Mononuclear Manganese Complexes Research Articles

Synthesis, characterization, and antibacterial activity of a manganese(II) complex of triaryltriazole

A manganese(II) complex of 4-(4-methylphenyl)-3,5-bis(2-pyridyl)-4H-1,2,4-triazole (MBPT) was synthesized and characterized by X-ray crystallography. [Mn(MBPT)2(H2O)2](ClO4)2 · 4H2O is a divalent mononuclear manganese(II) complex with manganese coordinated to four nitrogens from two triazole ligands and two oxygens from two water molecules in a slightly distorted octahedral geometry. The complex and ligand were tested in vitro for their antibacterial activities. The title complex showed a wide range of bactericidal activities.

Syntheses, spectral, electrochemical and thermal studies of mononuclear manganese(III) complexes with ligands derived from 1,2-propanediamine and 2-hydroxy-3 or 5-methoxybenzaldehyde: Self-assembled monolayer formation on nanostructure zinc oxide thin film

Mononuclear Mn(III) complexes have been prepared via the Mn(II) reaction of an equimolar of Schiff-bases derived from reaction of 2-hydroxy-3-methoxybenzaldehyde or 2-hydroxy-5-methoxybenzaldehyde with 1,2-diaminopropane. Axial ligands L include: pyridine (py) and H 2O. The resulting complexes have been characterized by FT-IR and UV–vis spectroscopy. The crystal structures of the complexes were determined and indicate that in the solid state the complex adopts a slightly distorted octahedral environment of the imine N and hydroxo O with the two axial ligands. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Mn III–Mn II is electrochemically quasi-reversible. Thermal stability of these complexes was determined by TG and DTG. Layers of these complexes were formed on nanostructure zinc oxide thin film and a red shift was observed when zinc oxide thin film is modified by complex.

Oxidation of glyoxylic acid by a mononuclear manganese(IV) complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane: A kinetics and mechanistic study

The oxidation of glyoxylic acid (HGl) by Mn IVL {L 4− = tetra deprotonated 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane} was investigated in the pH range 1.67–10.18, at 25–45 °C and 0.5 M ionic strength. The reaction exhibited biphasic kinetics with Mn IIIL − as the reactive intermediate. Mn IV was reduced to Mn II. The products of oxidation of HGl were identified as formic acid and CO 2 in acidic medium, and oxalate in basic medium, consistent with the stoichiometry: −Δ[Mn IV]/−Δ[HGl] = 1. In acidic medium, both Mn IVL and Mn IIIL − formed outer-sphere adducts with the neutral HGl {HC(OH) 2COOH} molecule, with an association constant Q av of 28 and 70 M −1, respectively. A similar adduct formation was not observed for the glyoxylate mono anion {Gl −, CH(OH) 2(CO 2 −)} and glyoxylate dianion {Gl 2−, CH(OH)(O −)CO 2 −}. The rate and activation parameters for the various paths are reported and an outer-sphere electron transfer mechanism is suggested.

π–π Stacking and magnetic coupling mechanism on a mono-nuclear Mn(II) complex

A novel magnetic coupling is observed in a unpublished crystal that consists of a mono-nuclear manganese(II) complex, namely, [Mn(DPP)(NCS) 2] (DPP = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline), in which neutral DPP molecule functions as tridentate chelated ligand. In the complex Mn(II) ion assumes a distorted trigonal bipyramidal geometry and in the crystal there is a π–π stacking interaction between the adjacent complexes, which involves pyridyl ring and the symmetry-related pyrazolyl ring and pyridyl ring. The fitting for the data of the variable-temperature magnetic susceptibilities with infinite uniform Mn(II) chain formula gave the magnetic coupling constant J = −0.11 cm −1, and theoretical calculations reveal that there exists a very weak anti-ferromagnetic coupling between the adjacent Mn(II) ions with J = −0.02 cm −1. The magnetic coupling sign is explained based on McConnell I spin-polarization mechanism with the analysis of the spin density population and the factors that dominate the magnetic coupling magnitude.

