Dinuclear Manganese Complex Research Articles

A mononuclear nickel(II) complex and a dinuclear manganese(III) complex derived from N,N'-bis(5-methoxysalicylidene)-1,2-ethanediamine: synthesis, crystal structures, and catalytic epoxidation property

A mononuclear nickel(II) complex and a dinuclear manganese(III) complex derived from N,N'-<i>bis</i>(5-methoxysalicylidene)-1,2-ethanediamine: synthesis, crystal structures, and catalytic epoxidation property

ChemInform Abstract: Dinuclear Manganese, Iron, Chromium, and Cobalt Complexes Derived from Aroylhydrazone Ligands: Synthetic Strategies, Crystal Structures, and Magnetic Properties

AbstractReview: 86 refs.

Dinuclear manganese, iron, chromium, and cobalt complexes derived from aroylhydrazone ligands: Synthetic strategies, crystal structures, and magnetic properties

• Synthetic strategies employed to obtain new and magnetically interesting dinuclear molecules based on iron, manganese, chromium, and cobalt metal ions. • Compared crystal structures of 15 dinuclear complexes. • Very strong ferromagnetic interactions in Mn 3+ dinuclear compounds. • Magnetostructural correlations discussed. • Compared data from theoretical calculations. Coordination clusters of 3d metals continue to attract the intense interest of the scientists from the synthetic inorganic chemistry, bioinorganic chemistry and molecular magnetism communities. We review here the synthetic strategies employed in a continuous effort to obtain new and potentially magnetically interesting dinuclear molecules based on iron, manganese, chromium, and cobalt metal ions. The reported systems are pure homometallic 3d materials. We have focused on describing aspects of the synthesis, the crystal structures and the magnetic behaviour of these coordination compounds with low nuclearity. A deep solid-state and magnetic characterization of these systems has allowed us to gain evidence regarding the role played by weak exchange interactions and geometrical factors on the slow dynamics of the magnetization. In addition, the analysis through ab initio calculations has provided a valuable insight into the influence of organic periphery, bridging ligands, and remote substituents on the exchange coupling constant ( J ). In the case of a dinuclear complex based on manganese, the largest ferromagnetic interaction between two Mn III has been observed ( J = 19.7 cm −1 ).

Macrocyclic dinuclear nickel(II) and manganese(II) complexes: synthesis, X-ray crystal structures, DNA cleavage, and antimicrobial activity studies

Three dinuclear macrocyclic complexes, [Ni2L1(μ-OAc)(H2O)(CH3O)](ClO4)2·4(H2O) (1), [Mn2L2(μ-OAc) (H2O)]ClO4·H2O (2) and [Mn2L3(μ-OAc)]ClO4·H2O (3), (where H2L1, H2L2 and H2L3 are the [2 + 2] condensation products of 2,6-diformyl-4-fluorophenol with diethylenetriamine and N,N-bis(3-aminopropyl)-2-thiopheno-ethylamine, respectively), have been synthesized and characterized. The electrochemical characteristics showed that the metal centers are more electropositive when strongly electron-withdrawing groups are attached to the macrocyclic ring, and hence more easily reduced. All three complexes have been found to promote cleavage of plasmid pBR322 DNA from the supercoiled form I to the open circular form II. The antibacterial activities of the complexes were also studied.

Dinuclear manganese(II) complexes of hexaazamacrocycles bearing N-benzoylated pendant separated by aromatic spacers: Antibacterial, DNA interaction, cytotoxic and molecular docking studies

