Triazine based Mn (II) and Mn (II)/Ln (III) complexes: Synthesis,characterization and catecholase activities

In the current work, two triazine‐based multidentate ligands (H₂L¹ and H₂L²) and their homo‐dinuclear Mn (II), mononuclear Ln (III) and hetero‐dinuclear Mn (II)/Ln (III) (Where Ln: Eu or La) complexes were synthesized and characterized by spectroscopic and analytical methods. Single crystals of a homo‐dinuclear Mn (II) complex {[Mn (HL¹)(CH₃OH)](ClO₄·CH₃OH}₂ ( 1 ) were obtained and the molecular structure was determined by X‐ray diffraction method. In the structure of the complex, each Mn (II) ion is seven‐coordinate and one of the phenolic oxygen bridges two Mn (II) centre forming a dimeric structure. The UV–Vis. and photoluminescence properties of synthesized ligands and their metal complexes were investigated in DMF solution and the compounds showed emission bands in the UV–Vis. region. The catecholase enzyme‐like activity of the complexes were studied for 3,5‐DTBC → 3,5‐DTBQ conversion in the presence of air oxygen. Homo‐dinuclear Mn (II) complexes ( 1 and 4 ) were found to efficiently catalyse 3,5‐DTBC → 3,5‐DTBQ conversion with the turnover numbers of 37.25 and 35.78 h^?1 (k_cat), respectively. Mononuclear Eu (III) and La (III) complexes did not show catecholase activity.     

Spectro-thermal characterization of chromium(III) and manganese(II) complexes with carboxyamide

Complexes of Cr(III) and Mn(II) with N′,N″-bis(3-carboxy-1-oxopropanyl) 2-amino-N-arylbenzamidine (H₂L¹) and N′,N″-bis(3-carboxy-1-oxophenelenyl) 2-amino-N-arylbenzamidine (H₂L²) have been synthesized and characterized by various physico-chemical techniques. The vibrational spectral data are in agreement with coordination of amide and carboxylate oxygen of the ligands with the metal ions. The electronic spectra indicate octahedral geometry around the metal ions, supported by magnetic susceptibility measurements. The thermal behavior of chromium(III) complexes shows that uncoordinated nitrate is removed in the first step, followed by two water molecules and then decomposition of the ligand; manganese(II) complexes show two waters removed in the first step, followed by removal of the ligand in subsequent steps. Kinetic and thermodynamic parameters were computed from the thermal data using Coats and Redfern method, which confirm first order kinetics. The thermal stability of metal complexes has been compared. X-ray powder diffraction determines the cell parameters of the complexes.     

Complexes derived from some biologically active ligands

Complexes derived from ampicillin (L1) and amoxicillin (L2) with (Mg(II), Ca(II), Zn(II), Cu(II), Ni(II), Co(II), Ce(III), Nd(III), UO₂(VI), Th(IV)) were prepared and characterized by elemental analysis, electrical conductivity measurements, magnetic susceptibility, IR, UV/Vis, and thermogravimetry. The formed complexes can be formulated as (ML(H₂O)₃(NO₃) _n ) except for Ce(III) which gave (CeL(H₂O)₃(Cl)₂). The ¹H NMR spectra of the Zn(II) complexes are compared to spectra of the ligands. The shift (δ) gave information about the chelating center of the ligands. The ligands and the synthesized complexes, derived from some alkali earth and transition metal ions, were tested as antibacterial reagents. The formed complexes had enhanced activity.     

Synthesis,characterization, cyclic voltammetry,and antimicrobial properties of N-(5-benzoyl-2-oxo-4-phenyl-2H-pyrimidine-1-yl)-malonamic acid and its metal complexes

A new heterocyclic compound, N-(5-benzoyl-2-oxo-4-phenyl-2H-pyrimidin-1-yl)-malonamic acid, was synthesized from N-aminopyrimidine-2-one and malonyldichloride. Bis-chelate complexes of the ligand were prepared from acetate/chloride salts of Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Cd(II), Fe(III), Cr(III), and Ru(III) in methanol. The structures of the ligand and its metal complexes were characterized by microanalyses, IR, NMR, API-ES, UV-Vis spectroscopy, magnetic susceptibility, and conductometric analyses. Octahedral geometry was suggested for all the complexes, in which the metal center coordinates to ONO donors of the ligand. Each ligand binds the metal using C=O, HN, and carboxylate. The cyclic voltammograms of the ligand and the complexes were also discussed. The compounds were evaluated for their antimicrobial activities against Gram-positive and Gram-negative bacteria, and fungi using microdilution procedure. The antimicrobial studies showed that Cu(II), Fe(III), and Ru(III) complexes exhibited good antibacterial activity against Gram-positive bacteria with minimum inhibitory concentrations between 20 and 80 µg mL^?1. However, the ligand and the complexes possess weak efficacy against Gram-negative bacterium and Candida strains. As a result, we suggest that these complexes containing pyrimidine might be a new group of antibacterial agents against Gram-positive bacteria.     

