Novel supramolecular assembly of symmetrical mixed-metal-ligand complexes of dioxouranium(VI)

Some binary and ternary novel complexes of dioxouranium(VI) with 8-hydroxy-7-quinolinecarboxaldehyde (OXH) have been prepared and characterized by elemental analyses, magnetic susceptibility measurements and spectral studies. Coordination effects on the vibrational spectra of the ligands have been investigated. The amine exchange reactions of coordinated Schiff bases in these complexes have been also studied, which reveal symmetrical tetradentate Schiff base complexes. Metal exchange reaction of dioxouranium(VI) complexes was obtained when reacted with tetradentate Schiff base complexes of Cu(II) with ZrCl(4)/UO(2)(CH(3)COO)(2) giving heterobinuclear complexes. Magnetic, electronic and IR spectral data suggest the configurations of distorted square planar ligand field copper(II) complexes. The ligands behave as bi-(O,O) and tetradentate (N(2),O(2)) donors. El-Sonbati equation has been used to evaluate the symmetric stretching frequency from which the F(U-O) and F(UO,UO)(-) were calculated. The bond distances of these complexes were also investigated.     

Cr(III), Fe(III) and Co(III) complexes of tetradentate (ONNO) Schiff base ligands: synthesis, characterization, properties and biological activity

A series of metal complexes were synthesized from equimolar amounts of Schiff bases: 1,4-bis[3-(2-hydroxy-1-naphthaldimine)propyl]piperazine (bappnaf) and 1,8-bis[3-(2-hydroxy-1-naphthaldimine)-p-menthane (damnaf) with metal chlorides. All of synthesized compounds were characterized by elemental analyses, spectral (UV-vis, IR, (1)H-(13)C NMR, LC-MS) and thermal (TGA-DTA) methods, magnetic and conductance measurements. Schiff base complexes supposed in tetragonal geometry have the general formula [M(bappnaf or damnaf)]Cl.nH(2)O, where M=Cr(III), Co(III) and n=2, 3. But also Fe(III) complexes have octahedral geometry by the coordination of two water molecules and the formula is [Fe(bappnaf or damnaf)(H(2)O)(2)]Cl. The changes in the selected vibration bands in FT-IR indicate that Schiff bases behave as (ONNO) tetradentate ligands and coordinate to metal ions from two phenolic oxygen atoms and two azomethine nitrogen atoms. Conductance measurements suggest 1:1 electrolytic nature of the metal complexes. The synthesized compounds except bappnaf ligand have the antimicrobial activity against the bacteria: Escherichia coli (ATCC 11230), Yersinia enterocolitica (ATCC 1501), Bacillus magaterium (RSKK 5117), Bacillus subtilis (RSKK 244), Bacillus cereus (RSKK 863) and the fungi: Candida albicans (ATCC 10239). These results have been considerably interest in piperazine derivatives due to their significant applications in antimicrobial studies.     

Synthesis and characterization of nitro-Schiff bases derived from 5-nitro-salicylaldehyde and various diamines and their complexes of Co(II)

Some neutral tetradentate N₂O₂ type complexes of Co(II) have been synthesized using Schiff bases formed by condensation of 5-nitro-salicylaldehyde with various diamines in alcohol. The nature of the ligands and complexes was established by spectroscopic techniques. The Schiff bases are bivalent anions with tetradentate ONNO donors derived from phenolic oxygen and azomethine nitrogen. IR and UV-Vis spectral data suggest that all the complexes are square-planar.     

Influence of the metal size in the structure of the complexes derived from a pentadentate [N(3)O(2)] hydrazone

