Manganese Schiff Base Complexes Research Articles

Catecholase activity of a manganese Schiff base complex functionalized over SBA-15 in aqueous heterogeneous medium

A novel manganese(III)-Schiff base complex anchored SBA-15 based heterogeneous catalyst SBA-15-SB-Mn was synthesized and characterized by various physicochemical techniques. The catalyst was found to exhibit excellent green catalysis for the aerial oxidation of 3,5-di-tert-butyl catechol (3,5-DTBC) to the corresponding 3,5-di-tert-butylcatechol-1,2-benzoquinone (3,5-DTBQ) with 83.17% conversion (TON = 515) within 1 h at room temperature and relevant to catechol oxidase behavior.

Synthesis, Characterization, DFT Study, Catechol Oxidase and Phenoxazinone Synthase Like Activities of Two New Manganese(IV) Schiff Base Complexes

Two manganese(IV) complexes [Mn(L)2](ClO4)2⋅0.88H2O (1) and [Mn(HL)2(N3)2](ClO4)2⋅2H2O (2) [where HL=3-(N,N-dimethylamino)propyliminomethyl-4-bromophenol] have been prepared and characterized. Manganese(IV) in each complex assumes distorted octahedral geometry. Structural features have been examined in detail that reveal the formation of interesting supramolecular networks generated through non-covalent forces including C−H⋅⋅⋅π and Br⋅⋅⋅Br interactions. These interactions have been studied energetically by means of theoretical DFT calculations using several computational tools, including Bader′s “atoms-in-molecules” (AIM) theory. Both complexes are found to show catechol oxidase and phenoxazinone synthase like activities.

Synthesis, Characterization and Antifungal Activity of Manganese (II) Complex with Schiff Base Derived from Acetylacetone and Leucine

This study was aimed at synthesizing, characterizing and evaluating the antifungal activity of the Schiff base and Mn (II) complex. The reaction of the mixture of ethanol solution of acetylacetone and leucine yielded a Schiff base. The interaction between the Schiff base in hot aqueous methanol mixture and manganese (II) chloride in ethanol gave the manganese (II) Schiff base complex. The complex was characterized by decomposition/melting point temperatures, solubility test, IR spectrophotometry, colour determination, dissociation constant of Schiff base and antifungal activity. The Schiff base obtained has yellow colour, with a melting point of 250°C and percentage yield of 54.67% while the manganese (II) complex obtained had a pink colour with decomposition temperature of 167°C and percentage yield of 76.40%. The Schiff base and the complex was soluble in some solvents but slightly soluble in others. The Infrared spectra of the Schiff base showed a band at a range of 1600cm -1 - 1622cm -1 attributed to v (C=N) stretching frequencies establishing it being a Schiff base. Similar bands were observed in the spectra of Manganese (II) Schiff base complex but in lower frequencies indicating that the Schiff base has coordinated to the Mn ion. The antifungal activity of manganese (II) complex showed significant activity on the fungal isolates Candida albican and Sacchromyces cerevisiae . The study concludes that Schiff base synthesized was a weak acid and the Schiff base was not an active drug against the fungal pathogens used but Mn (II) complex was active against the pathogens used.

Importance of C–H⋯π interactions in stabilizing the syn/anti arrangement of pendant alkoxy side arms in two manganese(iv) Schiff base complexes: exploration of catechol oxidase and phenoxazinone synthase like activities

Two manganese(iv) complexes have been prepared and characterized. Both complexes exhibit catechol oxidase and phenoxazinone synthase like activities.

Manganese mediated oxidation of progesterone in alkaline medium: Mechanism study and quantitative determination

We report here a non-immunosensing approach for the electrocatalytic oxidation of progesterone (P4) in alkaline medium using a salen-type manganese Schiff base complex (Mn(III)-SB) as a suitable electrocatalyst. We explored the role of carbon surface at glassy carbon electrode (GCE) and gold surface at glassy carbon/gold nanoparticles modified electrode (GCE/AuNPs) on immobilization of the Mn(III)-SB complex using cyclic voltammetry (CV) and density functional theory (DFT) calculations. The GCE/Mn(III)-SB displayed a pair of small redox peaks attributed to Mn(II)⇄Mn(III) with a small peak-to-peak separation (ΔEp), while GCE/AuNP/Mn(III)-SB displayed redox peaks with larger densities, but with a wider ΔEp. A combined molecular mechanics (MM) and quantum mechanics (QM) study were carried out to investigate the variation of surface configuration and energy barrier, when the Mn(III)-SB immobilization was modeled on GCE and GCE/Au surface. Cyclic voltammetry and hydrodynamic amperometry were used for the quantitative determination of P4. A limit of detection (LOD) of 11.4nM was obtained using amperometry. The sensor retained 91% of its original response after 3 months, which is improved compared to previously reported P4 immunosensors. For the first time, a detailed mechanism for oxidation of P4 in alkaline medium was suggested. The proposed sensor was utilized to determine progesterone in milk samples.

