Iron(III) complexes with 2‐pyridyl oxime ligands: Synthesis, structural and spectroscopic characterization, and magnetic studies

Reactions of FeIII sources with 2‐pyridyl oxime ligands, pyC(R)NOH (R=H, Me, Ph), afforded the trinuclear oxo‐centered complexes (NH4)[Fe3O(LH)6(H2O)3](ClO4)8 ⋅MeOH⋅1.14H2O (1⋅ MeOH⋅1.14H2O) and [Fe3O{pyC(H)NO)(PhCO2)6(H2O)]⋅MeCN (2⋅MeCN), the tetranuclear complex [Fe4(OH)4{pyC(Me)NO}4(H2O)4] (ClO4)4⋅3Me2CO⋅H2O (3⋅3Me2CO⋅H2O), and the hexanuclear complexes [Fe6(OH)6{pyC(Me)NO}6(H2O)6](ClO4)6⋅8Me2CO⋅2H2O (4⋅8Me2CO⋅2H2O), [Fe6(OH)6{pyC(Me)NO}6(MeCONH2)6](ClO4)6⋅2MeCN⋅H2O (5⋅2MeCN⋅H2O), [Fe6(OH)6 {pyC(Ph)NO}6(H2O)6](ClO4)6⋅4.4Me2CO ⋅1.6Et2O (6⋅4.4Me2CO ⋅1.6Et2O) and [Fe6(OH)6{pyC(Ph)NO}6(MeOH)6](ClO4)5.5(OH)0.5⋅MeOH⋅0.5H2O (7⋅MeOH ⋅0.5H2O), where LH is the zwitterion anionic form of 2‐pyridinecarboxylic acid (picolinic acid). Complex 3 can be described as inverse 12‐metallacrown‐4, whereas 4–7 can be described as inverse 18‐metallacrowns‐6 and represent the first examples of iron(III) metallacyclic clusters with pyC(R)NOH (R=H, Me, Ph) ligands. Complexes 3 and 6 were characterized by Mössbauer spectroscopy and magnetic susceptibility measurements, while complex 2 was characterized by EPR spectroscopy. The use of 2‐pyridyl oxime ligands, pyC(R)NOH (R=H, Me, Ph), in iron(III) chemistry afforded trinuclear oxo centered complexes and tetra‐/hexanuclear inverse metallacrown clusters, all of which were structurally characterized. Representative compounds were characterized by Mössbauer and EPR spectroscopy, and magnetic susceptibility measurements.