Mononuclear Iron Complexes Research Articles

Microwave-Assisted Synthesis, Crystal Structures, and In Vitro Antibacterial Studies of Manganese(III) and Iron(III) Complexes Derived From N,N′-1,2-ethylene-bis(3-ethoxysalicylideneimine)

The syntheses of a mononuclear manganese(III) complex [MnL (dca)(OH2)] and a mononuclear iron(III) complex [FeLL′]·ClO4 (H2L = N,N′-1,2-ethylene-bis(3-ethoxysalicylideneimine); L′ = 2- [(2-ammonioethylimino)methyl]-6-ethoxyphenolate; dca=dicyana mide), by a one-step sequence from the reaction of 3-ethox ysalicylaldehyde, 1,2-diaminoethane, dca, and metal salts under microwave irradiation are described. The newly prepared complexes were characterized by a combination of elemental analyses and IR spectra. Their structures were determined by single-crystal X-ray crystallography. The metal centers in the complexes are in octahedral coordination. The crystals of the complexes are stabilized by hydrogen bonds. In order to evaluate the biological activity of the ligand and to evaluate the role of manganese and iron ions on biological activity, the free ligands and the complexes have been studied in vitro antibacterial against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa.

Models for enzyme–substrate adduct of non-heme iron-containing enzymes, synthesis and characterization

Mononuclear iron(III) complexes of (HNEt3)[FeLNEC(TBC)], (HNEt3)[FeLNEB(TBC)] and (HNEt3)[FeLNEM(TBC)] as new models for enzyme–substrate adducts of catechol dioxygenases have been prepared and characterized, where H2LNEC, H2LNEB and H2LNEM are amine bis(phenolate) ligands with chlorine, bromine and methyl substituted phenol groups and TBC is a tetrabromo catecholate dianion. These complexes were characterized by IR, UV–vis, elemental analysis and magnetic measurements. X-ray structure analysis of complexes has revealed that the iron(III) core in the model compounds is a distorted octahedral coordination sphere and surrounded by two phenolate oxygen atoms, two amine nitrogens and two oxygen atoms of TBC. UV–vis spectroscopy exhibits two intense absorption bands in the range of 450–650nm in dichloromethane. These bands are assigned to the catecholate and ligand to Fe(III) charge-transfer bands. The electrochemical features of the adduct complexes were investigated in dichloromethane solution by employing cyclic voltammetry (CV).

Synthesis, spectroscopic, molecular orbital calculation, cytotoxic, molecular docking of DNA binding and DNA cleavage studies of transition metal complexes with N-benzylidene-N′-salicylidene-1,1-diaminopropane

Eight mononuclear chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of Schiff’s base ligand were synthesized and determined by different physical techniques. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMSO indicate that the complexes are non-electrolytic in nature. All the eight metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic data. The analytical data helped to elucidate the structure of the metal complexes. The Schiff base is found to act as tridentate ligand using N2O donor set of atoms leading to an octahedral geometry for the complexes around all the metal ions. Quantum chemical calculations were performed with semi-empirical method to find the optimum geometry of the ligand and its complexes. Additionally in silico, the docking studies and the calculated pharmacokinetic parameters show promising futures for application of the ligand and complexes as high potency agents for DNA binding activity. The interaction of the complexes with calf thymus DNA (CT-DNA) has been investigated by UV absorption method, and the mode of CT-DNA binding to the complexes has been explored. Furthermore, the DNA cleavage activity by the complexes was performed. The Schiff base and their complexes have been screened for their antibacterial activity against bacterial strains [Staphylococcus aureus (RCMB010027), Staphylococcus epidermidis (RCMB010024), Bacillis subtilis (RCMB010063), Proteous vulgaris (RCMB 010085), Klebsiella pneumonia (RCMB 010093) and Shigella flexneri (RCMB 0100542)] and fungi [(Aspergillus fumigates (RCMB 02564), Aspergillus clavatus (RCMB 02593) and Candida albicans (RCMB05035)] by disk diffusion method. All the metal complexes have potent biocidal activity than the free ligand.

A Novel Acylmethylpyridinol Ligand Containing Dinuclear Iron Complex Closely Related to [Fe]-Hydrogenase

On synthesizing the PMB-protected mononuclear iron complexes [2-C(O)CH2-6-PMBOC5H3N]Fe(CO)3I (6) and [2-C(O)CH2-6-PMBOC5H3N]Fe(CO)2(2-SC5H4N) (7), the novel acylmethylpyridinol ligand containing dinuclear iron complex [2-C(O)CH2-6-HOC5H3N]Fe2(CO)4[2′-C(O)CH2-6′-OC5H3N](2-SC5H4N) (9), which is closely related to the active site of [Fe]-hydrogenase, has been prepared unexpectedly via removal of the PMB protecting group from 7 under the action of excess trifluoroacetic acid. The [Fe]-hydrogenase-related complex 9 and its precursor complexes 6 and 7 have been fully characterized by elemental analysis, spectroscopy, and X-ray crystallography.

