σ‑Donation and π‑Backdonation Effects in Dative Bonds of Main-Group Elements

The
nature of donor–acceptor interactions is important for
the understanding of dative bonding and can provide vital insights
into many chemical processes. Here, we have performed a computational
study to elucidate substantial differences between different types
of dative interactions. For this purpose, a data set of 20 molecular
complexes stabilized by dative bonds was developed (DAT20). A benchmark
study that considers many popular density functionals with respect
to accurate quantum chemical interaction energies and geometries revealed
two different trends between the complexes of DAT20. This behavior
was further explored by means of frontier molecular orbitals, extended-transition-state
natural orbitals for chemical valence (ETS-NOCV), and natural energy
decomposition analysis (NEDA). These methods revealed the extent of
the forward and backdonation between the donor and acceptor molecules
and how they influence the total interaction energies and molecular
geometries. A new classification of dative bonds is suggested.