Synthesis,X-ray crystal structure and DFT studies of cobalt(II) and vanadium(V) complexes with N,N,O-tridentate aroyl-hydrazone based ligand

A new aroyl-hydrazone, 2-pyridine carboxaldehyde-derived hydrazone ligand and its cobalt(II) (1) and vanadium(V) (2) complexes were prepared. The structures of these compounds were investigated using elemental analysis, spectral (IR, UV), and X-ray diffraction measurements. The electrochemical properties of the complexes were studied by cyclic voltammetry. The hydrazone ligand acted as tridentate and coordinated to vanadium and cobalt via N-imine, N-pyridine, and O-benzohydrazide atoms. The Co(II) complex crystallizes in the monoclinic system, space group P2₁/c, and has a binuclear structure. Chloride ions behave as the linking bridge and a tridentate hydrazine ligand HL and water as the terminal capping ligands. The central Co(II) ion has distorted octahedral geometry. The vanadium(V) complex crystallizes in the monoclinic crystal system, space group P2₁/n, and can be described as having highly distorted trigonal-bipyramidal coordination. The geometries and electronic properties of the complexes were also obtained using DFT and TD-DFT calculations.     

Synthesis and characterization of 3-amino-5-methylisoxazole Schiff bases and their complexes with copper(II), nickel(II) and cobalt(II)

Schiff bases obtained by condensing 3-amino-5-methylisoxazole with salicylaldehyde, 2,3-dihydroxybenzaldehyde, 2,4-dihydroxy-benzaldehyde, 2,5-dihydroxybenzaldehyde or o-hydroxynaphthaldehyde were obtained and characterized by C, H, N analysis, mass, NMR and IR spectra. Copper, nickel and cobalt complexes of the Schiff bases were prepared and characterized using elemental analysis, conductivity measurements, magnetic moments, IR, UV-VIS and ESR spectra, X-ray diffraction, TGA, DTA and DSC thermal analysis. All the complexes are non-electrolytes. ESR spectra show isotropic as well as axial symmetry for the copper complexes. Thermal studies support the formulation of these complexes and showed that they decompose in two or three steps depending on the metal used. Activation energy E _a and enthalpies ΔH associated with the decomposition process were calculated and correlated with the complexed metal used.     

Copper(II) and molybdenum(VI) complexes with 5-bromosalicylaldehyde S-allylisothiosemicarbazone: Syntheses,characterizations and crystal structures

A new tridentate Schiff base, 5-bromosalicylaldehyde S-allylisothiosemicarbazone hydrobromide (H₂L), and several new mononuclear complexes of copper(II) and molybdenum(VI) of this ligand with general formulas ([Cu(L)Im] (1)), ([Cu(L)NH₃]·4H₂O (2)), and ([MoO₂(L)1-MeIm] (3), Imidazole: Im, 1-methylimidazole: 1-MeIm) were prepared and characterized by elemental analyses, IR, proton magnetic resonance Spectroscopy, and ultraviolet–visible techniques. The physico-chemical results suggested that the H₂L coordinates in the dianionic tridentate form. Crystal structures of the Cu(II) complexes reveal a square planar configuration surrounded by the dianionic tridentate isothiosemicarbazone (ONN) and Im and NH₃ for 1 and 2, respectively. The L^2-, two oxo, and 1-methylimidazole are coordinated to molybdenum(VI) in a distorted octahedral geometry in 3. Formation of pure metal oxide residues was confirmed by thermal degradation of the complexes.     

Coordination behavior of symmetrical hexadentate O2N2S2-donor Schiff bases toward zinc (II): synthesis,characterization, and crystal structure

Two series of zinc(II) complexes of two Schiff bases (H₂L¹ and H₂L²) formulated as [Zn(HL¹/HL²)]ClO₄ (1a and 1b) and [Zn(L¹/L²)] (2a and 2b), where H₂L¹ = 1,8-bis(salicylideneamino)-3,6-dithiaoctane and H₂L² = 1,9-bis(salicylideneamino)-3,7-dithianonane, have been prepared and isolated in pure form by changing the chemical environment. Elemental, spectral, and other physicochemical results characterize the complexes. A single crystal X-ray diffraction study confirms the structure of [Zn(HL¹)]ClO₄ (1a). In 1a, zinc(II) has a distorted octahedral environment with a ZnO₂N₂S₂ chromophore.     

