A Comparative Theoretical Investigation of Three Sodalite Systems: Cd4S(AlO2)6, Zn4O(BO2)6 and Zn4S(BO2)6

Periodic density functional calculations on three sodalites [Cd4S(AlO2)6, Zn4O(BO2)6, and Zn4S(BO2)6] were performed. Lowest-energy allowed electronic transitions were always found to be localized on the M4X (M = Cd, Zn; X = O, S) clusters encapsulated into lattice cages. Predicted excitation energies were only slightly affected by the adopted exchange correlation energy functional. A comparison between the optical behavior of Cd4S(AlO2)6, Zn4O(BO2)6, and Zn4S(BO2)6 and that of a series of polynuclear clusters ([Cd4(μ4-S){μ-S2As(CH3)2}6], [Zn4(μ4-O){μ-O2CCH3}6], [Zn4(μ4-O){μ-O2CNEt2}6], and [Zn4(μ4-S){μ-S2P(OC2H5)2}6]) indicates that only complexes with a central S atom reasonably mimic the electronic properties of the sodalite analogues. This is due to the higher energy of S 3p with respect to O 2p atomic orbitals, which causes a separation of the cluster states from the cage states.