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

ABSTRACT 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.