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.     

Synthesis,crystal structure and antibacterial activity of manganese(III) and cobalt(III) complexes containing pentadentate Schiff bases of a common amine and thiocyanate

Abstract

Four new mononuclear Schiff base manganese(III) and cobalt(III) complexes viz. [Mn(L¹)(NCS)] (1), [Mn(L²)(NCS)] (2), [Co(L³)(NCS)] (3), and [Co(L⁴)(NCS)]·0.5CH₃OH·0.5H₂O (4), containing thiocyanate as a common pseudohalide ion are reported. The pentadentate Schiff base ligands H₂L¹, H₂L², H₂L³, and H₂L⁴ were obtained by the condensation of substituted salicylaldehydes with N-(3-aminopropyl)-N-methylpropane-1,3-diamine. The syntheses of the complexes have been achieved by the reaction of manganese(II) perchlorate or cobalt(II) perchlorate with the respective Schiff bases in the presence of thiocyanate in methanol medium. Complexes 1–4 have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 adopt nearly similar structures containing the MN₄O₂ (M?=?Mn, Co) chromophore in which each central M(III) ion adopts a distorted octahedral geometry. Weak intermolecular H-bonding interactions are operative in these complexes to bind the molecular units. The antibacterial activity of 1–4 and their constituent Schiff bases has been tested against some common bacteria.     

Adsorption of some metal complexes derived from acetyl acetone on activated carbon and purolite S-930

A new Schiff base (HL) derived from condensation of p-anisidine and acetyl acetone has been prepared and used as a chelating ligand to prepare Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) complexes. The study of the nature of these complexes formed in ethanol solution following the mole ratio method (2:1, L:M) gave results which were compared successfully with these obtained from isolated solid state studies. These studies revealed that the complexes having square planner geometry of the type (ML₂), M = Co(II), Ni(II) and Cu(II), and octahedral geometry of the type [Cr^IIIL₂(H₂O)₂]Cl and [MN^IIL₂(H₂O)₂]. The adsorption studies of three complexes Cr(III), Mn(II), and Co(II) on activated carbon, H and Na-forms of purolite S-930 resin show high adsorption percentage for Cr(III) on purolite S-930 due to ion exchange interaction compared with high adsorption of neutral Mn(II), Co(II) complexes on activated charcoal. Linear plot of log Q_e versus log C_e showed that the adsorption isotherm of these three complexes on activated carbon, H and Na-forms of purolite S-930 surface obeys Freundlich isotherm and was similar to S-curve type according to Giles classification which investigates heterogeneous adsorption. The regression values indicate that the adsorption data for these complexes fitted well within the Freundlich isothermal plots for the concentration studied. The accuracy and precision of the concentration measurements of these complexes were determined by preparing standard laboratory samples, the results show relative error ranging from ±1.08 to 5.31, ±1.04 to 4.82 and ±0.28 to 3.09 and the relative standard deviation did not exceed ±6.23, ±2.77 and ±4.38% for A1, A2 and A3 complexes, respectively.     

Synthesis and characterization of metal 2-pyridine carboxaldehyde-N-methyl-N-2-pyridyl hydrazone complexes and their microbiological activity

Complexes of Cu(II), Mn(II), Co(II), Ni(II), Hg(II), Cd(II) and Rh(III) with 2-pyridine carboxaldehyde-N-methyl-N-2-pyridylhydrazone ( pamph) have been prepared and characterized. The new complexes have been characterized by elemental analysis, conductivity and magnetic measurements, IR, UV–vis and ¹H NMR spectroscopic methods. The microbiological activity of the complexes was investigated against bacteria and fungi. Most of the complexes studied appear to be active against bacteria while all are active against fungi. The Cu, Cd and Hg complexes exhibit the highest activity against both bacteria and fungi.     

