Landis et al. claim in their comment that Ca does not bind like a transition metal in Ca(CO)8. We reject their statement, which is based on a misconception of bonding models and misleading application and interpretation of quantum chemical methods for analyzing chemical bonds.
The application of quantum-chemical methods to both organic and transition-metal mixed-valence systems is reviewed, with particular emphasis on how to describe correctly delocalisation vs. localisation near the borderline between Robin–Day classes II and III.
Molecules which possess chemical bonds where a bare group-14 atom C–Pb is bonded to σ-donor ligands L or to a transition metal fragment [TM] through donor–acceptor interactions are discussed together with an analysis of the bonding situation with modern quantum chemical methods.
Response to Comment on “Observation of alkaline earth complexes M(CO)8 (M = Ca, Sr, or Ba) that mimic transition metals”