Structures and spin states of mono- and dinuclear iron(II) complexes of imidazole-4-carbaldehyde azine and its derivatives

摘要: Abstract Mononuclear [Fe(H2LR)2]X2 (R = H, 2-Me, 5-Me, 2-Et-5-Me; X = ClO4, BF4) and dinuclear [Fe2(H2LR)3]X4 complexes containing imidazole-4-carbaldehyde azine (H2LH) its derivatives prepared by condensation of 4-formylimidazole, 2-methyl- or 5-methyl-4-formylimidazole, 2-ethyl-4-methyl-5-formylimidazole, with hydrazine in a 2:1 mole ratio methanol, were their magnetostructural relationships studied. In the mononuclear complexes, H2LR acts as an unsymmetrical tridentate ligand two imidazole nitrogen atoms one atom, while dinucleating employing four to form triple helicate structure. At room temperature, [Fe2(H2LH)3](ClO4)4 [Fe2(H2L2-Me)3](ClO4)4 high-spin (HS) low-spin (LS) states, respectively. The results are accordance field strength H2L2-Me electron-donating methyl groups being stronger than H2LH, order strengths H2L2-Me > H2LH. However, [Fe(H2LH)2](ClO4)2 [Fe(H2L2-Me)2](ClO4)2 different strengths, H2LH > H2L2-Me, was observed because LS state HS at temperature. X-ray structural studies revealed that interligand steric repulsion between group other is responsible for change spin state. same true [Fe(H2L2-Et-5-Me)2](ClO4)2, [Fe(H2L5-Me)2](ClO4)2 does not involve such congestion stays over temperature range 5–300 K. Two kinds crystals (polymorphs) isolated [Fe2(H2LH)3](BF4)4 [Fe2(H2L2-Et-5-Me)3](ClO4)4, they exhibited magnetic behaviors.