Controlled Formation of Fused Metal Chalcogenide Nanoclusters Using Soft Landing of Gaseous Fragment Ions

The complete ligation of nanoclusters significantly reduces their chemical reactivity, catalytic activity, and charge transfer properties. Therefore, in applications, nanoclusters are activated through partial ligand removal to take advantage of their full potential. However, the precise control of ligand removal in the condensed phase is challenging. In this study, we examine the reactivity of well-defined activated nanoclusters on surfaces prepared through controlled ligand removal in the gas phase. To accomplish this, we utilized a specially designed ion soft-landing instrument equipped with a collision cell to prepare mass-selected fragment ions, which were then deposited onto self-assembled monolayer (SAM) surfaces. Specifically, we generated fragment ions by selectively removing one or two ligands from a series of atomically precise ligated metal sulfide clusters, Co₅MS₈(L₁)₆⁺ (M = Co, Mn, Fe, or Ni, L₁ = PEt₃). Removal of one ligand from Co₅MS₈(L₁)₆⁺ (M = Co, Mn, Ni) generates Co₅MS₈(L₁)₅⁺ species, which undergo selective dimerization on SAMs. Meanwhile, Co₅FeS₈(L₁)₅⁺ is unreactive and remains intact when it is deposited onto a SAM surface. In contrast, fragments formed by the removal of two ligands, Co₅MS₈(L₁)₄⁺, undergo several nonselective reactions and generate larger fused clusters. We found that the reactivity of the Co₅MS₈(L₁)₅⁺ fragment ions is correlated with the gas phase stability of the corresponding precursor ion toward ligand loss. Specifically, the relatively unstable precursor ion, Co₅FeS₈(L₁)₆⁺, generates the least reactive fragment. Meanwhile, the more stable precursor ions generate more reactive Co₅MS₈(L₁)₅⁺ fragments that dimerize on surfaces. This observation was also confirmed by co-deposition of fragment ions with two different ligands, Co₅MS₈(L₁)₅⁺ and Co₅MS₈(L₂)₅⁺ (L₁ = PEt₃ and L₂ = PEt₂Ph), where fragments generated from more stable precursor ions tend to dimerize and generate dimers with mixed ligands. This study unveils the previously unrecognized potential of fragment ions in generating compounds that are difficult to synthesize using conventional methods. Additionally, it provides a mechanistic understanding of the observed reactivity. Mass-selected deposition of well-defined fragment ions emerges as a powerful approach for designing materials by precisely activating and depositing undercoordinated ligated nanoclusters onto surfaces.