Case Study on a Rare Effect: The Experimental and Theoretical Analysis of a Manganese(III) Spin-Crossover System

The six-coordinated mononuclear manganese(III) complex [Mn(5-Br-sal-N-1,5,8,12)]ClO(4) has been synthesized and isolated in crystalline form. Magnetic measurements and variable-temperature single-crystal X-ray crystallography corroborated with theoretical analysis provided firm evidence for the spin-crossover effects of this system. The monomeric complex cations are made by a hexadentate mixed-donor Schiff base ligand imposing a distorted octahedral geometry and subtle structural effects determining the manifestation of the variable spin properties of the manganese(III) centers. The spin crossover in [Mn(5-Br-sal-N-1,5,8,12)]ClO(4) has resulted in an unprecedented crystallographic observation of the coexistence of high-spin (HS; S = 2) and low-spin (LS; S = 1) manganese(III) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct manganese centers are both HS. Only one of the two slightly different units undergoes spin crossover in the temperature range ∼250-50 K, whereas the other remains in the HS state down to 50 K. The density functional theory calculations, performed as relevant numerical experiments designed to identify the role of orbital and interelectron effects, revealed unedited aspects of the manganese(III) spin-conversion mechanisms, developed in the conceptual frame of ligand-field models.

Synthesis, structural characterization and alcohol oxidation activity of a new mononuclear manganese(II) complex

A manganese(II) complex of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) has been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR, and UV–Vis spectroscopic techniques. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this catalyst using oxone (2KHSO5·KHSO4·K2SO4) as an oxidant under biphasic reaction conditions (CH2Cl2/H2O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature. Easy preparation, mild reaction conditions, high yields of the products, short reaction times, no further oxidation to the corresponding carboxylic acids, high selectivity and inexpensive reagents make this catalytic system a useful oxidation method for aliphatic and benzylic alcohols.

Role of carboxamido nitrogen in mononuclear manganese complex: Superoxide scavenging activity and nuclease activity

The graphical abstract represents two important aspects of our manuscript namely, SOD activity and nuclease activity. Complex 3 ·CH 3 OH, which was structurally characterized (shown in the graphical abstract), possesses E 1/2 value for Mn II /Mn III couple which is in the proper range (between two arrows, −0.375 V ⩽ E 1/2 ⩽ +0.605 V vs Ag/AgCl) to exhibit SOD activity. In the redox potential value scale, values for complexes 1 and 2 are beyond the proper range and show very poor SOD activity. In terms of nuclease activity complex 3 ·CH 3 OH was more efficient as compared to complexes 1 and 2 . Schiff base complexes 1 and 2 afforded lower activity for SOD as well as nuclease activity due to the lack of N am donor in the ligand frames. Three new ligands Pyimpy (2-((2-phenyl-2-(pyridin-2-yl)hydazono)methyl)pyridine), Me-Pyimpy (1-phenyl-1-(pyridin-2-yl)-2-(1-(pyridin-2-yl)ethylidene)hydrazine) and PampH (N′-phenyl-N′-(pyridin-2-yl)picolinohydrazide) were synthesized. Hexa-coordinated mononuclear complexes [Mn(Pyimpy) 2 ](ClO 4 ) 2 ( 1) , [Mn(Me-Pyimpy) 2 ](ClO 4 ) 2 ( 2) , and [Mn(Pamp) 2 ](ClO 4 )·CH 3 OH, ( 3 ·CH 3 OH) were synthesized and characterized. The molecular structure of [Mn(Pamp) 2 ](ClO 4 )·CH 3 OH, ( 3 ·CH 3 OH) was determined by single crystal X-ray diffraction, which afforded distorted octahedral coordination sphere having meridionally spanning ligands. The redox properties were exploited to examine superoxide dismutase (SOD) activity using Mn(II)/Mn(III) couple. The complex 3 having ligands containing carboxamido nitrogen (N am ) donor, has been revealed to catalyze more effectively the dismutation of superoxide ( O 2 - ) ions in xanthine–xanthine oxidase–nitro blue tetrazolium assay as compared to 1 and 2 . Among the three complexes, complex 3 was found to be most effective in nuclease activity in the presence of H 2 O 2 .

Understanding the Zero-Field Splitting of Mononuclear Manganese(II) Complexes from Combined EPR Spectroscopy and Quantum Chemistry

This micro-review is devoted to the studies of the electronic structure, especially the zero-field splitting, of mononuclear Mn(II) complexes by electron paramagnetic resonance spectroscopy and quantum chemistry.

