Cubic gyroid frameworks in mesostructured metal selenides created from tetrahedral Zn ²⁺, Cd ²⁺, and in ³⁺ ions and the [SbSe ₄] ^3- precursor

We describe a new group of well-organized cubic mesostructured metal chalcogenides. They were obtained from the assembly of the tetrahedral [SbSe ₄] ^3- unit and the linking metal ions In ³⁺, Zn ²⁺, and Cd ₂₊ 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 In ³⁺ 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 < E _g < 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 L ^III edge. We observe an evolution in the spectra that is consistent with an increased proportion of the reduced [SbmSe3]3~ species at the expense of precursor [Sb ^VSe ₄] ^3- as the Lewis acidity of the metal ions increases along the series Zn ²⁺, Cd ²⁺, and In ³⁺, and this is in agreement with the Raman spectroscopic results which are also reported.