Bimetallic Bismuth-Based Nanoparticles From Pseudo-Tetrahedral Zintl Anions

While Zintl compounds comprising Bi-based anions of p-block elements have been used as starting materials for larger bismuth-based clusters, their potential to form nanoparticles has not yet been explored. Here, bimetallic nanoparticles are synthesized from the oxidation of bismuth-based pseudo-tetrahedral Zintl anions (InBi₃)^2-, (Sn₂Bi₂)^2-, (TlBi₃)^2-, and (Pb₂Bi₂)^2-. The anions rapidly oxidize at ambient conditions to form metallic seeds, with the mild oxidizing agent PVP (polyvinylpyrrolidone), which also serves as a stabilizing agent for nanoparticle growth. Each elemental combination behaves uniquely, resulting in bimetallic nanoparticles of varying forms (i.e., alloyed, core-shell, and Janus-type). The resulting nanoparticles show a relatively narrow size distribution with median diameters of ∼20-25 nm and exhibit ultraviolet (UV) absorption, with spectral features tunable by composition. The morphology and composition were analyzed by scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), micro-X-ray fluorescence spectroscopy (µ-XFS), powder X-ray diffraction (PXRD), synchrotron-based hard and soft X-ray photoelectron spectroscopy (HAXPES and PES), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). This approach demonstrates that binary Zintl anions can serve as versatile molecular precursors for designing heterometallic nanoparticles with controlled composition, morphology, and optical properties.