A unique supramolecular sandwich structure of a tetrabromocatechol-chelated iron(III) complex: Mutual reinforcement of H-bonding and π⋯π stacking interactions in the crystal lattice

A unique supramolecular sandwich structure of a tetrabromocatecholate chelated mononuclear iron(III) complex, [H3ntb]2[Fe(Br4Cat)3](ClO4)3·4CH3OH·4H2O (1) [ntb = tris(2-benzimidazolylmethyl)amine and Br4CatH2 = tetrabromocatechol], is reported. The most interesting feature of the crystal structure of 1 is that the central [Fe(Br4Cat)3]3 − anion is sandwiched by the triply-protonated two ntb ligands in which mutual reinforcement of the π⋯π stacking and hydrogen bonding interactions play significant role to stabilize the structural motif. Electrochemical studies disclose both the noninnocent ligand and metal based redox processes.

Iron(III) complexes of pyridine-based tetradentate aminophenol ligands as structural model complexes for the catechol-bound intermediate of catechol dioxygenases

Some pyridine-based tetradentate aminophenol ligands and their acetylacetonato iron(III) LFe(acac) complexes have been synthesized and characterized by spectroscopic techniques, cyclic voltammetry, single crystal X-ray diffraction and magnetic susceptibility studies. X-ray analysis revealed monomer complexes in which the iron centers have been surrounded by pairs of acetyl acetonate and phenolate oxygens and two nitrogen atoms of the ligands. It has been shown that the two Fe–Oacac bonds in these complexes are not equal, as seen for Fe–Ocat bonds in the catechol-bounded intermediate of catechol dioxygenases. Variable temperature magnetic susceptibility indicates a paramagnetic behavior for all the mononuclear high spin iron complexes. The investigated complexes undergo electrochemical oxidation and reduction.

Transformations of dinitrosyl iron complexes in an isolated rat heart after introduction of this substance into perfusion medium

The objective of the present research was to study transformations of various physiological NO forms in an isolated rat heart, perfused with the medium, containing dinitrosyl iron complexes with glutathione ligand (DNIC-GH). We showed that such aerobic perfusion resulted in accumulation of mostly diamagnetic NO physiological forms (S-nitrosothiols) in myocardial tissue. They were transformed into protein-bound mononuclear dinitrosyl iron complexes during subsequent total ischemia. Meantime, DNIC-GH injection on the onset of ischemia resulted in the changes in the state of mitochondrial respiratory state, characterized by the increase in myocardial concentration of flavosemiquinones.

A Bis(hexadentate) Biphenyl‐Based N12 Ligand and Its FeII Complexes

AbstractThe novel biphenyl‐based ligand N,N′,N″,N″′‐tetrakis(2,2′‐bipyridin‐6‐ylmethyl)‐4,4′‐dimethyl‐1,1′‐biphenyl‐2,2′,6,6′‐tetramine (6) with 12 nitrogen donor atoms has been synthesized. Ligand 6 is able to host two metal ions in an octahedral coordination sphere. This was shown by the synthesis of the dinuclear iron(II) complex 5 ([Fe2(6)]4+). Furthermore, the corresponding mononuclear iron(II) complex 4 ([Fe(6)]2+), where one coordination site is free, was obtained. Both FeII complexes show spin‐crossover behaviour, which was shown by 1H NMR spectroscopy and Evans' measurements. A comparison of the two complexes gives evidence of a sterically induced cooperative behaviour in the dinuclear complex 5.