Three new homodinuclear manganese(II) complexes of the type [Mn2L1–3(ClO4)(H2O)](ClO4)3 (1–3) have been synthesized via cyclocondensation of terephthalaldehyde with three different benzoylated pendants in the presence of manganese(II) perchlorate and characterized by spectroscopic methods. Cyclic voltammetric investigation of complexes (1–3) depict two quasi-reversible one electron reduction processes in the cathodic potential region (E1pc=–0.73 to–0.83V, E2pc=–1.31 to −1.40V) and two quasi-reversible one electron oxidation processes in the anodic potential region (E1pa=1.03 to 1.10V, E2pa=1.69 to 1.77V). Electronic absorption spectra of the complexes suggested tetrahedral geometry around the central metal ion. The observed low magnetic moment values (μeff, 5.60–5.68 B.M.) of the complexes indicate the presence of an antiferromagnetic spin–exchange interaction between two metal centers, which was also supported by the broad EPR signal. All the compounds were tested for antibacterial activity against Gram (–ve) and Gram (+ve) bacterial strains. The binding studies of complexes with CT-DNA suggested minor-groove mode of interaction. Molecular docking studies were carried out in order to find the binding affinity of complexes with DNA and protein EGFR Kinase. The complexes are stabilized by additional electrostatic and van der Waals interaction with the DNA, and support minor groove mode of binding. The cleavage activity of complexes on pBR322 plasmid DNA displays efficient activity through a mechanistic pathway involving hydroxyl radicals. The cytotoxicity of complexes 2 and 3 have been tested against human liver adenocarcinoma (HepG2) cell line. Nuclear-chromatin cleavage has also been observed with propidium iodide (PI) staining and alkaline single-cell gel electrophoresis (comet assay) techniques.

Distribution of manganese species in an oxidative dimerization reaction of a bis-terpyridine mononuclear manganese (II) complex and their heterogeneous water oxidation activities

Heterogeneous water oxidation catalyses were studied as a synthetic model of oxygen evolving complex (OEC) in photosynthesis using mica adsorbing various manganese species. Distribution of manganese species formed in the oxidative dimerization reaction of [MnII(terpy)2]2+ (terpy=2,2′:6′,2″-terpyridine) (1′) with various oxidants in water was revealed. 1′ was stoichiometrically oxidized to form di-μ-oxo dinuclear manganese complex, [(OH2)(terpy)MnIII(μ-O)2MnIV(terpy)(OH2)]3+ (1) by KMnO4 as an oxidant. When Oxone and Ce(IV) oxidants were used, the further oxidation of 1 to [(OH2)(terpy)MnIV(μ-O)2MnIV(terpy)(OH2)]4+ (2) was observed after the oxidative dimerization reaction of 1′. The mica adsorbates with various composition of 1′, 1 and 2 were prepared by adding mica suspension to the various oxidant-treated solutions followed by filtration. The heterogeneous water oxidation catalysis by the mica adsorbates was examined using a Ce(IV) oxidant. The observed catalytic activity of the mica adsorbates corresponded to a content of 1 (1ads) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1′ (1′ads) and 2 (2ads) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that 1ads works for the catalysis through cooperation with adjacent 1ads or 2ads, meaning that 2ads assists the cooperative catalysis by 1ads though 2ads is not able to work for the catalysis alone. For the Ce(IV)-treated system, O2 evolution was hardly observed although the sufficient amount of 1ads was contained in the mica adsorbates. This was explained by the impeded penetration of Ce(IV) ions (as an oxidant for water oxidation) into mica by Ce3+ cations (generated in oxidative dimerization of 1′) co-adsorbed with 1ads.

