Antibacterial Schiff bases of oxalyl-hydrazine/diamide incorporating pyrrolyl and salicylyl moieties and of their zinc(II) complexes

Schiff bases derived from oxaldiamide/oxalylhydrazine and pyrrol-2-carbaldehyde, or salicylaldehyde respectively, as well as their Zn(II) complexes have been prepared and tested as antibacterial agents. These Schiff bases function as tetradentate ligands, forming octahedral Zn(II) complexes. The ketonic form for the diamide derived Schiff base and the enolic form of the hydrazide derived Schiff base were the preferred tautomers for coordination of the metal ions. The title compounds and their Zn(II) derivatives were evaluated for antibacterial activity against several bacterial strains which easily develop resistance to classical antibiotics, such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Some of them showed promising biological activity in inhibiting the growth of such organisms.     

Antibacterial Schiff Bases of Oxalyl-hydrazine/diamide Incorporating Pyrrolyl and Salicylyl Moieties and of Their Zinc(II) Complexes

Schiff bases derived from oxaldiamide/oxalylhydrazine and pyrrol-2-carbaldehyde, or salicylaldehyde respectively, as well as their Zn(II) complexes have been prepared and tested as antibacterial agents. These Schiff bases function as tetradentate ligands, forming octahedral Zn(II) complexes. The ketonic form for the diamide derived Schiff base and the enolic form of the hydrazide derived Schiff base were the preferred tautomers for coordination of the metal ions. The title compounds and their Zn(II) derivatives were evaluated for antibacterial activity against several bacterial strains which easily develop resistance to classical antibiotics, such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Some of them showed promising biological activity in inhibiting the growth of such organisms.     

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.     

Studies on some iridium(III) complexes with Schiff bases derived from amino carboxylic acids

The reactions of iridium(III) chloride with different Schiff bases gave complexes of types [Ir(SB)3], [Ir(SB')Cl(H2O)2], [Ir(SB')Cl2]n, [Ir(SB' ')Cl(H2O)]n (SBH = Schiff bases derived from anthranilic acid and benzaldehyde, acetophenone, vanillin, cinnamaldehyde or m-hydroxyacetophenone; SB'H2 = Schiff bases derived from anthranilic acid and salicylaldehyde or o-hydroxyacetophenone; SB'H = Schiff bases derived from p-aminobenzoic acid and benzaldehyde, acetophenone, vanillin, cinnamaldehyde, or m-hydroxyacetophenone; SB' 'H2 = Schiff bases derived from p-aminobenzoic acid and salicylaldehyde or o-hydroxyacetophenone). These complexes have been characterized on the basis of elemental analyses, conductance, magnetic moment, and spectral (electronic, i.r., and 1H n.m.r.) data. The electronic spectra reveals octahedral geometry for these complexes except for [Ir(SB')Cl2]n, which is trigonal bipyramidal. The thermal behavior of these complexes has also been studied by TG, DTG, and DSC techniques. The different kinetic parameters, viz., order of reaction, activation of energy, and heat of reaction were calculated. The antifungal and antiviral activities of the complexes with Schiff bases derived from anthranilic acid have also been investigated.     

Synthesis, characterization and X-ray crystal structures of dinuclear nickel(II) complexes of a novel potentially hexadentate but functionally tetradentate binucleating ligand

A binucleating potentially hexadentate chelating agent containing oxygen, nitrogen and sulfur as potential donor atoms (H₂ONNO) has been synthesized by condensing α,α-xylenebis(N-methyldithiocarbazate) with 2,4-pentanedione. An X-ray crystallographic structure determination shows that the Schiff base remains in its ketoimine tautomeric form with the protons attached to the imine nitrogen atoms. The reaction of the Schiff base with nickel(II) acetate in a 1:1 stoichiometry leads to the formation of a dinuclear nickel(II) complex [Ni(ONNO)]₂ (ONNO²⁻ = dianionic form of the Schiff base) containing N,O-chelated tetradentate ligands, the sulfur donors remaining uncoordinated. A single crystal X-ray structure determination of this dimer reveals that each ligand binds two low spin nickel(II) ions, bridged by a xylyl group. The nickel(II) atoms adopt a distorted square-planar geometry in a trans-N₂O₂ donor environment. Reaction of the Schiff base with nickel(II) acetate in the presence of excess pyridine leads to the formation of a similar dinuclear complex, [Ni(ONNO)(py)]₂, but in this case comprises five coordinate high-spin Ni(II) ions with pyridine ligands occupying the axial coordination sites as revealed by X-ray crystallographic analysis.     

