Mechanistic Insights into ZIF-8 Encapsulation of Atom-Precise Pt(M) Carbonyl Clusters

Precisely designing metal nanoparticles (NPs) is the cornerstone for maximizing their efficiency in applications like catalysis or sensor technology. Metal-organic frameworks (MOFs) with their defined and tunable pore systems provide a confined space to host and stabilize small metal NPs. In this work, the MOF encapsulation of various atom-precise clusters following the bottle-around-ship approach is investigated, providing general insights into the scaffolding mechanism. Eleven carbonyl-stabilized Pt(M) (M = Co, Ni, Fe, and Sn) clusters are employed for the encapsulation in the zeolitic imidazolate framework (ZIF)-8. Infrared and UV/Vis spectroscopy, density functional theory, and ab initio molecular dynamics revealed structure-encapsulation relationship guidelines. Thereby, cluster polarization, size, and composition were found to condition the scaffolding behavior. Encaging of [NBnMe₃]₂[Co₈Pt₄C₂(CO)₂₄] (Co₈Pt₄) is thus achieved as the first MOF-encapsulated bimetallic carbonyl cluster, Co₈Pt₄@ZIF-8, and is fully characterized including X-ray absorption near edge and extended X-ray absorption spectroscopy. ZIF-8 confinement not only promotes property changes, like the T-dependent magnetism, but it also further allows heat-induced ligand-stripping without altering the cluster size, enabling the synthesis of naked, heterometallic, close to atom-precise clusters.