New metal(II) complexes with ceftazidime Schiff base

Complexes of Co(II), Ni(II) and Cu(II) with the Schiff base (LH) derived from ceftazidime and salicylaldehyde were synthesized. The proposed structures of the new metal complexes based on the results of elemental analyses, molar conductivity, IR, DRUV and ¹H NMR spectra, effective magnetic moment and thermal analysis were discussed. The surface morphology of Schiff base and metal complexes was studied by SEM. The composition of the metal complexes was ML₂, where L is the deprotonated Schiff base ligand and M = Co(II), Ni(II) and Cu(II). IR spectral data indicated the Schiff base ligand being bidentately coordinated to the metallic ions with N and O atoms from azomethine and phenolic groups. All the complexes have square-planar geometry and are nonelectrolytes. The thermal analysis recorded that TG, DTG, DTA and DSC experiments confirmed the assigned composition and gave information about the thermal stability of complexes in dynamic air atmosphere. Theoretical investigation of the molecular structure of Schiff base ligand and its complexes was studied using programs dedicated to chemical modeling and quantomolecular calculation of chemical properties. The newly synthesized complexes were tested for in vitro antibacterial activity against selected Gram-negative and Gram-positive bacterial strains, and they exhibited an antibacterial activity superior to that of the Schiff base ligand.     

Solvent directed templated synthesis of mono- and di(Schiff base) complexes of Ni(II)

The mono- and binuclear complexes Ni(Salen) (I) and Ni₂(Salen)₂ (II) (H₂Salen = N,N′-bis(salicylidene)ethane-1,2-diamine), have been synthesized and structurally characterized by single-crystal X-ray diffraction studies. The X-ray structural analyses show that the metal center of complex I is mononuclear and tetracoordinate with a distorted tetrahedron, whereas the metal-centered complex II is binuclear and pentacoordinate with rectangular pyramid geometries, respectively. The electrochemical studies evidenced for the mononuclear Ni(II) complex shows one quasireversible reduction potential at −0.80 V (E _pc ) and the binuclear Ni(II) complex shows a reduction potential at −0.90 V (E _pc ) in the cathodic region. The article is published in the original.     

The role of chiral dopants in organic/inorganic hybrid materials containing chiral Schiff base Ni(II), Cu(II) and Zn(II) complexes

Chiral Schiff base complexes containing azo-groups, bis(N-R-1-cyclohexylethyl-4-phenyldiazenylsalicydenaminato) nickel(II), copper(II) and zinc(II) complexes, and without azo-groups, bis(N-R-1-cyclohexylethyl-3,5-dichlorosalicydenaminato) nickel(II), copper(II) and zinc(II) complexes, affording a distorted square planar trans-[MN₂O₂] coordination geometry were prepared. Organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) spincoat films of the complexes (both the azobenzene (AZ) containing type and the latter complexes of the AZ separated type) were assembled for a comparison of polarized UV light induced molecular arrangement caused by the Weigert effect. Investigation of the parameters for the optical anisotropy of the metal complexes as well as AZ suggested that the degree of increasing optical anisotropy of the containing type was higher than that of the separated type based on π-π^∗ (of which a characteristic band appeared around 380 nm) and n-π^∗ bands of polarized absorption electronic spectra. In the AZ containing type, the rigid nickel(II) or zinc(II) complexes easily increase the optical anisotropy compared to the flexible copper(II) complexes. In the AZ separated type, interestingly, enhancement of some CD bands suggests the role of chiral dopants of some complexes without azo-groups for AZ.     

Polarized spectroscopy and hybrid materials of chiral Schiff base Ni(II), Cu(II), Zn(II) complexes with included or separated azo-groups

Chiral Schiff base complexes containing azo-groups, bis(N-R-1-naphtylethyl-4-phenyldiazenylsalicydenaminato) nickel(II), copper(II), and zinc(II) complexes affording a distorted square planar trans-[MN₂O₂] coordination geometry were prepared newly. Organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) cast films of them (a containing type) or the analogous chiral Schiff base complexes, bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato) nickel(II), copper(II), and zinc(II), and azobenzene (AZ) (a separated type) were assembled for comparison of polarized UV light induced molecular arrangement caused by Weigert effect. Investigation of parameters for optical anisotropy of metal complexes as well as AZ suggested that the degree of increasing optical anisotropy of the containing type is higher than that of the separated type based on π-π^∗ (of which characteristic band appeared around 380 nm), n-π^∗, and d-d bands of polarized absorption electronic spectra. Rigid nickel(II) or zinc(II) complexes are easy to increase optical anisotropy than flexible copper(II) complexes for both types.     

