Trinuclear Manganese Complexes of Unsymmetrical Polypodal Diamino N₃O₃ Ligands with an Unusual [Mn₃(μ-OR)₄]⁵⁺ Triangular Core: Synthesis, Characterization, and Catalase Activity

Abstract

Two new tri-Mn(III) complexes of general formula [Mn3L2(μ-OH)(OAc)]ClO4 (H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N'-(2-hydroxybenzyl),N'-(4-X-benzyl)amino]propan-2-ol; 1ClO4, X = Me; 2ClO4, X = H) have been prepared and characterized. X-ray diffraction analysis of 1ClO4 reveals that the complex cation possesses a Mn3(μ-alkoxo)2(μ-hydroxo)(μ-phenoxo)(4+) core, with the three Mn atoms bound to two fully deprotonated N3O3 chelating L(3-), one exogenous acetato ligand, and one hydroxo bridge, the structure of which is retained upon dissolution in acetonitrile or methanol. The three Mn atoms occupy the vertices of a nearly isosceles triangle (Mn1···Mn3 = 3.6374(12) Å, Mn2···Mn3 3.5583(13) Å, and Mn1···Mn2 3.2400(12) Å), with one substitution-labile site on the apical Mn ion occupied by terminally bound monodentate acetate. Temperature-dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between Mn(III) ions in 1ClO4. Complexes 1ClO4 and 2ClO4 decompose H2O2 at comparable rates upon initial binding of peroxide through acetate substitution, with retention of core structure during catalysis. Kinetic and spectroscopic studies suggest that these complexes employ the [Mn-(μ-oxo/aquo)-Mn](4+) moiety to activate peroxide, with the additional (μ-alkoxo)(μ-phenoxo)Mn(μ-alkoxo) metallobridge carrying out a structural function.

A new mononuclear manganese(III) complex of an unsymmetrical hexadentate N3O3 ligand exhibiting superoxide dismutase and catalase-like activity: synthesis, characterization, properties and kinetics studies

“…The conductivity data for this compound in methanol show non-electrolytic behavior in this solvent (same conductivity as for the neat solvent), indicating that the complex is neutral in solution. Analytical results, magnetic and conductivity measurements point to a neutral complex of formula Mn III L. This result evidences the versatility of L 3− , which in basic methanol, when higher metal to ligand ratio is used, yields a trinuclear Mn complex with 3:2 Mn to ligand ratio [26].…”

Functional modeling of the MnCAT active site with a dimanganese(III) complex of an unsymmetrical polydentate N 3 O 3 ligand

“…While the band at 504 nm is absent or is of very low intensity in the spectrum of the mononuclear complex, the trinuclear complex exhibits an intense band (ε 504 = 1500 M −1 cm −1 ) at this wavelength. The trinuclear complex contains a dinuclear moiety with the two Mn ions bound to a ligand donor set similar to complex 1, and the third Mn ion placed at the corner of an isosceles triangle, at a longer distance from the other two Mn ions [15]. So this band can be considered a common pattern for the dinuclear fragment of the Mn 2 and Mn 3 complexes formed with L 3− .…”

“…Fig. 1 shows IR spectra of the dimanganese complex 1, together with trinuclear [15] and mononuclear [14] complexes obtained with the same ligand under different conditions, as well as free ligand H 3 L [13]. The spectrum of 1 retains the fingerprint of the coordinated ligand but differs from those belonging to the mono-and trinuclear complexes, particularly in the regions corresponding to the stretching frequencies of the coordinated acetate ligands and BPh 4 − counteranion.…”

“…The dinucleating ligand H 3 L (H 3 L = 1-[N- (2pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N′- (2-hydroxybenzyl),N′-(benzyl)amino]propan-2-ol) is an unsymmetrical diamine that provides two different coordination compartments and can be used to mimic bimetallic sites with different environment around the two metal centers [13]. This and other ligands of the same family have already been used to generate mononuclear Mn III L [14] and trinuclear [Mn III 3 (μ-OH)(OAc)L 2 ] + complexes [15]. We have decided to explore the possibility of obtaining dinuclear manganese complexes employing the same ligand, in order to assess the influence of the ligand asymmetry on the CAT activity of diMn mimics.…”

Synthesis, Structure, and Magnetic Properties of a Mn4 Cluster derived from Benzimidazole‐Alcohol Ligands

“…The synthesis and characterization of paramagnetic 3d metal clusters with polynuclear and various topologies attract considerable attention in inorganic chemistry and molecular magnet science primarily because of their aesthetically pleasing structures and magnetic/electronic properties 1–4. Particularly, numerous groups have been highly interested in paramagnetic 3d metal clusters 5–10.…”