Quaternary supertetrahedra-layered telluride CsMnInTe3: why does this type of chalcogenide tilt?

Dark-red CsMnInTe3 is synthesized by a solid-state approach using CsCl as the reactive flux. This layered compound is constructed by T3 supertetrahedra and crystallizes in the space group C2/c with a = 12.400(7) A, b = 12.400(7) A, c = 24.32(2) A, β = 97.31(2)°, and V = 927.07(6) A3. The electrostatic interactions cause tilting of the supertetrahedra layers, and the value of the tilting angle is fixed by a structure index, β′ = 180° – arccos(a/4c). Such an index is valid for all of the members in this family known to date.