Triel Bonds─Interactions without Borders, Similarly as Hydrogen Bonds

ωB97XD/aug-cc-pVTZ results of calculations on complexes linked by triel bonds are analyzed here. The systems connected by different kinds of triel bonds are considered: those with the one-center electron donor, among which are complexes with halide anions playing the role of Lewis bases. Complexes with π-electron units as electron donors are also considered, i.e., complexes of acetylene, ethylene, and benzene. Finally, species are considered where interactions may be classified as bifurcated triel bonds or as halide and hydride bonds. Apart from ab initio calculations, other theoretical approaches are applied such as the Quantum Theory of Atoms in Molecules (QTAIM) approach and the energy decomposition analysis scheme (EDA). The theoretical analyses are supported by examples of crystal structures where similar interactions occur. The Cambridge Structural Database (CSD) searches were performed to find such structures. The theoretical results and the results of CSD searches show that the triel bond possesses characteristics like those occurring in hydrogen bonded systems. The triel center often changes its trigonal configuration to the tetrahedral configuration in complexes that are linked by strong triel bonds.