Synthesis and Characterization of Symmetrically Unsymmetrically Proton-Bridged Hexa-Iron Clusters.

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF)·6HO with each ligand (H and H ) in a methanolic-pyridine solution resulted in hexa-iron compounds ( and , respectively), which each contain two near-parallel metal triangles of [Fe-μ-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ-O groups. Within each metal triangle of , Fe(III) ions are connected the amine "straps" of (H -2H). Variable-temperature magnetic susceptibility and Mössbauer data of and indicate the presence of dominant antiferromagnetic interactions between the high-spin ( = 5/2) Fe(III) centers. For , two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe-μ-O] and [Fe-μ-OH] species were inferred. For , a single sharp quadrupole doublet with splitting intermediate between those determined for was observed, consistent with the symmetric [Fe-μ-O···H···μ-O-Fe] species inferred crystallographically from the very short μ-O···μ-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands.