Ferromagnetic dinuclear mixed-valence Mn(II)/Mn(III) complexes: building blocks for the higher nuclearity complexes. structure, magnetic properties, and density functional theory calculations

Oxo-bridged trinuclear and tetranuclear manganese complexes supported with nitrogen donor ligands: syntheses, structures and properties

This work illustrates syntheses, structures, redox and magnetic properties as well as catalase activities of rare μ₃-oxo bridged mixed-valent trinuclear Mn^IIMn^III complexes (1 and 2) and a μ₄-oxo bridged tetranuclear MnII4 complex (3) supported with nitrogen donor ligands.

A New Mixed-Valence Mn(II)Mn(III) Compound With Catalase and Superoxide Dismutase Activities

The synthesis, X-ray molecular structure, physico-chemical characterization and dual antioxidant activity (catalase and superoxide dismutase) of a new polymeric mixed valence Mn(III)Mn(II) complex, containing the ligand H₂BPClNOL (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)] propylamine) is described. The monomeric unit is composed of a dinuclear Mn(II)Mn(III) moiety, [Mn(III)(μ-HBPClNOL)(μ-BPClNOL)Mn(II)(Cl)](ClO₄)·2H₂O, 1, in which the Mn ions are connected by two different bridging groups provided by two molecules of the ligand H₂BPClNOL, a phenoxide and an alkoxide group. In the solid state, this mixed valence dinuclear unit is connected to its neighbors through chloro bridges. Magnetic measurements indicated the presence of ferromagnetic [J = +0.076(13) cm⁻¹] and antiferromagnetic [J = −5.224(13) cm⁻¹] interactions. The compound promotes O2•- dismutation in aqueous solution (IC₅₀ = 0.370 μmol dm⁻³, k_cat = 3.6x10⁶ M⁻¹ s⁻¹). EPR studies revealed that a high-valent Mn(III)-O-Mn(IV) species is involved in the superoxide dismutation catalytic cycle. Complex 1 shows catalase activity only in the presence of a base, e.g., piperazine or triethylamine. Kinetic studies were carried out in the presence of piperazine and employing two different methods, resulting in k_cat values of 0.58 ± 0.03 s⁻¹ (detection of O₂ production employing a Clark electrode) and 2.59 ± 0.12 s⁻¹ (H₂O₂ consuption recorded via UV-Vis). EPR and ESI-(+)-MS studies indicate that piperazine induces the oxidation of 1, resulting in the formation of the catalytically active Mn(III)-O-Mn(IV) species.

Understanding and tuning the properties of redox-accumulating manganese helicates

The multiple redox transitions of pentanuclear Mn clusters and the tuning of their redox potentials by ligand design are investigated computationally.

Ferromagnetism in polynuclear systems based on non-linear [MnII2MnIII] building blocks

Design of new polynuclear transition metal complexes showing ferromagnetic interactions to achieve high spin values is an important challenge due to the scarcity of bridging ligands that provide such coupling.