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.