A Complete Macroion−“Blackberry” Assembly−Macroion Transition with Continuously Adjustable Assembly Sizes in {Mo132} Water/Acetone Systems

Abstract

A complete, continuous transition from discrete macroions to blackberry structures, and then back to discrete macroions, is reported for the first time in the system of {Mo₁₃₂}/water/acetone, with {Mo₁₃₂} (full formula (NH₄)₄₂[Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]·ca.300H₂O·ca.10CH₃COONH₄) as the C₆₀-like anionic polyoxomolybdate molecular clusters. Laser light scattering studies reveal the presence of the self-assembled {Mo₁₃₂} blackberry structures in water/acetone mixed solvents containing 3 vol % to 70 vol % acetone, with the average hydrodynamic radius (R_h) of blackberries ranging from 45 to 100 nm with increasing acetone content. Only discrete {Mo₁₃₂} clusters are found in solutions containing 70 vol % acetone. The complete discrete macroion (cluster)−blackberry−discrete macroion transition helps to identify the driving forces behind the blackberry formation, a new type of self-assembly process. The charge density on the macroions is found to greatly affect the blackberry formation and dissociation, as the counterion association is very dominant around blackberries. The transitions between single {Mo₁₃₂} clusters and blackberries, and between the blackberries with different sizes, are achieved by only changing the solvent quality.