Structural insights into T2-cluster-containing chalcogenides with vertex-, edge- and face-sharing connection modes of NaQ6 ligands: Na3ZnMIIIQ4 (MIII = In, Ga; Q = S, Se)
A series of quaternary chalcogenides, Na3ZnMIIIQ4 (MIII = In, Ga; Q = S, Se), were successfully synthesized for the first time through a high temperature solid-state reaction method. All of them exhibit similar structures and crystallize in the I41/acd space group of the tetragonal system. In their structures, typical super-tetrahedron (T2-type) clusters composed of four vertex-sharing (Zn/MIII)S4 tetrahedra are discovered and these T2-clusters further link together to form interesting wavelike chains. Adjacent T2 clusters present a torsion angle of 24.6° with each other when viewed along the c-axis, which has rarely been found among all the reported T2-containing chalcogenides. Moreover, we have systematically investigated the connection modes of NaSn (n = 4–6) in all the known Na-contained quaternary sulfides, and the result shows that the connection modes (corner-, edge-, and face-sharing) of NaS6 ligands in the title sulfides are also rarely (only 3%) found. Besides, the optical properties including diffuse-reflection and Raman spectra are systematically characterized. Theoretical calculations based on the first principles theory were also used to analyze their structure–performance relationships.