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

Manganese(II) complexes, Mn2L13(ClO4)4, MnL1(H2O)2(ClO4)2, MnL2(H2O)2(ClO4)2, and {(μ-Cl)MnL2(PF6)}2 based on N,N′-bis(2-pyridinylmethylene) ethanediamine (L1) and N,N′-bis(2-pyridinylmethylene) propanediamine (L2) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn2L23(ClO4)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, L1 and Mn(II) yielded a one-dimensional polymer, MnL1(H2O)2(ClO4)2. Ligand L2 when reacted with manganese(II) perchlorate gives contrarily to L1 mononuclear MnL2(H2O)2(ClO4)2 complex. The analysis of the structural properties of the MnL2(H2O)2(ClO4)2 lead to the design of dinuclear complex {(μ-Cl)MnL2(PF6)} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn2Cl2 core with a Mn–Mn distance of 3.726 Å. At room temperature {(μ-Cl)MnL2(PF6)} is ferromagnetic with observed μeff = 4.04 μB per Mn(II) ion. With cooling, μeff grows reaching 4.81 μB per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition.

Schiff base ligands, N,N′-bis(2-pyridinylmethylene) ethane (or propane) diamine, yielded various, new mono- and bi-metallic manganese(II) complexes. One bi-metallic complex, with a ligand/metal ratio of 3:2 showed weak antiferromagnetic behavior even though there was no orbital overlap between the manganese centers. Another rhomboidal complex with a Mn2Cl2 core is ferromagnetic above 8 K where a ferromagnetic-to-antiferromagnetic phase switch occurs.Figure optionsDownload as PowerPoint slide