Photoelectron Spectroscopy and Theoretical Studies of Ge₆MnO^– Cluster with a Mn^V≡O Unit Interacting with a Double Aromatic Ge₆^4– Ligand

The structures and chemical bonding of Ge₆MnO^– are investigated using anion photoelectron spectroscopy and theoretical calculations. The lowest energy structure of Ge₆MnO^– is found to have a C_5v symmetric structure with an O atom attached to a pentagonal bipyramidal MnGe₆. Chemical bonding analyses reveal that Ge₆MnO^– can be considered as a [Mn^VO]³⁺[Ge₆^4–] complex with two unpaired 3d electrons on Mn. The Ge₆^4– ligand is highly stable in Ge₆MnO^– and exhibits double aromaticity with 10 delocalized σ electrons and 6 delocalized π electrons. Our calculations show that the Ge₆^4– ligand could also form [Cr^IVO]²⁺[Ge₆^4–] in Na₂Ge₆CrO and [Fe^IVO]²⁺[Ge₆^4–] in Na₂Ge₆FeO. The results suggest the possibility of designing and synthesizing a series of stable high-valent metal oxide anionic species with the composition [MO]ⁿ⁺[Ge₆^4–] in the gas phase or in the salt-stabilized bulk solid materials.