Synthesis,characterization, and antimicrobial activities of nickel(II) and copper(II) Schiff-base complexes

Ni(II) and Cu(II) metal complexes of simple unsymmetrical Schiff-base ligands derived from salicylaldehyde/5-methylsalicylaldehyde and ethylenediamine or diaminomaleonitrile (DMN) were synthesized. The ligands and their complexes were characterized by elemental analysis, ¹H NMR, FT IR, and mass spectroscopy. The electronic spectra of the complexes show d–d transitions in the region at 450–600 nm. Electrochemical studies of the complexes reveal that all mononuclear complexes show a one-electron quasi-reversible reduction wave in the cathodic region. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ _eff = 1.70–1.74 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts were also carried out. The in vitro antimicrobial activity of the investigated compounds was tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia, Pseudomonas aeruginosa and Escherichia coli. The antifungal activity was tested against Candida albicans. Generally, the metal complexes have higher antimicrobial activity than the free ligands.     

Synthesis and characterization of new dioxomolybdenum(VI) complexes of ONS donor Schiff bases derived from thiosemicarbazide,S-methyldithiocarbazate,S-benzyldithiocarbazate ando-hydroxy-aromatic aldehydes/ketones

Summary Syntheses of several new dioxomolybdenum(VI) complexes with composition MoO₂L · MeOH (where LH₂ = Schiff base derived from salicylaldehyde, 2-hydroxy-1-naphthaldehyde,o-hydroxyacetophenone,o-hydroxybenzophenone, pyridoxal and thiosemicarbazide,S-methyldithiocarbazate orS-benzyldithiocarbazate) are reported. The complexes have been characterized by elemental analysis, i.r., n.m.r. and electronic spectra, conductance, molecular weight and magnetic susceptibility measurements. The complexes are monomers, nonelectrolytes, diamagnetic and six-coordinated. The Schiff bases behave as dibasic tridentate ligands and coordinate through phenolic oxygen, thioenolic sulphur and azomethine nitrogen atoms. The complexes have acis-O=Mo=O structure as evidenced by the presence of two strong bands at 880–915 and 925–955 cm^–1. All of the complexes exhibit a band atca. 25000 cm^–1 due to the ligand to metal charge transfer transition.     

Spectroscopic,magnetic and thermal studies on complexes of Cu(II) and VO2+ with diacetylmonoxime derivatives: new method for extraction of Cu(II)

The coordination behavior of Cu(II) and VO²⁺ towards some oximes has been investigated. The isolated complexes were characterized by elemental analysis, molar conductance, magnetic moment, spectra (electronic, IR, ESR and mass) and thermal measurements. The IR spectra showed most ligands are deprotonated during complex formation acting as mononegative bi- or tridentate, binegative tetradentate and neutral tridentate. The magnetic moments and electronic spectra showed octahedral, square pyramidal and square-planar structures for the Cu(II) and VO²⁺ complexes. The ESR spectra of the complexes are quite similar and exhibit axial symmetric g-tensor parameters with g _∥ > g _⊥ > 2.0023 and confirmed the structures. The TG curves showed decomposition steps and indicate stability of the complexes. The ligands can remove Cu(II) ions from water by flotation technology using oleic acid surfactant with high efficiency.     

Synthesis,characterization, crystal structures,and superoxide dismutase activity of copper(II) octahedral complexes containing tri- and monodentate ligands

Three new copper(II) complexes [Cu(PSBP)₂](NO₃)(BF₄) (1), [Cu(DAPBMA)₂](BF₄)₂ (2), and [Cu(ImH)₄(NO₃)₂] (3), where PSBP = 4-phenylsemicarbazide-2-benzoylpyridine, DAPBMA = 2,6-diacetylpyridine-bis-4-methoxyaniline, and ImH = Imidazole, have been synthesized and characterized by elemental analysis, FAB mass spectrometry, magnetic susceptibility, X-band electron paramagnetic resonance (EPR), electronic spectroscopy, and cyclic voltammetry. Frozen solution EPR spectra of the complexes have axial features with g _∥ > g _⊥ > 2.003 suggesting the presence of a d _{x ²? y ²} ground state. Single crystal X-ray analyses of 1–3 reveal the presence of distorted octahedral geometry. All complexes exhibit significant superoxide dismutase activity.     

