(C₅M_2-n)^n- (M = Li, Na, K, and n = 0, 1, 2). A New Family of Molecules Containing Planar Tetracoordinate Carbons

By highly correlated ab initio methods and DFT calculations, we have shown that alkaline metals can stabilize planar tetracoordinate carbon-containing molecules with the C(C₄) skeleton. This family of molecules is C₅M₂, where M is an alkaline metal. The stability of these compounds is rationalized in terms of the delocalization of the p-orbital perpendicular to the molecular plane, the global hardness, and the electrophilicity. The analysis of several molecular scalar fields shows that the bonding between the C₅^2- dianion and the metals is strongly ionic. The structures reported are the first examples with a planar tetracoordinate carbon, surrounded by carbon atoms, and stabilized, only, by electronic factors.