Binuclear Cu-Pyrazinylthiolate Molecular Precursor as a Gateway to Binary CuS and Ternary CuInS₂, Cu₂SnS₃, and CuSbS₂ Nanoparticles

Copper-based binary and ternary sulfides have attracted significant attention due to their excellent photophysical properties, making them highly promising for high-performance photovoltaic devices. This study focuses on the synthesis and structural characterization of an air-stable binuclear Cu-pyrazinethiolate-phosphine complex, which serves as an efficient single-source molecular precursor for the preparation of CuS nanoplatelets. Furthermore, the utility of this complex as a versatile molecular precursor for the preparation of copper-based ternary sulfides, such as CuInS2, Cu2SnS3, and CuSbS2, has been demonstrated. A plausible mechanism for the facile formation of these ternary materials is proposed based on the presence of disulfide (S–S) linkages in CuS. The crystal structure, phase purity, and compositions of the nanoparticles were confirmed using powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and area elemental mapping. Electron microscopic studies revealed the formation of a two-dimensional (2D) nanoplatelet morphology with varied shapes and sizes. Ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy showed a slight blue shift in the band gap of the nanoparticles compared to their bulk counterparts, which can be attributed to quantum confinement or surface lattice distortion effects. The band gap and the pristine nanoparticles were found to be blue-shifted compared to the bulk material. Prototype photoelectrochemical cells, fabricated using pristine nanoparticles, exhibit nice photocurrent generation along with optimum photoswitching, which poses them as suitable materials for clean-energy applications.