Structural,spectroscopic, and biological aspects of S∩N donor Schiff-base ligands and their chromium(III) complexes

New chromium(III) complexes are synthesized by classical thermal and microwave (MW)-irradiated techniques. The Schiff bases 2-acetylfuran-S-benzyldithiocarbazate (L¹H), 2-acetylthiophene-S-benzyldithiocarbazate (L²H), 2-acetylpyridine-S-benzyldithiocarbazate (L³H), and 2-acetylnaphthalene-S-benzyldithiocarbazate (L⁴H) were prepared by condensation of -S-benzyldithiocarbazate in ethanol with the respective ketones by using MW as well as conventional methods. The chromium(III) complexes have been prepared by mixing CrCl₃ · 6H₂O in 1 : 1 and 1 : 2 molar ratios with monofunctional bidentate ketimines. The structure of the ligands and their transition metal complexes were confirmed by elemental analysis, melting point determinations, molecular weight determinations, infrared (IR), electronic and electron paramagnetic resonance (EPR) spectral, and X-ray powder diffraction studies. On the basis of these studies it is clear that the ligands coordinated to the metal atom in a monobasic bidentate mode by S∩N donors. Thus, an octahedral environment around the chromium(III) has been proposed. The growth inhibiting potential of the ligands and complexes has been assessed against a variety of fungal and bacterial strains.     

Synthesis,characterization and catalytic studies of iron(III), cobalt(II), nickel(II) and copper(II) complexes containing triphenylphosphine and β-diketones

A series of new β-diketonato complexes have been synthesized from the reactions of iron(III), cobalt(II), nickel(II) and copper(II) Ph₃P complexes with β-diketones (acetylacetone, benzoylacetone and dibenzoylmethane). All the complexes have been characterized by elemental analyses, spectral studies (i.r., electronic., magnetic., e.p.r., ¹H-n.m.r.) and cyclic voltammetry. The new complexes have been used as catalysts for aromatic coupling and oxidation reactions. Higher catalytic activity has been observed for the nickel(II) complexes compared to the other complexes.     

The complexes of aluminium,gallium, and indium with calmagite: Evaluation of stepwise stability constants

Summary Calmagite [1-(1-hydroxy-4-methyl-2-phenyl azo)-2-naphthol sulphonic acid], dissociates in two steps. It forms violet complexes with Al³⁺, Ga³⁺ and In³⁺. The stepwise proton-ligand stability constants of calmagite and stepwise metal-ligand stability constants of these complexes were evaluated by potentiometric titration technique ofBjerrum andIrving andRossotti. The order of the stabilities of complexes is In³⁺ > Ga³⁺ > > Al³⁺.

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Zusammenfassung Camalgit [1-(1-Hydroxy-4-methyl-2-phenylazo)-2-naphtholsulfonsäure] dissoziiert in zwei Stufen und bildet violette Komplexe mit Al(III), Ga(III) und In(III). Die Konstanten der Dissoziationsstufen der freien Säure und die der Metallkomplexe wurden potentiometrisch nachBjerrum bzw.Irving undRossotti ermittelt. Die Stabilität der Komplexe nimmt in der Reihe In(III) > Ga(III) > Al(III) ab.

     

Synthesis and characterization of cobalt(III) tetraaza macrocyclic complexes containing chloro and azido ligands

The complexes [Co(L)Cl₂]Cl · 4H₂O (1) and [Co(L)(N₃)₂]N₃ · 2H₂O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18,0^7.12]docosane) have been synthesized, and structurally characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of (1) is centrosymmetric and the cobalt(III) atom has an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two chloride ligands. The cobalt(III) ion in (2) is coordinated to four nitrogen atoms from the macrocycle, and two azide ligands in an octahedral environment, which forms the 1D polymer through hydrogen bonding contacts involving the cation, azide anion and solvent water molecules. Electronic spectra of the complexes also exhibit a low-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to Co(III)/Co(II) processes. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.     

pH-metric studies on formation constants of the complexes of substituted pyrazoles with some lanthanide metal ions and the influence of ionic strengths on complex equilibria in a 70% dioxane-water mixture

