Observation of Aromatic Three-Membered Rings in Ge3C and Ge3O via Photoelectron Spectroscopy and Theoretical Calculations.

The structures and chemical bonding of Ge3C- and Ge3O- as well as their neutrals are explored with anion photoelectron spectroscopy and theoretical calculations. The vertical detachment energies of Ge3C- and Ge3O- are measured to be 1.51 ± 0.04 and 2.00 ± 0.04 eV, respectively. It is found that Ge3C-/0 have a C2v symmetric planar structure with the C atom interacting with three Ge atoms. Ge3O-/0 have the O atom interacting with two Ge atoms of the triangular Ge3 unit. Ge3O- has a Cs symmetric nonplanar structure, while Ge3O has a C2v symmetric planar structure. Theoretical results show that the multiconfigurational effects in Ge3C-/0 and Ge3O-/0 are insignificant. Chemical bonding analyses reveal that there exist the C-Ge3 π⊥ orbital interaction and two π aromatic Ge2C units in Ge3C. There are O-Ge3 π⊥ orbital interaction and one doubly aromatic Ge3 unit in Ge3O, but the π⊥ orbital interaction is relatively weak.