The influence of the metal size in the nuclearity of the complexes derived from the hydrazone ligand 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H(4)daps] has been investigated. We have synthesised a series of new complexes [M(H(x)daps)] x yH(2)O, (x = 2,3; y = 0-3) with M = Ag (1), Cd (2), Al (3), Sn (4) and Pb (6), using an electrochemical procedure. The crystal and molecular structures have been determined for the mononuclear complexes [Sn(H(2)daps)(H(2)O)(2)] x 4H(2)O (5) and [Pb(H(2)daps)(CN)][Et(4)N] (7). Complex is the first neutral Sn(II) complex derived from a pentadentate hydrazone Schiff base ligand. Complex shows the lead coordinated to the hydrazone donor set and a cyanide ligand, being the first reported complex with the lead atom coordinated to a monodentate cyanide group. Additionally, we have synthesised the lead complex using chemical conditions, in the presence of sodium cyanide which allowed us to isolate the neutral complex [Pb(H(2)daps)] (8). Evaporation of these mother liquors led the novel compound [Pb(Hdaphs)(CH(3)COO)] (9). Complex 9 shows the initial ligand hydrolysed in one of the imine bonds giving rise to a new tetradentate ligand [H(2)daphs] coordinated to the lead atom and a bidentate acetate group. Moreover, the solution behaviour of the complexes has been investigated by (1)H, (113)Cd, (117)Sn and (207)Pb NMR techniques. In particular multinuclear NMR has provided new useful data to correlate factors such as oxidation state, coordination number and nature of the kernel donor atoms due to the new coordination found in complexes 5 and 7. The comparative study of the structures of the complexes derived from this pentadentate [N(3)O(2)] hydrazone ligand let us to conclude that the metal size is a key factor to control the nuclearity of the complexes derived from the ligand [H(4)daps].     

Stereochemistry of new nitrogen containing heterocyclic aldehyde. IX. Spectroscopic studies on novel mixed-ligand complexes of Rh(III)

Mono, bis and tris complexes of rhodium(III) oxine (systematic name 8-hydroxy-7-quinolinecarboxaldehyde) and mixed ligand have been prepared. The amine exchange reaction of coordinated Schiff base in these complexes has also been carried out, which gives symmetrical tetradentate Schiff base complexes. The complexes are characterized by elemental and thermal analysis, IR, magnetic and electronic spectral analysis methods were also employed as well as conductivity measurements. An octahedral structure is proposed for all the new complexes in which chloride is attached to the metal ion in 1:1; 1:2 (metal:ligand) ratio. The spectral data were utilized to compute the important ligand field parameter B, beta and Dq. The B-values suggest a strong covalency in the metal-ligand sigma-bond and the Dq-values indicate a medium strong ligand field. 1H NMR spectra show that the tris (ligand) complex is cis isomer. IR spectra show that the ligand is mono-basic bidentate.     

Synthesis and spectroscopic characterization of nickel(II) complexes of 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one

The reaction of NiCl(2).H(2)O with 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one, X=H (HL(1)), X=Cl (HL(2)), X=Br (HL(3)) and X=Me (HL(4)), gave the complexes [(HL)NiCl(2)] x nH(2)O and [LNi(OH)](2), where L is the monobasic anion of HL(2) or HL(3). The nature of the products is solvent and ligand dependent. The complexes are characterized by elemental analyses, molar conductivity, magnetic moments and spectroscopic (IR and UV/vis) measurements. The IR showed that the ligands act as neutral bidentate coordinated to the nickel(II) through the azomethine nitrogen and carbonyl oxygen atoms in case of [(HL)NiCl(2)] x nH(2)O. In case of [LNi(OH)](2), the ligands are monobasic bidentate bonded to the nickel(II) through the azomethine nitrogen and the enolato oxygen atoms. The room temperature magnetic moment values of 1.58-2.49 B.M. for [(HL)NiCl(2)] x nH(2)O and [LNi(OH)](2) and their electronic spectral data indicate that these complexes have square planar-tetrahedral equilibrium. The values of 1.61 and 1.58 B.M. for the hydroxo-complexes support their dimeric nature. The electronic spectral of [(HL)NiCl(2)] x nH(2)O and [LNi(OH)](2) in pyridine or alpha-picoline indicated the formation of six-coordinate adducts. The hydroxo-complexes reacted with different Lewis bases to give the complexes [L(2)Ni(L(s))(2)], where L(s)=Py, 2-Pic, 3-Pic, 4-Pic or n-PrNH(2). The relationship between the pK(b) of the Lewis base and the upsilon(Ni-O) of the ligand and upsilon(Ni-N) of the Lewis base was studied. The different ligand field parameters are calculated for the parent ligands in solutions and the solid mixed ligand complexes. The data showed that both are associated with a distorted octahedral ligand field around the nickel(II) and the ligand fields in solution are different from that in solid. The extent of distortion for the parent complexes is more than that in the solid adducts. Furthermore, the data showed that the nickel-ligand bonding in [LNi(OH)](2) is more covalent than in [L(2)Ni(L(s))(2)].     

