UV–visible, XANES and EXAFS investigations of a cobalt complex grafted in micelle templated silica

Abstract

The coordination of the trans-[Co(en)₂Cl₂]⁺ ion exchanged on as-synthesized micelle-templated silica (MTS) is investigated using X-ray absorption near edge structure (XANES), Extended X-ray absorption fine structure (EXAFS) and diffuse reflectance UV–visible spectroscopies. XANES and UV–visible data show that most of the adsorbed complexes adopt the cis configuration and that both chloride ligands are likely substituted during the displacement of the templating surfactants. This is confirmed by EXAFS the multiple scattering analysis of which reveals the formation of a single Co–O–Si bridge; the Co–O and Co–Si bond lengths are 1.91±0.03 and 3.22±0.03 Å, respectively. According to pH considerations, the second substitution position is occupied by a hydroxy group which leads to a grafted complex formula of cis-[Co(en)₂(OH)(â–·SiO)]Cl. A direct synthesis of Co–MTS using the same cobalt complex does not lead to mononuclear grafted species.