The pK a values of N-heterocyclic compounds (substituted pyrazoles) in a 70% (v/v) dioxane-water mixture have been determined using pH-metric measurements. The stability constants of the complexes of Dy(III), Nd(III), Sm(III), and Tb(III) with 3-(2-hydroxyphenyl)-5-methylpyrazole, l-phenyl-3-(2-hydimyphenyl)-5-methylpyrazole 3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole, and l-phenyl-3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole have been determined by the pH-metric method at ( 300 ± 0.1) K. The effect of ionic strengths on the complexes of Sm³⁺ and Pr³⁺ ions with pyrazole has been investigated in the internal from 0.02 to 0.1 mol dm⁻³ (sodium perchlorate) in the pH range 2–3.     

Copper(II), iron(III), and chromium(III) complexes with 5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene derivatives

Six copper(II), iron(III), and chromium(III) complexes with 5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene derivatives (H₂L¹-H₂L³) have been synthesized and studied by physical methods (IR and electronic absorption spectroscopy, quantum-chemical calculations). The composition of the complexes has been determined and their stability constants in aqueous dimethylformamide solutions have been calculated. The energy characteristics, electronic structure and geometry of isolated diazapyrenes and their tautomeric forms have been calculated by the PM6 method, and their complexes have been modeled.     

Synthesis,crystal structure,and antimicrobial activity of a series of cobalt(III) Schiff base complexes

Abstract

A series of six new mononuclear Schiff base complexes, 1–6 of cobalt(III) of the general formula, [CoLX] or its adduct with methanol, is reported. The pentadentate Schiff base ligand (H₂L) was obtained by the condensation of N-(3-aminopropyl)-N-methylpropane-1,3-diamine with 1-(2-hydroxyphenyl)ethanone (H₂L¹) or 1-(2-hydroxyphenyl)propan-1-one (H₂L²). X stands for the pseudohalides, N₃^–, N(CN)₂^? , and NCS^–. The complexes have been synthesized by the reaction of equimolar amounts of cobalt(II) nitrate with H₂L¹ or H₂L² in the presence of the respective pseudohalide in methanol medium. All the complexes have been characterized by microanalytical, spectroscopic, single crystal XRD (except 3), and other physicochemical studies. Structural studies reveal that the central Co(III) ion in 1, 2, 4, 5, and 6 adopts a distorted octahedral geometry with a CoN₄O₂ chromophore. Weak intermolecular H-bonding and/or π-interactions are operative in these complexes to bind the molecular units. The antimicrobial activity of all the complexes and their constituent Schiff bases has been tested against some common bacteria and fungi.     

Synthesis and characterization of novel oxime-imine ligands and their heteronuclear ruthenium(III) complexes

Vicinal carbonyl oxime (HL¹) and oxime-imine (H₂L²) ligands and their mononuclear Ru(III) and Cu(II), heterodinuclear Ru(III)-Mn(II), Ru(III)-Ni(II), Ru(III)-Cu(II), and heterotrinuclear Ru(III)-Cu(II)-Ru(III) chelates were synthesized and characterized by elemental analysis, molar conductivity, IR, ESR, ICP-OES, magnetic moment measurements, and thermal analyses studies. The free ligands were also characterized by ¹H NMR spectra. The carbonyl-oxime ligand coordinates through the oxygen of =N-OH to form a six-membered chelate ring. The quadridentate tetraaza ligand (H₂L²) obtained by condensing of the bidentate ligand 1-p-diphenylmethane-2-hydroxyimino-2-(1-naphthylamino)-1-ethanone (HL¹) with 1,2-phenylenediamine coordinates with Ru(III) through its nitrogen donors in the equatorial position with the loss of one of the oxime protons and concomitant formation of an intramolecular hydrogen bond. Stoichiometric and spectral results of the metal complexes indicated that the metal: ligand ratios in the mononuclear complexes of the ligand (HL¹) were found to be 1: 2, while these ratios were 1: 1 in the mononuclear complexes of the ligand (H₂L²). The metal: ligand ratios of the dinuclear complexes were found to be 2: 1, and this ratio was 3: 2 in the trinuclear complex. The article is published in the original.     