Antibacterial cobalt(II), nickel(II) and zinc(II) complexes of nicotinic acid-derived Schiff-bases

Nicotinic acid derived Schiff bases and their transition metal [cobalt(II), nickel(II) and zinc(II)] complexes have been prepared and characterized by physical, spectral and analytical data. The Schiff bases act as deprotonated tridentate ligands for the complexation of the above mentioned metal ions. These complexes, possessing the general formula [M(L)2] [where M = Co(II), Ni(II) and Zn(II) and L = HL1-HL4] showed an octahedral geometry of the metal ions. For determining the effect of metal ions upon chelation, the Schiff bases and their complexes have been screened for antibacterial activity against several pathogenic strains of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The new metal derivatives reported here were more bactericidal against one or more bacterial species as compared to the uncomplexed Schiff bases.     

Alkylcobalt chelates with Schiff bases derived from a β-diketone bearing both alkyl and aryl groups

Organocobalt(III) complexes with Schiff bases derived from a β-diketone bearing both an alkyl and an aryl group have been prepared. The template syntheses using benzoylacetone and ethylenediamine as complexing agents provide a route to alkylcobalt chelates with the corresponding tri- and tetradentate Schiff bases. However, if a β-diketone with two aryl groups, e.g. dibenzoylmethane, was employed as the starting ketoenol component, no organometallic products were detected; a new mixed-ligand ‘inorganic’ chelate of cobalt(II), [Co{O=C(Ph)CH=C(Ph)O}₂(en)], was isolated instead. Its structure as well as that of one of the alkylcobalt complexes with a tridentate Schiff base composed of benzoylacetone and ethylenediamine have been established by X-ray techniques. The current scope of the template synthesis of alkylcobalt complexes with Schiff bases is summarized.     

Synthesis, spectra, dioxygen affinity and antifungal activity of Ru(III) Schiff base complexes

The reaction of ruthenium(III) complexes, [RuX(3)(EPh(3))(3)] (E=As, X=Cl or Br; E=P, X=Cl) and [RuBr(3)(PPh(3))(2)(CH(3)OH)] with bidendate Schiff base ligands derived by condensing salicylaldehyde with methylamine (Hsalmet), cyclohexylamine (Hsalchx), 2-aminopyridine (Hsalampy) have been carried out. The complexes were characterized by analytical and spectral studies (IR, electronic and EPR) and are formulated as [RuX(EPh(3))(LL')(2)] (where LL'=monobasic bidentate Schiff base ligand; E=P or As, X=Cl or Br). An octahedral geometry has been tentatively proposed for the new complexes. Dioxygen affinity of some of the Ru(III) Schiff base complexes was studied by cyclic voltammetry. The representative Schiff bases and their complexes were tested in vitro to evaluate their activity against fungi, namely, Aspergillus flavus (A. flavus) and Fusarium species.     

Chemistry of selenium/tellurium-containing Schiff base macrocycles

This paper highlights our work to establish a new class of macrocycles based on Schiff base condensation chemistry. The chemistry of a series of azomethine macrocycles, with selenium/tellurium atoms in o-positions with respect to the CN bond is discussed. These are the first Schiff base macrocycles to incorporate selenium or tellurium atom in the ring. The strong stabilization of the 10-E-3 (E = Se/Te) structures of these macrocycles by E-N coordination permits the access to these novel macrocycles by [2+2] template-free condensation of bis(aldehyde) with primary diamines. The success of cyclization has been confirmed by the usual methods of IR, NMR and X-ray structural determinations. After a brief discussion of the synthetic methods adopted for these macrocycles, their complexing abilities toward different metal ions are covered. The macrocyclic polyamine ligands, derived by reduction of the corresponding Schiff bases, readily form complexes with a range of metal ions. This allows a comparison of the properties of complexes of these ligands with those derived from the Schiff bases containing the same denticity but having a different flexibility. The selena- and tellura-macrocycles reported by other groups in the field are also included for comparison. Also discussed is the anion binding studies of some of these macrocycles.     

