Aromaticity of the bare osmium trimers and the bindings to group IA/IIA all-metal series

The molecular structures, stabilities, and electronic properties of the bare and complex (with group IA/IIA metals) Os32+/0/2− clusters have been investigated systematically using the density-functional theory (DFT) B3LYP method. It is found that the non-linear structures in their heptet states are energetically favored for these bare and complex osmium trimers, i.e. (7A′, Cs), (7A2, C2v) and (7A″, Cs) for bare Os32+/0/2− respectively, and as (7A′, Cs) and (7B1, 7B2, C2v) for isoelectronic (as compared to Os32−) pyramidal Os3M−/0 and bipyramidal Os3M20/2+ (M = Li, Na, K and Be, Mg, Ca) complexes. The detailed molecular orbital (MO) were analyzed. The ground-states of bare Os32+/0/2− clusters were observed to possess the multiple (partial σ- and partial δ-) aromaticity. The Os32− motif structure was perfectly preserved in these pyramidal and bipyramidal all-metal complexes, which also possess corresponding d-orbital aromatic character.