Theoretical studies on novel main group metallocene-like complexes involving planar hexacoordinate carbon η⁶-B₆C ^2- ligand

The geometric structures for a novel series of main group 1 and 2 metal atom complexes with planar hexacoordinate carbon dianion (η⁶- B₆C)2- ligand, involving metallocene-like, K[(η⁶- B₆C)_n(η⁶-B₆C)K (n= 1-3) and (η⁶-B₆C)Ca]_n (n⁶ - B ₆C)^2- (n = 1, 2), as well as relative pyramidal [(η⁶-B₆C)M]^i- (M = Na, K, and CaCl, i = 1; M = Ca, i = 0) and bipyramidal (η⁶-B₆C)(CaCl) ₂, have been optimized to be the local minima on the corresponding potential hypersurfaces at the B3LYP/6-311+G(d) level of theory. Natural bond orbital analysis indicates that the electrostatic interaction between the metal ions and the planar hexacoordinate carbon B₆C^2- rings plays a crucial role in stabilizing these highly symmetrical complexes. The π - d interaction in Ca-containing complexes also plays an important role in the stabilization of these molecules. It is found that the Ca²⁺ cation could be considered the best candidate for (η⁶-B ₆C)^2- to build ionic organometallic compounds. In these predicted multideck metallocene-like complexes there exist similarities in many structural properties, such as geometry parameters, Wiberg bond indices, natural atomic charges, atomic electronic configurations, and frontier orbital energies, as well as increments of the dissociation energy (to -[(η⁶-B₆C)Ca]- units and metal cations) for adding one -[(η⁶-B₆C)Ca]- unit and so on, which suggests that the -[(η⁶-B₆C)Ca]- unit could be used as a building block to construct more K[(η⁶-B₆C)Ca] _n(η⁶-B₆C)K chain-type metallocene-like complexes along their sixfold molecular axis.