Synthesis and Crystal Structure of 1,3-Bis(5-nitrosalicylideneamino)-2-propanol

1,3-Bis(5-nitrosalicylideneamino)-2-propanol (H3nsalpr) is an interesting pentadentate ligand, having two phenolic oxygen, two imino-nitrogen, and one alcohol-oxygen donor atoms to give a mononuclear copper(II) complex with a tetradentate O,N,N,O-chelate1 as well as dinuclear manganese(II)2 and manganese(III)3 complexes with tridentate O,N,O-chelates. A similar dinuclear manganese(III) complex with 1,3-bis(salicylideneamino)-2-propanol was also reported.4 However, there have been no report on the structure of the Schiff-base ligand, itself, regarding H3nsalpr. In this study, we successfully prepared single-crystals of H3nsalpr (Fig. 1), and determined the crystal structure in order to understand the unique coordination behavior. 1,3-Diamino-2-propanol (1.025 g, 0.0114 mol) and 5-nitrosalicylaldehyde (3.802 g, 0.0228 mol) were dissolved in methanol (100 cm3). The solution was refluxed for 3 h, and then left at room temperature. The resulting yellow precipitate was filtered off, washed by methanol, and dried under a vacuum. Yield, 4.200 g (94%). IR (KBr, cm–1): 2982 (n(Ar-H), 2936 (nCH), 1666 (nCO), 1549 (nasNO2), 1360 (nsNO2). X-ray quality crystals were grown by slow evaporation of the reaction solution. A preliminary examination was made, and data were collected on a Bruker CCD X-ray diffractometer (SMART APEX) using graphite-monochromated Mo-Ka radiation. Crystal data and details concerning the data collection are given in Table 1. The structures were solved by direct methods and refined by fullmatrix least-squares methods. The hydrogen atoms attached to the imino nitrogen atoms were located from difference Fourier maps and refined; the other hydrogen atoms were inserted at their calculated positions, and fixed there. All of the calculations were carried out on a Windows 7 Core i5 computer utilizing the SHELXTL software package and SHELXL-2014/7.5 Synthesis and Crystal Structure of 1,3-Bis(5-nitrosalicylideneamino)-2propanol

A novel homodinuclear manganese(III) complex with N,N′-bis(salicylidene)diethylenetriamine: Synthesis, structure and catalytic activity

A novel chloride bridged dinuclear manganese(III) complex was prepared and its structure established by X-ray diffraction analysis. The complex showed high selectivity in H2O2 promoted oxidation of cyclohexane and cyclic alkenes. Under optimized conditions, 72% of cyclohexane conversion with 85% of selectivity for alcohol was achieved after 5h. To the best of our knowledge this activity and remarkable selectivity to cyclohexanol is the highest for a manganese catalyst.

Syntheses, crystal structures, and magnetic properties of a series of double end-on azido-bridged dinuclear manganese(II) complexes

Four azido-bridged dinuclear Mn(II) complexes, [Mn2(phen)4 μ-1,1-N3)2][FeIII(bpmb)(CN)2]2·H2O (1), [Mn2(phen)4(μ-1,1-N3)2][FeIII(bpClb)(CN)2]2·H2O (2), and [Mn2(phen)4(μ-1,1-N3)2][MIII(bpdmb)(CN)2]2·3H2O [M = Fe (3) or Cr (4); phen = 1,10-phenanthroline, bpmb2– = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate, bpClb2– = 1,2-bis(pyridine-2-carboxamido) 4-chloro-benzenate, bpdmb2– = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-benzenate], have been synthesized using the synthetic strategy of large anion inducement. Single-crystal X-ray diffraction analysis reveals that all four complexes are doubly end-on (EO) azido-bridged binuclear Mn(II) complexes with two large [M(L)(CN)2]– (L = bpmb2−, bpClb2−, or bpdmb2−) building blocks acting as charge-compensating anions. The magnetic properties of the complexes have been investigated, and the results indicate that the magnetic coupling between two Mn(II) centers through the EO azide bridges is ferromagnetic, with J = 0.64(1) cm−1 for 1, 0.43(1) cm−1 for 2, 0.50(1) cm−1 for 3, and 0.66(2) cm−1 for 4. The magneto-structural relationships of EO azido-bridged Mn(II) systems are discussed.

Probing the Influence of the Ligands on the Magnetism of Dinuclear Manganese, Iron, and Chromium Complexes Supported by Aroylhydrazone

AbstractThe influence of aroylhydrazone and bridging ligands on the exchange coupling constant (J) of five dinuclear metal complexes is analyzed through ab initio calculations. The complete active space second‐order perturbation theory with localized orbitals offers not only estimates of J but also detailed information about the contributions of the molecular regions to the overall magnetism. This computational strategy is first validated for two previously reported ferromagnetic MnIII/MnIII and antiferromagnetic FeIII/FeIII complexes. Such calculations are extended to three new dinuclear complexes of MnIV, FeIII and CrIII constructed with a chemically simpler ligand (HL). We provide the synthesis and structural characterization (X‐ray diffraction crystallography) of these three new compounds. The HL ligand exhibits little electronic influence over the J value, but it directs the magnetic properties of the compound by conditioning the relative arrangement of the metal centres.

