From large 3D assembly to highly dispersed spherical assembly: weak and strong coordination mediated self-aggregation of Au colloids

Distinctly different 3D assemblies of similar to 1.6 nm Au nanoparticles are constructed based on weak and strong coordination strategies. Reduction of KAuCl4 with NaBH4 in the presence of newly-synthesized 4-(4-phenylmethanethiol)- 2,2': 6',2 ''-terpyridine ( 1) yields functionalized Au nanoparticles which assemble in situ into large 3D aggregates via weak coordination between alkali metal ions and terpyridine attached to separated particles. These assemblies are disassembled into individual nanoparticles via addition of DMF solvent and further reassembled into highly dispersed 3D spherical nanostructures via addition of Co2+ ( strong coordination with 1). Wide and small angle XRD measurements show that the assemblies are formed from small Au nanoparticles, consistent with TEM results. It is significant that the large aggregates formed in situ can be directly transformed into nearly monodispersed 3D spherical assemblies via strong coordination ( with Co2+), presenting the first example of a direct transformation of one 3D nanonetwork into another distinctly different 3D nanonetwork. The controlled assembly and disassembly processes are accompanied by distinct shifts in the surface plasmon resonance.