Octahedral Co(II) and Ni(II) complexes of Schiff bases,semicarbazone and thiosemicarbazone,synthesis, biological,spectral, and thermal studies

A new series of cobalt(II) and nickel(II) complexes, [M(ligand)(H₂O)₂(Y)] (M = Co(II) or Ni(II); Y = Cl^?, Br^? or NO₃ ^?), containing the Schiff-base semicarbazone and thiosemicarbazone, HL¹ and HL², formed from 4-hydroxycoumarin-3-carbaldehyde have been synthesized. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, infrared, electronic spectra, magnetic susceptibility, and conductivity measurements. An octahedral geometry has been suggested for the complexes. The metal complexes were screened for their antifungal and antibacterial activities on different species of pathogenic fungi and bacteria and their biopotency has been discussed.     

Synthesis,spectral, and catalytic studies of ruthenium(II) unsymmetrical Schiff-base complexes

Unsymmetrically-substituted ruthenium(II) Schiff-base complexes, [Ru(CO)(B)(L ^x )] [B = PPh₃, AsPh₃ or Py; L ^x = dianion of tetradentate unsymmetrical Schiff-base ligand; x = 4–7, L⁴ = salen-o-hyac, L⁵ = valen-o-hyac, L⁶ = salphen-o-hyac, L⁷ = valen-2-hacn], were prepared and characterized by analytical, IR, electronic, and ¹H NMR spectral studies. The new complexes were tested for their catalytic activity towards the oxidation of benzylalcohol to benzaldehyde.     

Synthesis,spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

New metal based triazoles (1–12) have been synthesized by the interaction of novel Schiff base ligands (L¹–L³) with the Co(II), Ni(II), Cu(II) and Zn(II) metal ions. The Schiff base ligands and their all metal(II) complexes have been thoroughly characterized using various physical, analytical and spectroscopic techniques. In vitro bacterial and fungal inhibition studies were carried out to examine the antibacterial and antifungal profile of the Schiff bases in comparison to their metal(II) complexes against two Gram‐positive, four Gram‐negative and six fungal strains. The bioactivity data showed the metal(II) complexes to have more potent antibacterial and antifungal activity than their uncomplexed parent Schiff bases against one or more bacterial and fungal species. Copyright © 2012 John Wiley & Sons, Ltd.     

Ruthenium(II/IV) complexes with potentially tridentate Schiff base chelates containing the uracil moiety

Herein we report the synthesis and characterization of trans-[Ru^IICl₂(PPh₃)₃] with potentially tridentate Schiff bases derived from 5,6-diamino-1,3-dimethyl uracil (H₂ddd) and two 2-substituted aromatic aldehydes. In the diamagnetic ruthenium(II) complexes, trans-[RuCl(PPh₃)₂(Htdp)] (1) {H₂tdp = 5-((thiophen-3-yl)methyleneamino)-6-amino-1,3-dimethyluracil} and trans-[RuCl(PPh₃)₂(Hsdp)] (2) {H₂sdp = 5-(2-(methylthio)benzylideneamino)-6-amino-1,3-dimethyluracil}, the Schiff base ligands (i.e. Htdp and Hsdp) act as mono-anionic tridentate chelators. Upon reacting 5-(2-hydroxybenzylideneamino)-6-amino-1,3-dimethyluracil (H₃hdp) with the metal precursor, the paramagnetic complex, trans-[Ru^IVCl₂(ddd)(PPh₃)₂] (3), was isolated, in which the bidentate dianionic ddd co-ligand was formed by hydrolysis. The metal complexes were fully characterized via multinuclear NMR-, IR-, and UV–Vis spectroscopy, single crystal XRD analysis and conductivity measurements. The redox properties were probed via cyclic voltammetry with all complexes exhibiting comparable electrochemical behavior with half-wave potentials (E_½) at 0.70 V (for 1), 0.725 V (for 2), and 0.68 V (for 3) versus Ag|AgCl, respectively. The presence of the paramagnetic metal center for 3 was confirmed by ESR spectroscopy.     

