Preparation and characterization of chemically bonded argon-boroxol ring cation complexes.

The cation complexes [ArB3O4](+), [ArB3O5](+), [ArB4O6](+) and [ArB5O7](+) were prepared via a laser vaporization supersonic ion source in the gas phase. Their vibrational spectra were measured via mass-selected infrared photodissociation spectroscopy. Spectroscopy combined with quantum chemical calculations revealed that the [ArB3O5](+), [ArB4O6](+) and [ArB5O7](+) cation complexes have planar structures each involving an aromatic boroxol ring and an argon-boron covalent bond. In contrast, the [ArB3O4](+) cation is characterized to be a weakly bound complex with a B3O4(+) chain structure.