In-Depth Magnetic Characterization of a [2 × 2] Mn(III) Square Grid Using SQUID Magnetometry, Inelastic Neutron Scattering, and High-Field Electron Paramagnetic Resonance Spectroscopy.

A tetranuclear [2 × 2] grid-like manganese(III) Schiff base complex, Mn4, has been synthesized and characterized by single-crystal X-ray crystallography. Direct-current magnetization measurements were performed on the system and proved to be insufficient for an accurate magnetic model to be deduced. Combined inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) experiments provided the necessary information in order to successfully model the magnetic properties of Mn4. The resulting model takes into account both the magnitude and the relative orientations of the single-ion anisotropy tensors.

Novel Schiff base Mn(iii) and Co(ii) complexes supported on Co nanoparticles: efficient and recyclable magnetic nanocatalysts for alcohol oxidation

In this study, efficient and highly selective heterogeneous catalysts were developed by immobilization of manganese and cobalt Schiff base complexes on Co magnetite nanoparticles (MNPs).

Synthesis, characterization, and catalytic application of Cr and Mn Schiff base complexes immobilized on modified nanoporous MCM-41

Immobilization of chromium and manganese Schiff base complexes by postgrafting of ligand then metal salts on the walls of mesoporous MCM-41 functionalized with (3-aminopropyl)triethoxysilane is described. Characterization of the resulting heterogeneous catalysts by Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and Brunauer–Emmett–Teller (BET) techniques indicated successful grafting of these two complexes inside the nanochannels of MCM-41. The complexes were found to be efficient, selective catalysts for oxidation of various sulfides to sulfoxides and oxidative coupling of thiols to corresponding disulfides using H2O2 as oxidant at room temperature. The recycling results of these heterogeneous catalysts showed good recyclability without significant loss of activity or selectivity in successive runs, indicating that the Cr and Mn Schiff base complexes supported on nanoporous MCM-41 remained intact and the coordination environments were not altered during the reaction.

A Selective and Sustainable Sulfoxidation Method Catalyzed by Reusable Manganese (III) Schiff Base Complexes

A Selective and Sustainable Sulfoxidation Method Catalyzed by Reusable Manganese (III) Schiff Base Complexes

New salen-type manganese(III) Schiff base complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine: In vitro anticancer activity, mechanism of action, and molecular docking studies

Four new manganese(III) Schiff base complexes (1–4) were synthesized and characterized. The complexes have general formula [MnClLx] in which L represents a Schiff base ligand derived from condensation of meso-1,2-diphenyl-1,2-ethylenediamine with salicylaldehyde or its 3-OMe-, 5-Br-, or 5-OMe-derivatives (x = 1–4, respectively). The crystal structure of [MnClL1] (1) was characterized by X-ray crystallography. The in vitro anticancer activity of these complexes was evaluated by MTT and apoptosis assays against human breast (MCF-7) and liver (Hep G2) cancer cells. The complexes exhibited considerable antiproliferative activity against both cell lines (IC50 = 10.8–21.02 μM) comparable to cis-platin, except 4 (MCF-7). The highest activity was found for 1 with IC50 values of 13.62 μM (MCF-7) and 10.8 μM (Hep G2). Flow cytometry experiments showed that 1 induced apoptosis on MCF-7 tumor cell line. Docking simulations using AUTODOCK were also carried out. The results showed that all complexes fitted into the minor groove region of DNA.

Electrocatalytic oxidation of 2-mercaptoethanol using modified glassy carbon electrode by MWCNT in combination with unsymmetrical manganese (II) Schiff base complexes

The performance of modified hybrid glassy carbon electrode with composite of carbon nanotubes and manganese complexes for the electrocatalytic oxidation of 2-mercaptoethanol is developed. GC electrode was modified using MWCNT and new N2O2 unsymmetrical tetradentate Schiff base complexes of manganese namely Manganese Saloph complexes 1-5, with general formula Mn[(5-x-4-y-Sal)(5-x′-4-y′-Sal) Ph], where x, x′=H, Br, NO2 and y, y′=H, MeO. Direct immobilization of CNT on the surface of GCE is performed by abrasive immobilization, and then modified by manganese(II) complexes via direct deposition method. These novel modified electrodes clearly demonstrate the necessity of modifying bare carbon electrodes to endow them with the desired behavior and were identified by HRTEM. Also complexes were characterized by elemental analyses, MS, UV–vis and IR spectroscopy. Modified hybrid GC/MWCNT/MnSaloph electrode exhibits strong and stable electrocatalytic activity towards the electrooxidation of 2-mercaptoethanol molecules in comparison with bare glassy carbon electrode with advantages of very low over potential and high catalytic current. Such ability promotes the thiol’s electron transfer reaction. Also, electron withdrawing substituent on the Saloph was enhanced electrocatalytic oxidation activity.