Synthesis and reactivity of new functionalized Pd(II) cyclometallated complexes with boronic esters

Treatment of the functionalized Schiff base ligands with boronic esters 1a, 1b, 1c and 1d with palladium (II) acetate in toluene gave the polynuclear cyclometallated complexes 2a, 2b, 2c and 2d, respectively, as air-stable solids, with the ligand as a terdentate [C,N,O] moiety after deprotonation of the -OH group. Reaction of 1j with palladium (II) acetate in toluene gave the dinuclear cyclometallated complex 5j. Reaction of the cyclometallated complexes with triphenylphosphine gave the mononuclear species 3a, 3b, 3c, 3d and 6j with cleavage of the polynuclear structure. Treatment of 2c with the diphosphine Ph₂PC₅H₄FeC₅H₄PPh₂ (dppf) in 1:2 molar ratio gave the dinuclear cyclometallated complex 4c as an air-stable solid.Deprotection of the boronic ester can be easily achieved; thus, by stirring the cyclometallated complex 3a in a mixture of acetone/water, 3e is obtained in good yield. Reaction of the tetrameric complex 2a with cis-1,2-cyclopentanediol in chloroform gave complex 2c after a transesterification reaction. Under similar conditions complexes 3a and 3d behaved similarly: with cis-1,2-cyclopentanediol, pinacol or diethanolamine complexes 3c, 3b, 3g and 3f, were obtained. The pinacol derivatives 3b and 3g experiment the Petasis reaction with glyoxylic acid and morpholine in dichloromethane to give complexes 3h, and 3i, respectively.     

Syntheses,EPR spectral studies and crystal structures of manganese(II) complexes of neutral N,N donor bidentate Schiff bases and azide/thiocyanate as coligand

Four manganese(II) complexes Mn₂(paa)₂(N₃)₄ (1), [Mn(paa)₂(NCS)₂]·³/₂H₂O (2), Mn(papea)₂(NCS)₂ (3), [Mn(dpka)₂(NCS)₂]·¹/₂H₂O (4) of three neutral N,N donor bidentate Schiff bases were synthesized and physico-chemically characterized by means of partial elemental analyses, electronic, infrared and EPR spectral studies. Compounds 3 and 4 were obtained as single crystals suitable for X-ray diffraction. Compound 4 recrystallized as Mn(dpka)₂(NCS)₂. Both the compounds crystallized in the monoclinic space groups P2₁ for 3 and C2/c for 4. Manganese(II) is found to be in a distorted octahedral geometry in both the monomeric complexes with thiocyanate anion as a terminal ligand coordinating through the nitrogen atom. EPR spectra in DMF solutions at 77 K show hyperfine sextets with low intensity forbidden lines lying between each of the two main hyperfine lines and the zero field splitting parameters (D and E) were calculated.     

Copper(II) azide complexes with mono-anionic tridentate Schiff-base ligands: monomer versus dimer

Three new copper(II) complexes [CuL¹N₃]₂ (1), [CuL²N₃] (2) and [CuL³N₃] (3) with three very similar tridentate Schiff base ligands [HL¹?=?6-diethylamino-3-methyl-1-phenyl-4-azahex-3-en-1-one, HL²?=?6-amino-3-methyl-1-phenyl-4-azahex-3-en-1-one and HL³?=?6-amino-3-methyl-1-phenyl-4-azasept-3-en-1-one] have been synthesized and structurally characterized by X-ray crystallography. In complex 1 half of the molecules are basal-apical, end-on azido bridged dimers and the remaining half are square-planar monomers whereas all the molecules in complexes 2 and 3 are monomers with square-planar geometry around Cu(II). A competition between the coordinate bond and H-bond seems to be responsible for the difference in structure of the complexes.     

