Quantum Theory of Atoms in Molecules (QTAIM) computations applied to the experimental geometry of the compounds depicted in Figures 1 and 2 show the existence of weak bond critical points of noncovalent type between the uncoordinated nitrogen atom of the formamidinate (N3) and a carbonyl ligand (and the bipyridine ligand as well) of the complex <i>fac</i>-[Mn(PhN=C(H)NPh)bipy(CO)<sub>3</sub>] (Complex 1), which appears to be an isolable intermediate species that precedes the formation of metallacyclic complexes (Complex 2). These two stabilizing intramolecular noncovalent interactions may be viewed as a combination of electrostatics (π-hole interaction) and n → π* donor-acceptor interaction, which has been confirmed by calculating not only local and integral topological properties whithin the framework of the QTAIM theory (e.g. delocalization indexes and atomic charges) but also using other computational tools, such as the Source Function and the Electron Localization Function, among others. For instance, the N3-C4 bond in complex 1 shows properties basically identical to the ones shown by the N3-C20 bond in the same complex, which are very different to those of a typical covalent bond between non-metal atoms, just like the ones exhibited by N3-C2 and N1-C2 bonds (as well as many others) in the metallacycle complex 2. Moreover, when using DFT theoretically optimized geometries previous to QTAIM calculations (i.e. gas phase), no such non-covalent interactions are found, giving a metallacycle instead of complex 1, which is rather similar to the one found for complex 2; in particular, with a N3-C4 typical covalent bond.

Non-covalent interactions in carbonyl complexes of Mn: Theoretical QTAIM study

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.