We report a valence state-controlled synthesis of vanadium oxide nanocrystalline particles via a non-hydrothermal process using an alcohol and an amine ligand. A non-stoichiometric V3O5 (V4+V3+ 2O5), which is known for its difficulty of formation due to the narrow allowances in the vanadium-to-oxygen ratio, was obtained for the first time as nanocrystals in the anosovite phasea rare phase discovered only recently in bulk form. The time course of the nanocrystal formation revealed a slow seeded growth process, separated from a subsequent fast growth via Ostwald ripening. We highlight the role of vanadium precursor-to-alcohol-to-ligand ratios in precisely controlling the reduction of V5+. Polyvalence of metals, particularly the unusual stability of vanadium(II)–(V), has been considered a negative factor in achieving the targeted oxidation state in nanocrystal syntheses. In the present system, the polyvalence allowed formations of different oxide nanocrystals in a parameter-controlled manner, including anosovite V3O5 (V4+ + 2V3+) and corundum V2O3 (V3+). Such control is unprecedented in metal oxide nanocrystal syntheses.

Gold(I) (Au(I))−thiolate complexes are widely believed as the precursors to Au nanoparticle formations. While the literature suggests that the Au(III)-to-thiol ligand stoichiometric ratio of 1:3 is required to reduce a Au(III) and yield a Au(I)−thiolate, other stoichiometric ratios are also known to produce Au nanoparticles upon reduction. Using the characteristic red luminescence of Au(I)-alkanethiolates, we examined the process of their formations and their implications on the Au nanoparticle synthesis in detail. The onset of the luminescence, correlated with the Au(I)−thiolate formation, as well as the kinetics of the luminophore formation were evaluated in terms of the Au(III)-to-alkanethiol ratios. The onset of the luminescence was affected significantly by the solvent polarity during reaction but not post reaction. We found that the kinetics of the luminophore formation can vary widely, requiring from minutes to 24 h for completion depending on the thiol ligands and molar ratios, as well as solvents. This information could help in designing Au nanoparticle syntheses with the logical choice of Au(III)-to-thiol ratio, solvent, and the timing of reduction.

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