Two distinct manganese(II) complexes with hexadentate 1,3-propanediaminetetraacetate ligand: The ability of metal(II) complexes with 1,3-pdta ligand to form solid solutions

The ability of Mn(II) ion to form two distinctly different complexes with 1,3-propanediaminetetraacetate (1,3-pdta) ligand has been demonstrated by performing X-ray analyses of their crystalline Mg(II) salts. The two types of Mn(II) complexes have been obtained by different synthetic routes and their crystals constitute, respectively, the solid solution of the composition [Mg(H₂O)₆][Mg_0.5Mn_0.5(1,3-pdta)] · 2H₂O (1) and the ordered crystals of the composition [Mg(H₂O)₆][Mn(1,3-pdta)(H₂O)] · 2H₂O (2). In both, six- 1 and seven-coordinated 2 Mn(II) complexes the 1,3-pdta ligand acts as a hexadentate. As 2 makes the second example of the seven-coordinated 1,3-pdta complex with divalent transition metal ion, the other being the [Mg(H₂O)₆][Cd(1,3-pdta)(H₂O)] · 2H₂O (3) complex, the paper reports the results of X-ray investigations of both of these complexes at 130 K.     

Nickel(II), copper(II), and cobalt(II) complexes derived from a new unsymmetrical ONS donor Schiff base ligand: synthesis,characterization, crystal structure,and catalytic activities

Ni(II), Cu(II), and Co(II) complexes, ML₂, with a new thioether containing ONS donors were synthesized, where L = deprotonated Schiff base. The analytical, spectral (FTIR, ¹H NMR, and UV-vis), conductivity, and magnetic studies show that the metal complexes possess octahedral geometry and are non-electrolytes. The coordination mode of ligand, 1, and nickel(II) complex, NiL₂, 2, was determined by single-crystal X-ray diffraction studies. Here, the nickel is coordinated to two oxygens, two nitrogens, and two sulfurs of two tridentate ligands with slightly distorted octahedral environment around nickel. The copper complex shows very good catalytic activities towards oxidation of organic thioethers to the corresponding sulfoxide predominantly using H₂O₂ as the oxidant.     

Studies on mononuclear chelates derived from substituted Schiff-base ligands (part 2): synthesis and characterization of a new 5-bromosalicyliden- p -aminoacetophenoneoxime and its complexes with Co(II), Ni(II), Cu(II) and Zn(II)

In this study, 5-bromosalicyliden-p-aminoacetophenoneoxime (LH) was synthesized starting from p-aminoacetophenoneoxime and 5-bromosalicylaldehyde. Complexes of this ligand with Co^+?2, Ni^+?2, Cu^+?2 and Zn^+?2 were prepared with a metal?:?ligand ratio of 1?:?2. Their structures have been elucidated on the basis of elemental analyses, IR, ¹H and ¹³C NMR spectra, electronic spectra, magnetic susceptibility measurements, molar conductivity and thermogravimetric analyses (TGA).     

Synthesis,spectral, electrochemical and biological studies of Co(II), Ni(II) and Cu(II) complexes with Schiff bases of 8-formyl-7-hydroxy-4-methyl coumarin

A series of Co(II), Ni(II) and Cu(II) complexes have been synthesized with Schiff bases derived from 8-formyl-7-hydroxy-4-methyl coumarin and o-chloroaniline/o-toluidine. The structures of the complexes have been proposed from analytical, spectral (IR, UV-Vis, ESR and FAB-mass), magnetic, thermal and fluorescence studies. The complexes are soluble in DMF and DMSO and molar conductance values indicate the complexes are non-electrolytes. Elemental analyses indicate ML₂ · 2H₂O [M = Co(II), Ni(II) and Cu(II)] stoichiometry. Spectroscopic studies (IR, UV-Vis, ESR and fluorescence) indicate octahedral geometry, in which ligand coordinates through azomethine nitrogen and phenolic oxygen via deprotonation. Thermal studies suggest coordination of water to the metal ion. Redox behavior of the complexes was investigated by cyclic voltammetry. The Schiff bases and their complexes were screened for their antibacterial (E. coli, S. aureus, P. aeruginosa and S. typhi) and antifungal activities (A. niger, A. flavus and Cladosporium) by MIC method.     

Equilibrium and spectral studies of putrescine complexes with copper(II)

Summary It has been found that in the putrescine-copper system several types of complex compounds (MHL,ML,ML ₂,ML ₂OH) are formed. In thepH range of 7–9, despite a multiple excess of ligand, a precipitation occurs. When adenosine is introduced to the system, the ability to observe the complexation reaction in solution is largely increased, because the additional ligand prevents precipitation. On the basis of computer analysis of potentiometric titration data the stability constants of the compounds have been determined. The coordination mode of the complexes is discussed.

