Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The CNDO/2 method was used for a physico-chemical characterization of faujasite zeolites, modelled by T₆O₆(OH)₁₂ clusters containing Ni⁺, Ni²⁺, Ni(OH)⁺, Co²⁺, Co³⁺, Co(OH)⁺ cations localized in the S_II and S_I' cationic positions. It is shown that the cations are bound preferentially to the oxygen atoms of the zeolite skeleton by a strong electron donor-acceptor bond. As the consequence of the bond formation, the electron charge is significantly shifted from a skeleton to the cation. The charge densities calculated on the cations (Ni⁺ ~ 0.3, Ni²⁺ ~ 0.35, Co²⁺ ~ 0.4, Co³⁺ ~ 1.1 respectively) show that with uni- and bivalent cations the positive charge is in main part compensated by donation of electrons from the skeleton, while with trivalent cations the compensation is only partial. The Ni⁺ cation possesses significant electron donor properties whereas the Co³⁺ cation has a strong electron acceptor character. For both cations bivalency appears to be the most stable valent state. Both studied cations show great affinity to hydratation, however, their corresponding hydroxyl adducts - the Ni(OH)⁺ and Co(OH)⁺ cations exhibit substantially less acid properties, compared with the hydroxyl groups of the skeleton.