Thermal and Photoinduced Spin Crossover in a Mononuclear Iron(II) Complex with a Bis(pyrazolyl)pyridine Type of Ligand

AbstractA mononuclear iron(II) compound 1 of the general formula [Fe(L)2](ClO4)2 {L = 4‐[2,6‐bis(pyrazol‐1‐yl)pyridin‐4‐yl]benzaldehyde} was prepared and structurally characterised. Single‐crystal X‐ray structure analysis revealed the presence of a complex dication [Fe(L)2]2+ and two ClO4– counteranions within the unit cell. The bond lengths and angles within the coordination polyhedron FeN6 indicate the low‐spin state of the central iron(II) metal ion at T = 180 K. Magnetic investigations elucidate spin crossover with T1/2 = 285 K. The experimental magnetic susceptibility data could be satisfactorily fitted with the Curie law in combination with the Ising‐like model. The room‐temperature character of the spin crossover was further studied by variable‐temperature far‐IR, Vis and Mössbauer spectroscopy. Laser irradiation of 1 carried out at 10 K gives rise to a complete low‐spin to high‐spin photoconversion. A subsequent temperature‐dependent investigation revealed the existence of a photoexcited metastable HS state up to TLIESST = 70 K (LIESST = light‐induced excited‐spin‐state trapping) as well as the presence of a light‐induced thermal hysteresis loop with a width of 10 K.

An iron(iii) tetradentate monoamido complex as a nonheme iron-based peroxidase mimetic

A mononuclear iron(III) complex of a noncyclic tetradentate monoamido ligand, Fe(III)mpaq, catalyses the oxidation of Orange II, guaiacol, ABTS and Amplex Red with H2O2 in aqueous solutions at neutral pH. Under identical conditions, other structurally related nonheme iron complexes showed only negligible activities.

Dinitrosyl iron complexes with glutathione as NO and NO+ donors

It has been found that heating of solutions of the binuclear form of dinitrosyl iron complexes (B-DNIC) with glutathione in a degassed Thunberg apparatus (рН 1.0, 70°С, 6h) results in their decomposition with a concomitant release of four gaseous NO molecules per one B-DNIC. Further injection of air into the Thunberg apparatus initiates fast oxidation of NO to NO2 and formation of two GS-NO molecules per one B-DNIC. Under similar conditions, the decomposition of B-DNIC solutions in the Thunberg apparatus in the presence of air is complete within 30–40min and is accompanied by formation of four GS-NO molecules per one B-DNIC. It is suggested that the latter events are determined by oxidation of B-DNIC iron and concominant release of four nitrosonium ions (NO+) from each complex. Binding of NO+ to thiol groups of glutathione provokes GS-NO synthesis. At neutral рН, decomposition of B-DNIC is initiated by strong iron chelators, viz., о-phenanthroline and N-methyl-d-glucamine dithiocarbamate (MGD). In the former case, the reaction occurs under anaerobic conditions (degassed Thunberg apparatus) and is accompanied by a release of four NO molecules from B-DNIC. Under identical conditions, MGD-induced decomposition of B-DNIC gives two EPR-active mononuclear mononitrosyl iron complexes with MGD (MNIC–MGD) able to incorporate two iron molecules and two NO molecules from each B-DNIC. The other two NO molecules released from B-DNIC (most probably, in the form of nitrosonium ions) bind to thiol groups of MGD to give corresponding S-nitrosothiols. Acidification of test solutions to рН 1.0 initiates hydrolysis of MGD and, as a consequence, decomposition of MNIC–MGD and the S-nitrosated form of MGD; the gaseous phase contains four NO molecules (as calculated per each B-DNIC). The data obtained testify to the ability of B-DNIC with glutathione (and, probably, of B-DNIC with other thiol-containing ligands) to release both NO molecules and nitrosonium ions upon their decomposition. As far as nitrosyl iron complexes with non-thiol-containing ligands predominantly represented by the mononuclear mononitrosyl iron form (MNIC) are concerned, their decomposition yields exclusively NO molecules.

Bis(isothiocyanato)iron(II) complexes with bithiazole ligands: Structure and magnetic studies

Two new mononuclear iron(II) complexes, [Fe(4bt)2(NCS)2] (1) and [Fe(dm4bt)2(NCS)2] (2), were prepared from the treatment of FeCl2·4H2O and KSCN salts with 4,4′-bithiazole (4bt) and 2,2′-dimethyl-4,4′-bithiazole (dm4bt), respectively and their structures and magnetisms were studied. Crystal structure determination revealed similar distorted octahedral [FeN6] moiety for both high spin iron(II) complexes. Fe–N distances are seen in 1 and 2 to be in the range of 2.085(8)–2.173(3) for Fe–NNCS and 2.178(3)–2.279(7)Å for Fe–Nbt which is consistent with the assigned iron spin and oxidation states. Temperature dependent χmT showed that the complexes are magnetically resembled and behave as S=2 systems with some zero-field splitting. Complexes 1 and 2 were also studied in solution by means of 1H NMR and UV–Vis spectroscopy techniques.