The formation of 'classical' and 'half unit' Schiff-base ligands from their components on a molybdenum(IV) centre

The in situ synthesis of the complex, (PPh₄)[Mo(CN)₃O(aceen)] (aceen = N-[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine), with a 'half unit' Schiff base ligand (with a free amino group) is described and compared with that of [Mo(CN)₂O(diaceen)]·H₂O (diaceen = N,N-bis[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine) in which a 'classical', tetradentate Schiff base ligand is formed. The mechanism of the 'half unit' and 'classical' template Schiff bases ligand formation is discussed.     

Synthesis,characterization, biological activity,and corrosion inhibition in acid medium of unsymmetrical tetradentate N2O2 Schiff base complexes

Four divalent metal(II) complexes, namely [Co(II)L(H₂O)Cl]·2H₂O, [Ni(II)L(H₂O)Cl]·4H₂O, [Cu(II)L(H₂O)Cl]·3H₂O, and [Zn(II)L(H₂O)Cl]·5H₂O, {L = 2‐furan‐2‐ylmethyleneamino‐phenyl‐iminomethylphenol}, were synthesized and characterized by several techniques. The molar conductance measurement of all analyzed complexes in DMSO showed their non‐electrolytic nature. The new Schiff base ligand (HL) acts as tetradentate ligand, coordinated through deprotonated phenolic oxygen, furan ring oxygen, and two azomethine nitrogen atoms. The ligand field parameters were measured for the metal complexes, which were found to be in the range notified for an octahedral structure. The molecular structural parameters of the synthesized HL ligand and its related metal(II) complexes were calculated and correlated with the experimental parameters such as infrared (IR) data. The investigated ligand and metal complexes were screened for their in vitro antimicrobial activities against different types of fungal and bacterial strains. The resulting data confirmed the examined compounds as a highly promising bactericides and fungicides. The antitumor activities of all inspected compounds were evaluated against colon carcinoma (HCT‐116) and mouse myelogenous leukemia carcinoma (M‐NFS‐60) cell lines. The inhibition effect of HL ligand and its isolated complexes on the corrosion carbon in the form of a rod of area 0.35 cm² in HCl was investigated by measuring the weight loss at 25 °C.     

Synthesis,characterization, and in vitro antioxidant and anticancer studies of ruthenium(III) complexes of symmetric and asymmetric tetradentate Schiff bases

Ruthenium(III) complexes of three tetradentate Schiff bases with N₂O₂ donors formulated as [RuCl(LL¹)(H₂O)], [RuCl(LL²)(H₂O)] and [RuCl(LL³)(H₂O)] were synthesized and characterized by elemental analyses, molar conductance, FTIR, and electronic spectral measurements. The FTIR data showed that the tetradentate Schiff base ligands coordinate to Ru ions through the azomethine nitrogen and enolic oxygen. The antioxidant activities of the complexes were investigated through scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radicals. The DPPH activity for [RuCl(LL²)(H₂O)] with IC₅₀ = 0.031 mg mL^?1 was higher than the values obtained for the other Ru(III) compounds. The study revealed that the synthesized Ru(III) complexes of the tetradentate Schiff base exhibited strong scavenging activities against DPPH and moderate against ABTS radicals. In addition, the antiproliferative studies of the complexes were also tested against human renal cancer cells (TK10), human melanoma cancer cells (UACC62), and human breast cancer cells (MCF7) using the SRB assay. The results indicated that the Ru(III) complexes showed low anticancer activities against the tested human cancer cell lines.     

Spectral,magnetic, biological,and thermal studies of metal(II) complexes of some unsymmetrical Schiff bases

New nickel(II) and copper(II) complexes with unsymmetrical Schiff bases derived from aromatic 2-hydroxy aldehydes were synthesized and characterized by elemental analyses, melting points, ¹H-NMR, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry (DSC), infrared (IR), and electronic spectral measurements. Comparison of IR spectra of the Schiff bases and their metal complexes indicated that the Schiff bases are tetradentate, coordinated via the two azomethine nitrogens and the two phenolic oxygens. Magnetic moments and electronic spectral data confirm square-planar geometry for the complexes. Thermal studies reveal a general decomposition pattern, whereby the complexes decomposed partially in a single step due to loss of part of the organic moiety. A single endothermic profile, corresponding to melting point, was observed from the DSC of all complexes, except those whose ligand contained the nitro group, which decomposed exothermally without melting. The Schiff bases and their complexes were screened in vitro against 10 human pathogenic bacteria. The metal(II) complexes exhibited higher antibacterial activity than their corresponding Schiff bases.     

