Structure of Ni(II) and Ru(III) Ammine Complexes Grafted onto Mesoporous Silicate Sieve

摘要

Ru(III) and Ni(II) ammine complexes were grafted onto the pore surface of MCM-41 by ion exchange from basic aqueous solution. Covalent anchoring of the type M-O-Si (M = Ru or Ni) is obtained by this method. The structure of the grafted complexes was studied by UV-vis, FT-IR, and X-ray absorption spectroscopy. [Ru(NH_3)_5Cl]~(2+) readily yielded monopodal grafting, while dehydration was needed in the case of [Ru(NH_3]_6]~(3+) to achieve substitution of a NH_3 ligand with a siloxy group. The interaction of charge-compensating siloxy groups with remaining NH_3 ligand with a siloxy group. The interaction of charge-compensating siloxy groups with remaining NH_3 ligands further stabilized the grafted Ru(III) centers. Dipodal grafting of Ni(II) was obtained with [Ni(NH_3)_(6-x)(H_2O_x]~(2+) (x = 1 or 2). Upon dehydration, the dipodally grafted Ni(II) complexes are converted in a reversible process to a tripodally anchored form through substitution of a H_2O ligand by a silanol group. The formation of layered Ni silicate structures, a dominant product in the Ni grafted amorphous silica, was not observed. This demonstrates that simple coordination complexes can be used for accomplishing covalent attachment of isolated metal centers on a mesoporous silicate sieve in high yield. Grafting of Ni(II) onto MCM-41 containing isolated Ti(IV) centers resulted in the formation Ti(IV)-O-Ni(II) moieties, which are of special interest for photochemical applications.