Two-Step Spin-Transition lron(Hl) Compound with a Wide [High Spin-Low Spin] Plateau

摘要

A new iron(lll) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl)phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)_2](ClO_4)(MeOH)_0.5(H_20)_0.5}_2 (1) determined at 150 K reveals the presence of two slightly different iron(lIl) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and ~57Fe M_ssbauer spectroscopy, which all confirm the occurrence of a two-step transition. ln.addition, the iron(lll) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies