Abstract
The CNDO (complete neglect of differential overlap) method is used for calculation of the physico-chemical characteristics of faujasites with CrII, CrIII, CrV and CrVI ions in the SII cation position, modelled by Si3Al3O6(OH)12Cr clusters. It is demonstrated that the Cr ions are bonded to the zeolite skeleton by electron donor–acceptor bonds whose formation leads to electron donation from the skeleton to the cation, thus stabilizing the valence states of the Cr ions. The most probable valence state of the Cr ions in the zeolites was found to be CrIII; however, it can readily be oxidized to CrV. In contrast, CrVI and CrV ions were found to exhibit high electron-acceptor ability and thus are readily reduced.
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