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

Abstract

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(NH3)5Cl]2+ readily yielded monopodal grafting, while dehydration was needed in the case of [Ru(NH3)6]3+ to achieve substitution of a NH3 ligand with a siloxy group. The interaction of charge-compensating siloxy groups with remaining NH3 ligands further stabilized the grafted Ru(III) centers. Dipodal grafting of Ni(II) was obtained with [Ni(NH3)6-x(H2O)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 H2O 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 simpl...