Synthesis, Structural Characterization, and Magnetic Studies of Polynuclear Iron Complexes with a New Disubstituted Pyridine Ligand

A series of novel polyiron species have been prepared from the reaction of iron chloride with the 2,5-disubstituted
pyridines H2Ln (H2L1 = N,N‘-bis(n-butylcarbamoyl)pyridine-2,6-dicarboxamide; H2L2 = N,N‘-bis(n-ethylcarbamoyl)pyridine-2,6-dicarboxamide). By small modifications of the experimental conditions under which the reactions are
carried out, it has been possible to prepare the quadruply stranded diiron(II) complex [Fe2(μ-H2L1)4(μ-Cl)2][FeCl4]2
(1), the metallamacrocycle [Fe2(μ-H2L1)2(THF)4Cl2][FeCl4]2 (2), the hexairon(III) compound [Fe6(L1)2(μ-OMe)6(μ4-O)2Cl4] (3), and the mixed-valence trinuclear iron complexes [Fe3(Ln)3(μ3-O)] (n = 1, 4; n = 2, 5). The X-ray
crystal structures of 3 and 5 and magnetic studies for all the compounds are herein presented. Interestingly, the
structural analysis of 5 at room temperature indicates that one of the iron centers is FeIII while the other two have
an average valence state between FeII and FeIII. The five complexes herein presented demonstrate the great
versatility that the new ligand has as a building block for the formation of supramolecular coordination assemblies.