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

Context

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.

Methods

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.