Iron(III) Schiff base complexes with asymmetric tetradentate ligands: synthesis,spectroscopy, and antimicrobial properties

The synthesis and characterization is reported of four iron(III) complexes of general formula [Fe(pythsalX)(H₂O)₂]Cl₂, derived from the NSNO-donor tetradentate Schiff base ligands pythsalHX ([5-X-N-(2-pyridylethylsulfanylethyl)salicylideneimine] (X = OMe, N₂Ph, I, NO₂). The complexes were characterized by physico-chemical and spectroscopic methods. The thermal stabilities of both the free Schiff bases and their complexes were studied by differential scanning calorimetry and thermogravimetric analyses. The spectroscopic data suggest that the Schiff base ligands coordinate through deprotonated phenolic oxygen, imine, and pyridine-type nitrogens and the thioether sulfur atoms to give an octahedral geometry around the iron(III) atom in all these complexes. The free Schiff bases and their complexes have been screened for antimicrobial activities and the results show that the free Schiff bases are more potent antibacterials than the complexes.     

Rare-earth complexes of mesomorphic Schiff's base ligands

Rare-earth complexes of mesomorphic Schiff 's bases, 4-[(alkylimino)methyl]-3-hydroxyphenyl 4-alkyloxybenzoates, were synthesized. Whereas the ligands LH display a nematic and/or a smectic C phase, the metal complexes show a viscous smectic A phase and decompose at the clearing point. The mesophase was investigated by hot-stage polarizing optical microscopy, by differential scanning calorimetry and by high temperature X-ray diffraction. Two types of complex were found, [Ln(LH)₃ (NO₃)₃] and [Ln(LH)₂L(NO₃)₂], depending on the ligand or the central metal ion. The first coordination sphere of the rare-earth ion in these metallomesogens is comparable to that in the structure of complexes with 4-alkoxy-N-alkyl2-hydroxybenzaldimine ligands.     

Synthesis,spectroscopic and electrochemical studies of mixed ligand ruthenium(II) chiral Schiff base complexes with nitrogen donors

Summary Mixed ligand complexes (1)-(18) of composition [RuL-(PPh₃)Y] and [RuL(PPh₃)(H₂O)Y]^- (L = chiral Schiff bases derived from l-alanine, l-valine, l-serine, l-cystein, l-arginine or l-aspartic acid with salicylaldehyde; Y = azide, 2,2-bipyridyl or 1,10-phenanthroline) have been prepared and characterized by microanalysis, spectroscopy and polarography. The conformational aspects regarding the relationship of the asymmetric carbon atom to the nitrogen donors around the Ru^II are discussed. All complexes showed quasi-reversible c.v. behaviour and the redox potentials of the Ru^II/Ru^I couple lie in the -0.31 to-0.16 V range.     

2-[(8-Hydroxyquinolinyl)methylene]hydrazinecarboxamide: expanding the coordination sphere of 8-hydroxyquinoline for coordination of rare-earth metal(III) ions

The semicarbazone of 8-hydroxyquinoline-2-carbaldehyde can be easily synthesized and is an effective tetradentate ligand for the coordination of rare-earth(III) ions. Investigations with yttrium(III) and lanthanum(III) in solution and in the solid state show, that the small yttrium ion can form 2 : 2 (1 : 1 stoichiometry) and 2 : 1 ligand to metal complexes (X-ray structures: [LY(NO3)(DMF)2]2Cl2 x 2DMF and [LL'Y] x 3MeOH x Et2O). With the larger lanthanum(III) ion only a well defined 1 : 1 complex (X-ray structure: [LLa(NO3)(MeOH)2]2(NO3)2) can be observed but probably 2 : 1 complexes are also formed. The X-ray structure analyses of [(L-H)MCl3] x MeOH (M = Er, Ho) and Na[(micro-NO3){LEu(NO3)2}2] x 2DMF show different coordination modes of the ligand. It can coordinate in its deprotonated but also in the protonated form.     

