Chemisorption of ethylene on Si5+ cluster ions. A theoretical study

The chemisorption of ethylene on Si5+ clusters is investigated using MP2/6-31G*, higher-order correlation and DFT methods. Eight different approaches of C2H4 to the quasi bipyramidal Si5+ lead to a number of stable σ and π-adducts. It is shown that approach to the most stable σ-adduct (C2H4 di-σ bonded to Si5+) occurs without or only with a low barrier. The Si5+–C2H4 binding energy, calculated to be 1.7 eV, is in reasonably good agreement with experimentally estimated values of 1.8–2.0 eV. This explains the experimentally observed high reactivity of Si5+ compared to other silicon clusters, in particular to the less reactive Si4+.