Terminal Phosphinidene Complex Adducts with Neutral and Anionic O-Donors and Halides and the Search for a Differentiating Bonding Descriptor.

The stability and some characteristic bonding features of a variety of ligand (L)-stabilized phosphinidene complexes derived from adduct formation with halides, and both anionic or neutral O-donor bases were explored. Furthermore, the main features of L → P pnictogen bonding in such adducts were studied not only by using geometric criteria such as L-P bond distances and pyramidalization or planarity at P but also by turning the spotlight on bond-strength-related (including atoms-in-molecules-derived) parameters, thermodynamic stability dependence with electronic characteristics of the free ligand, and dative-bonding participation. We propose the new descriptor, τ, which, together with the sign and magnitude of ∇ρ at the bond critical point, constitutes the required criteria to differentiate L-P linkages as van der Waals interactions, dative bonding, or mostly covalent bonds.