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

摘要

The reaction of Fe(ClO_4)_3·9H_2O with 2-pyrrole aldoxime (pyroxH2) and two equivalents of sodium benzoate in MeCN afforded the complex {[Fe~(III) _6O_2(OH)_2(pyroxH)_2(PhCOO)_(10)(H_2O)_2]-[Fe~(III) _3O(pyroxH_2)_2 (PhCOO)_6(MeCN)](ClO_4)·6.6MeCN} (1-6.6MeCN) in moderate yield. Repeating the same reaction in EtOH gave the complex [Fe~(III) _6O_2(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 [Fe~(III) _3] molecule and a hexanuclear [Fe~(III) _6] unit, both of which contain different forms of the 2-pyrrole aldoxime ligand. Complex 2 is a hexanuclear [Fe~(III) _6] 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 H_2O 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 M?ssbauer studies performed at 77 K.