Cubic gyroid frameworks in mesostructured metal selenides created from tetrahedral Zn2+, Cd2+, and In3+ ions and the [SbSe4]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 Ia (3) over bard 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 [Sb(III)Se(3)](3-) species at the expense of precursor [Sb(V)Se(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.