# Ab initio insights into the face, edge, and vertex interactions of BH41− with electron-accepting molecules

## TL;DR

This paper uses ab initio calculations to explore how BH41− interacts with various molecules through its faces, edges, and vertices, revealing preferences for specific interaction sites.

## Contribution

The study provides new insights into BH41−'s σ-hole interactions and triel bonding with electron-accepting molecules using computational methods.

## Key findings

- BH41− interacts with molecules via faces, edges, and vertices, with preferences for specific geometries.
- σ-hole interactions and triel bonding play significant roles in BH4(L)f1− adducts.
- Bader's QTAIM and NBO analyses confirm the nature of noncovalent interactions in BH4(L)1− complexes.

## Abstract

The ab initio calculations at the MP2/aug-cc-pvdz computational level were used to analyze the interactions of FCN, ClCN, BrCN, CF3H, CF3Cl, CH3OH, HF, HCl, HCN, SH2, SHF, SF2, H2O, HOCl, HOBr, CO, N2, and H2 molecules with BH41−. On BH41−, three sites were accessible for interactions with L molecules to form BH4(L)1− aggregates. The faces, edges, and vertices of BH41− as electron donors, could interact with electron acceptor species. In addition, the BH41− anion, through its σ-holes, could obtain electrons from interacting molecules. The significant preference of some molecules was interaction along the triangular faces, BH4(L)f1− (where L = ClCN, BrCN, FCN, CF3Cl, CF3H) whereas, for others, the vertices, BH4(L)v1− (where L = HOCl, HOBr, PF3) or edges, BH4(L)e1− (where L = H2O, HF, HCl) of BH41− might be more suitable for interaction. Some molecules, such as CH4 and H2, despite their preferred facial interactions, could interplay with the vertex counterpart through an edge intermediate. It seems that accepting electrons (triel bonding) by BH41− σ-holes had important roles in the face interactions for BH4(L)f1− adducts. Bader's Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) calculations were used to analyze optimized complexes. Noncovalent interaction (NCI) analysis was used for further determination of interactions in BH4(L)1− adducts.

Simple adducts, including common interactions, bi and trifurcated dihydrogen bonds in which BH41- through its vertices, edges, and faces acts as an electron donor and through its σ-holes, acts as an electron acceptor for triel bond were considered.