Ternary hybrid nanoparticle isomers: Directing the nucleation of Ag on Pt-Fe₃O₄ using a solid-state protecting group

Colloidal hybrid nanoparticles are an important class of materials that incorporate multiple nanoparticles into a single system through solid-state interfaces, which can result in multifunctionality and the emergence of synergistic properties not found in the individual components. These hybrid structures are typically produced using seeded-growth methods, where preformed nanoparticles serve as seeds onto which additional domains are added through subsequent reactions. For hybrid nanoparticles that contain more than two domains, multiple configurations with distinct connectivities and functionalities are possible, and these can be considered as nanoparticle analogues of molecular isomers. However, accessing one isomer relative to others in the same hybrid nanoparticle system is challenging, particularly when the formation of a target isomer is disfavored relative to more stable or synthetically accessible configurations. Here, we show that an iron oxide shell installed onto the Pt domain of Pt-Fe₃O₄ hybrid nanoparticles serves as a solid-state protecting group that can direct the nucleation of a third domain to an otherwise disfavored site. Under traditional conditions, Ag nucleates exclusively onto the Pt domain of Pt-Fe ₃O₄ heterodimers, resulting in the formation of the Ag-Pt-Fe₃O₄ heterotrimer isomer. When the Pt surface is covered with an iron oxide protecting group, the nucleation of Ag is redirected onto the Fe₃O₄ domain, producing the distinct and otherwise inaccessible Pt-Fe₃O₄-Ag isomer. Similar results are obtained for the Au-Pt-Fe₃O₄ system, where formation of the favored Au-Pt-Fe₃O₄ configuration is blocked by the iron oxide protecting group. The thickness of the iron oxide shell that protects the Pt domain can be systematically tuned by adjusting the ratio of oleic acid to iron pentacarbonyl during the synthesis of the Pt-Fe ₃O₄ heterodimers, and this insight is important for controllably implementing the protecting group chemistry.