New Molecular Geometries with Pentagonal-Pyramidal Structure

In this work, we propose the design of molecular ions that present the same structure as the benzene dication, which has a pentagonal-pyramidal geometry. The chosen systems were obtained by replacing atoms or functional groups in C₆H₆ ²⁺ to form other species with eight valence electrons. They are C₅H₆Si²⁺, C₅H₅N²⁺, C₅H₅P²⁺, C₅H₆B⁺, and C₅H₆Al⁺. Applying a global minimum (GM) search combined with DFT computations, we were able to obtain GM candidates for all of the cases. Except for the pyridine dication, all GM candidates for the ions exhibit a pentagonal-pyramidal geometry, indicating that eight valence electrons stabilize systems with penta- or hexacoordinated main group elements, completely analogous to the benzene case. Based on the analysis of our results, we encourage the experimental realization and laboratory detection of the phosphorine dication in a similar way to the original work on the detection of the low-energy isomers of benzene dications.