Electrochemical and spectroscopic characterization of new cobalt(II) complexes. Catalytic activity in oxidation reactions by molecular oxygen

The synthesis and characterization of some new complexes with tetradentate Schiff bases derived from bis(salicylaldehyde)etylenediimine, H₂Salen are reported in this paper. The Co(II) Schiff bases complexes investigated are: (bis(5-nitro-salicylaldehyde) ethylenediiminato)cobalt(II), (CoNSalen); (bis(-ethyl-salicylaldehyde) ethylenediiminato)cobalt(II) (CoEtSalen); (bis(-ethyl-3,5-diiode-salicylaldehyde) ethylenediiminato) cobalt(II),(CoDIEtSalen); (bis(,5-dimethyl-3-iode-salicylaldehyde)ethylenediiminato)cobalt(II) (CoDMISalen) and (bis(salicylaldehyde)methylene-p,p′-diphenylene)cobalt(II), (CoSalmbfn). The characterization of the complexes was performed by elemental analysis, UV–Vis, FTIR spectroscopy, powder X-ray diffraction and cyclic voltammetry. Pyridine (py), present in the solution of complexes in DMF, coordinates to the metal ion in axial position, inducing a significant decrease of the redox potentials. Significant influences have the substituents grafted on ligands’ molecules. The separated complexes evince catalytic activity in the oxidation reaction of 2,6-di-t-butylphenol with molecular oxygen. These complexes seem capable of forming reversible adducts with molecular oxygen.     

Antibacterial Co(II), Ni(II), Cu(II) and Zn(II) complexes of Schiff bases derived from fluorobenzaldehyde and triazoles

Antibacterial Schiff bases derived from 1,2,4-triazoles as well as their metal complexes incorporating cobalt(II), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. Physico-chemical studies suggest that an octahedral geometry for the cobalt(II), nickel(II) and zinc(II)and square-planer geometry for the copper(II) complexes. These complexes have been screened for antibacterial activity against three Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and two Gram-negative (Salmonella typhi and Pseudomonas aeruginosa) bacterial strains, and results compared with the activity of the free ligands. The metal complexes were found to be more potent against one or more bacterial strains than the free ligands.     

Uranyl nitrate complexes of some Schiff bases of 4-aminoantipyrine and certain carbonyl compounds

A series of nine complexes of uranyl nitrate with some Schiff bases derived from 4-aminoantipyrine and certain carbonyl compounds, such as benzaldehyde, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4- methylbenzaldehyde, 4-N,N-dimethylaminobenzaldehyde, 2-hydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde, acetylacetone and benzoylacetone have been synthesized. These complexes have been characterized by elemental analysis, molecular weight determination and IR spectral, conductance and magnetic studies. From these studies they can be formulated as [UO₂L₂(NO₃)₂], in which the first five ligands (in the order given above) and nitrate ions are coordinated bidentately, while the last four ligands (which have either a phenolic hydroxyl group or a side-chain carbonyl group as an additional site) act as terdentate ligands, and nitrate ions are coordinated monodentately. Hence the proposed general formula for the complexes suggests that the uranyl ion has a coordination number of eight in addition to the two oxygen atoms which have already been bonded to the U(VI) species.     

Antibacterial and antifungal metal based triazole Schiff bases

A new series of four biologically active triazole derived Schiff base ligands (L¹–L⁴) and their cobalt(II), nickel(II), copper(II) and zinc(II) complexes (1–16) have been synthesized and characterized. The ligands were prepared by the condensation reaction of 3-amino-5-methylthio-1H-1,2,4-triazole with chloro-, bromo- and nitro-substituted 2-hydroxybenzaldehyde in an equimolar ratio. The antibacterial and antifungal bioactivity data showed the metal(II) complexes to be more potent antibacterial and antifungal than the parent Schiff bases against one or more bacterial and fungal species.     