Redox and antimicrobial studies of transition metal(II) tetradentate Schiff base complexes

Neutral tetradentate chelate complexes of Cu^II, Ni^II, Co^II, Mn^II, Zn^II and VO^II have been prepared in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. Microanalytical data, magnetic susceptibility, i.r., u.v.–vis., ¹H-n.m.r. and e.s.r. spectral techniques were used to confirm the structures of the chelates. Electronic absorption and i.r. spectra of the complexes suggest a square-planar geometry around the central metal ion, except for VO^II and Mn^II complexes which have square-pyramidal and octahedral geometry respectively. The cyclic voltammetric data for the Cu^II complexes in MeCN show two waves for copper(II) copper(III) and copper(II) copper(I) couples, whereas the VO^II complexes in MeCN show two waves for vanadium(IV) vanadium(V) and vanadium(IV) vanadium(III) couples. The e.s.r. spectra of the Cu^II, VO^II and Mn^II complexes were recorded in DMSO solution and their salient features reported. The in vitro antimicrobial activity of the investigated compounds was tested against the microorganisms such as Salmonella typhi, Staphylococcus aureus, Klebsiella pneumoniae, Bacillus subtilis, Shigella flexneri, Pseudomonas aeruginosa, Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates have higher antimicrobial activity than the free ligands.     

The synthesis,characterization and antibacterial activities of dinuclear Ni(II), Cu(II) and Fe(III) Schiff base complexes

Schiff base; N,N′-bis-(2-hydroxy-1-naphthaldimine)-1,3-diaminopropanol (napdapOH) reacts with metal chlorides to form dinuclear complexes of the type [M₂L₂] · nCl₂ where M = Ni, Cu, Fe and n = 0, 1. Schiff base complexes were characterized by using FT-IR, LC-MS, magnetic moments and conductance measurements. Coordination was found to be through the phenolic oxygen atoms and azomethine nitrogen atoms. The electronic properties of the compounds were investigated theoretically by performing semiempirical molecular orbital theory PM3 method in Hyperchem 7 (Release). The antibacterial activities of the compounds were investigated against Escherichia coli ATCC 11230, Bacillus subtilis RSKK 244, Bacillus megaterium RSKK 5117, Salmonella enteritidis ATCC 13076, Staphylococcus aureus ATCC 25923 by using microdilution method.     

New platinum(II) complexes with Schiff base ligands

Summary New neutral platinum complexes of Schiff bases or their hydrated derivatives were prepared and a new path to mixed ligand platinum(II) complexes is proposed. Reactions of [PtCl₄]^2– with multidentate Schiff bases give chelates which react further, resulting in cis-coordinated mixed N-donor ligand complexes. Structures are proposed on the basis of chemical analyses, electrical conductivities and i.r. studies.     

Enantioselective catalytic epoxidation of nonfunctionalized prochiral olefins by dissymmetric chiral Schiff base complexes of Mn(III) and Ru(III) metal ions II

A series of new dissymmetric chiral Schiff base complexes has been obtained by a systematic condensation of (1S,2S)(+)-diaminocyclohexane and 3-acetyl-4-hydroxy-6-methyl-2-pyrone with salicylaldehyde, 5-chloro-, 5-methoxy-and 5-nitrosalicylaldehyde and by subsequent metallation with manganese and ruthenium. The characterization of the complexes 1–8 was accomplished by physico chemical studies viz. microanalysis, IR-, UV/VIS-, and CD spectral studies, optical rotation, molar conductance measurements and cyclic voltammetry. Enantioselective epoxidation of non functionalised olefins, viz. cis-stilbene, trans-3-nonene and trans-4-octene with iodosyl benzene as oxidant was demonstrated in the presence of catalytic amounts of chiral Mn(III) and Ru(III) dissymmetric Schiff base complexes. Good optical yields of epoxides were obtained for the catalyst 4 with the substrates trans-3-nonene and cis-stilbene.     

Schiff base complexes of ruthenium(II) with tridentateN-methyl-S-methyldithiocarbazate ligands

Summary Schiff bases (HL) produced by the condensation ofN-methyl-S-methyldithiocarbazate with -diketones and aromatic aldehydes or ketones react with [RuHClCO(PPh₃)₃] to yield hexacoordinated complexes of the type [RuClCO(PPh₃)₂(L)]. These Schiff bases react with [RuCl₂{P(OR)₃}₄] in 11 molar ratio to yield [RuCl{P(OR)₃}₂(L)] in which L is a tridentate. The chlorine atom in the complex can be removed in coordinating solvents in the presence of anions such as [BPh₄]^– to give cationic complexes. Bis chelate complexes, [Ru{P(OR)₃}₂(L)₂] are prepared from 12 molar proportions of the reactants. These complexes were characterised by elemental analyses, i.r.,¹H n.m.r., u.v. and conductivity studies.NCL Communication No. 4224.     

