Condensation reactions in silanol–water clusters

Two types of complexes were found in the 2H3SiOH+nH2O (n=1,2) systems by B3LYP and MP2 methods. Global energy minima correspond to cyclic structures and less stable open isomers, in which one hydrogen bond is eliminated, are higher in energy by 3–7 kcal/mol. The decrease in the stability of open structures due to the rupture of one hydrogen bond is partly compensated by a weak silicon–oxygen intermolecular interaction. This interaction favors condensation and results in a substantially lower barrier height for the reaction path emerging from the open complex. The catalytic effect of water reveals in the substantial lowering of the barriers heights for both types of transition states in going from n=0 to n=2.