Magnetic Interactions through Fluoride: Magnetic and Spectroscopic Characterization of Discrete, Linearly Bridged [MnIII2(μ-F)F4(Me3tacn)2](PF6)

The nature of the magnetic interaction through fluoride in a simple, dinuclear manganese(III) complex (1), bridged by a single fluoride ion in a perfectly linear fashion, is established by experiment and density functional theory. The magnitude of the antiferromagnetic exchange interaction and the manganese(III) zero-field-splitting parameters are unambiguously determined by inelastic neutron scattering to yield J = 33.0(2) cm(-1) (Ĥ = JŜ1·Ŝ2 Hamiltonian definition) and single-ion D = -4.0(1) cm(-1). Additionally, high-field, high-frequency electron paramagnetic resonance and magnetic measurements support the parameter values and resolve |E| ≈ 0.04 cm(-1). The exchange coupling constant (J) is 1 order of magnitude smaller than that found in comparable systems with linear oxide bridging but comparable to typical magnitudes through cyanide, thus underlining the potential of fluoride complexes as promising building blocks for novel magnetic systems.

Bioinspired manganese(II) complexes with a clickable ligand for immobilisation on a solid support.

Clickable ligands like N,N'-bis((pyridin-2-yl)methyl)prop-2-yn-1-amine (L(1)) and N-((1-methyl-1H-imidazol-2-yl)methyl)-N-(pyridin-2-ylmethyl)prop-2-yn-1-amine (L(2)) have been used to synthesise a series of manganese(ii) complexes for grafting onto appropriate solid supports. These ligands mimic the 2-His-1-carboxylate facial chelation present in the active site of the manganese-dependent dioxygenase (MndD), while the alkyne side function allows grafting of the ligand onto an azido-functionalised support using "click chemistry" methodologies. Such synthetic analogues of the MndD crystallise in the solid state as double halide or pseudohalide-bridged dinuclear manganese(ii) complexes of the general formula [Mn2(μ-X)2X2L2] [L = L(1) with X = Cl (), Br (), and N3 (); L = L(2) with X = N3 ()]. Complexes are characterised by a weak magnetic exchange interaction between the two high-spin Mn(II) ions through the two X(-) bridges (J in the range of -0.059 to +5.30 cm(-1), H = -J·SMn1·SMn2 with SMn1 = SMn2 = 5/2). A new magneto-structural correlation of superexchange bis(μ1,1-azido)dimanganese(ii) complexes has been proposed using both structural parameters, the Mn-N-Mn bridging angle and the Mn-Nazido distance. In MeOH-EtOH solution the dimeric species are present together with few percents of mononuclear manganese(ii) complexes as evidenced by electron paramagnetic resonance (EPR) spectroscopy. Grafting the complexes onto mesoporous silica of MCM-41 type stabilises both dimers and monomers in the nanopores of the solid.

Dinuclear manganese complexes for water oxidation: evaluation of electronic effects and catalytic activity

During recent years significant progress has been made towards the realization of a sustainable and carbon-neutral energy economy. One promising approach is photochemical splitting of H2O into O2 and solar fuels, such as H2. However, the bottleneck in such artificial photosynthetic schemes is the H2O oxidation half reaction where more efficient catalysts are required that lower the kinetic barrier for this process. In particular catalysts based on earth-abundant metals are highly attractive compared to catalysts comprised of noble metals. We have now synthesized a library of dinuclear Mn2(II,III) catalysts for H2O oxidation and studied how the incorporation of different substituents affected the electronics and catalytic efficiency. It was found that the incorporation of a distal carboxyl group into the ligand scaffold resulted in a catalyst with increased catalytic activity, most likely because of the fact that the distal group is able to promote proton-coupled electron transfer (PCET) from the high-valent Mn species, thus facilitating O-O bond formation.

