Metal-centered monocyclic carbon wheel clusters with record coordination numbers in planar species.

The highest coordination number identified to date in planar species is CN = 10 in metal-centered monocyclic boron wheel clusters M©B (M = Ta and Nb) (Galeev , , 2012, , 2101). Extensive global minimum searches and first-principles theory calculations performed herein indicate that the experimentally observed LaC and LaC possess the well-defined global minima of perfect metal-centered monocyclic carbon wheel La©C (1) and slightly off-centered La©C (4) (A) with record coordination numbers of CN = 13 and 11 in planar structures, respectively, further pushing the boundary of our understanding of chemical structures and bonding. Detailed molecular orbital, nucleus-independent chemical shift, and ring current analyses indicate that La©C (1) is σ + π dually aromatic in nature, with 14 totally delocalized in-plane σ electrons and 14 totally delocalized out-of-plane π electrons each matching the 4 + 2 aromatic rule ( = = 3). Similar σ + π dually aromatic metal-centered monocyclic wheel clusters Ca©C (2), Ac©C (3), Y©BC (5), and Sc©BC (6) have also been obtained with CN = 13, 13, 12, and 11, respectively. The results obtained in this work effectively enrich the chemical structures and bonding patterns of planar hypercoordinated complexes.