Light-induced access to a fluorescent Cd7Ag21 nanocluster from a halide-supported Cd8X nanocluster directed by a face-capping macrocyclic metalloligand

Abstract

Metalloligands with multiple preorganized binding sites provide unique advantages for modulating structural patterns and enhancing the surface stability of metal nanoclusters. However, the precise structure-directing effect of metalloligands in nanocluster transformation remains a missing puzzle piece. Herein, three nested concentric bitetrahedral Cd₈X nanoclusters were synthesized through a stepwise evolutionary pathway. These nano-sized architectures comprise tetrahedrally arranged tripodal Cd^II macrocyclic metalloligands encapsulating a halide-supported Cd₄ tetrahedron, and the template effect of halide ions on the stabilization of Cd₈X was dependent on their ionic size. Initiated by Ag^I, the released metalloligands from Cd₈Cl precisely direct the light-activated fabrication of a yellow-emissive 8e⁻ superatomic Cd₇Ag₂₁ nanocluster. Evidently, different carboxylate O-donor triads and tetrads from the metalloligands geometrically adaptively cap the surface Ag₃ triangles of the convex polyhedral kernel in Cd₇Ag₂₁, thus shaping and protecting the multi-silver kernel in the post-transformed nanocluster. Due to the labile coordination between the carboxylate-rich metalloligand and surface atoms of the Ag₂₀ kernel, the selective fluorescence quenching response of Cd₇Ag₂₁ towards cysteine (Cys) can be rationalized by a ligand replacement-cluster aggregation process. This study demonstrates the distinctive utility of the preformed tripodal metalloligand as a passivating agent, facilitating shape- and size-matching with the surface motifs of metal nanoclusters to induce structural transformation, thereby enabling the synthesis of novel nanocluster architectures.