Syntheses,structures and magnetic properties of multinuculear manganese complexes with Schiff base ligands

Multinulear manganese complexes with Schiff base ligands, [{Mn^III₄(μ₃-O)(sae)₄(μ-N₃)(CH₃OH)}₂(μ-N₃)]N₃ ([1]N₃), [Mn^III₆(μ₃-O)₂(sae)₆(NCS)₂] (2) and [Mn^II₄Mn^III₂(sae)₆(CH₃OH)₂Cl₂] (3) (H₂sae=2-salicylideneaminoethanol), were prepared and the crystal structures and magnetic properties were studied.     

Syntheses and magnetic properties of trinuclear trithiocyanurato-bridged manganese(II) complexes involving bidentate aromatic N-donor heterocycles

Trinuclear manganese(II) complexes of the compositions [Mn₃(phen)₆(ttc)](ClO₄)₃ (1), [Mn₃(dmbpy)₆(ttc)](ClO₄)₃? 2H₂O (2) and [Mn₃(bpy)₆(ttc)](ClO₄)₃? 3H₂O (3), where phen = 1,10-phenanthroline, dmbpy = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine and H₃ttc = trithiocyanuric acid (2,4,6-trimercapto-1,3,5-triazine), were prepared and characterized by elemental analysis, FTIR and Raman spectroscopies, MALDI-TOF mass spectrometry, magnetic and conductivity measurements. The magnetic analysis incorporating simultaneous fitting of the temperature dependence and the field dependence of the magnetization using the isosceles triangle spin Hamiltonian model revealed a weak antiferromagnetic exchange within the trinuclear units.     

Syntheses,structures and properties of cobalt and manganese complexes based on pyridine-2,3,5,6-tetracarboxylic acid

Two new complexes based on pyridine-2,3,5,6-tetracarboxylic acid(H₄pdtc) as ligand, {[Co₂(pdtc)(H₂O)₄] · H₂O}_n (1) and {Mn₂(pdtc)(H₂O)₄}_n (2), have been obtained by hydrothermal syntheses and characterized by IR, elemental analysis, X-ray diffraction single crystal structure analysis, PXRD, thermal gravimetric analysis, and magnetic measurements. Complex 1 is 3D coordination polymer and complex 2 belongs to 2D grid structure by covalent bonds. In 1 and 2, the metal ions show antiferromagnetic interactions.     

Syntheses,structures and luminescence of three copper(I) cyanide coordination polymers incorporating flexible N-donor ligands

Three copper(I) cyanide coordination polymers, namely [Cu₈(CN)₈(btmb)₂]_n (1), [Cu(CN)(btmb)_0.5]_n (2) and [Cu₂(CN)₂(dpa)]_n (3) (btmb = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene, dpa = di(4-pyridyl)amine), were synthesized under hydrothermal conditions and characterized by elemental analyses, IR spectra, PXRD and thermogravimetric analyses. Single-crystal X-ray diffraction analyses reveal that complex 1 is an interesting 2D double-layered network constructing from eight distinct Cu(I) centers, eight μ₂-cyanides and two tetradentate cis-btmb ligands. Complex 2 is a ladder-like coordination polymer assembled by CuCN linear chain and bidentate trans-btmb linker. Complex 3 has a 2D wave-like network constructing from CuCN zigzag chain and V-shape dpa spacer. These coordination polymers are thermally stable up to 270–300 °C. They emit blue luminescence originating from ligand-centered emission.     

The extraction of anionic complexes of divalent manganese,cobalt, nickel and copper from aqueous thiocyanate solutions by tricaprylmethylammonium chloride

The extraction of divalent manganese, cobalt, nickel and copper-thiocyanato anionic species from aqueous solutions by tricaprylmethylammonium chloride (R₃R′NCl) in benzene has been investigated under different conditions. Both the aqueous and organic phases have been examined by spectrophotometry. Infrared spectro-photometry and measurements of water content, apparent molecular weight and magnetic moment have been applied to the organic extracts, and electron spin resonance experiments to the organic manganese(II)- and copper(II)-complexes. The mechanism of the extractions and the structures of the extracted complexes are discussed on the basis of the results obtained. As a result, it is found that although the extraction efficiency follows the order Co > Cu > Mn > Ni, the extraction of divalent transition metals is expressed as [M(NCS)₄]²-(aq) + 2R₃R′NNCS(org)→(R₃R′N)₂-[M(NCS)₄](org) + 2NCS-(aq) in which M = Mn, Co, Ni and Cu. The extracted species of divalent manganese, cobalt and nickel give a tetrahedral T_d symmetry, and the copper(II) species is in a distorted tetrahedron (point group D_2d symmetry). In addition the species of nickel (II) extracted at low aqueous concentration exists as a complex (R₃R′N)₂[Ni(NCS)₄(H₂O)₂] in an octahedral arrangement.     

