Planar pentacoordinate carbons in CBe₅ ^4- derivatives

The potential energy surfaces of a series of clusters with formula CBe₅Li_n ^n-4 (n = 1 to 5) have been systematically explored. Our computations show that the lithium cations preserve the CBe₅ ^4- pentagon, such that the global minimum structure for these series of clusters has a planar pentacoordinate carbon (ppC) atom. The systems are primarily connected via a network of multicenter σ-bonds, in which the C atom acts as σ-acceptor and this acceptance of charge is balanced by the donation of the 2p_z electrons to the π-cloud. The induced magnetic field analysis suggests that the clusters with formula CBe₅Li_n ^n-4 (n = 1 to 5) are fully delocalized. The fact that these ppC-containing clusters are the lowest-energy forms on the corresponding potential energy surfaces raises expectations that these species can be prepared experimentally in the gas phase.