Morphological Programming in Gold(III) Coordination Assemblies via pH-Modulated Noncovalent Hierarchy

Gold-centered self-assemblies exhibit unique structures, physicochemical and pharmacokinetic properties, which are widely explored for the applications of catalysis, analytic devices, optical devices, and biomedicines. Most of these materials are based on gold nanoparticles (AuNPs) and gold nanoclusters (AuNCs). However, the use of Au(III) complexes as building blocks for functionally tailored self-assembled architectures remains underexplored. Herein, we develop a facile self-assembly strategy using gold-nicotinamide complex as a building block to construct uniform nanospheres. Remarkably, these nanoparticles can undergo reversible disassembly and reassembly to give cubic nanoparticles upon pH stimulation via alkaline or acidic additions. Through systematic experimental and theoretical calculations, we identified the driving force and rules for these behaviors: the primary building blocks were formed via metal coordination between Au and nicotinamide, which further self-organized into uniform spherical nanoparticles through noncovalent interactions (π-π stacking and hydrogen-bonding N-H···O═C between amide groups). The mechanistic insights reveal that pH-mediated changes alter the balance of these interactions, enabling morphological switching. This work establishes valuable design principles for stimuli-responsive organometallic nanomaterials and highlights the critical role of ligand architecture in controlling self-assembly behaviors.