Magnetic properties of a mononuclear iron(II) complex with a typical FeN6coordination octahedron

A mononuclear iron(II) complex with the tripodal ligand bis(pyridin-2-ylmethyl)(quinolin-2-ylmethyl)amine (dpqa) has been synthesized and structurally characterized, namely [bis(pyridin-2-ylmethyl)(quinolin-2-ylmethyl)amine-κ(4)N,N',N'',N''']bis(thiocyanato-κS)iron(II), [Fe(NCS)(2)(C(22)H(20)N(4))], exhibits a three-dimensional supramolecular network via π-π interactions and S...H-C hydrogen-bonding interactions between adjacent Fe(II) centres. Temperature-dependent magnetic measurements under different external pressures and X-ray diffraction measurements indicate that all the Fe(II) centres in this complex retain a high-spin state upon cooling from 300 to 2 K. The surprising absence of spin-crossover behaviour for this mononuclear iron(II) complex is attributed to the steric hindrance originating from the substituted quinoline ring in the dpqa ligand.

Comparative Spectroscopic Studies of Iron(III) and Manganese(III) Salen Complexes Having a Weakly Coordinating Triflate Axial Ligand

Abstract We thoroughly compared spectroscopic and magnetic properties of mononuclear iron(III) and manganese(III) complexes with symmetric and nonsymmetrical salen ligands, in order to investigate the relation between spectroscopic properties and electronic structures. Magnetic susceptibility and dual-mode electron paramagnetic resonance data show the assignment of [FeIII(salen)(OTf)] and [MnIII(salen)(OTf)] as high-spin S = 5/2 and S = 2 electronic configurations, respectively, irrespective of the electron-donating properties and symmetry of the salen ligand. Further insights into electronic structures of central metal are obtained from 2H NMR spectra of selectively deuterated complexes, in which [FeIII(salen)(OTf)] and [MnIII(salen)(OTf)] exhibit well-resolved paramagnetic NMR signals of quite different shift patterns, due to the presence or absence of the unpaired electron in the dx2 - y2 orbital expected for S = 5/2 iron(III) or S = 2 manganese(III) centers.

Efficient and Selective Oxidation of Primary and Secondary Alcohols Using an Iron(III)/Phenanthroline Complex: Structural Studies and Catalytic Activity

AbstractAn efficient catalytic system for the oxidation of alcohols has been developed by using iron(III) catalyst [Fe(phen)2Cl2]NO3 (1) (phen = 1,10‐phenanthroline) and H2O2 as terminal oxidant. A series of primary and secondary alcohols were oxidized into aldehydes and ketones in good yields and excellent selectivities after a short reaction time. The mononuclear iron(III) complex [Fe(phen)2Cl2]NO3 was characterized by several independent methods. The X‐ray structure shows distorted octahedral geometry around the FeIII center, which is in a high‐spin state (S = 5/2) according to Mössbauer study.

Synthesis, Crystal Structures, and Biological Activity of Cu(II), Mn(III), and Fe(III) Complexes Derived from N,N’-Bis(4-methoxysalicylidene)ethylenediamine

Three mononuclear copper(II), manganese(III), and iron(III) complexes, [CuL(OH2)] (1), [MnClL] (2), and [FeClL] (3), where L is the deprotonated form of N,N’-bis(4-methoxysalicylidene) ethylenediamine, were synthesized and structurally characterized by physicochemical methods and single-crystal X-ray diffraction. Each metal atom in the complexes adopts a square pyramidal coordination, with the four donor atoms of the Schiff base defining the basal plane, and with the water molecule for 1, and chloride atom for 2 and 3 occupying the apical position. The complexes were evaluated in vitro for their inhibitory activities against Jack bean urease. The copper complex showed effective inhibitory activity against the urease. A docking simulation was performed for the copper complex into the active site of the urease to investigate the probable binding conformation.

The Ubiquity of Iron

The importance of iron in living systems can be traced to the many complexes within which it is found, to its chemical mobility in undergoing oxidation-reduction reactions, and to the abundance of iron in Earth's crust. Iron is the most abundant element, by mass, in the Earth, constituting about 80% of the inner and outer cores of Earth. The molten outer core is about 8000 km in diameter, and the solid inner core is about 2400 km in diameter. Iron is the fourth most abundant element in Earth's crust. It is the chemically functional component of mononuclear iron complexes, dinuclear iron complexes, [2Fe-2S] and [4Fe-4S] clusters, [Fe-Ni-S] clusters, iron protophorphyrin IX, and many other complexes in protein biochemistry. Metals such as nickel, cobalt, copper, and manganese are present in the crust and could in principle function chemically in place of iron, but they are scarce in Earth's crust. Iron is plentiful because of its nuclear stability in stellar nuclear fusion reactions. It seems likely that other solid planets, formed by the same processes as Earth, would also foster the evolution of life and that iron would be similarly important to life on those planets as it is on Earth.

