Samples of original and acid-washed Beypazari lignite were treated with I-2 and the effects of the I-2 treatment on the coal structure was investigated. It was found that I-2 attachment to the coal structure obeyed Langmuir-type of adsorption model. Treatment of coals with I-2 produced new iodine chemical compounds and the emergence of newly created chemical iodine structures was followed with the FTIR spectra. I-2 treatment also created charge transfer complexes. Increase in the free radical concentrations of the I-2-treated coals was due to the formation of charge transfer complexes between I-2 and aromatic systems in the coal by single electron extraction from the donor to the I-2. The splitting of aromatic stretching vibrations in the FTIR spectra of I-2-treated coals towards lower wavelengths also indicated the creation of charge transfer complexes in the coals after I-2 treatment where the I-2 acted as the electron acceptor. (C) 2001 Elsevier Science B.V. All rights reserved.