Transformation of K₂Sb₈Q₁₃and KSb₅Q₈Bulk Crystals to Sb₂Q₃(Q = S, Se) Nanofibers by Acid-Base Solution Chemistry

The ability to manipulate crystal structures using kinetic control is of broad interest because it enables the design of materials with structures, compositions, and morphologies that may otherwise be unattainable. Herein, we report the low-temperature structural transformation of bulk inorganic crystals driven by hard-soft acid-base (HSAB) chemistry. We show that the three-dimensional framework K₂Sb₈Q₁₃and layered KSb₅Q₈(Q = S, Se, and Se/S solid solutions) compounds transform to one-dimensional Sb₂Q₃nano/microfibers in N₂H₄·H₂O solution by releasing Q^2-and K⁺ions. At 100 °C and ambient pressure, a transformation process takes place that leads to significant structural changes in the materials, including the formation and breakage of covalent bonds between Sb and Q. Despite the insolubility of the starting crystals in N₂H₄·H₂O under the given conditions, the mechanism of this transformation can be rationalized by applying the HSAB principle. By adjusting factors such as the reactants' acid/base properties, temperature, and pressure, the process can be controlled, allowing for the achievement of a wide range of optical band gaps (ranging from 1.14 to 1.59 eV) while maintaining the solid solution nature of the anion sublattice in the Sb₂Q₃nanofibers.