Spectroscopic investigation of new water soluble [formula omitted] and [formula omitted] complexes for the substrate binding models of xylose/glucose isomerases

In methanol, the reaction of stoichiometric amounts of Mn(OAc)2·4H2O and the ligand H3hpnbpda [H3hpnbpda=N,N′-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N′-diacetic acid] in the presence of NaOH, afforded a new water soluble dinuclear manganese(II) complex, [Mn2(hpnbpda)(μ-OAc)] (1). Similarly, the reaction of Mg(OAc)2·4H2O and the ligand H3hpnbpda in the presence of NaOH, in methanol, yielded a new water soluble dinuclear magnesium(II) complex, [Mg2(hpnbpda)(μ-OAc)(H2O)2] (2). DFT calculations have been performed for the structural optimization of complexes 1 and 2. The DFT optimized structure of complex 1 shows that two manganese(II) centers are in a distorted square pyramidal geometry, whereas the DFT optimized structure of complex 2 reveals that two magnesium(II) centers adopt a six-coordinate distorted octahedral geometry. To understand the mode of substrate binding and the mechanistic details of the active site metals in xylose/glucose isomerases (XGI), we have investigated the binding interactions of biologically important monosaccharides d-glucose and d-xylose with complexes 1 and 2, in aqueous alkaline solution by a combined approach of FTIR, UV–vis, fluorescence, and 13C NMR spectroscopic techniques. Fluorescence spectra show the binding-induced gradual decrease in emission of complexes 1 and 2 accompanied by a significant blue shift upon increasing the concentration of sugar substrates. The binding modes of d-glucose and d-xylose with complex 2 are indicated by their characteristic coordination induced shift (CIS) values in 13C NMR spectra for C1 and C2 carbon atoms.

Synthesis and crystal structures of N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine and its dinuclear manganese(III) complex with antibacterial activities

A new dinuclear manganese complex, [Mn2L2(N3)2], was prepared by reaction of bis-Schiff base N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine (H2L) with manganese acetate and sodium azide in methanol. Both the Schiff base and the complex were characterized by physico-chemical methods and single crystal X-ray determination. The Schiff base crystallized in the orthorhombic space group Pbca with unit cell dimensions a = 7.3191(7) Å, b = 6.0948(6) Å, c = 35.382(3) Å, V = 1578.3(3) Å3, Z = 4, R1 = 0.0481, wR2 = 0.1488. The manganese complex crystallized in the monoclinic space group P21/c with unit cell dimensions a = 8.802(1) Å, b = 14.928(2) Å, c = 14.478(2) Å, β = 105.517(2)°, V = 1833.0(4) Å3, Z = 2, R1 = 0.0768, wR2 = 0.1640. There are crystallographic inversion centers in both the ligand and the complex. The ligand coordinates to Mn through all the phenolate oxygens and imino nitrogens. The two Mn in the complex are bridged by two phenolate oxygens with separation of 3.549(1) Å. Each Mn is octahedral with four donors of the Schiff base ligand defining the equatorial plane, and with one azido nitrogen and one phenolate oxygen of an adjacent Schiff base ligand occupying the axial positions. The Schiff base and the complex were tested in vitro for their antibacterial activities.

Exchange interactions in a dinuclear manganese (II) complex with cyanopyridine-N-oxide bridging ligands

The magnetic properties of dinuclear manganese(II) complex [Mn(hfa)2cpo]2 (where hfa is hexafluoroacetylacetonate anion and cpo is 4-cyanopyridine-N-oxide) are presented. The non-monotonous dependence of magnetic susceptibility is explained in terms of the hierarchy of exchange parameters by using exact diagonalization. The thermodynamic behavior of pure cpo and [Mn(hfa)2(cpo)]2 is simulated numerically by an extrapolation to spin S=5/2. The Mn–Mn exchange integral is evaluated.

