Counterion-assisted shaping of nanocluster supracrystals.

Ag44 (p-MBA)30 (4-) (p-MBA=para-mercaptobenzoic acid) nanocluster (NC) supracrystals (SCs) with customizable shapes can be obtained by simply altering the type and concentration of the counterions of the p-MBA ligands in the dimethylsulfoxide (DMSO)/water crystallization system. Changing the counterion of the p-MBA ligand from H(+) to Cs(+) eliminates the directional hydrogen bonds in the SCs, resulting in the packing of deprotonated Ag44 (p-MBA)30 (4-) NCs into octahedral SCs, which is in stark contrast to the rhombohedral SCs that were formed by the packing of protonated Ag44 (p-MBA)30 (4-) NCs in previous studies. Furthermore, the double layer of deprotonated Ag44 (p-MBA)30 (4-) NCs is sensitive to charge screening induced by increasing the Cs(+) concentration, thereby providing a means to regulate the precipitation kinetics of the Ag44 (p-MBA)30 (4-) NCs for SC shape engineering. Slow precipitation kinetics was found to favor over-growth at the corners and edges of the octahedral SC nuclei, shaping the SCs into concave octahedra.