Some bivalent metal complexes of Schiff bases containing N and S donor atoms

Schiff bases have been synthesized by the reaction of p-nitrobenzaldehyde, o-nitrobenzaldehyde and p-toluyaldehyde with 4-amino-5-mercapto-1,2,4-triazole. The ligands react with Co(II), Ni(II) and Zn(II) metals to yield (1:1) and (1:2) [metal:ligand] complexes. Elemental analyses, IR, 1H NMR, electronic spectral data, magnetic susceptibility measurements, molar conductivity measurements and thermal studies have investigated the structure of the ligands and their metal complexes. The electronic spectral data suggests octahedral geometry for Co(II), Ni(II) and Zn(II). The antibacterial activities of the ligands and their metal complexes have been screened in vitro against three Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and two Gram-negative (Salmonella typhi and Pseudomonas aeruginosa) organisms. The coordination of the metal ion had a pronounced effect on the microbial activities of the ligands and the metal complexes have higher antimicrobial effect than the free ligands.     

Antibacterial Co(II), Ni(II), Cu(II) and Zn(II) Complexes of Schiff bases Derived from Fluorobenzaldehyde and Triazoles

Antibacterial Schiff bases derived from 1,2,4-triazoles as well as their metal complexes incorporating cobalt(II), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. Physico-chemical studies suggest that an octahedral geometry for the cobalt(II), nickel(II) and zinc(II)and square-planer geometry for the copper(II) complexes. These complexes have been screened for antibacterial activity against three Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and two Gram-negative (Salmonella typhi and Pseudomonas aeruginosa) bacterial strains, and results compared with the activity of the free ligands. The metal complexes were found to be more potent against one or more bacterial strains than the free ligands.     

Synthesis and characterization of a series of new mixed ligand complexes of manganese(III), iron(III), nickel(II), copper(II) and zinc(II) with schiff bases of N,N-diethylamino-dithiocarbamate as ligands

Twenty new bioactive complexes of Mn(III), Fe(III), Ni(II), Cu(II) and Zn(II) have been prepared containing Schiff bases of N,N-diethylaminodithio- carbamate as ligands. These complexes have been characterized by elemental analyses, IR and UV-Vis spectroscopy as well as by magnetic susceptibility measurements. The spectra of the complexes suggest that the ligands are coordinated to the metal ions via the sulfur atoms of the dithiocarbamato group.     

Mono- and dinuclear Fe(III) complexes with the N2O2 donor 5-chlorosalicylideneimine ligands; synthesis, X-ray structural characterization and magnetic properties

Two novel monomeric [C₁₈H₁₇Cl₃N₂O₂Fe] (1) and dimeric [C₃₈H₃₆N₄O₄Cl₆Fe₂] (2) Fe(III) tetradentate Schiff base complexes have been synthesized and their crystal structures have been determined by single crystal X-ray diffraction analysis. In complex (1) the Schiff base ligand coordinates toward one iron atom in a tetradentate mode and each iron atom is five coordinated with the coordination geometry around iron atom which can be described as a distorted square pyramid. The presence of a short (2.89 Å) non-bonding interatomic Fe···O distances between adjacent monomeric Fe(III) complexes results in the formation of a dimer. Structural analysis of compound (2) shows that the structure is a centrosymmetric dimer in which the six coordinated Fe(III) atoms are linked by μ-phenoxo bridges from one of the phenolic oxygen atoms of each Schiff base ligand to the opposite metal center. The variable-temperature (2-300 K) magnetic susceptibility (χ) data of these two compounds have been investigated. The results show that for both complexes Fe(III) centers are in the high spin configuration (S = 5/2) and indicate antiferromagnetic spin-exchange interaction between Fe(III) ions. The obtained results are briefly discussed using magnetostructural correlations developed for other class of iron(III) complexes.     