Synthesis, characterization, reactivity and catalytic activity of a novel chiral manganese Schiff base complex

A new type of manganese-Schiff base complex was synthesized and used as a catalyst for the oxidation of alcohols to the carbonyl compounds.

Synthesis, characterization and crystal structure of a manganese(III) Schiff base complex and investigation of its catalytic activity in the oxidation of benzylic alcohols

A new Mn(III) Schiff base complex was prepared by the reaction of 6,6′-diethoxy-2,2′-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenol with Mn(OAc)2·4H2O. The complex was characterized by physicochemical and spectroscopic methods. Also, its molecular structure was determined by single-crystal X-ray diffraction. The complex was used as a catalyst for the efficient oxidation of benzylic alcohols with tetrabutylammonium periodate. Various reaction parameters were optimized for the reaction of benzyl alcohol.

Manganese–Schiff base complex immobilized silica materials for electrocatalytic oxygen reduction

Curtailment of platinum catalysts loading in fuel cell is a recent central issue. As substitutes, these days several organic metal chelate compounds having featured moieties of M–N4 or M–N2O2 (M = transition metal ion) are being used as cathode catalysts in fuel cells. Here, in this study, we report in detail the electrocatalytic activity of manganese–Schiff base complexes for oxygen reduction reaction in 0·05 M HClO4 at room temperature. Actually, [Mn(salen)]+: [N,N′-bis(salicylaldehyde) ethylenediimino manganese(III)]+ and [Mn(salophen)]+: [N,N′-bis(salicylaldehyde)-1,2-phenylenediimino manganese(III)]+ were introduced into/onto the MCM-41 type silica spheres and used for the electrocatalytic reduction of oxygen. Synthesized materials were characterized by UV–Vis, FT–IR and electrochemical techniques. Significant low overpotential for oxygen reduction in 0·05 M HClO4 on [Mn(salen)]+- and [Mn(salophen)]+-incorporated silica-modified glassy carbon electrodes was observed.

Facile Preparation of Mn3O4 Hausmanite Nanoplates from a New Octahedral Manganese (III) Schiff Base Complex

A novel bidentate Schiff base ligand L (L = N-(4-amino-2-chloro-phenyl)-2-hydroxybenzaldehyde) and the subsequent octahedral manganese(III) Schiff base complex MnL3 have been synthesized and characterized by, FT-IR spectroscopy and elemental analyses (CHN). Additionally, Schiff base ligand has been characterized by 1H NMR spectroscopy. Thermogravimetric analysis of the ligand and its metal complexes reveals their thermal stability and decomposition pattern. Thus, the MnL3 complex has been investigated as a novel precursor for the facile preparation of Mn3O4 nanoparticles via solid-state thermal decomposition under aerobic conditions, at a temperature of ca. 450 °C The resulting Mn3O4 nanocrystals were characterized by FT-IR spectroscopy, X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The XRPD studies reveal the characteristic diffraction peaks indexed to the Mn3O4 hausmanite structure, while the absence of additional peaks tends to clearly indicate the high purity of the sample. In addition, the TEM/SEM investigations displayed the nanoplate shape of the rather monodisperse crystalline Mn3O4 nanoparticles, with an average diameter of ca. 10 nm. The statistical distribution of the nanoparticles size has to be provided with an histogram graphic.

Investigation of Magnetic Exchange Pathways in Heterotrinuclear Manganese(III) Schiff Base Complexes Involving Tetrathiocyanidoplatinate(II) Bridges

AbstractThe first heterotrinuclear manganese(III) Schiff base complexes involving tetrathiocyanidoplatinum(II) bridges with the general formula [{MnIII(L4)(Solv)}2{μ‐PtII(SCN)4}] {for which L42– is a tetradentate dianionic Schiff base ligand; L412– = N,N′‐benzene‐bis(salicylideneiminate) dianion (1a), L422– = N,N′‐ethylene‐bis(salicylidenebenzeneiminate) dianion (1b), L432– = N,N′‐benzene‐bis(4‐aminodiethylenesalicylideneiminate) dianion (1c), and Solv = CH3OH (1a, 1b) or H2O (1c)} were synthesized and characterized. The two terminal [Mn(L4)(Solv)]+ subunits are covalently bridged by [Pt(SCN)4]2– moieties in a trans arrangement. The coordinated solvent (Solv) ligands form intermolecular hydrogen bonds with the phenolate oxygen atoms of the neighboring molecules, which results in supramolecular 1D chain structures. Extensive networks of weak noncovalent interactions stabilize the crystal structures of all the compounds; moreover, hydrogen bonding within the chains was identified as a dominant exchange pathway. Magnetic analyses including the zero‐field splitting term revealed that the antiferromagnetic exchange interaction is stronger for compounds involving water molecules as ligands [1c, J = –1.31(6) cm–1] than for those containing methanol molecules [1a, J = –0.530(9) cm–1; 1b, J = –0.467(7) cm–1]. DFT calculations at the B3LYP/def2‐TZVP level supported the experimental findings that dominant antiferromagnetic exchange paths proceed through hydrogen bonds associated with the Solv ligands, whereas the [Pt(SCN)4]2– bridges prevent effective magnetic exchange.

