Iron -II- or vanadium -IV- - containing siliceous gels

Iron(II)-containing SiO sub 2 gels can be prepared by the hydrolysis and condensation of tetramethoxysilane in methanolic solutions of iron(II) chloride. These gels show an absorption at 1000 nm indicating the presence of iron(II). In opposition to that, iron(II) cannot be introduced into organically modified gels of the 3-glycidyloxypropyltrimethoxysilane type. Vanadium(IV) can be incorporated into both gels. Unlike the SiO sub 2 gels, the organically modified gels are compact and elastic. The spectra of the vanadium(IV)-containing gels show a characteristic absorption at about 800nm. In some cases these gels change their colours with time, presumably due to the exchange of ligands in the coordination sphere of vanadium.