The interaction of nitrobenzene with the hydrate basal surface of montmorillonite: an ab initio study

The results of an ab initio Hartree–Fock study of the cluster molecular model mimicking the ditrigonal cavity of montmorillonite are reported. Full optimization of the geometry has been applied for the Si6Al6O30H18 cluster using the HF/6-31G(d) basis set. In order to obtain a model of the isomorphic substitution in the alumino oxygen layer of clay minerals, a magnesium atom has replaced one of the aluminium atoms of the alumino–oxygen layer in the cluster. To compensate for the negative charge which inevitably appears in this type of substitution, the Na+ exchangeable cation has been placed in the area with the most negative electrostatic potential in the basal plane of the cluster model. Finally, we have calculated the geometry and interaction energy for the adsorption complex which is formed by the interaction of nitrobenzene (the simplest nitroaromatic compound, having the chemical formula C6H5NO2) with the hydrated surface of clay minerals. The predicted BSSE corrected energy of the interaction is of the same order (11.8 kcal mol−1 at the B3LYP/6-31G(d)//HF/6-31G(d) level) as has been estimated for the adsorption of nitro-compounds interacting with full molecular contacts. We have concluded that this type of adsorption of nitro-compounds should be at least as effective as the adsorbtion which includes the donor–acceptor type of interactions with a nonhydrated silicon–oxygen surface.