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.