Spectral,magnetic, thermal and electrochemical studies on new copper(II) thiosemicarbazone complexes

The chelation behavior of some =N(1) and NH(4) thiosemicarbazones towards copper(II) ions has been investigated. The isolated complexes are characterized by elemental analysis, magnetic moment, electronic, IR, ESR and ms spectra, and by thermal and voltammetric measurements. The substituents on =N(1) and/or NH(4) thiosemicarbazones and the log K values of the ligands play an important role in complex formation. The IR spectra showed that the reagents HAT, HAET, HAPT, HApClPT, H₂ST and HBT are deprotonated in the complexes and act as mononegative SN donors; H₂SET, H₂SpClPT, H₂HyMBPT and H₂HyMBpClPT, as binegative NSO donors while H₂SPT is a mononegative NSO donor. The ESR spectra of the complexes are quite similar and exhibit axially symmetric g-tensor parameters with g _‖?>?g _⊥?>?2.0023. The loss of thiol and/or hydroxyl hydrogen was confirmed from potentiometric titrations of the ligands and their copper(II) complexes. The protonation constants of the ligands as well as the stability constants of their Cu(II) complexes were calculated. Thermogravimetric analysis of the complexes suggests different decomposition steps. The Coats–Redfern and Horowitz–Metzger equations have been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. The redox properties, nature of the electroactive species and the stability of the complexes towards oxidation are strongly dependent on the substituents on the precursor NH(4) thiosemicarbazone. The redox data are discussed in terms of the kinetic parameters and the reaction mechanism.     

o-hydroxyaroyl-isonicotinoyl hydrazones as chelating agents with divalent transition metal ions

Summary Two series of bivalent metal complexes of the type M(Sal)· xH₂O and M(Naph) have been synthesized; where M = Co, Ni, Cu, Zn, Pd and Cd, and H₂-Sal and H₂-Naph are salicylaldehyde and o-hydroxynaphthaldehyde isonicotinoyl hydrazones which acted as dibasic terdentate ligands. The polymeric nature and coordination sites of the complexes have been characterized by elemental, d.t.a. and t.g.a analyses, molar conductance, pH, room temperature magnetic susceptibility and spectral (i.r., ¹H n.m.r, u.v.) measurements. The protonation constants of the ligands have been determined potentiometrically at different temperatures, ionic strengths and at different EtOH-H₂O compositions.     

Polydentate Schiff-base ligands and their Cd(II) and Cu(II) metal complexes: synthesis,characterization, biological activity and electrochemical properties

Synthesis, characterization, microbiological activity and electrochemical properties of the Schiff-base ligands A¹–A⁵ and their Cd(II) and Cu(II) metal complexes are reported. The ligands and their complexes have been characterized by elemental analysis, FT–IR, UV–Vis, ¹H- and ¹³C-NMR, mass spectra, magnetic susceptibility and conductance measurements. In the complexes, all the ligands are bidentate, the oxygen in the ortho position and azomethine nitrogen atoms of the ligands coordinate to the metal ions. The keto-enol tautomeric forms of the Schiff-base ligands A¹–A⁵ have been investigated in polar and non-polar organic solvents. Antimicrobial activity of the ligands and metal complexes were tested using the disc diffusion method and the chosen strains include Bacillus megaterium and Candida tropicalis. The electrochemical properties of the ligands A¹–A⁵ and their Cu(II) metal complexes have been investigated at different scan rates (100–500?mV?s^?1) in DMSO.     

Synthesis and study of binuclear vanadyl complexes with acyldihydrazones of salicylaldehyde and dicarboxylic acids

The binuclear vanadyl(ii) complexes [(VO)₂·2Py·2EtOH]·mH₂O with acyldihydrazones of salicylaldehyde (H₄L) and dicarboxylic acids were synthesized and studied. In these complexes, two chelate vanadyl(ii) complexes with the tridentate bicyclic ligands are linked to each other by the polymethylene bridges —(CH₂) _n — of different lengths varying from one to four units. The ESR spectra of solutions of these complexes, unlike those of analogous copper(ii) complexes, have an isotropic signal with an eight-line hyperfine structure (g = 1.972, a _V = 93·10^–4 cm^–1) typical of monomeric vanadyl complexes, which indicates that no exchange interactions occur between the paramagnetic centers through the polymethylene chain.     

