An Intriguing Structural and Functional Analogy Between Large Cations and Anion-Centered (X2−Mn+) Clusters Exemplifiedby Double Chalcogenides K, Rb, Cs, TI(I) and Ag(I), Cu(I)

The structures of chalcogenides where some large S 2− , Se 2− , Te 2− anions are closely surrounded by 6–12 Cu + or Ag + cations in 3–4 coordination are considered. These compact (X 2− M n + ) groups, being the anion-centered clusters (ACCs), can be thought as highly charged voluminous analogues of large K, Rb, T1 (I) , Cs cations. Together they perform related structural functions.