Synthesis, structure and antibacterial activity of manganese(III) complexes of a Schiff base derived from furfurylamine

Two new mononuclear complexes of manganese(III) viz. [MnL 2(LH) 2]ClO 4 ( 1) and [MnL 2(N 3)]·0.5CH 3OH ( 2) have been synthesized by reacting manganese perchlorate with furfurylamine and salicylaldehyde (plus sodium azide in 2) where L = (2-hydroxybenzyl-2-furylmethyl)imine, an asymmetric bidentate Schiff base formed in situ to bind the Mn(III) ion. The complexes have been characterized by elemental analysis, IR spectroscopy, TGA and single crystal X-ray diffraction studies. Structural studies reveal that the complexes 1 and 2 adopt an octahedral and a square pyramidal geometry, respectively. The antibacterial activity of the complexes has been tested against Gram(+) and Gram(−) bacteria.

Synthesis, Crystal Structure and Bioactivities of a Novel Propeller Shaped Manganese Complex with the Ligand N′‐Benzylidenesalicylhydrazide

AbstractA new propeller shaped mononuclear manganese(III) complex of the general formula: [MnL3(H2O)], where HL is N′‐benzylidenesalicylhydrazide, was synthesized and characterized. The crystal structure of the title compound was characterized by X‐ray single crystal diffractometry, which belongs to a triclinic system with space group P‐1, cell dimensions of a=11.6411 Å, b=12.728 Å, c=16.346 Å, α=110.357°, β=96.555°, γ=108.996°, V=2075.2 Å3, Z=2 and Dcalc=1.265 g/cm3. In this complex, the metal ion is in an octahedral coordination environment, enforcing the stereochemistry of the ligands as a propeller configuration. Antibacterial screening data indicate that the complex has stronger antibacterial activity against the tested microorganisms than the ligand.

Synthesis and Reactivity of a Mononuclear Manganese(II) Complex Having Pseudo-Seven Coordination Environment

Utilizing a planar five coordinating N3S2 ligand, 2,6-bis(2-methylthiophenyliminomethyl)pyridine, a pseudo 7-coordinated manganese(II) complex with two labile triflate anions in the axial positions was synthesized. The reaction of the manganese(II) complex with an oxidant, iodosylbenzene, produced a metastable high-valent manganese(IV)-oxo species at 0 o C. The high-valent Mn(IV)-oxo intermediate was characterized with a UV-vis spectrophotometer and an electrospray ionization mass spectroscopy. Reactivity studies of the Mn(IV)=O species revealed that the intermediate is capable of oxygenating PPh3 and N-dealkylating N,N-dimethyl-toludine.

Tetra-, Tri-, and Mononuclear Manganese(II/III) Complexes of a Phenol-Based N2O2Capping Ligand: Use of Carboxylates as Ancillary Ligands in Tuning the Nuclearity of the Complexes

Manganese(II/III) complexes of a phenol-based tetradentate ligand L(2-) [H(2)L = N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)-ethylenediamine], namely, [Mn(4)(L)(2)(PhCOO)(6)] (1), [Mn(3)(L)(2)(CH(3)CH(2)COO)(2)(OMe)(2)].H(2)O (2), and [Mn(L){(CH(3))(3)CCOO}(CH(3)OH)].CH(3)OH (3), have been synthesized. The basicity and steric congestion provided by the carboxylate moiety used as an ancillary ligand have profound influence on tuning the nuclearity of these compounds. Results of X-ray crystallography, electronic spectroscopy, and variable-temperature (1.8-300 K) magnetic measurements have been used to characterize these compounds. Complex 1 has a very interesting centrosymmetric structure that involves two crystallographically equivalent binuclear [Mn(II)-Mn(III)] units, connected together by a pair of syn-anti bridging benzoates to generate a "dimer of dimers" structural motif. Compound 2 with propionate as the ancillary ligand, on the other hand, has a nearly linear Mn(III)-Mn(II)-Mn(III) core with antiferromagnetically coupled (J = -0.13 cm(-1)) metal centers. Compound 1 has an S(T) = 9 spin ground state with ferromagneticlly coupled metal centers (J(wb)= 2.8(1) and J(bb) = 0.09(2) cm(-1)) that failed to function as a single molecule magnet due to the presence of low-lying excited states with smaller spin values and a weak magnetic anisotropy. The electron paramagnetic resonance spectrum of 1 in the frozen solution (12 K) displays two signals in the g = 2 and g = 4 regions, each split into six lines due to (55)Mn (I = 5/2) superhyperfine couplings. The use of bulky pivalate as a replacement for benzoate provides enough steric bulk to generate a mononuclear species [Mn(L){(CH(3))(3)CCOO}(CH(3)OH)].CH(3)OH (3). The lone manganese(III) center in this compound has an octahedral geometry, completed by the tetradentate ligand L(2-) together with an axially coordinated methanol molecule and a monodentate pivalate. The latter two are connected by a hydrogen bond, thus stabilizing the monodentate carboxylate moiety. Redox behaviors (CV) of 1 and 3 are grossly similar, each undergoing a quasi-reversible reduction process at E(1/2) = -0.03 and -0.11 V, respectively, versus a Ag/AgCl reference.