Synthesis of Mn3O4 Nanorods by Solid-State Thermal Decomposition of Manganese(III) Schiff Base Complex [Mn(Brsal-mepn)(μ1,3-N3)

Hausmannite Mn3O4 nanorods were successfully prepared via solid-state thermal decomposition route with manganese(III) Schiff base complex [Mn(Brsal-mepn)(μ1,3-N3)]n as manganese source in air at 400 °C for 4 h. Powder X-ray diffraction, Fourier transform infrared spectrometry and scanning electron microscopy were used to characterize Mn3O4 nanoparticles. These results confirm that the resulting manganese oxide was pure single-phase Mn3O4 nanoparticles. Using the present method, Mn3O4 nanorods can be product without expensive organic solvent and complicated equipment.

Synthesis, X-ray crystal structure, and electrochemistry of polynuclear azido-bridged manganese(III) and copper(II) Schiff base complexes

Abstract New azido-bridged [MnIII(salabza)(μ-1,3-N3)]n (1), and [CuII4(salabza)2(μ-1,1-N3)2(N3)2(HOCH3)2],(2) complexes with an unsymmetrical Schiff base ligand, {H2salabza = N,N’-bis(salicylidene)-2-aminobenzylamine}, have been synthesized, characterized by spectroscopic and electrochemical methods, and their crystal structures have been determined by X-ray diffraction. In complex 1, each manganese(III) atom is coordinated with N2O2 donor atoms from salabza and two adjacent Mn(III) centers are linked by an end-to-end (EE) azide bridge to form a helical polymeric chain with octahedral geometry around the Mn(III) centers. Complex 2 is a centrosymmetric tetranuclear compound containing two types of Cu(II) centers with square pyramidal geometry. Each terminal copper atom is surrounded by N2O2 atoms of a salabza ligand, and the oxygen atom of the methanol molecule. Each central copper(II) ion is coordinated with two phenoxo oxygen atoms from one salabza, one terminal azido, and two end-on (EO) bridging azido ligands. The central copper(II) ions are linked to each other by the two end-on (EO) azido groups.

H-bonded Chains and Networks: A Recurring Feature in the Solid State Structures of Manganese (III) Carboxylate Schiff Base Complexes

Two new manganese(III) Schiff base complexes, [Mn(salen)(m-NO2-C6H4CO2)(H2O)] (1) and [Mn(msalen) (p-OH-C6H4CO2)(H2O)] (2), where H2salen = N,N'-bis(salicylidene)-1,2-diaminoethane, H2msalen = N,N'-bis (3-methoxysalicylidene)-1,2-diaminoethane were synthesized from the manganese (II) carboxylates. Single crystal X-ray diffraction studies show that the Jahn-Teller distorted octahedral complexes are stabilized by H-bonded chains and networks in the solid state.

Electronic Structure and Spectroscopic Properties of Mononuclear Manganese(III) Schiff Base Complexes: A Systematic Study on [Mn(acen)X] Complexes by EPR, UV/vis, and MCD Spectroscopy (X = Hal, NCS)

The manganese(III) Schiff base complexes [Mn(acen)X] (H2acen: N,N'-ethylenebis(acetylacetone)imine, X: I(-), Br(-), Cl(-), NCS(-)) are considered as model systems for a combined study of the electronic structure using vibrational, UV/vis absorption, parallel-mode electron paramagnetic resonance (EPR) and low-temperature magnetic circular dichroism (MCD) spectroscopy. By variation of the co-ligand X, the influence of the axial ligand field within a given square-pyramidal coordination geometry on the UV/vis, EPR, and MCD spectra of the title compounds is investigated. Between 25000 and 35000 cm(-1), the low-temperature MCD spectra are dominated by two very intense, oppositely signed pseudo-A terms, referred to as "double pseudo-A terms", which change their signs within the [Mn(acen)X] series dependent on the axial ligand X. Based on molecular orbital (MO) and symmetry considerations, these features are assigned to π(n.b.)(s, a) → yz, z(2) ligand-to-metal charge transfer transitions. The individual MCD signs are directly determined from the calculated MOs of the [Mn(acen)X] complexes. The observed sign change is explained by an inversion of symmetry among the π(n.b.)(s, a) donor orbitals which leads to an interchange of the positive and negative pseudo-A terms constituting the "double pseudo-A term".