Cubic Gyroid Frameworks in Mesostructured Metal Selenides Created from Tetrahedral Zn²⁺, Cd²⁺, and In³⁺ Ions and the [SbSe₄]³^- Precursor

Abstract

We describe a new group of well-organized cubic mesostructured metal chalcogenides. They were obtained from the assembly of the tetrahedral [SbSe4]3- unit and the linking metal ions In3+, Zn2+, and Cd2+ in the presence of Cn (n = 12, 14, 16) pyridinium surfactants acting as structure-directing agents. The assembly of the cubic gyroid mesostructure is immediate upon mixing the reactants. The cubic structure, confirmed with X-ray diffraction and transmission electron microscopy, contains an infinitely extended M/Sb/Se network that defines a well-known periodic minimal surface known as the gyroid and possesses an Ia3̄d space group symmetry. The ion In3+ is a more versatile linking metal and can also form a hexagonal mesostructure by changing the surfactant concentration or carbon chain length. The pore−pore separations and pore sizes are a function of surfactant chain length in all cases. The cubic mesophases exhibit reversible ion-exchange properties, although the cubic symmetry cannot be retained. All mesophases are mid-gap semiconductor materials with 1.5 < Eg < 2.0 eV. The nature of the Sb/Se species in the structure was probed with X-ray absorption near edge structure (XANES) measurements at the Sb LIII edge. We observe an evolution in the spectra that is consistent with an increased proportion of the reduced [SbIIISe3]3- species at the expense of precursor [SbVSe4]3- as the Lewis acidity of the metal ions increases along the series Zn2+, Cd2+, and In3+, and this is in agreement with the Raman spectroscopic results which are also reported.