Supercrystal engineering of atomically precise gold nanoparticles promoted by surface dynamics

The controllable packing of functional nanoparticles (NPs) into crystalline lattices is of interest in the development of NP-based materials. Here we demonstrate that the size, morphology and symmetry of such supercrystals can be tailored by adjusting the surface dynamics of their constituent NPs. In the presence of excess tetraethylammonium cations, atomically precise [Au 25 (SR) 18 ] − NPs (where SR is a thiolate ligand) can be crystallized into micrometre-sized hexagonal rod-like supercrystals, rather than as face-centred-cubic superlattices otherwise. Experimental characterization supported by theoretical modelling shows that the rod-like crystals consist of polymeric chains in which Au 25 NPs are held together by a linear SR–[Au(I)–SR] 4 interparticle linker. This linker is formed by conjugation of two dynamically detached SR–[Au(I)–SR] 2 protecting motifs from adjacent Au 25 particles, and is stabilized by a combination of CH⋯ π and ion-pairing interactions between tetraethylammonium cations and SR ligands. The symmetry, morphology and size of the resulting supercrystals can be systematically tuned by changing the concentration and type of the tetraalkylammonium cations. Gold nanoparticles typically exhibit hard-sphere-like assembly behaviour, but now the size, morphology and symmetry of crystals of Au 25 nanoparticles have been tuned. The presence of excess tetraethylammonium cations has been shown to promote the one-dimensional assembly of the nanoparticles, which in turn form rod-like crystals, by stabilizing dynamically detached ligands from adjacent particles into interparticle linkers through CH⋯ π and ion-pairing interactions.