Two highly connected frameworks and one polythreading architecture based on multidentate N-donor ligands: Syntheses,structures, characterizations and photoluminescent properties

Three coordination polymers based on multidentate N-donor ligands and polycarboxylate anions, namely, [Co₃(4,4′-tmbpt)₄(btc)₂]·9.5H₂O (1), [Ag₄(4,4′-tmbpt)(btec)(H₂O)₂]·H₂O (2) and [Zn(4,4′-tmbpt)(btec)_0.5(H₂O)]·0.5H₂O (3) (4,4′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(4-pyridyl)-1,2,4-triazole, H₃btc = 1,3,5-benzenetricarboxylic acid, and H₄btec = 1,2,4,5-benzenetetracarboxylic acid) have been prepared under hydrothermal condition. Compound 1 displays a 3D (3,6,8)-connected framework with (4·6²)(4⁴·6¹⁰·8)(4¹⁴·6¹²·8²) topology. Compound 2 is a 3D (4,5,8)-connected framework with (4³·6²·8)(4³·6⁵·8²)(4⁸·6²)(4¹⁰·6¹⁰·8⁸) topology. Compound 3 exhibits a 2D → 3D polythreading architecture. The photoluminescent spectra indicate that at room temperature, compounds 2 and 3 emit green and blue luminescence, respectively.     

Two cobalt complexes derived from 1H-1,2,3-triazole-4,5-dicarboxylic acid: Syntheses,structures and magnetic properties

Two cobalt(II) homometallic complexes, [Co₂(HTDA)₂(H₂O)₆·2H₂O] (1) and {[Co₃(TDA)₂(H₂O)₈]·H₂O}_n (2) (H₃TDA = 1H-1,2,3-triazole-4,5-dicarboxylic acid) have been synthesized and structurally characterized in detail. Single-crystal X-ray crystallographic study reveals that they crystallize in trigonal space group R-3 and orthorhombic space group Pna2₁, respectively. In 1, two Co^2 + cations are bonded by two HTDA^2 − ligands to generate a binuclear Co^II unit, which can further be extended to a 3D supermolecular structure via the hydrogen bonds. At variance with 1, the nearest Co^2 + cations of 2 are connected via TDA^3 − ligands to form a 1D coordination polymer and can be further linked to each other to result in a 3D supermolecular framework through the hydrogen bonding interactions as well. The magnetic properties of them were studied in detail.     

Surface properties of self-assembled monolayer films of tetra-substituted cobalt, iron and manganese alkylthio phthalocyanine complexes

Self-assembled monolayer (SAM) films of iron (SAM-1), cobalt (SAM-2) and manganese (SAM-3) phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the non-peripheral positions, were formed on gold electrode in dimethylformamide (DMF). Electrochemical, impedimentary and surface properties of the SAM films were investigated. Cyclic voltammetry was used to investigate the electrochemical properties of the films. Ability of the films to inhibit common faradaic processes on bare gold surface (gold oxidation, solution redox chemistry of [Fe(H₂O)₆]³⁺/[Fe(H₂O)₆]²⁺ and underpotential deposition (UDP) of copper) was investigated. Electrochemical impedance spectroscopy (EIS), using [Fe(CN)₆]^3−/4− redox process as a probe, offered insights into the electrical properties of the films/electrode interfaces. Surface properties of the films were probed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The films were employed for the electrocatalytic oxidation of the pesticide, carbofuran. Electrocatalysis was evidenced from enhanced current signal and less positive oxidation potential of the pesticide on each film, relative to that observed on the bare gold electrode. Mechanism of electrocatalytic oxidation of the pesticide was studied using rotating disc electrode voltammetry.     

