Valence-directed assembly and magnetic properties of two polynuclear pyrazine-2-amidoxime Fe complexes

The reaction of FeCl3·6H2O/FeCl2·4H2O, pyrazine-2-amidoxime (H2pzaox) and triethylamine (1:1:2 mol ratio) in MeOH/H2O (v/v = 1:1) affords undecanuclear and trinuclear complexes [Fe11(μ4-O)7(μ2-O)3(Hpzaox)9(H2O)6Cl]Cl3·5CH3OH·5H2O (1) and [Fe3(Hpzaox)6]Cl2·10H2O (2), respectively. The compounds were characterized by IR, X-ray crystallography and temperature-/field-magnetic susceptibility measurements. Complexes 1 contains the [FeIII11(O)10]13 + core comprising eleven FeIII ions in a two floors ‘Tower’ disposition which was linked by nine oxime “Nsingle bondO” groups of the H2pzaox ligands. In complex 1, Hpzaox- anion shows μ2:η1η1η1 and μ3:η1η1η2 two coordination modes. Trinuclear complex 2 is a mix valence with Fe(III)–Fe(II)–Fe(III) coordinated compound in which the ligands are only coordinated through μ2:η1η1η1 mode. Three oxime groups “Nsingle bondO” bridge the adjacent metal centers with Fe⋯Fe separation of 3.5255(8) Å. Magnetic measurements of undecanuclear and trinuclear compounds in the 2–300 K temperature range reveal anti-ferromagnetic interactions between the Fe ions.