Structural variability in manganese(II) complexes of N,N′-bis(2-pyridinylmethylene) ethane (and propane) diamine ligands

Abstract

Manganese(II) complexes, Mn 2 L 1 3(ClO 4) 4, Mn L 1 (H 2O) 2(ClO 4) 2, Mn L 2 (H 2O) 2(ClO 4) 2, and {(μ-Cl)Mn L 2 (PF 6)} 2 based on N,N′-bis(2-pyridinylmethylene) ethanediamine ( L 1) and N,N′-bis(2-pyridinylmethylene) propanediamine ( L 2 ) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn 2 L 2 3(ClO 4) 4 shows that each of the two Mn(II) ion centers with a Mn–Mn distance of 7.15 Å are coordinated by one ligand while a common third ligand bridges the metal centers. Solid-state magnetic susceptibility measurements as well as DFT calculations confirm that each of the manganese centers is high-spin S = 5/2. The electronic structure obtained shows no orbital overlap between the Mn(II) centers indicating that the observed weak antiferromagentism is a result of through space interactions between the two Mn(II) centers. Under different reaction conditions, L 1 and Mn(II) yielded a one-dimensional polymer, Mn L 1 (H 2O) 2(ClO 4) 2. Ligand L 2 when reacted with manganese(II) perchlorate gives contrarily to L 1 mononuclear Mn L 2 (H 2O) 2(ClO 4) 2 complex. The analysis of the structural properties of the Mn L 2 (H 2O) 2(ClO 4) 2 lead to the design of dinuclear complex {(μ-Cl)Mn L 2 (PF 6)} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn 2Cl 2 core with a Mn–Mn distance of 3.726 Å. At room temperature {(μ-Cl)Mn L 2 (PF 6)} is ferromagnetic with observed μ eff = 4.04 μ B per Mn(II) ion. With cooling, μ eff grows reaching 4.81 μ B per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition.