Near size-monodisperse silver nanocrystals stabilized by chemisorption of a mixture of an alkane thiol (85%) and an alkane thiol incorporating a dibenzo-24-crown-8 moiety (15%) have been prepared. Using dynamic light scattering and nuclear magnetic resonance, it is shown that addition of bis-dibcnzylammonium dication initiates aggregation of the silver nanocrystal dispersion by pseudorotaxane assembly. It is also shown that addition of excess dibenzylammonium cation or dibenzo-24-crown-8 inhibits further aggregation. This novel demonstration of controlled nanocrystal aggregation points the way toward the programmed assembly of complex nanocrystal architectures in solution.