Mononuclear cobalt(III) and iron(II) complexes with diimine ligands: Synthesis, structure, DNA binding and cleavage activities, and oxidation of 2-aminophenol

Mononuclear cobalt(III) and iron(II) complexes with diimine ligands were synthesized and characterized by elemental analyses, spectroscopic and electrochemical techniques. Single crystal X-ray diffraction studies revealed that the metal ions in both complexes are situated in distorted octahedral environments comprised of six nitrogen atoms from three diimine ligands. Interaction of the complexes with calf thymus DNA was investigated through UV–Vis and fluorescence spectroscopic methods and viscosity measurements. These results suggest that both complexes preferably interact with CT-DNA through the grove binding mode. Moreover, both complexes are capable of promoting DNA cleavage in the presence of suitable activating agent(s). The nuclease activity is strongly suggested to be oxidative, possibly due to the involvement of a diffusible hydroxyl radical mechanism. Furthermore, the cobalt(III) complex has been found to be an excellent oxidant for oxidative coupling of 2-aminophenol to the phenoxazinone chromophore under aerobic conditions.

The structures of the dicationic tetranitrosyl iron complex with cysteamine [Fe2S2(CH2CH2NH3)2(NO)4]2+ and its decomposition products in protic media: an experimental and theoretical study

Decomposition products of [Fe2S2(CH2CH2NH3)2(NO)4]SO4·2.5H2O (1′) were studied by electrochemistry and mass spectrometry. The structures of the dicationic tetranitrosyl iron complex with cysteamine of the composition [Fe2S2(CH2CH2NH3)2(NO)4]2+ (1) and possible products of its decomposition and NO replacement by an aqua ligand were studied by quantum chemical methods at the density functional theory level. Taking into account the solvation effects, the replacement of the nitrosyl ligand in dication 1 by an aqua ligand was found to be less favorable in aqueous solution than in the gas phase. The pK value was calculated for the proton abstraction from the NH3 group of compound 1 (7.2), and the removal of NO from the deprotonated form of the complex was found to be much easier. This result is consistent with the experimental data on an increase in the rate of NO formation in aqueous solutions of 1 with increasing pH from 6 to 8 assuming that the increase in pH is accompanied by an increase in the percentage of the less stable deprotonated form of the complex and that OH− does not participate in the elementary step of NO formation. The kinetic curves of NO formation are well described by a two-step scheme of consecutive first-order reactions of the NO formation and consumption. In the gas phase, dication 1 was found to be unstable to decomposition into two mononuclear cationic dinitrosyl iron complexes with cysteamine. This result is consistent with the fact that these cations are observed in the electrospray ionization mass spectrometric experiment. The major peak in the mass spectra is associated with the [Fe2S2(CH2CH2NH3)2(NO)4 − H]+ ion. As follows from the calculations, this is due to the deprotonation of the dication as it gets rid of the hydration shell, because even the dimer of water molecules is more basic than dication 1.

Anion driven modulation of magnetic intermolecular interactions and spin crossover properties in an isomorphous series of mononuclear iron(iii) complexes with a hexadentate Schiff base ligand

A series of spin crossover iron(III) complexes with the general composition [Fe(4OH-L6)]X (H2-4OH-L6 = 1,8-bis(4-hydroxysalicylaldiminato)-3,6-diazaoctane; X = Cl, 1a; Br, 1b; I, 1c) was prepared. A combination of the results following the single crystal X-ray analysis, infrared and EPR spectroscopy, and temperature dependent magnetic experiments revealed that the Fe(III) atoms occur in the low-spin state below room temperature and the crystal structures of the complexes involve rich networks of non-covalent intermolecular contacts resulting in two-dimensional supramolecular structures. Alterations in the halide anions influence the strength of the non-covalent contacts and affect the magnetic properties of the studied complexes. The antiferromagnetic exchange interaction between the non-covalently bound cations is the most obvious in the case of 1a and it weakens with the growing anionic volume of X. The 1D and 2D spin Hamiltonian models were applied to quantitatively extract the information about the intermolecular magnetic exchange (fit on 1D infinite chain gives J(1a) = −2.86 cm−1, J(1b) = −2.02 cm−1, J(1c) = −1.16 cm−1). Furthermore, gradual spin crossover behaviour for all of the compounds of the series was observed above room temperature in the solid state. Spin crossover accompanied by thermochromism was also demonstrated by EPR experiments in solution.