Structure and vibrational frequencies of di- and monomethyl aluminum, zinc, and boron derivatives on a chemically modified SiO2 surface

The geometrical and electronic structure of (H3SiO)(3)Si-O-R clusters (R=H, B(CH3)(2), Al(CH3)(2), and ZnCH3; n = 0, 1, or 2) modeling a -OR group che misorbed on a SiO2 surface was studied theoretically with the use of ab ini tio quantum chemical calculations at the MP2 and B3LYP levels. Various mode s of coordination of the organometallic groups at the SiO2 surface were con sidered. For the Al-containing surface group, two stable structures were fo und: an open structure and a cyclic structure with the Al atom involved in additional coordination with one of the neighboring oxygen atoms. At the be st computational level, only one stable structure was located for the B- an d Zn-containing surface fragments, in which the central atom of the surface group (Zn or B) only weakly interacts with the second surface oxygen atom. The calculated vibrational frequencies were compared with the experimental ones and, on this basis, the possible reaction pathways of chemical modifi cation were discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.