Dichloro and amino acid cobalt(III) complexes of N,N′-diethylethylenediamine-N,N′-Di-α-butyrate ligand

A novel linear flexible ONNO-type tetradentate ligand, N,N′-diethylethylenediamine-N,N′-di-α-butyrate (deedba), and the dichloro, diaqua and amino acid (glycine, -alanine, -phenylalanine) cobalt(III) complexes of deedba have been synthesized via an H₂O₂ oxidation method. During the preparation of these complexes, the ligand has coordinated geospecifically to the cobalt(III) ion to give only one isomer, s-cis, which has been characterized by electronic absorption, ¹H NMR and IR spectra, and elemental analysis. It is of interest that this is one of the few Co^III(edda)X₂-type complex preparations, which gives only one isomer with geoselectivity.     

Synthesis and spectroscopic characterization of new iron(III) complexes of S-Alkyl/Aryl dithiocarbazates of 5-methyl-3-formylpyrazole and 5-methyl-3-formylpyrazolyl-thiosemicarbazones

New iron (III) complexes of S-methyl-βN-(5-methylpyrazole-3-yl)methylenedithiocarbazate, S-benzyl-β-N-β-(5-methylpyrazole-3-yl)methylenedithiocarbazate, 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone, and 5-methyl-3-formylpyrazole-⁴N-benzylthiosemicarbazone have been synthesized and physicochemically characterized by elemental analyses, magnetic moment measurements (polycrystalline state), electronic, IR, and EPR spectra, as well as conductance measurements, are used to confirm the coordination geometry. The spectral studies reveal the low-spin distorted octahedral structure of the iron (III) complexes containing two uninegative tridentate ligands with NNS donor sites, where the EPR data confirm the presence of a spin — paired iron (III) with d _xz ² d _yz ² d _xy ¹ configuration in the ground state. The article is published in the original.     

The synthesis and characterization of a new (E,E)-dioxime and its mono and heterotrinuclear complexes containing dioxadithiadiazamacrobicyclic moieties

A new (E,E)-dioxime (2Z,3Z)-1,4,7,8,15,16-hexahydro-9,14-(ethanothioethanothioethano)quinoxalino[6,7-e] [4,7,1,10]benzodioxadiazacyclododecine-2,3,19,26-tetrone2,3-dioxime (H₂L) has been synthesized by reacting cyanogen-di-N-oxide with 2,3-diamino-6,7,14,15-tetrahydro-8,13-(ethanothioethanothioethano)dibenzo[b,h] [1,4,7,10]dioxadiazacyclodecine-17,24-dione (6). Mononuclear complexes (8, 9) of this ligand have been synthesized by reacting the vic-dioxime (H₂L) with NiCl₂ · 6H_2O and COCl₂ · 6H₂O respectively. The BF ₂ ⁺ capped cobalt(III) complex (10) of the new (E,E) vic-dioxime has been synthesized by using as precursor a hydrogen-bridged mononuclear cobalt(III) complex (9). The heterotrinuclear complex (11) has been prepared by reacting one mononuclear cobalt(III) complex (10) with [Cu(MeCN)₄]PF₆. The new compounds were characterized by a combination of elemental analysis, ¹H- and ¹³C-n.m.r, i.r. and m.s. spectral data.     

Synthesis and spectral characterization of lanthanide complexes with sulfamethoxazole and their antibacterial activity

A series of nonelectrolytic lanthanide(III) complexes, [ML₂Cl₃]·2H₂O, where M is lanthanum(III), praseodymium(III), neodymium(III), samarium(III), gadolinium(III), terbium(III), dysprosium(III), and yttrium(III), containing sulfamethoxazole ligand (L) are prepared. The structure and bonding of the ligand are studied by elemental analysis, magnetic susceptibility measurements, IR, ¹HNMR, TG/DTA, X-ray diffraction studies, and electronic spectra of the complexes. The stereochemistry around the metal ions is a monocapped trigonal prism in which four of the coordination sites are occupied by two each from two chelating ligands, sulfonyl oxygen, and nitrogen of the amide group and the remaining three positions are occupied by three chlorines. The ligand and the new complexes were tested in vitro to evaluate their activity against the bacteria Escherichia coli and Staphylococcus aureus. The text was submitted by the authors in English.     

