Effect of CO Pressure Gradients on the Photochemistry and Thermal Chemistry of Fe(CO)5 Physisorbed into Porous Vycor Glass

Abstract

Photolysis of Fe(CO)5 physisorbed into porous Vycor glass creates CO pressure gradients within the nanoporous matrix that promote Fe(CO)5 diffusion within the matrix and change the distribution of the complex within the matrix. Occurring on a time scale of the lifetimes of the sub-carbonyl photoproducts, pressure induced diffusion influences both the chemistry of the sub-carbonyl photoproducts and the subsequent oxidation of the elemental iron. High-resolution X-ray absorption near-edge structure (XANES) and Mossbauer spectra reveal photolysis creates an asymmetric distribution of Fe(III) and elemental iron, Fe0. The distribution of oxidation states within the matrix and the effect of temperature on the distribution indicate two oxidation pathways. Both pathways are complementary with respect to Fe(II), yet in contrast to that found in other silica matrices, neither process leads to the net formation of Fe(II) within this silica matrix.