MH50/+/-: σ Aromatic Cluster

Abstract

Aromaticity is one of the central concepts in chemistry. Herein, quantum chemical calculations have been carried out to search for σ aromatic metal pentahydrides of the general formula MH₅^- (M = Ni, Pd, Pt). All these group 10 metals form true local minimum in their planar D_5h symmetry. The presence of σ aromaticity in these clusters were ascertained from molecular orbital, electron density of delocalized bonds (EDDB) and iso-chemical shielding surface (ICSS_ZZ) analyses. Detailed potential energy surface analyses reveal that D_5h geometry of PtH₅^- is the lowest energy one while NiH₅^- and PdH₅^- clusters form stable C_2V dihydrogen M(η²-H₂)H₃ complexes. Similarly, M(η²-H₂)H₃ geometry is the lowest energy one for AuH₅ cluster. However, D_5h geometry of CsH₅ and BaH₅⁺ is the lowest one with aromatic character.