Coating two-dimensional (2D) materials with molecules bearing tunable properties imparts their surfaces with functionalities for applications in sensing, nanoelectronics, nanofabrication, and electrochemistry. Here, we report a method for the site-selective surface functionalization of 2D superatomic Re₆Se₈Cl₂ monolayers. First, we activate bulk layered Re₆Se₈Cl₂ by intercalating lithium and then exfoliate the intercalation compound Li₂Re₆Se₈Cl₂ in N-methylformamide (NMF). Heating the resulting solution eliminates LiCl to produce monolayer Re₆Se₈(NMF)_2−x (x ~ 0.4) as high-quality nanosheets. The unpaired electrons on each cluster in Re₆Se₈(NMF)_2−x enable covalent surface functionalization through radical-based chemistry. We demonstrate this to produce four previously unknown surface-functionalized 2D superatomic materials: Re₆Se₈I₂, Re₆Se₈(SPh)₂, Re₆Se₈(SPhNH₂)₂, and Re₆Se₈(SC₁₆H₃₃)₂. Transmission electron microscopy, chemical analysis, and vibrational spectroscopy reveal that the in-plane structure of the 2D Re₆Se₈ material is preserved through surface functionalization. We find that the incoming groups control the density of vacancy defects and the solubility of the 2D material. This approach will find utility in installing a broad array of chemical functionalities on the surface of 2D superatomic materials as a means to systematically tune their physical properties, chemical reactivity, and solution processability.

Colin Nuckolls

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