Synthesis,characterization, electrochemistry,catalytic, and antimicrobial studies of ruthenium(III) complexes containing ONO donor ligands

A series of ruthenium(III) complexes [RuX(EPh₃)₂L] (where X = Cl or Br; E = P or As; L = deprotonated dibasic tridentate ligand) were prepared by the reaction of [RuX₃(EPh₃)₃] with Schiff bases (H₂L¹–H₂L⁴). The ligands were prepared by the condensation of N-4 phenyl/methyl semicarbazide with o-vanillin/o-hydroxy acetophenone. The complexes were characterized by elemental, physico-chemical, and electrochemical methods. Catalytic studies of these complexes for the oxidation of alcohols and aryl–aryl coupling were carried out. Antimicrobial experiments were also carried out.     

Preparation of Schiff’s base complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) and their spectroscopic, magnetic, thermal, and antifungal studies

The potassium salt of salicylidene-DL-alanine (KHL), bis(benzylidene)ethylenediamine (A¹), thiophene-o-carboxaldene-p-toluidine (A²), and its metal complexes of the formula [(M^II(L)(A)(H₂O)] (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); A = A¹ or A²) are prepared. They are characterized by elemental analysis, magnetic susceptibility measurements, thermogravimetric analysis, and infrared and electronic spectral studies. The electronic spectral and magnetic moment data suggest an octahedral geometry for the complexes. All of these complexes, metal nitrates, fungicides (bavistin and emcarb), and ligands are screened for their antifungal activity against Aspergillus niger, Fusarium oxysporum, and Aspergillus flavus using a plate poison technique. The complexes show higher activity than those of the free ligands, metal nitrate, and the control (DMSO) and moderate activity against bavistin and emcarb. The text was submitted by the authors in English.     

EPR studies of a molybdenyl complex in single crystals of NH4Cl

Electron paramagnetic resonance of [MoOCl₅]^2? has been studied in single crystals of NH₄Cl. At room temperature the interaction of the unpaired electron with both the even and odd isotopes of molybdenum has been observed. The existence of metal-halogen π bonding is established by the observation of the ligand superhyperfine interaction at liquid nitrogen temperatures. Various possible models corresponding to the different spatial configurations of the molybdenyl complex in the lattice are considered to explain the experimentally observed features. The spectra are analysed using the usual spin-hamiltonian corresponding to tetragonal symmetry. The spin-hamiltonian parameters obtained are: g_∥ = 1.964, g_? = 1.945, A_∥ = 75.53 × 10^?4 cm^?1, A_⊥ = 38.42 × 10^?4 cm^?1.     

Synthesis, spectroscopic characterization, and 3D molecular modeling of lead(II) complexes of unsymmetrical tetradentate Schiff-base ligands

Solid complexes of Pb(II) with unsymmetrical Schiff-base ligands (H₂L) derived from 2-aminobenzophenone, thiosemicarbazide, semicarbazide, salicylaldehyde, 2-hydroxynaphthaldehyde, and o-hydroxyacetophenone have been synthesized and characterized by elemental analysis, conductance measurements, molecular weight measurement, and UV–Vis, FTIR, ¹H NMR, and ¹³C NMR spectroscopy. The spectral studies suggest the ligands behave as dibasic tetradentate ligands with ONNO/ONNS donor atom sequences toward the central metal ion. From the microanalytical data, the stoichiometry of the complexes was found to be 1:1 (metal:ligand). The physicochemical data suggest a tetracoordinated environment around the metal ion. Three-dimensional molecular modeling and analysis of bond lengths and bond angles have also been conducted for a representative compound, [PbL¹], to substantiate the proposed structures.     

Oxocation complexes,Part X. Oxomolybdenum(V) and dioxomolybdenum(VI) complexes with tri- and tetra-dentate Schiff bases

Summary Many new oxomolybdenum(V) and dioxomolybdenum(VI) complexes have been synthesized with tri- and tetradentate Schiff bases derived by the condensation of salicylaldehyde, thiosalicylaldehyde,o-hydroxyacetophenone, 3-carboxysalicyclaldehyde or acetylacetone with aminoalcohols, polymethylenediamines ando-phenylenediamines. Mononuclear oxothiolato Schiff base complexes of molybdenum(V) have been prepared for the first time. Quadridentate Schiff bases derived from salicylaldehyde and substituted salicylaldehydes ando-phenylenediamine have also been successfully employed to isolate dioxomolybdenum(VI) complexes in the solid state, in which two oxygen atoms of the MoO₂ group arecis- to each other, similar to the situation observed for other dioxomolybdenum(VI) complexes of salicylaldehyde-polymethylenediamine Schiff base ligands.Structures have been determined with the help of elemental analyses, magnetic susceptibilities, molar conductances, i.r., electronic and¹H n.m.r. spectral data.For Part IX, K. Dey, R. K. Maiti and J. K. Bhar,Indian J. Chem., in press.     

