Reduction-Controlled Tunable Synthesis of Covellite (CuS) Nanoparticles from Water-Soluble Single-Source Precursors

The single source precursor (SSP) approach has been extensively used in preparing technologically important covellite (CuS) nanoparticles (NPs) for its high atom-efficiency and facile control over NPs. However, current SSPs often require time-consuming decomposition in organic solvents at temperatures typically above 100°C. Here, we propose amino acid-derived copper(II)-dithiocarbamate (DTC) complexes, as water-soluble SSPs for low-temperature hydrothermal decomposition. We demonstrate that Cu(II)-DTCs follow a reduction-mediated molecular decomposition pathway to CuS, with the Cu(I) intermediates, Cu(I)-DTCs, isolated and confirmed via formation of crystallographically-characterized phosphine adducts. The Cu(II)-Cu(I) reduction occurs via the intramolecular ligand-to-metal charge-transfer (LMCT), which proves rate-limiting in the decomposition and sensitive to changes in pH and ligand metalation. Tuning the rate of intramolecular LMCT and concomitant formation of Cu(I)-DTC species by varying pH and metalation, monitored by UV-vis spectroscopy, allows the formation rate of molecular building blocks to be controlled, in turn controlling nucleation and growth of NPs. Thus, the same copper-ligand combinations can be utilized to generate a wide range of size-shape tunable CuS NPs (ca. 10-150 nm) cost-effectively and sustainably. These results not only highlight the synthetic utility of this approach but also provide mechanistic insights into the poorly defined molecules-to-materials transformation.