Synthesis, Crystal Structure, and Antibacterial Activity of N′-(2-hydroxy-3-methoxybenzylidene)isonicotinohydrazide and Its Dinuclear Manganese(II) Complex with N′-(2-hydroxy-3-methoxybenzylidene)isonicotinohydrazide

A phenolate oxygen bridged dinuclear manganese(2) complex [Mn2Cl2L2(OH2)2]·2CH3OH (2) was obtained from N′-(2-hydroxy-3-methoxybenzyl-idene)isonicotinohydrazide (HL, 1) and MnCl2. Both the ligand HL and the complex were characterized by IR spectra and single-crystal X-ray diffraction. The crystal of 1 crystallizes in the monoclinic space group P21/c, with a = 7.6711(2), b = 16.2568(4), c = 10.8787(3) Å, β = 110.428(2)°, V = 1271.34(6) Å3, Z = 4. The crystal of 2 crystallizes in the monoclinic space group P21/n, with a = 9.4984(8), b = 12.1361(12), c = 15.3414(15) Å, β = 96.269(5)°, V = 1757.9(3) Å3, Z = 2. The ligand HL coordinates to the Mn atom through the deprotonated phenolate O atom, the imine N atom, and the carboxy O atom. The Mn atom is in a pentagonal bipyramidal coordination. The antibacterial activity of the complex and the ligand against the bacteria Staphylococcus aureus, Bacillus anthracis, Pseudomonas aeruginosa, and Streptococcus agalactiae was investigated.

Syntheses, characterizations and bioactivities on HeLa cells and KB cells of two dinuclear manganese complexes with carboxylate bridges

To explore anti-tumor activities of manganese complexes, two complexes have been synthesized and characterized. Complex 1 is bridged by 1,10-phenanthroline and 2,4-biphenyl dicarboxylate. The two complexes have strong fluorescent emission and interact with DNA in an intercalative mode. The complexes also exhibit significant cytotoxic specificity and cancer cell inhibition.

Synthesis, crystal structures, and catalytic properties of phenoxo-bridged dinuclear manganese(III) complexes with bis-Schiff bases

Two structurally similar centrosymmetric phenoxo-bridged dinuclear manganese(III) complexes, [Mn2(L1)2(N3)2] (1) and [Mn2(L2)2(NCS)2] (2), were prepared from the tetradentate bis-Schiff base ligands, N,N’-bis(salicylidene)propane-1,2-diamine (H2L1) and N,N’-bis(salicylidene)ethane-1,2-diamine (H2L2), respectively, in the presence of pseudohalides. The complexes have been characterized by FTIR, elemental analyses, and molar conductivity. Structures of the complexes have been confirmed by single-crystal X-ray determination. The bis-Schiff base ligands coordinate with Mn through their phenolate oxygen and imino nitrogen. Each Mn is an octahedral. The complexes showed that they exhibit high activity in catalytic olefin oxidation.

Synthesis, crystal structure, and spectroscopic characterization of two new binuclear complexes of manganese(II) and vanadium(V) with dipicolinate ligands containing 2-aminopyrimidinium as a counter cation

Two new binuclear complexes, formulated as [(Hamp)[Mn(μ-dipic)Cl(H2O)2]]2 and [(Hamp)[V(μ-O)(O)(dipic)]·H2O]2 (dipicH2 = pyridine-2,6-dicarboxylic (dipicolinic) acid; amp = 2-aminopyrimidine), were synthesized by a hydrothermal process and characterized by elemental analysis, IR spectroscopy, thermal analysis, and X-ray single crystal diffraction. Both compounds contain two Hamp cations and a dinuclear manganese(II) or vanadium(V) anion complex. In addition, the vanadium complex contains two lattice water molecules. Two manganese(II) ions are bridged by pyridine-2,6-dicarboxylate ions in the manganese complex, and they are both coordinated by O,N,O of the tridentate dipicolinate ligand, one oxygen of another dipicolinate ligand, one chlorine, and two water molecules in a distorted pentagonal-bipyramidal geometry. Vanadium(V) ions are coordinated octahedrally by O,N,O of the tridentate dipicolinate ligand, one oxo ion, and two bridging μ-O ions in cis position in the vanadium complex. The crystal structures of both complexes are stabilized by a complex network of hydrogen bonds comprising water molecules, counter ion, and carboxyl groups of dipic2−.