Thermal analyses and spectral characterization of some synthesized metal(II) Schiff base complexes

Schiff base metal complexes derived from 2-thiophenecarboxylidine-4-anisidine, 3,4-dihydroxy-5-nitrobenzylidine-2-amino-5-methylthiazole and 3,4-dihydroxy-5-nitrobenzylidine-4-chloroaniline have been synthesized and characterized by elemental analysis, IR, UV?CVis, molar conductance and thermal analyses. The complexes are coloured and stable in air at room temperature. The complexes exhibit coordination number to be 4 and 6. The thermal behaviour of metal complexes shows that the hydrated complexes lose water molecules of hydration in the first and then is immediately followed by decomposition of ligand molecules in the subsequent steps.     

Co(II) and Ni(II) complexes with Schiff base ligands: Synthesis,characterization, and biological activity

The ligands, 1-acetylferrocenehydrazinecarboxamide (HL¹) and 1-acetylferrocenehydrazinecarbothioamide (HL²), and their Ni(II) and Co(II) complexes were synthesized. The properties of the synthesized compounds were determined by the elemental and spectroscopic analyses. Ni(II) and Co(II) acetates interact with the ligands at the molar ratios 1 : 1 and 1 : 2 to give coloured products. The complexes have octahedral geometry. The ligands are coordinated to Co(II) and Ni(II) centers via the azomethine nitrogen and thiolic sulfur /enolic oxygen atom. The ligands and their Co(II) and Ni(II) complexes were screened for antibacterial and antifungal activities. The Co(II) and Ni(II) complexes show enhanced inhibitory activity as compared to their parent ligands. The DNA cleavage activity of the Co(II) and Ni(II) complexes was determined by gel electrophoresis. It was shown that the complexes have better cleavage activity than the ligands. The antioxidant activity of the complexes was also evaluated and used to examine their scavenging ability on hydrogen peroxide.     

Homogeneous precipitation of layered Ni(II)-Cr(III) double hydroxides

An adequate account of the hydrolytic properties of Cr3+ and Ni2+ allows setting the conditions for homogeneous nucleation of layered Ni(II)-Cr(III) double hydroxides; water exchange and hydrolysis rate constants indicate that, at very high rates of base dosing, formation of heteronuclear Cr(III)-Ni(II) hydroxo species should prevail over precipitation of active Cr(OH)3. This is realized by the urea method under microwave-assisted hydrothermal conditions. This approach yields crystalline Ni1-xCrx(OH)2(CO3)x/2nH2O (x approximately 0.32-0.36) in less than 5 min at 453 K; higher degrees of crystallinity are obtained at higher temperatures and/or longer aging times. Formation of Ni(II)-Cr(III) LDHs upon microwave-assisted hydrothermal aging of freshly coprecipitated Ni(OH)2+Cr(OH)3 mixtures takes longer, due to a different operating mechanism. The implications of the advanced rationale for the design of synthesis procedures are stressed. It is proposed that homogeneous nucleation of Ni(II)-Cr(III) LDHs involves the edge-on condensation of planar heteronuclear Cr(III)-Ni(II) hydroxo trimers. Ordered aggregation of primary particles leads to the final platelet crystals, a process that involves the exchange of CO2-(3) ions dangling at the crystallites' edges by bridging OH-.     

New copper(II), manganese(III), nickel(II) and zinc(II) complexes with a chiral quadridentate Schiff base

A chiral Schiff base ligand (H₂L) was obtained by condensing 2-hydroxynaphthalene-1-carbaldehyde with substituted (1R,2R)-(–)-diaminocyclohexane. Chiral Schiff base complexes [CuL], [NiL], [ZnL] and [MnLOH] have been synthesized and characterized by elemental analyses, _M, i.r., u.v.–vis. and ¹H-n.m.r. and magnetic measurements.     

New complexes of Ni(II) and Cu(II) with tridentate ONO Schiff base ligand: synthesis,crystal structures,electrochemical and theoretical investigation

In this research, we prepared a new series of the Cu(II) (1) and Ni(II) (2) metal complexes of a tridentate Schiff base ligand, (E)-2-(5-bromo-2-hydroxybenzylideneamino) phenol (H₂L). These complexes were characterized by elemental analysis, FT-IR, UV–Vis, and ¹H-NMR spectroscopy. The crystal structures of (1) and (2) were determined by X-ray diffraction studies. The single crystal X-ray diffraction analyses revealed that copper(II) cation is five-coordinated and the coordination polyhedron is a slightly distorted square pyramid. Nickel(II), on the other hand, is four-coordinated, and has a regular, square planar geometry. Further discussed were the electrochemical reduction of these complexes. We also analyzed the nature of the metal–ligand bond in the complexes through NBO and EDA analysis. Besides, vibrational sample magnetometer (VSM) revealed complex (1) was ferromagnetic.     

