Mössbauer and infrared studies of some Schiff-base iron(III) compounds

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Abstract
Previous studies on iron(III) Schiff-base compounds such as (Fe salen Cl) indicate that either dimeric or monomeric compounds can be prepared depending on the solvent used for recrystallization. These compounds usually contain one or more solvent molecules in the crystal structure. We report Mössbauer and i.r. spectra and magnetic susceptibilities of a number of iron(III) Schiff-base compounds, many of which have not been prepared previously. On recrystallization of (Fe salen Cl) and (Fe salen Br) from acetone, chloroform, methanol, and pyridine, very similar Mössbauer spectra are obtained, and the i.r. spectra all show a rather intense band around 850 cm.–1, which may be atributed to an Fe–O–Fe band. The evidence suggests that these are binuclear. However, on recrystallization of (Fe salen Cl) from nitromethane and methyl cyanide, appreciably different Mössbauer spectra are obtained, and the i.r. band at 850 cm.–1 is very weak. These compounds appear to be monomeric. On recrystallization of (Fe salen Br) from nitromethane and methanol, both dimeric and monomeric compounds are obtained, whereas from methyl cyanide, a monomer is obtained. The Mössbauer and i.r. spectra indicate that magnetic susceptibility is not a reliable method for determining the molecularity of these compounds. The use of the Mössbauer parameters centre shifts (C.S.), quadrupole splitting (Q.S.), and line-widths for the elucidation of the molecularity, spin state of FeIII, and the bonding in these compounds is discussed.
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