Tetraaza macrocyclic complexes: synthesis,spectral and antimicrobial studies

A tetradentate nitrogen donor [N₄] macrocyclic ligand, 1,3,7,9-tetraaza-2,8-dithia-4,10-dimethyl-6,12-diphenylcyclododeca-4,6,10,12-tetraene has been synthesized by using thiourea and benzoylacetone. Complexes of Mn(II), Co(II), Ni(II), and Cu(II) have been synthesized with this ligand and characterized by element chemical analysis, molar conductance, magnetic susceptibility, mass, ¹H nuclear magnetic resonance, Fourier transform–infrared, electronic, and electron paramagnetic resonance spectral studies. The molar conductance measurements of Mn(II), Co(II), and Cu(II) complexes in dimethyformamide correspond to nonelectrolytes, whereas Ni(II) complex is a 1: 2 electrolyte. The complexes are high-spin except for Ni(II) which is diamagnetic. Octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square planar for Ni(II) and tetragonal geometry for Cu(II). The ligand and its complexes were screened in vitro against two pathogenic fungi (Fusarium moniliformae and Rhizoctonia solani) and bacteria (Staphylococcus aureus and Pseudomonas aeruginosa) to assess their growth inhibiting potential.     

Electrochemistry of phosphaferrocenes: II. Electrochemical behavior of 3,3′,4,4′-tetramethyl-1,1′- diphosphaferrocene bonded to M(CO)5 (M = Cr,Mo, W) fragments forming heterometallic complexes with multiple redox centers

The redox behaviour of a series of heterometallic phosphaferrocenes (hereafter refered to as I, II and III) has been studied in propylene carbonate containing 0.1 M (C₂H₅)₄N⁺ ClO₄^? both mercury and platinum electrodes.Complex I (DPF) undergoes a reversible one-electron reduction. Complexes II and III exhibit the same reversible reduction step and one (species II) or two (species III) additional irreversible reduction step(s) generating [M(CO)₅]^? anions (M = Cr, Mo, W).Oxidation of the complexes II and III indicates that fragment I is involved in the first, easiest, oxidation step, whereas further step(s) involve the M(CO)₅ moieties. The redox characteristics of the complexes I, II, III, clearly indicate the absence of cooperation between metallic centers in II and III and the very effective barrier provided by the central iron in moiety I towards mutual effects of both phospholyl rings.     

Unsymmetrical Tetradentate Schiff Base Complexes Derived from 2,3-diaminophenol and Salicylaldehyde or 5-bromosalicylaldehyde

Salicylaldehyde or 5-bromosalicylaldehyde reacted with 2,3-diaminophenol in absolute EtOH in a 2:1 molar ratio to give new unsymmetrical Schiff bases (H₂L). The bases were used as ligands to coordinate Mn(III), Ni(II) and Cu(II) chlorides leading to [Mn^IIIClL] · EtOH and [M^IIL] or [M^IIL] · 2H₂O (M = Ni or Cu) complexes. Their structures were determined using mass spectroscopy, IR, u.v.–vis and ¹H-n.m.r. The cyclic voltammetry in acetonitrile showed irreversible waves for both ligands. Under the same experimental conditions, the complexes exhibited mainly the non-reversible reduction of the Ni(II) or Cu(II) ion to Ni(0) or Cu(0), while the reduction of Mn(III) to Mn(II) was found to be a quite reversible phenomenon.     

Synthesis and characterization of the complexes of some transition metals with 2-acetyl pyridine (N-benzoyl) glycyl hydrazone

Complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with 2-acetyl pyridine (N-benzoyl) glycyl hydrazone(2-ApBzGH) have been synthesized and characterized by elemental analyses, molar conductances, magnetic susceptibility, IR, electronic, ESR,¹H,¹³C and¹¹³Cd NMR spectral and X-ray diffraction studies. IR and NMR data suggest the tridentate nature of the ligand coordinating as a neutral species in the addition complexes and as a uninegative species in the deprotonated complexes. The presence of more than one isomer of the ligand has been established by¹H NMR spectra of the ligand and complexes recorded over the 298–396 K range. The X-ray powder diffraction patterns of [Cd(2-ApBzGH)Cl]Cl and [Cu(2-ApBzGH)Cl(H₂O)₂]Cl are indexed for orthorhombic and tetragonal crystal systems respectively.     

