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

Abstract The reaction of FeCl 3 ·6H 2 O/FeCl 2 ·4H 2 O, pyrazine-2-amidoxime (H 2 pzaox) and triethylamine (1:1:2 mol ratio) in MeOH/H 2 O (v/v = 1:1) affords undecanuclear and trinuclear complexes [Fe 11 (μ 4 -O) 7 (μ 2 -O) 3 (Hpzaox) 9 (H 2 O) 6 Cl]Cl 3 ·5CH 3 OH·5H 2 O ( 1 ) and [Fe 3 (Hpzaox) 6 ]Cl 2 ·10H 2 O ( 2 ), respectively. The compounds were characterized by IR, X-ray crystallography and temperature-/field-magnetic susceptibility measurements. Complexes 1 contains the [Fe III 11 (O) 10 ] 13 + core comprising eleven Fe III ions in a two floors ‘Tower’ disposition which was linked by nine oxime “N O” groups of the H 2 pzaox ligands. In complex 1 , Hpzaox - anion shows μ 2 : η 1 η 1 η 1 and μ 3 : η 1 η 1 η 2 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 μ 2 : η 1 η 1 η 1 mode. Three oxime groups “N O” bridge the adjacent metal centers with Fe⋯Fe separation of 3.5255(8) A. Magnetic measurements of undecanuclear and trinuclear compounds in the 2–300 K temperature range reveal anti-ferromagnetic interactions between the Fe ions.