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Gleichgewichte und spektroskopische Untersuchungen an Putrescin-Komplexen mit Kupfer(II)

Zusammenfassung Es wurde festgestellt, daß sich im Putrescin-Kupfer System einige Typen von Komplexen bilden (MHL,ML,ML ₂ andML ₂OH). ImpH-Bereich von 7–9 tritt trotz eines mehrfachen Ligandenüberschusses ein Niederschlag auf. Bei Einführung von Adenosin in das System wird die Beobachtbarkeit der Komplexreaktion verbessert, da der zusätzliche Ligand die Niederschlagsbildung verhindert. Mittels Computeranalyse der potentiometrischen Titrationsdaten wurden die Stabilitätskonstanten der Verbindungen ermittelt. Die Art der Komplexierung wird ebenfalls diskutiert.

     

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.     

Copper(II) complexes with neutral Schiff bases: Syntheses, crystal structures and DNA interactions

The synthesis and X-ray structural characterisation of a new Cu(II) complex, [Cu(L¹)Cl](ClO₄)·CH₃OH (1) [L¹ = N,N′-bis((pyridine-2-yl)phenylidene)-1,3-diaminopropan-2-ol], has been described in this work. The structural study reveals that the Cu(II) centre in 1 has a square pyramidal geometry with a trigonality index τ = 0.43, being coordinated by the organic ligand and a chloro group. The interaction of complex 1 and another complex previously reported by our group, [Cu(L²)](ClO₄)₂ (2) [L² = N-(1-pyridin-2-yl-phenylidene)-N′-[2-({2-[(1-pyridin-2-ylphenylidene)amino]ethyl}amino)ethyl]ethane-1,2diamine], with calf thymus DNA (CT-DNA) has been investigated using absorption and emission spectral studies. The binding constant (K_b) and the linear Stern-Volmer quenching constant (K_sv) have been determined.     

Schiff bases of 1′-hydroxy-2′-acetonaphthone containing chalcogen functionalities and their complexes with and (p-cymene)Ru(II), Pd(II), Pt(II) and Hg(II): Synthesis, structures and applications in C-C coupling reactions

Schiff bases of 1′-hydroxy-2′-acetonaphthone (HAN) containing chalcogen functionalities, 1-HO-C₁₀H₆-2-CH₃)CN-(CH₂)_nEC₆H₄-4-R (R = H or OMe; n = 2 or 3; E = S (L¹-L²), Se (L³-L⁴) or Te (L⁵-L⁶)) have been synthesized in yield 90-95%. They show characteristic ¹H, ¹³C{¹H} ⁷⁷Se{¹H} and ¹²⁵Te{¹H} (in case of selenated and tellurated species, respectively) NMR spectra. Their complexation with Pd(II), Pt(II), Hg(II) and (p-cymene)Ru(II) has been explored. The single-crystal structures of ligands L¹, L³ and L⁶ and complexes of Pd(II) with L¹, L², L³ and L⁵ have been determined. The geometry of Pd is close to square planar in all the complexes and the ligands coordinate in a uni-negative tridentate mode. The Pd-N bond lengths are in the range 1.996(7)-2.019(5) ?. The Pd-Se bond distance is 2.3600(5) ? whereas Pd-Te is 2.5025(7) ?. The Pd(II) complexes of L¹-L⁵ have been found promising as homogeneous catalyst for Heck and Suzuki reactions. The yields obtained were up to 85%.     

Copper(II) complexes with singly condensed tridentate Schiff-base ligands incorporating 1-benzoylacetone

Two copper(II) complexes [CuL¹Cl]_n (1) and [CuL²Cl] (2) with singly condensed tridentate Schiff-base ligands [HL¹ = 6-amino-3-methyl-1-phenyl-4-azahex-3-en-1-one and HL² = 6-diethylamino-3-methyl-1-phenyl-4-azahex-3-en-1-one] have been synthesized and structurally characterized by X-ray crystallography. Complex 1 is a single-chloro-bridged one-dimensional polymer, whereas 2 is a monomeric square-planar complex. The H-bonding interactions of the amine hydrogen and the non-bonding interactions of phenyl groups in the Schiff base play important roles for the structural variations.