Biological activity of palladium(II) and platinum(II) complexes of the acetone Schiff bases of S-methyl- and S-benzyldithiocarbazate and the X-ray crystal structure of the [Pd(asme)2] (asme=anionic form of the acetone Schiff base of S-methyldithiocarbazate) complex

Palladium(II) and platinum(II) complexes of general empirical formula, [M(NS)(2)] (NS=uninegatively charged acetone Schiff bases of S-methyl- and S-benzyldithiocarbazate; M=Pt(II) and Pd(II)) have been prepared and characterized by a variety of physicochemical techniques. Based on conductance, IR and electronic spectral evidence, a square-planar structure is assigned to these complexes. The crystal and molecular structure of the [Pd(asme)(2)] complex (asme=anionic form of the acetone Schiff base of S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted cis-square planar structure with the ligands coordinated to the palladium(II) ions as uninegatively charged bidentate NS chelating agents via the azomethine nitrogen and the mercaptide sulfur atoms. The distortion from a regular square-planar geometry is attributed to the restricted bite angles of the ligands. Antimicrobial tests indicate that the Schiff bases exhibit strong activities against the pathogenic bacteria, Bacillus subtilis (mutant defective DNA repair), methicillin-resistant Staphylococcus aureus, B. subtilis (wild type) and Pseudomonas aeruginosa and the fungi, Candida albicans (CA), Candida lypotica (2075), Saccharomyces cerevisiae (20341) and Aspergillus ochraceous (398)-the activities exhibited by these compounds being greater than that of the standard antibacterial and antifungal drugs, streptomycin and nystatin, respectively. The palladium(II) and platinum(II) complexes are inactive against most of these organisms but, the microbe, Pseudomonas aeruginosa shows strong sensitivity to the platinum(II) complexes. Screening of the compounds for their cytotoxicities against T-lymphoblastic leukemia cancer cells has shown that the acetone Schiff base of S-methyldithiocarbazate (Hasme) exhibits a very weak activity, whereas the S-benzyl derivative (Hasbz) is inactive. However, the palladium(II) complexes exhibit strong cytotoxicities against this cancer; their activities being more than that of the standard anticancer drug, tamoxifen. The [Pt(asme)(2)] complex exhibits a very weak cytotoxicity, whereas [Pt(asbz)(2)] is inactive against leukemic cells.     

Ferrocenylboronates: Crystal structures and electrochemical properties

The electrochemical behavior of a series of eight previously reported monoferrocenyl- and diferrocenyl-boronates derived from tridentate ligands has been studied. Even if most mononuclear and all the dinuclear complexes examined showed to undergo slow decomposition in nonaqueous solution (releasing free ferrocenyl boronic acid), their redox activity has been investigated. It has been proved that the oxidation of the two ferrocenyl subunits in the dimeric species proceeds simultaneously, indicating that no mutual electronic interaction exists between them. Additionally, the solid-state molecular structures of two diferrocenyl complexes (2a and 2b) were studied by X-ray diffraction. The analysis confirms the formation of a [5.4.0] heterobicycle with the presence of two different boron atoms, one in a tetrahedral geometry and the other one in a trigonal geometry.     

Characterization and toxicity of lanthanide complexes with nitrogen- and sulphur-containing Schiff bases

La(III), Ce(III), Pr(III), Nd(III), Gd(III), Dy(III), Ho(III) and Er(III) complexes of Schiff bases derived from sulphamethoxazole and salicylaldehyde (I), and thiophene-2-aldehyde (II) have been characterized on the basis of IR, NMR, UV-Vis spectroscopy, elemental analysis, conductance measurements and molecular weight determinations. The Schiff bases act as monobasic bidentate ligands, rendering the metal eight-coordinated. The equilibrium constants have been studied in solution at 25, 30 and 35 °C. The nephelauxetic effect (1 - β), bonding parameter (β), b^1/2 and Sinha covalency parameter (δ) have been calculated. The positive values indicate the covalent nature of the metal-ligand bond. The covalent nature of the complexes is also supported by molar conductance measurements. The toxicities of the Schiff bases and their complexes were evaluated against insects. The LD₅₀ value for cockroaches and percent growth inhibition of the fungi show greater efficacy for the complexes than the Schiff bases.