Metal-directed assembly of chiral bis-Zn(II) Schiff base structures

Tetra-Schiff bases derived from (chiral) bis-salphen ligand scaffolds furnish, upon metalation with appropriate metal reagents, their multinuclear structures with associated Zn(OAc)(2) or Zn(OH)(2) fragments. The tendency of retaining these salts was investigated using four different (chiral) bis-salphen scaffolds. The presence of the additional Zn ions was supported by NMR studies, mass determinations and X-ray crystallography showing in two cases the possible mode of coordination within these multinuclear structures. In one case, dimerization of the Zn(3) complex leads to a unique hexanuclear Zn(6) complex being a mixture of diastereoisomeric complexes as revealed by NMR spectroscopy.     

Copper(II) and ruthenium(II)/(III) Schiff base complexes

Metal complexes of general formula [Cu(L)](ClO4)2, [Ru(L)(PPh3)2]Cl2 and [Ru(L)(PPh3)Cl]Cl2[L = 1,4-di- (o-benzylidiminophenoxy/benzylidiminophenylthio)butane] containing N2O2 or N2S2 donor atoms have been prepared and characterised by spectral, magnetic and cyclic voltammetric studies. The rhombic nature of the e.s.r. spectra of the RuIII complexes indicates an asymmetry in the electronic environment around the Ru atom. e.s.r. spectra of the CuII complexes show a typical four-line spectrum with approximate tetrahedral distortion. The observed low A values in the CuII complexes, of the order of 132–160 × 10–4cm–1, indicates a tetrahedrally distorted square planar structure.The influence of modified ligands is reflected in the metal-centered redox potentials. CuII complexes having the N2S2 chromophore, in MeCN on a glassy carbon electrode, undergo quasi-reversible reduction in the 540–680 mV range. A depression in E1/2 values for the open chain N2S2 chromophoric macrocyclic CuII complexes, compared to electronically similar cyclic tetradentate CuII analogues, is due to the increased stabilization of the CuI state by added flexibility provided through the open chain donor sites.     

Catalytic amination reactions mediated by Co(II) Schiff base complexes

Co(acacen), 1, (acacen = 2,11-dihydroxy-4,9-dimethyl-5,8-diaza-2,4,8,10-dodecatetraene dianion) was found to be a highly efficient catalyst for the allylic amination of non activated alkenes, using N-(p-toluensulfonyl)iminophenyliodinane (PhINTs) as nitrene precursor. This reactivity has been extended to the less reactive C-H bond of toluene. The effect of reaction times and of added cosolvent on yields and selectivities was investigated. Under the best conditions, allylic amines were obtained in a 40-70% isolated yield. A complex derived from the stoichiometric reaction of Co(acacen), 1, with PhINTs has been isolated and spectroscopically characterized. Such a complex, although not able to transfer its NTs moiety to alkenes, is still active in catalyzing allylic amination of cyclohexene.     

Synthesis and characterization of chiral nickel(II) Schiff base complexes and their CD spectra-absolute configuration correlations

Some nickel(II) complexes of quadridentate Schiff bases prepared from the condensation of 2 mol of 2-hydroxyacetophenone (HACP) or dehydroacetic acid (DHA) with 1 mol of optically active propylene-1,2-diamine (pn), trans-cyclohexane-1,2-diamine (chxn) or 1,2-diphenylethylenediamine (dpen) were synthesized and characterized by EA, IR, UV–vis, and CD spectra. The absolute configurations of the three complexes were determined by X-ray single crystal structure measurement and correlated with CD spectroscopy. In this study, special attention is focussed on the CD signals of the related complexes in the d–d transition region, in the hope of obtaining a tentative correlation between the CD pattern and the absolute configuration about the central metal. A new empirical rule for the assignment of the absolute configuration around the nickel ion in each complex and the handedness of the chiral diamine contained in the Schiff base ligand is put forward. In the case of tetra-coordinated pseudo-planar Ni(II) complexes, the rule can be stated as follows: (i) a positive Cotton effect in the d–d region around 550 nm is assigned to the (S)Δλ-configuration for the HACP-(S)-pn-Ni, HACP-(SS)-dpen-Ni, DHA-S-pn-Ni, and DHA-(SS)-dpen-Ni derivatives; and (ii) a concomitant inversion of the Cotton effect in the same range is assigned to the (S)Λδ-configuration for the HACP-(SS)-chxn-Ni and DHA-(SS)-chxn-Ni derivatives.