Synthesis, structure, and catalase-like activity of a novel manganese(II) complex: Dichloro[1,3-bis(2′-benzimidazolylimino)isoindoline]manganese(II)

Reaction of the ligand 1,3-bis(2′-benzimidazolylimino)isoindoline with manganese(II) chloride in acetonitrile/methanol leads to the novel mononuclear manganese(II) complex 1,3-bis(2′-benzimidazolylimino)isoindolinedichloro manganese(II) [Mn(bimindH)Cl 2], which has been characterized by various techniques such as elemental analysis, IR, UV–Vis, ESR spectroscopy, and X-ray diffraction. The ligand bimindH was synthesized by fusing phthalonitrile and 2-aminobenzimidazole at high temperature until ammonia evolution ceased. The catalase-like activity of the complex was tested in propionitrile, and it proved to be active in the dihydrogen peroxide dismutation. Based on kinetic studies the reaction is first-order in relation to both the complex and hydrogen peroxide.

Mono- and dinuclear manganese(III) complexes showing efficient catechol oxidase activity: syntheses, characterization and spectroscopic studies

Four side-off compartmental ligands L1-L4 [L1 = N,N'-ethylenebis(3-formyl-5-methyl-salicylaldimine), L2 = N,N'-1-methylethylenebis(3-formyl-5-methylsalicylaldimine), L3 = N,N'-1,1-dimethylethylenebis(3-formyl-5-methylsalicylaldimine) and L4= N,N'-cyclohexenebis(3-formyl-5-methylsalicylaldimine)] having two binding sites, N2O2 and O4, have been chosen to synthesize mononuclear and dinuclear manganese(III) complexes with the aim to study their catecholase activity using 3,5-di-tert-butylcatechol (3,5-DTBC) as substrate in the presence of molecular oxygen. In all cases only mononuclear manganese complexes (1-4) were obtained, with manganese coordination taking place at the N2O2 binding site only, irrespective of the amount of manganese salt used. All these complexes have been characterized by routine physico-chemical techniques. Complex MnL2Cl.4H2O (2) has further been structurally characterized by X-ray single crystal structure analysis. Four dinuclear manganese complexes, 5-8, were obtained after condensing the two pending formyl groups on each ligand (L1-L4) with aniline followed by reaction with MnCl2 to put the second Mn atom onto another N2O2 site. The catalytic activity of all complexes 1-8 has been investigated following the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) with molecular oxygen in two different solvents, methanol and acetonitrile. The study reveals that the catalytic activity is influenced by the solvent and to a significant extent by the backbone of the diamine and the behavior seems to be related mainly to steric rather than electronic factors. Experimental data suggest that a correlation, the lower the E(1/2) value the higher the catalytic activity, can be drawn between E(1/2) and Vmax of the complexes in a particular solvent. The EPR measurements suggest that the catalytic property of the complexes is related to the metal center(s) participation rather than to a radical mechanism.

Multifrequency high-field EPR investigation of a mononuclear manganese(iv) complex

Electronic properties of [Mn(IV)(tacn)(OMe)(3)](+), especially the axial zero field splitting term D, which characterizes the magnetic anisotropy, have been investigated by multifrequency high-field EPR.

Syntheses and structures of mononuclear manganese(II) complexes bearing bis(1-methylimidazol-2-yl)ketone ligands

The ligand bis(1-methylimidazol-2-yl)ketone (bik) ( 1) was applied in the synthesis of mononuclear manganese(II) complexes. The complexes [Mn(bik) 2Cl 2] ( 2), [Mn(bik) 2(OH 2)Br]Br × H 2O ( 3b) and [Mn(bik) 3](ClO 4) ( 4) were characterised by X-ray crystallography, ESR and UV–Vis methods.

