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Nanoparticle syntheses are designed to produce thedesired product in high yield but traditionally neglect atom economy. Here we report that the simple, but significant, change of the solvent from 1-octadecene (1-ODE) to the operationally inert octadecane (ODA) permits an atom-economical synthesis of copper selenophosphate (Cu3PSe4) nanoparticles. This change eliminates the competing selenium (Se) delivery pathways from our first report that required an excess of Se. Instead Se0 powder is dispersed in ODA, which promotes a formal eight-electron transfer between Cu3−xP and Se0. Powder X-ray diffraction and transmission electron microscopy confirm the purity of the Cu3PSe4, while 1H and 13C NMR indicate the absence of oxidized ODA or Se species. We utilize the direct pathway to gain insights into stoichiometry and ligand identity using thermogravimetric analysis and X-ray photoelectron spectroscopy. Given the prevalence of 1- ODE in nanoparticle synthesis, this approach could be applied to other chalcogenide reaction pathways to improve stoichiometry and atom-economy. 

The family of copper antimony selenides is important for renewable energy applications. Several phases are accessible within narrow energy and compositional ranges, and tunability between phases is not well-established. Thus, this system provides a rich landscape to understand the phase transformations that occur in hot-injection nanoparticle syntheses. Rietveld refinements on X-ray diffraction patterns model anisotropic morphologies to obtain phase percentages. Reactions targeting the stoichiometry of CuSbSe2 formed Cu3SbSe3 before decomposing to thermodynamically stable CuSbSe2 over time. An amide base was added to balance cation reactivity and directly form CuSbSe2. Interestingly, Cu3SbSe3 remained present but converted to CuSbSe2 more rapidly. We propose that initial Cu3SbSe3 formation may be due to the selenium species not being reactive enough to balance the high reactivity of the copper complex. The unexpected effect of a base on cation reactivity in this system provides insight into the advantages and limitations for its use in other multivalent systems.