Syntheses,crystal structures,spectroscopy, and catalytic properties of two nickel-based hexaazamacrocyclic complexes with carboxylate ligands

Two new hexaazamacrocyclic nickel(II) complexes with the formula [NiL¹(4-nba)₂] (1) and [NiL²(sal)₂] (2) (L¹ = 3,10-dioctyl-1,3,5,8,10,12-hexaazacyclotetradecane, L² = 3,10-diisobutyl-1,3,5,8,10,12-hexaazacyclotetradecane, 4-nba = p-nitrobenzoate, and sal = salicylate) were synthesized at room temperature. These complexes were characterized by physico-chemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis. The coordination geometry in complexes 1 and 2 exhibit a distorted octahedron around the nickel(II) ion with hexaazamacrocyclic unit in the equatorial positions and two p-nitrobenzoate (or salicylate) anions in the axial positions. The degradation of methyl orange by potassium persulfate (KPS) in the presence of complex 1 (or 2) oxidation system occurred to near completion in 60 min compared to only 55% with KPS alone under UV light irradiation. Thus, both complexes in cooperation with KPS could be an attractive choice for degradation of organic pollutants for environmental remediation.     

Syntheses and investigation of thermal properties of copper complexes with azo-containing Schiff-base dyes

In the present study a series of azo dyes: 5-((4-pentyloxyphenyl)azo)-salicylaldimine-N-R (R = phenyl, 4-methoxyphenyl, cyclohexyl) and related copper(II) bis chelates have been synthesized and characterized by IR, NMR, mass spectroscopies and elemental analyses. The thermal stability of free ligands and related copper(II) bis(chelate) was studied by using differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA). The differences in the thermal stability were related to the structure of free ligands and copper complexes and decomposition products were characterized according to their X-ray diffraction pattern.     

Syntheses,structures, and magnetic properties of ethoxy-bridged dinuclear iron(III) complexes containing tetradentate ligands

Dinuclear iron(III) complexes, [(phenO)Fe(SO₄)]₂·2CH₃OH (1) and [(bpmapO)Fe(NO₃)]₂(NO₃)₂·3CH₃OH (2) have been prepared by the reaction of phenOH/bpmapOH and FeSO₄·7H₂O/Fe(NO₃)₃·9H₂O in methanol, respectively (phenOH = N-(2-pyridylmethyl)-N′-(2-hydroxyethyl)ethylenediamine, bpmapOH = N-(bis(2-pyridylmethyl)amino)-2-methylpropan-2-ol). Both complexes are ethoxy-bridged dinuclear species and the iron(III) ions in 1 and 2 have distorted octahedral geometries. Both complexes show strong antiferromagnetic interactions through the bridged ethoxy groups within the dimeric units.     

Homochiral iron(II) complexes based on imidazole Schiff-base ligands: Syntheses,structures, and spin-crossover properties

A pair of mononuclear iron(II) enantiomeric complexes: fac-Λ-[Fe(R-L)₃](BF₄)₂·MeCN (1) and fac-Δ-[Fe(S-L)₃](BF₄)₂·MeCN (2) [L = 1-phenyl-N-(1-methyl-imidazol-2-ylmethylene)ethanamine] have been synthesized and characterized. X-ray crystallography reveals that iron(II) center is surrounded by three bidentate ligands defining a pseudooctahedral [FeN₆] coordination environment. R-L ligand induces the fac-Λ isomer, while S-L ligand induces the fac-Δ isomer. Magnetic measurements reveal that both of them display obviously spin-crossover behavior at 365 K. After desolvation, they exhibit a reversible spin transition with a small hysteresis loop of ca. 3 K appearing at about T_1/2↑ = 222 K and T_1/2↓ = 219 K.     

Purification of nickel sulphate solutions containing iron,copper, cobalt,zinc and manganese

Acidic nickel-bearing solution containing iron, cobalt, manganese, zinc and copper was processed through a solvent extraction and precipitation technique to obtain a pure nickel sulphate solution. Iron was extracted using 0.2M Cyanex-272 (partially neutralised) as the extractant. Stripping of iron from the loaded organic has also been studied. After iron recovery through solvent extraction the raffinate still contained 0·25 g dm^?3 of iron which was quantitatively separated by a lime precipitation technique. During this iron precipitation there was no loss of cobalt and nickel but copper, manganese and zinc were coprecipitated to some extent. From the iron-free nickel sulphate solution the other impurities were extracted using the same extractant (Cyanex-272) in a single stage. The metal ions from the loaded organic were stripped using a 0·5% (v/v) H₂SO₄ solution in a single stage. The entire operation needs only seven stages: two stages for iron extraction, three stages for iron stripping from the loaded organic, and one stage each for extraction and stripping of other impurities. In the entire operation the loss of nickel was less than 0·5%.     

