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 ([Cd-4(mu(4)-S){mu-S-2-As(CH3)(2)}(6)], [Zn-4(mu(4)-O){mu-O2CCH3}(6)], [Zn-4(mu(4)-O){mu-O2CNEt2}(6)], and [Zn-4(mu(4)-S){mu-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.