Synthesis, structural characterization, and antifungal activity of Schiff bases and their transition metal mixed-ligand complexes

Mixed-ligand complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) have been prepared with biologically active Schiff bases, viz. potassium salt of o-hydroxyacetophenoneglycine [KHL] and bis(benzylidene)ethylenediamine [A¹] or thiophene-o-carboxaldene-p-toluidine [A²]. The synthesized mixed-ligand complexes have been characterized on the basis of elemental analysis, thermogravimetric analysis, magnetic measurements, and electronic and infrared spectra. The mixed-ligand complexes show higher antifungal activity as compared to the free ligands, metal salts, and the control (dimethylsulfoxide) but moderate activity as compared to the standard fungicides (bavistin and emcarb). This text was submitted by the authors in English.     

Synthesis,characterization, and spectroscopic studies of tetradentate Schiff base chromium(III) complexes

Eight chromium(III) complexes of tetradentate Schiff bases have been prepared in situ by condensing of a substituted salicylaldehyde compound with ethylenediamine. These were characterized by elemental analysis, m.p., IR, molar conductivity, magnetic moment measurements, and electronic spectra. The free ligands were also characterized by ¹H and ¹³C NMR spectra. The ¹³C NMR spectra are discussed in terms of possible substituent effects. The IR and electronic spectra of the free ligand and the complexes are compared and discussed. The electrospray ionization (ESI) mass spectra of four free ligands and their complexes were measured. The deconvolution of the visible spectra of the complexes, C_2v symmetry, in DMSO yields three peaks at ca. 15 600–17 600, 18 400–20 400 and 20 000–23 100, and are assigned to the three d–d transitions, ⁴B_1g → ⁴E_g(⁴T_2g); ⁴B_1g → ⁴B_2g(⁴T_2g); ⁴B_1g → ⁴E_g(⁴T_1g), respectively. The complexes showed magnetic moment in the range of 3.5–4.2 BM which corresponds to three unpaired electrons.     

Synthesis,spectral characterization,electrochemistry and catalytic activities of Cu(II) complexes of bifunctional tridentate Schiff bases containing O?N?O donors

Paramagnetic copper(II) complexes of the type [Cu(PPh₃)(L)] (where L = bifunctional tridentate Schiff bases) were synthesized from the reaction of anthranillic acid with salicylaldehyde (H₂L¹), 2‐hydroxy‐1‐naphthaldehyde (H₂L²), o‐hydroxyacetophenone (H₂L³) and o‐vanillin (H₂L⁴) with monomeric metal precursor [CuCl₂(PPh₃)₂]. The obtained complexes were characterized by elemental analysis, magnetic susceptility and spectroscopic methods (FT‐IR, UV–vis and EPR and cyclic voltammetry). EPR and redox potential studies have been carried out to elucidate the electronic structure, nature of metal–ligand bonding and electrochemical features. EPR spectra exhibit a four line pattern with nitrogen super‐hyperfine couplings originating from imine nitrogen atom. These planar complexes possess a significant amount of tetrahedral distortion leading to a pseudo‐square planar geometry, as is evidenced from EPR properties. Cyclic voltammograms of all the complexes display quasireversible oxidations, Cu(III)? Cu(II), in the range 0.31–0.45 V and reduction peaks, Cu(II)? Cu(I),in the range ?0.29 to ?0.36 V, involving a large geometrical change and irreversible. The observed redox potentials vary with respect to the size of the chelate ring of the Schiff base ligands. Further, the catalytic activity of all the complexes has been found to be high towards the oxidation of alcohols into aldehydes and ketones in the presence of N‐methylmorpholine‐N‐oxide as co‐oxidant. The formation of high valent Cu^IV?O oxo species as a catalytic intermediate is proposed for the catalytic process. Copyright © 2008 John Wiley & Sons, Ltd.     

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate—Part II: VO(II)—a case of substitutional site

Single crystal electron paramagnetic resonance (EPR) studies were carried at room temperature for VO(II) doped zinc potassium phosphate hexahydrate. The results indicate that the paramagnetic impurity has entered the lattice only substitutionally, as confirmed by the single crystal rotations. The spin Hamiltonian parameters calculated from the spectra are g_//=1.9356, g=1.9764, A_//=200.9 G and A=76.5 G. The optical absorption spectrum exhibits three bands (800, 670 and 340 nm) suggesting the C_4v symmetry and the optical parameters evaluated are Dq=1492, Ds=−3854 and Dt=186 cm⁻¹.     