The synthesis, characterization, thermal and optical properties of copper, nickel, and vanadyl complexes derived from azo dyes

Two, novel, tetradentate Schiff-base ligands, namely bis-5-phenylazosalicylaldehyde diethylenetriimine and bis-5-[(4-methoxyphenyl)azo]salicylaldehyde diethylenetriimine, as well as their Cu²⁺, Ni²⁺, and VO²⁺ complexes, were synthesized and characterized using elemental analysis, infrared and also UV–Visible spectroscopy, ¹HNMR and mass spectra. The thermal stability of the free ligands and the related metal complexes, as determined using differential scanning calorimetry and thermal gravimetric analysis, were found to be thermally stable upto 240–275 °C depending on the type of ligand and the central metal atom. The λ_max of the ligands and their transition metal complexes in the region 300–800 nm are discussed. The novel metal complexes offer potential for application as recording media owing to both their absorption spectra in the blue-violet light region and high thermal stability.     

Synthesis, electrochemical and electrocatalytic behaviour of thiophene-appended cobalt, manganese and zinc phthalocyanine complexes

This work reports on the syntheses of new thiophene tetra substituted cobalt, manganese and zinc phthalocyanine (CoTETPc, (Cl)MnTETPc and ZnTETPc) complexes. The redox processes due to the thiophene substituent on the ring of the metallophthalocyanines (MPcs) were observed, in addition to Pc ring and metal (for Co and Mn complexes) based redox activity. The electrocatalytic activity of the CoTETPc complex adsorbed on glassy carbon electrode (GCE) by drop/dry-thermal annealing was investigated using l-cysteine. The modified electrode was stable to repetitive use without any signs of deactivation by oxidation products and was used to determine l-cysteine at concentrations between 0.0015 and 1 mM in pH 4 aqueous conditions.     

Synthesis,characterization and DNA interaction of copper (II) complexes with Schiff base ligands derived from 2-pyridinecarboxaldehyde and polyamines

A series of copper (II) complexes a–d with Schiff bases ligands derived from the condensation reactions between 2-pyridinecarboxaldehyde and different polyamines (ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, HRMS, molar conductance and molecular modeling studies. The interactions of the copper complexes a–d with DNA were investigated by the UV spectra, viscosity measurements and gel electrophoresis under physiological conditions. The experimental results indicated that four complexes could bind to DNA via an intercalative mode and showed a different DNA cleavage activity with the sequence: d > c > a > b.     

Divalent cobalt,zinc, and copper coordination polymers based on a new bifunctional ligand: Syntheses,crystal structures,and properties

Three new coordination polymers, namely, [ML(H₂O)]_n (M = Co (1), Zn (2)) and [CuL(DMF)]_n (3), have been hydrothermally synthesized through the reaction of bifunctional ligand 5-((2-methyl-1H-imidazol-1-yl)methyl)benzene-1,3-dioic acid (H₂L) with divalent cobalt, zinc and copper salts, and structurally characterized by elemental analysis, IR and X-ray diffraction. Both complexes 1 and 2 are two-fold interpenetration 3D frameworks. Complex 3 exhibits (3,6)-connected framework with (4.6²)₂(4².6¹⁰.8³) topology. Furthermore, UV–vis absorption spectra and powder X-ray diffraction (PXRD) were investigated as well.     

Magnetic,magnetostrictive, and AC impedance properties of manganese substituted cobalt ferrites

In this study, we investigated the effects of substituting Mn³⁺ for some Fe³⁺ in spinel lattice on the structure, magnetic properties, magnetostriction behavior, and AC impedance characteristics of cobalt ferrites. The manganese substituted cobalt ferrites (Co–Mn ferrites), CoMn_xFe_2−xO₄, with x varied from 0 to 0.3 in 0.1 increments, were prepared by solid-state reaction. XRD examination confirmed that all sintered Co-based ferrites had a single-phase spinel structure. The average grain size, obtained from SEM micrographs, increased from 8.2 μm to 12.5 μm as the Mn content (x) increased from 0 to 0.3. Both the Curie temperature and coercivity of Co-based ferrites decreased with greater amounts of Mn, while the maximum magnetization (at H=6 kOe) of Mn-substituted cobalt ferrites was larger than that of the pure Co-ferrite. Magnetostrictive properties revealed that the pure Co-ferrite had the largest saturation magnetostriction (λ_S), about −167 ppm, and the CoMn_0.2Fe_1.8O₄ sample exhibited the highest strain sensitivity (|dλ_⊥/dH|_m) of 2.23×10⁻⁹ A⁻¹m among all as-prepared Co-based ferrites. In addition, AC impedance spectra analysis revealed that the real part (Z′) of the complex impedance of Co–Mn ferrites was lower than that of pure Co-ferrite in the low frequency region, and the Co-based ferrites exhibited semiconductor-like behavior.