Mononuclear Manganese(III) Complexes as Building Blocks for the Design of Trinuclear Manganese Clusters: Study of the Ligand Influence on the Magnetic Properties of the [Mn3(μ3-O)]7+ Core

Mononuclear Manganese(III) Complexes as Building Blocks for the Design of Trinuclear Manganese Clusters: Study of the Ligand Influence on the Magnetic Properties of the [Mn₃(μ₃-O)]⁷⁺ Core

Spectroscopic and Theoretical Study of a Mononuclear Manganese(III) Complex Exhibiting a Tetragonally Compressed Geometry

Inelastic neutron scattering and high-field electron paramagnetic resonance data are presented for [Mn(bpia)(OAc)(OCH(3))](PF(6)), where bpia is bis(picolyl)(N-methylimidazole-2-yl)amine. Modeling of the data to the conventional fourth-order spin-Hamiltonian yielded the following parameters: D = 3.526(3) cm(-1), E = 0.588(6) cm(-1), B(0)(4) = -0.00084(7) cm(-1), B(2)( 4)= -0.002(2) cm(-1), (4)(4) = -0.0082(5) cm(-1), g(x) = 1.98(1), g(y) = 1.952(6), and g(z) = 1.978(5). The complex is of particular interest given the biochemical activity and the unusual stereochemistry distinguished by a rare example of a tetragonally compressed octahedron and a pronounced angular distortion imposed by the tetradentate tripodal bpia ligand. Ligand field, density functional theory, and complete active space self-consistent field ab initio calculations are presented that aim to relate the spectroscopic data to the molecular geometry.

Binuclear Schiff Base Complex of Manganese(III) as a Neutral Carrier for a Highly Selective Iodide Electrode

A new highly selective iodide electrode incorporating a binuclear manganese(III) complex, bis(salicylaldehyde-aminopropanol)dichloroaceticdimanganese(III) [Mn(III)(2)-BSAPDCA], as a neutral carrier is described. The electrode displays an anti-Hofmeister selectivity sequence: iodide >> perchlorate > salicylate > thiocyanate > nitrate > bromide > nitrite > chloride > sulfate. The excellent selectivity for iodide is related to a direct interaction between the central Mn(III) atom and iodide and a steric effect associated with the structure of the carrier, which is supported by UV spectroscopy and AC impedance techniques. The electrode exhibits a near-Nernstian potentiometric linear response range to iodide from 1.0 x 10(-1) to 2.0 x 10(-5) mol/L with a detection limit of 8.0 x 10(-6) mol/L and a slope of -60.3 mV/decade in pH 3.0 of phosphate buffer solutions at 20 degrees C. From a comparison of the potentiometric response characteristics between a binuclear manganese(III) complex, Mn(III)(2)-BSAPDCA, and a mononuclear manganese(III) complex, Mn(III)-BSAPB, an enhanced response towards iodide from a binuclear metallic complex-based electrode was observed. The electrode, based on binuclear manganese(III) complex, was successfully applied to the determination of inorganic total iodine in iodized table salt with satisfactory results.

One Novel Three-dimensional Network Constructed from [Mn(4,4′-bip)2(OH2)4]2+ Cations and DBA2− Anions via Hydrogen-bonding and π–π Interactions

One new mononuclear manganese complex of [Mn(4,4′-bip)2(OH2)4](DBA) · 4H2O (1) (4,4′-bipyridine, 4,4′-bip; H2DBA, benzene-1,3-dicarboxylic acid) has been obtained from the hydrothermal reaction of MnCl2 · 4H2O, 4,4′-bipyridine and H2DBA in the solvent of H2O at 140 °C for 3 days, characterized by X-ray analysis, spectroscopic methods, and thermal analysis. Packing diagram shows that the three-dimensional network was formed via hydrogen bonds and strong π–π interactions. One Novel Three-dimensional Network Constructed from [Mn(4,4′-bip) 2 (OH 2 ) 4 ] 2+ Cations and DBA 2− Anions via Hydrogen-bonding and π–π Interactions Ying Liu, Bao Zhang, Jian-min Dou, Da-qi Wang, Da-cheng Li, Lei Zhou One new mononuclear manganese complex of [Mn(4,4’-bip)2(OH2)4](DBA) · 4H2O (1) (4,4’-bipyridine, 4,4’-bip; H2DBA, benzene-1, 3-dicarboxylic acid) has been obtained and haracterized by X-ray analysis, spectroscopic methods, and thermal analysis. Packing diagram shows that the three-dimensional network was formed via hydrogen bonds and strong π-π interactions.