Anion coordination selective [Mn₃] and [Mn₄] assemblies: synthesis, structural diversity, magnetic properties and catechol oxidase activity

Abstract

Syntheses, crystal structures, magnetic properties and catechol oxidation behavior are presented for [Mn3] and [Mn4] aggregates, [MnMn(II)(O2CMe)4(dmp)2(H2O)2]·2H2O (1·2H2O), [MnMn(II)(O2CCH2Cl)4(dmp)2(H2O)2]·H2O·MeOH (2·H2O·MeOH), [Mn(μ3-O)(dmp)4(μ-DMSO)(N3)(DMSO)(H2O)]ClO4·DMSO (3·ClO4·DMSO), and [Mn(μ3-O)(dmp)4(μ-DMSO)(ClO4)(DMSO)(H2O)]ClO4·DMSO (4·ClO4·DMSO), developed with single type ligand H2dmp, 2-[(2-hydroxy-1,1-dimethyl-ethylimino)-methyl]-phenol. The successful isolation of 1-4 resulted from a systematic exploration of the effect of Mn(II) salts, added carboxylates, Mn/H2dmp ratio, presence of azide, and other reaction conditions. The cores of 1 and 2 are similar and consist of a linear Mn(III)Mn(II)Mn(III) unit in a carboxylate and H2dmp environment, revealing a central Mn(II) ion in a different environment and terminal Mn(III) ions available for the introduction of structural and magnetic anisotropy to the system. The cores of 3 and 4 are also similar and consist of a distorted incomplete-adamantane type Mn4 coordination assembly in a carboxylate-free environment built on a triangular [Mn(μ3-O)] unit. The magnetic behavior of complexes 1-3 is dominated by antiferromagnetic exchange coupling that results in ground state spin values of S = 3/2 for 1 and 2 and S = 0 for 3. In solution, all four complexes 1-4 show catechol oxidation activity towards 3,5-DTBC. The catalytic activity for the oxidation of 3,5-DTBC in air followed the order 4 < 3 < 1 < 2.

Dangling and Hydrolyzed Ligand Arms in [Mn3] and [Mn6] Coordination Assemblies: Synthesis, Characterization, and Functional Activity

“…One coupling constant, J 1 , was considered between the outer Mn­(III) ions and the central Mn­(II) ion (see inset of Figure ), and the g -value was fixed at 2.0. Any possible exchange interaction between the outer Mn­(III) ions was neglected, based on previous studies. , The single-ion axial zero-field splitting parameter d was included in the fit for both Mn­(III) ions. An intermolecular interaction zJ ′ of 0.02 cm –1 and a temperature-independent paramagnetism (TIP) contribution of 3.2 × 10 –6 cm 3 mol –1 were also included .…”

“…Any possible exchange interaction between the outer Mn(III) ions was neglected, based on previous studies. 54,55 The single-ion axial zero-field splitting parameter d was included in the fit for both Mn(III) ions. An intermolecular interaction zJ′ of 0.02 cm −1 and a temperature-independent paramagnetism (TIP) contribution of 3.2 × 10 −6 cm 3 mol −1 were also included.…”

Introducing Supramolecular Interactions into Robust Bis(tetrabromocatecholate) Chelated Manganese(III) Systems and Biomimetic Catalytic Activity

“…The rate saturation kinetics clearly support the formation of a stable complex‐substrate aggregate prior to the production of 3,5‐DTBQ. The mechanistic pathways of functioning catecholase activity of such manganese(III) complexes are well explored, and the direct redox participation of manganese(III) was suggested in most cases . To get insight into the mechanistic pathway through which the present complexes exhibit catecholase activity, the UV−vis spectra of the complex by itself and in the presence of excess substrate were recorded.…”

“…The latter is a dicopper metalloenzyme, the function of which is the oxidation of a wide range of o ‐diphenols (catechols) to the corresponding o ‐quinones, which undergo auto‐polymerization to produce a brown pigment melanin as a natural antiseptic to protect the damaged tissues against both bacterial and fungal diseases . Whereas several mono‐ and multinuclear copper complexes have been found to be successful models for such metalloenzymes,, functional models with other transition metals have been limited, and thus need further attention …”

Synthesis and characterization of two self-assembled [Cu6Gd3] and [Cu5Dy2] complexes exhibiting the magnetocaloric effect, slow relaxation of magnetization, and anticancer activity

“…Earlier we have used 2-amino-2methylpropan-1-ol as an amine alcohol Schiff base tail for synthesizing the Mn 3 and Mn 4 aggregates. 44…”