Genesis of a Co-Salicylaldimine Complex on Silica Followed in Situ by FTIR and XAS.

Several strategies have been proposed to replace soluble metallorganic complexes in organic solvents by similar molecular entities immobilized on non-reactive solids. The characterization of these complexes at atomic and molecular level during synthesis is demanding but essential to guide rational design. In the present work, the formation of cobalt salicylaldimine complex on γ-aminopropyl modified silica (SiO2 ) was monitored in ethanol on-line by Fourier transform infrared spectroscopy (FTIR) and in situ X-ray absorption spectroscopy (XAS) simultaneously using two independent cells. The organic ligand was monitored by FTIR to follow the stepwise synthesis of the Co-salicylaldimine complex. The oxidation state of Co, obtained by XANES, was found to be +2, while different coordination environments were observed in the presence or absence of the pendant organic ligand produced in situ on SiO2 . EXAFS analysis inferred that the oxidation state and the local structure of the Co2+ ion on the modified SiO2 surface was similar to that of a salen-complex with four Co-O/N bonds.