degree of protonation of this cluster to give the cations [Bi6O5(OH)3]5+ and [Bi6O4(OH)4]6+. The former exists as water hydrogen-bonded dimers, while the more acidified compound is monomeric in the solid state. The same cationic unit is formed in the hydrolysis of bismuth perchlorate658,659 to give [Bi6O4- (OH)4](ClO4)6‚7H2O.660