EPR spectra and structures of dinuclear copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with acyldihydrazones of benzenedicarboxylic acids

Spacer-armed dinuclear copper(II) complexes with condensation products of isophthalic and terephthalic acid dihydrazides with salicylaldehyde and 2-hydroxyacetophenone were synthesized and studied by EPR and X-ray diffraction. The compositions and structures of most of the complexes were determined by elemental analysis, thermogravimetric analysis, and IR spectroscopy. The structure of the copper(II) complex with acyldihydrazone of salicylaldehyde and 1,3-benzenedicarboxylic acid (H₄L) with the composition [Cu₂L¹·2morph·MeOH] (morph is morpholine) was established by X-ray diffraction. The Cu^II atoms are spaced by 10.29 Å and are structurally nonequivalent. One copper cation has a square-planar coordination formed by donor atoms (2 N + O) of the doubly deprotonated acylhydrazine fragment and the N atom of the morpholine molecule. The second copper atom is additionally coordinated by a methanol molecule through the oxygen atom, so that this copper atom is in a tetragonal-pyramidal coordination with the oxygen atom in the axial position. The EPR spectra of liquid solutions of the complexes based on 1,4-benzenedicarboxylic acid acyldihydrazones and 1,3-benzenedicarboxylic acid bis(salicylidene)hydrazone at room temperature show a four-line hyperfine structure with the constant a _Cu = 54.4–67.0·10⁻⁴ cm⁻¹ (g = 2.105–2.147), which is indicative of the independent behavior of the paramagnetic centers. The EPR spectrum of a solution of the complex based on isophthalic acid and 2-hydroxyacetophenone shows the seven-line hyperfine structure corresponding to two equivalent copper nuclei (g = 2.11, a _Cu = 36.5·10⁻⁴ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1898–1905, October, 2007.     

Synthesis,characterization, EPR,electrochemical, and in situ spectroelectrochemical studies of salen-type oxovanadium(IV) and copper(II) complexes derived from 3,4-diaminobenzophenone

A new half unit and some new symmetrical or asymmetrical VO(IV) and Cu(II) complexes of tetradentate ONNO Schiff base ligands were synthesized. The probable structures of the complexes have been proposed on the basis of elemental analyses and spectral (IR, UV–Vis, electron paramagnetic resonance, ESI-MS) data. VO(IV) and Cu(II) complexes exhibit square pyramidal and square-planar geometries, respectively. The complexes are non-electrolytes in dimethylformamide (DMF) and dimethylsulfoxide. Electrochemical behaviors of the complexes were studied using cyclic voltammetry and square wave voltammetry. Half-wave potentials (E _1/2) are significantly influenced by the central metal and slightly influenced by the nature of substituents on salen. While VO(IV) complexes give VO^IV/VO^V redox couples and a ligand-based reduction process, Cu(II) complexes give only a ligand-based reduction. In situ spectroelectrochemical studies were employed to determine the spectra of electrogenerated species of the complexes and to assign the redox processes. The g-values were calculated for all these complexes in polycrystalline state at 298?K and in frozen DMF (113?K). The evaluated metal–ligand bonding parameters showed strong in-plane σ-bonding for some Cu(II) complexes.     

Monooxovanadium(V) 2-phenylphenoxides: synthesis,characterization, and antimicrobial potential

Monooxovanadium(V) complexes of the composition VOCl_{3? n} (L) _n (where L = 2-phenylphenoxide ion; n = 1–3) (1–3) have been synthesized in quantitative yields by the reaction of VOCl₃ with 2-phenylphenol in toluene. The characterization of the complexes has been accomplished by elemental analysis, molar conductance measurements, IR, ¹H-NMR, electronic, mass spectral, and thermal studies. The ligands as well as the complexes have been screened for their in vitro antimicrobial activity against the pathogenic bacteria Escherichia coli and Staphylococcus aureus and fungi Candida albicans, Aspergillus niger, and Fusarium oxysporum by a twofold serial dilution. An increase in the biocidal activity was observed for the vanadium complexes. The minimum inhibitory concentration (MIC) values were 6.25–25 µg mL^?1 for complexes, relative to that of the free ligand of 25–50 µg mL^?1.