Novel bidentate ruthenium(III) Schiff base complexes: synthetic,spectral, electrochemical,catalytic and antimicrobial studies

Ru^III complexes of the type [RuX(L)₂(E)] (X = Cl or Br; L = novel bidentate Schiff base ligand; E = PPh₃ or AsPh₃) have been prepared by reacting [RuX₃(E)₃] or [RuBr₃(PPh₃)₂(MeOH)] with two novel bidentate Schiff base ligands derived from 4-(1-methyl-1-mesitylcyclobutane-3-yl)-2-aminothiazole, in a 1:2 molar ratio in benzene, and characterised by analytical, spectral (i.r., electronic, ¹H-, ¹³C- n.m.r., and e.p.r.) and electrochemical data. An octahedral structure has been tentatively proposed for all the new complexes. The thermal properties of the ligands and their complexes have been studied by t.g.a. The new Ru^III complexes are effective catalysts for the oxidation of alcohols to carbonyl compounds but are unable to oxidise alkenes in the presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant. The antimicrobial activity of the ligands and complexes have also been tested against six microorganisms.     

Synthesis,Characterization, Antimicrobial Activities,and Structural Studies of Lanthanide (III) Complexes with 1-(4-Chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1-thiosemicarbazone

Twelve coordinate lanthanide (III) complexes with the general composition [Ln L₃X_n(H₂O)_n] where Ln = Pr(III), Sm(III), Eu (III), Gd (III), Tb (III), Dy (III), X = Cl^?1, NO₃ ^?2, n = 2–7, and L is 1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1- thiosemicarbazone have been prepared. The lanthanide complexes (5) were derived from the reaction between 1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1-thiosemicarbazone (4) with an aqueous solution of lanthanide salt. Chalcone thiosemicarbazone ligand (4) was prepared by the reaction of [1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)]prop-2-enone (chalcone) (3) with thiosemicarbazide in the presence of hot ethanol. All the lanthanide-ligand 1:3 complexes have been isolated in the solid state, are stable in air, and characterized on the basis of their elemental and spectral data.

Thiosemicarbazone ligands behave as bidentate ligands by coordinating through the sulfur of the isocyanide group and nitrogen of the cyanide residue. The probable structure for all the lanthanide complexes is also proposed. The chalcone thiosemicarbazone ligands and their lanthanide complexes have been screened for their antifungal and antibacterial studies. Some of the synthesized lanthanide complexes have shown enhanced activity compared with that of the free ligand.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Adsorption profile of preheated Cr(III)-SCN complexes on polyurethane foam

The accumulation of preheated chromium(III)-thiocyanate complexes onto polyurethane foam (PUF) has been studied. The maximum sorption of Cr(III) (7.01^.10^-5M) is occurred at pH 2 from 1.2M thiocyanate solution in 10 minute agitation time using 7.25 mg/ml PUF. The sorption data have been investigated by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich parameters 1/n = 0.31 and of K _F = 9.7^.10^-4 mol^.g^-1, Langmuir constants M = 7.03^.10^-5 mol^.g^-1 and of b = 1.5^.10⁵ l^.mol^-1 and of D-R constants, C _m = 1.91^.10^-4 mol^.g^-1, affinity coefficient b = -0.0023 mol^2.kJ^-2 and sorption energy E = 14.7 kJ^.mol^-1 have been evaluated. Thermodynamic parameters of enthalpy, entropy and Gibbs free energy suggest the endothermic and spontaneous adsorption of Cr(III)-SCN complex onto PUF at higher temperature. The influence of common anions and cations on the accumulation of chromium-thiocyanate on PUF and possible sorption mechanism of [Cr(SCN)₄]^- species on PUF is discussed.     

