Synthesis, structure, and optical properties of the quaternary diamond-like compounds I2-II-IV-VI4 (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se)

Three new diamond-like compounds, Cu2MgSiS4, Cu2MgGeS4, and Cu2MgSiSe4, have been synthesized. All the three compounds crystallize in the space group Pmn21 and all atoms are tetrahedrally coordinated.