Carbon, nitrogen, and oxygen hypercoordination in half-sandwich and sandwich structures

The structures and stabilities of a number of neutral and charged half-sandwich (pyramidal) and sandwich compounds, which obey the electron octet rule and contain hypercoordinate carbon, nitrogen, and oxygen atoms, were studied by ab initio MP2(full)/6-311 +G** and density functional B3LYP/6-31 I +G** methods. Introduction of lithium counterions or bridging hydrogen atoms can provide an additional stabilization of non-classical systems with hypercoordinate centers.