molecules, the potential for functionalization with organic ligands like pyridine to form novel hybrid materials, such as borospherene-organic frameworks (BOFs), remains largely unexplored. This study investigates the structure, stability, and nature of interactions in B₄₀-pyridine (B₄₀-Py) complexes. Structural searches identified 18 isomers, with detailed analysis revealing that the most stable complexes form through direct B-N interactions. The B-N bonding exhibits a synergistic combination of covalent and ionic character, as evidenced by multiple computational analyses. The most stable isomer (involving B(4) site) provides crucial insights for designing B-N functional molecules and BOFs based on borospherene.

Density functional theory (DFT) calculations were performed using Gaussian 16. Initial structural searches employed the Molclus program coupled with xTB pre-optimization. Geometry optimizations and frequency calculations (confirming no imaginary frequencies) for isomers were carried out at the M062X/6-311G(d), PBE0-D3/6-311G(d), and B3LYP-D3/6-311G(d) levels, incorporating Grimme's D3 dispersion correction. Basis-set superposition error (BSSE) corrections were applied using the counterpoise method. Subsequent analyses for the six lowest-energy isomers included: electrostatic potential (ESP) mapping, quantum theory of atoms in molecules (AIM) analysis, charge-density difference analysis, and visualization of non-covalent interactions using the independent gradient model based on Hirshfeld partition (IGMH) and the interaction region indicator (IRI). These analyses utilized the Multiwfn 3.8 software package.