Synthesis, magnetic susceptibility, and Moessbauer spectra of iron(III) dimers and iron(II) polymers containing 2,5-dihydroxy-1,4-benzoquinones

Abstract

Abstract : Several iron complexes of the dianions of 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and 2, 5-dichloro-3,6-dihydroxy-1,4-benzoquinone (CA, chloranilate dianion) have been prepared and studied by magnetic susceptibility and Moessbauer spectroscopic methods. Iron(II) salts react with these dihydroxybenzoquinones to give polymeric Fe(DHBQ)(H2O)2 and Fe(CA)(H2O)2. If the reaction is carried out in the presence of pyrazine, pyr, (Fe(CA)(pyr))(n) and (Fe(DHBQ)(pyr)) are obtained. Infrared spectral results are consistent with the presence of bridging bidentate pyr in these complexes, and thus sheet polymers. Dimeric Fe2(DHBQ)3(H2O)4 and Fe2(CA)3(H2O)4 .4H2O are obtained by reacting FeCl3 with the respective dihydroxybenzoquinones. Magnetic susceptibility vs. temperature data obtained for the polymeric materials are fit to a S=2 Heisenberg linear chain model. The presence of an anisotropy in the recoilless fraction (Goldanskii-Karyagin effect) is observed in the Fe57 Moessbauer spectra of the Fe(III) dimers and is substantiated by measurements on the temperature dependence of the Moessbauer parameters.