Metal complexes of sulphur-nitrogen chelating agents. Part 14. Nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) complexes of the tetradentate schiff bases having ONNS donor sites

Summary Complexes of nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) with methyl-2-(-salicylaldiminoethyl)-cyclopent-1-en-dithiocarboxylate (H₂L¹) and methyl-2-(-salicylaldiminoisopropyl)cyclopent-1-en-dithiocarboxylate (H₂L²) have been prepared. They contain the donor sites ONNS. The metal(II) ions from neutral, monomeric square planar chelate complexes. The cobalt(III) complexes [CoL¹-(H₂O)₂]X (X=Cl or ClO₄) appear to betrans-diaqua-species. All compounds have been characterized by a number of physico-chemical methods.     

Infrared Spectra of α-Thenoyl-trifluoroacetonates of Metal Ions of the First Transition Series

The IR. spectra of α-thenoyl-trifluoroacetone (HTTA) and seventeen of its chelates with metal(II) and -(III) ions of the first transition series have been determined. Three series of complexes are represented: the anhydrous metal(II) species, [M(TTA)₂]_n (M ? Ca, Mn, Co, Ni, Cu, Zn); metal(II) dihydrates, [M(TTA)₂(H₂O)₂] (M ? Mn, Fe, Co, Ni, Zn); and the metal(III) chelates, [M(TTA)₃] (M ? Sc, V, Cr, Mn, Fe, Ga). For each metal(II) complex, the spectra of the anhydrous and hydrated compounds are practically identical, suggesting that the anhydrous complexes have the polynuclear octahedral structure established for the corresponding acetylacetonates. Magnetic moment determinations reveal that complexes of the 3d⁴?3d⁷ ions all have spin-free configuration. Several vibrational bands with frequencies < 700 cm^?1 are found to exhibit a frequency variation with d-orbital population which is consistent with the order of crystal field stabilization energies and hence with their assignment as coupled metal-oxygen stretching modes. Unique features of the spectra of [Cu(TTA)₂] and [Mn(TTA)₃] are ascribed to structural differences arising from Jahn-Teller distortion. Tentative assignments for the majority of the ligand vibrations are given.     

Synthesis and Characterization of Manganese Dithiocarbamate Complexes: New Evidence of Dioxygen Activation

(1) Background: Metal dithiocarbamate compounds have long been the subject of research due to their ease of formation, excellent properties and potential applications. However, manganese complexes with dithiocarbamates, to our knowledge, have never been used for medical imaging applications. With the aim of developing a new class of mononuclear manganese(II)-based agents for molecular imaging applications, we performed a specific investigation into the synthesis of mononuclear bis-substituted Mn(II) complexes with dithiocarbamate ligands. (2) Methods: Synthesis in either open or inert atmosphere at different Mn(II) to diethyldithiocarbamate molar ratios were performed and the products characterized by IR, EA, ESI-MS and XRD analysis. (3) Results: We found that only under oxygen-free atmospheric conditions the Mn(II) complex MnL₂, where L = diethyldithiocarbamate ligand, is obtained, which was further observed to react with dioxygen in the solid state to form the intermediate superoxo Mn(III) complex [MnL₂(η²-O₂)]. The existence of the superoxo complex was revealed by mass spectroscopy, and this species was interpreted as an intermediate step in the reaction that led the bis-substituted Mn(II) complex, MnL₂, to transform into the tris-substituted Mn(III) complex, MnL₃. A similar result was found with the ligand L’ (= bis(N-ethoxyethyl)dithiocarbamate). (4) Conclusions: We found that in open atmosphere and in aqueous solution, only manganese(III) diethyldithiocarbamate complexes can be prepared. We report here a new example of a small-molecule Mn(II) complex that efficiently activates dioxygen in the solid state through the formation of an intermediate superoxide adduct.     

Synthesis,crystal structure,electrochemistry and antioxidative activity of copper(II), manganese(II) and nickel(II) complexes containing bis(N‐ethylbenzimidazol‐2‐ylmethyl)aniline

Bis(N‐ethylbenzimidazol‐2‐ylmethyl)aniline (Etbba) and its transition metal complexes, [Cu(Etbba)(Cl)₂]?DMF ( 1 ), [Mn(Etbba)(Cl)₂] ( 2 ) and [Ni(Etbba)(Cl)₂] ( 3 ), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, UV–visible, infrared and NMR spectroscopies and X‐ray crystallography. The coordination environment of complex 1 can be described as distorted square‐based pyramidal, while complexes 2 and 3 each have a distorted trigonal bipyramidal geometry. Cyclic voltammograms of complex 1 indicate an electrochemically quasi‐reversible Cu²⁺/Cu⁺ couple. In addition, the antioxidant activities of the free ligand and its complexes were investigated using the superoxide and hydroxyl radical scavenging methods in vitro. Complexes 1 , 2 , 3 are found to possess potent hydroxyl radical scavenging activity and to be better than standard antioxidants like vitamin C and mannitol. Furthermore, complexes 1 and 2 exhibit significant superoxide radical activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Stepwise synthesis of peripherally dimetallated metallo-tetraazaporphyrins with linear and bent motifs

