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, Na(3)ZnM(III)Q(4) (M-III = 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 I4(1)/acd space group of the tetragonal system. In their structures, typical super-tetrahedron (T-2-type) clusters composed of four vertex-sharing (Zn/M-III)S-4 tetrahedra are discovered and these T-2-clusters further link together to form interesting wavelike chains. Adjacent T-2 clusters present a torsion angle of 24.6 degrees with each other when viewed along the c-axis, which has rarely been found among all the reported T-2-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.