The coordination state of copper(II) complexes anchored and grafted onto the surface of organically modified silicates

Amine derivatives of alkoxides such as (3-aminopropyl)trimethoxysilane and (3-(2-aminoethyl)aminopropyl)trimethoxysilane are reagents in the sol-gel process and, at the same time, versatile ligands forming complexes with transition metal ions (e.g., Cu(II)). One of the major advantages of the sol-gel process is the possibility of preparing Cu(II) complexes in the interior of and on the surface of organically modified silicate xerogels. This paper compares Cu(IT) complexes prepared in the interior of silica xerogels with those grafted and anchored onto the surface of such xerogels. Grafting and anchoring require prior preparation of supports with functionalized surfaces. In the former process Cu(II) ions are chemisorbed, and in the latter Cu(II) complexes are immobilized by a condensation reaction. The following spectroscopic results are presented: FT-IR, optical absorption in the visible region, and electron paramagnetic resonance (EPR). The EPR studies are summarized in three identified models of the coordination sites on the modified silica xerogel surfaces. The materials studied are put for ward as catalyst precursors.