Employment of 2-pyrrole aldoxime in iron cluster chemistry: Trinuclear and hexanuclear clusters

The reaction of Fe(ClO4)3·9H2O with 2-pyrrole aldoxime (pyroxH2) and two equivalents of sodium benzoate in MeCN afforded the complex {[FeIII6O2(OH)2(pyroxH)2(PhCOO)10(H2O)2]·[FeIII3O(pyroxH2)2(PhCOO)6(MeCN)](ClO4)·6.6MeCN} (1·6.6MeCN) in moderate yield. Repeating the same reaction in EtOH gave the complex [FeIII6O2(OH)2(pyroxH)2(PhCOO)10(EtOH)2] (2) in good yield. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Complex 1 contains two different clusters in the crystal: a trinuclear [FeIII3] molecule and a hexanuclear [FeIII6] unit, both of which contain different forms of the 2-pyrrole aldoxime ligand. Complex 2 is a hexanuclear [FeIII6] cluster almost identical with the hexametallic unit found in 1, with the difference being the presence of two terminal EtOH molecules in 2 versus two terminal H2O molecules in the hexametallic sub-unit of 1. DC magnetic susceptibility studies were performed on polycrystalline sample of 2, revealing the presence of strong antiferromagnetic interactions within the cluster leading to a well isolated diamagnetic ground-state. The oxidation state of the iron atoms in 2 were further established by Mossbauer studies performed at 77 K.