Electrospray ionization mass spectrometry shows arylstibonic acids, p-XC₆H₄SbO₃H₂ (X = methyl, nitro, or chloro), and 1-naphthylstibonic acid exist in MeCN as dodecanuclear aggregates [H₈(RSb)₁₂O₂₈]. With KOH or NaOH these form polyoxometalate ions [M₂H₈(RSb)₁₂O₃₀]²⁻ (M = K or Na) with a hexagonal antiprismatic array of the Sb atoms, as shown by X-ray crystallographic structures for three new examples. There is one firmly encapsulated 10-coordinate M⁺ ion within an inorganic 12-crown-6 moiety {Sb₆O₆} in the hexagonal channel and one six-coordinate M⁺.