STRUCTURE AND COORDINATION OF ORGANOMETALLIC GROUPS ON A CHEMICALLY-MODIFIED SIO2 SURFACE

The structural, electronic, and energy parameters of the metal-contain ing clusters (H3SiO)(3)Si-O-XMen (X = H, B, Al, or Zn; n = 0, 1, or 2) , which model organometallic groups on a SiO2 surface modified with B- , Al-, and Zn-containing alkyls, have been studied by quantum-chemical methods. Full geometry optimization for these clusters was carried ou t by the SCF MO LCAO method taking into account the electron correlati on within the frameworks of the MP2 and B3LYP schemes using the 6-31G( d) (6-311G(d) for Zn) basis set. The effect of the crystal environment was taken into account in calculations of silicon-oxygen clusters con taining 10 and 30 silicon atoms using the ob initio SCF/6-31G(d) and s emiempirical MNDO-PM3 methods. Various modes of coordination and inter actions of organometallic groups with oxygen atoms of surface groups w ere studied. For the organoaluminum group on the surface, two stable c onformations were found, namely, the three-coordinate structure with t he chain -O-AlMe2 ligand and the four-coordinate (quasicyclic) structu re with the Al atom that forms two nonequivalent bonds with the O atom s at the same Si atom. The four-coordinate structure is energetically more favorable. No stable structures were found for the organoboron an d organozinc fragments.