Mononuclear Bis(tridentate)-Type and Dinuclear Triple Helicate Iron(II) Complexes Containing 2-Ethyl-5-methylimidazole-4-carbaldehyde Azine

Mononuclear [Fe(H2L2-Et-5-Me)2]2+ and dinuclear [Fe2(H2L2-Et-5-Me)3]4+ complexes, where H2L2-Et-5-Me denotes 2-ethyl-5-methylimidazole-4-carbaldehyde azine, were prepared and isolated as the perchlorate salts, and their structures and magnetic properties were studied. In the mononuclear complex, the ligand acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom. The complex was in the HS state above 50 K. In the dinuclear complex, each ligand acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate structure. Two types of crystals, plates and blocks, were isolated for the dinuclear complex. The plate crystals exhibited a sharp spin transition, [LS–HS] ↔ [HS–HS], with no [LS–LS] state being observed. The block crystals remained in the [HS–HS] state above 50 K.