D3hX3Li3+ (X = C, Si and Ge): Superalkali cations containing three planar tetracoordinate X atoms

Abstract A new class of superalkali cations X 3 Li 3 + (X = C, Si and Ge) containing three planar tetracoordinate X atom have been characterized using ab initio methods. These perfect planar high-symmetric ( D 3 h ) species are the global minimum of the systems based on extensive stochastic structural searches, followed by high level quantum chemistry calculations. The vertical electron affinities (VEAs) of the X 3 Li 3 + cations range from 2.88 to 3.02 eV at OVGF//MP2/6-311+G(3df) level, which are lower than 3.89 eV of Cs atom. Thus, they represent the first series of superalkali cations with three ptX (X = C, Si and Ge) atoms. Bonding analyses reveal that there are mainly ionic bonds between X and Li atoms, while there are covalent bonds between X atoms. AdNDP, NICS analyses indicate that X 3 Li 3 + (X = C, Si and Ge) cations are π aromatic with two delocalized π electrons. Large HOMO–LUMO energy gaps 7.62–10.41 eV further support their thermodynamic stability. Born–Oppenheimer molecular dynamics (BOMD) investigations indicate that the structures of these ptX species are well maintained during 20 ps simulations. The current results may motivate theoretical and experimental studies on novel ptX (X = C, Si and Ge) complexes as well as superalkali species.