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

Abstract

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.

Selective Formation of Unsymmetric Multidentate Azine-Based Ligands in Nickel(II) Complexes

“…Pyridyl ketazine is one of the unique azine-based ligands that have been explored by several researchers for its coordinating abilities and modes, thus paving way for the investigation of several azine-based ligands for their unique coordination chemistry [ 25 , 26 , 27 ]. Our previous studies reported a series of mono- and dinuclear iron(II) complexes with imidazole-4-carbaldehyde azine and other imidazole groups as azine ligands showcasing different modes of coordination towards the iron(II) in the various complexes [ 28 , 29 , 30 ].…”

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

“…We have reported the synthesis, characterization, structure, and magnetic properties of mononuclear [Fe(H 2 L R ) 2 ] 2+ (R = H, 2-Me, 5-Me, 2-Et-5-Me) and dinuclear [Fe 2 (H 2 L R ) 3 ] 4+ complexes, where H 2 L H , H 2 L 2-Me , H 2 L 5-Me , and H 2 L 2-Et-5-Me denote imidazole-4-carbaldehyde azine, 2-methylimidazole-4-carbaldehyde azine, 5-methylimidazole-4-carbaldehyde azine, and 2-ethyl-5-methylimidazole-4-carbaldehyde azine, respectively [17,18]. Comparison of the SCO behaviors of the mononuclear complexes with those of the dinuclear triple-helicate complexes involving the same ligands is particularly important in studying the structural effects.…”