Two new dinuclear and two new trinuclear complexes of 2,3,7,8,12,13,17,18-octakis(methylthio)tetraazaporphyrinatomagnesium(II), [Mg(OMTTAP)] were synthesized using a convenient stepwise process. These complexes possess (bpy)₂Ru^II and Cp(PPh₃)Ru^II metal moieties directly attached to the β-positions in the [Mg(OMTTAP)] through thioether chelation. Complexes were characterized using ¹H-n.m.r., u.v.–vis and mass spectroscopic data. The peripheral binding of the two Ru^II units significantly influenced redox potentials of the OMTTAP core by lowering E_1/2 for the OMTTAP centered oxidation and reduction processes, both, as evident from their cyclic voltammograms. The stepwise synthesis reported here demonstrates success of a convenient strategy to obtain hybrid, trimetallic, redox active chromophores with linear and bent motifs.     

含末端炔基的Salen型金属配合物的合成、表征及性质

设计合成了新型含有末端炔基的Salen型配体H2Ln及其系列金属配合物MLn(n=1,2;M=Ni,Cu,Mn),并用氢核磁共振(1H NHR)谱、电喷雾质谱(ESI-MS)、元素分析(EA)、傅里叶变换红外(FT-IR)光谱和紫外-可见(UV-Vis)光谱等对各目标化合物进行了表征.采用循环伏安法研究了配体及其金属配合物的电化学氧化还原性质.研究发现,配体除H2L1外均在测试范围内出现特征的亚胺氧化还原峰.镍和铜的配合物均经历了两个单电子的氧化还原过程;锰的配合物均出现由Mn(III)/Mn(II)产生的一对氧化还原峰,该过程为准可逆的单电子过程.H2Ln及MLn的溶液摩尔电导率数据显示,各目标化合物为弱电解质,具有一定的导电性.     

Iron(II), cobalt(III), nickel(II) and copper(II) chelates of furan and thiophene azo-oximes

Summary Complexes of furan and thiophene azo-oximes with iron(II), cobalt(III), nickel(II) and copper(II) have been prepared and characterised. Iron(II), cobalt(III) and copper(II) complexes are diamagnetic in the solid state. The diamagnetism of the copper(II) chelates is suggestive of antiferromagnetic interaction between two copper centres.¹H n.m.r. spectral data suggest atrans-octahedral geometry for the tris-chelates of cobalt(III). Nickel(II) complexes are paramagnetic, in contrast to the diamagnetism of the analogous complexes of arylazooximes. The electronic spectra are suggestive of octahedral geometry for the iron(II), cobalt(III) and nickel(II) complexes, andD _4h -symmetry for copper(II). Infrared data indicate N-bonding of the oximino-group to the metal ions.     

Redox, thermodynamic and spectroscopic of some transition metal complexes containing heterocyclic Schiff base ligands

Complexes of two series of Schiff base ligands, H₂L_a and H₂L_bderived from the reaction of 2,6-diacetyl pyridine with semicarbazide, H₂L_a and thiosemicarbazide, H₂L_b, with the metal ions, Co(II), Ni(II), Cu(II), VO(IV) and UO₂(VI) have been prepared. The ligands are characterized by elemental analysis, IR, UV–vis and ¹H NMR. The structures of the complexes are investigated with the IR, UV–vis, X-band ESR spectra, ¹H NMR and thermal gravimetric analysis as well as conductivity and magnetic moment measurements. The IR-spectra reveal the presence of variable modes of chelation for the investigated ligands. A variety of binuclear or mononuclear complexes were obtained with the two ligands in tri-, tetra or pentadentate forms. The bonding sites are the pyridine nitrogen, two azomethine nitrogen atoms and ketonic oxygen in case of H₂L_a or sulphur atoms in case of H₂L_b. The Coats–Redfern equation has been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. Cyclic voltammograms of Co(II) and Ni(II) show quasi-reversible peaks. The redox properties and the nature of the electro-active species of the complexes have been characterized.