A reaction of iron(HI) acetylacetonate with silica surface OH groups results in the formation of iron-organic groups on SiO2 surface. Large dimension organic ligands inhibit an interaction between iron(III) atoms. According to magnetic and Mossbauer spectroscopy data, samples with surface iron-oxygen groups differ from samples with iron-organic groups by the absence of detectable magnetic ordering. (C) 2002 Elsevier Science B.V. All rights reserved.