Synthesis,characterization and ascorbic acid oxidase mimetic catalytic activity of copper(II) picolyl hydrazone complexes

Four new picolyl hydrazones were prepared via Schiff-base condensation of picolonic acid hydrazide with α-formyl-(L¹), α-acetyl-(L²), α-benzoyl-(L³) pyridine and α-formyl-(L⁴) thiophene. Copper(II) complexes of these hydrazones and a series of copper(II) complexes containing (L²) and various anions (Cl, Br, NO₃, SCN, SO₄, ClO₄, AcO, PF₆ and BF₄) have been synthesized. Elemental, thermal analysis, molar conductivity, magnetic moment measurements and spectral (i.r., electronic and e.s.r.) studies have been used to characterize the prepared compounds. The overall structure and reactivity of the reported copper(II) chelates critically depend on the ligand structure and the nature of counter anion incorporated in the complex molecule. Octahedral [complex (7)], square-pyramidal [complex (8)] and square-planar monomeric species [complexes (1–6), (9) and (10)] and a dimeric structure with oxygen bridge in square-planar geometry [complexes (11) and (12)] were suggested. The reported copper(II) complexes exhibit promising oxidase catalytic activity towards the aerobic oxidation of vitamin C. A linear correlation exists between the oxidase catalytic activity and the Lewis-acidity of the central copper(II) ion created by the donating properties of the parent ligand, as well the irregularity of the coordination environment. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

Alkyl substituents triggered an unexpected formation of mono-and dinuclear zirconium hydrazonate complexes: synthesis,characterization and their catalytic behavior toward ethylene polymerization

Mononuclear zirconium complex 3a of the molecular identity [Zr[η²-(C₄H₃O)C (Et) = NNPh]Cl₃(THF)₂], dinuclear zirconium complexes 3b [{Zr[η²-(C₄H₃O)C(i-Pr) = NNPh]₂}₂(μ²-Cl)₃(μ³-Cl)₂Li(Et₂O)] and 3c [{Zr[η²-(C₄H₃O)C(t-Bu) = NNPh]₂}₂Cl₂(μ²-Cl)₂] have been synthesized by the treatment of lithium salt of (C₄H₃O)C(R) = NNHPh (R = CH₃CH₂, 1a ; R = (CH₃)₂CH, 1b ; R = (CH₃)₃C, 1c ), with different molar ratios of anhydrous zirconium tetrachloride. Of these, complex 3b was formed with lithium adduct and no such adduct was found in complex 3c . Compound 1a and all the zirconium complexes ( 3a - 3c ) were structurally characterized by single-crystal X-ray diffraction studies. Thus, it revealed that each hydrazonato ligand acts in a strained η²-coordination fashion for the three zirconium complexes. The molecular structures of the three zirconium complexes ( 3a - 3c ) reveal the existence of intramolecular hydrogen bonding interactions. Interestingly, complexes 3a and 3b assemble into a two-dimensional network structure through intermolecular hydrogen-bonding interactions. Upon activation with methylaluminoxane (MAO), all the complexes namely 3a , 3b , and 3c exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylene with narrow molecular weight distributions.     

Cobalt-thioalkylazoimidazole complexes: Structures, spectra and redox properties

1-Alkyl-2-{(o-thioalkyl)phenylazo}imidazole (SRaaiNR^/, 1) reacts with Co(ClO₄)₂·6H₂O to form [Co(SRaaiNR^/)₂](ClO₄)₂ (2). The single crystal X-ray structure of one of the complexes of 2 shows a tridentate chelation N(imidazole), N(azo), S(thioether) system. In the structure one of ClO₄⁻ anions shows disorder and forms an (imidazole)C–H···O(ClO₃) interaction leading to a 1-D chain. Co(OAc)₂.4H₂O and SRaaiNR^/ react in the presence of NH₄SCN (1:1:2 mole ratio) in methanol and the complex [Co(SRaaiNR^/)₂(SCN)₂] (3) has been separated. The single crystal X-ray structure determination has established the structure of the complexes in which the ligand SRaaiNR^/ acts in a bidentate N(imidazole), N(azo) chelation mode. A cyclic voltammogram shows a Co(III)/Co(II) oxidative response at 0.6–0.8 V and azo reductions. DFT computation using optimized geometry support the electronic spectral and redox properties of the complexes.     

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.     

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.