Synthesis, structural characterization and antibacterial activity of 2,6-diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases and their copper(II) complexes

2,6-Diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases (L¹, L² and L³) and their Cu(II) complexes of the general formula [CuL·H₂O] were synthesized and characterized by various spectroscopic techniques. The crystal structure of [CuL³·(py)]·py was investigated by single crystal X-ray structure analysis. The Cu(II) cation has near square pyramidal, penta-coordinate geometry. The binegatively charged tetradentate Schiff base is asymmetrically coordinated to the Cu(II) ion via the pyridine N atom, the azomethine N atom, the sulfonyl O atom and the deprotonated hydrazine N atom. There is a pyridine molecule apically coordinated to the Cu(II) ion. All the Schiff bases and their copper(II) complexes were screened by the disc diffusion method against multi-drug resistant (MDR) gram-negative and gram-positive bacteria. The minimum inhibitory concentration (MIC) values were also determined. These results show that the antibacterial activity of the Schiff bases against Methicillin-resistant Staphylococcus aureus (MRSA) is enhanced when they are chelated with the copper(II) ion.     

Microwave assisted synthesis and characterization of unsymmetrical tetradentate Schiff base complexes of VO(IV) and MoO(V)

Microwave synthesis, is green chemical method, simple, sensitive, reducing solvent amount and reaction time. The attempt was made to synthesize the unsymmetrical tetradentate N(2)O(2) ligands and their VO(IV) and MoO(V) unsymmetrical tetradentate Schiff base complexes by classical and microwave techniques using domestic microwave oven. The resulting unsymmetrical Schiff base ligands L(1)-L(3) characterized by different spectral methods. Their complexes with oxocations of VO(IV) and MoO(V) have been synthesized and characterized by elemental analyses, conductometric measurements, infrared and electronic absorption, (1)H NMR spectra, mass spectrometry, ESR spectra, magnetic susceptibility measurement and thermal study. The study suggests that the oxo metal ion is bonded to the ligand through the oxygen and imino nitrogen and the geometry around metal ion is distorted octahedral.     

Spectroscopic and structural characterizations of novel water-soluble tetraperoxo and diperoxo[polyaminocarboxylato bis(N-oxido)]tantalate(V) complexes

New water-soluble homoleptic peroxo complexes and heteroleptic peroxo-polyaminocarboxylato (PAC) complexes of tantalum(V) have been prepared. In the case of the peroxo-PAC complexes, the synthesis in the presence of excess H2O2 leads to the oxidation of the nitrogen atoms of the ligand into N-oxides. The compounds correspond to the general formula (gu)3[Ta(O2)2(LO2)] x xH2O (gu = guanidinium, L = edta or pdta) in which H4LO2 refers to the bis(N-oxide) derivative of the PAC ligand. The TaV complexes have been characterized on the basis of elemental and thermal analysis and by IR and 13C and 15N NMR spectroscopy. These last two spectroscopic methods have been used to suggest the coordination mode of the PAC ligand in the complexes. ESI mass spectrometry measurements have also been carried out for the peroxo-PAC compounds. The crystal structures of the homoleptic tetraperoxotantalate, (gu)3[Ta(O2)4] (1), and the heteroleptic complex, (gu)3[Ta(O2)2(edtaO2)] x 2.32H2O x 0.68H2O2 (2b), have been determined, showing, for both cases, an 8-fold-coordinated Ta atom surrounded either by four bidentate peroxides or by two peroxides and one tetradentate edtaO2 ligand.     

Stereoselective formation of dinuclear complexes with anomalous CD spectra

A novel chiral tetradentate Schiff base ligand forms dinuclear lambda,lambda-[M2L2Cl2]2+ complexes with high diastereoselectivity; the complexes exhibit anomalous CD spectra due to exciton coupling of chromophores located on different metal centres.     

Synthesis and Biological Evaluation of some 3d Metal Complexes with a Novel Heterocyclic Schiff Base

A heterocyclic Schiff base was prepared by condensing 3‐acetylcoumarin with 2‐amino‐3‐carboxyethyl‐4,5,6,7‐tetrahydrobenzo[b ]thiophene. Such Schiff bases derived from two different heterocyclic moieties are rare and expected to have properties surpassing those of either of the parent compounds in effectiveness of complex formation and biological activities. This ligand formed a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) ions. The ligand and the metal complexes were characterized by various physicochemical and spectral studies. These included elemental analysis, molar conductance, magnetic susceptibility, as well as UV–vis, IR, ¹H NMR, ¹³C NMR, and ESR spectral studies. The ESR spectral data adequately supported the covalent nature of the metal–ligand bonds. The ligand possessed a hexagonal crystal structure, but on complexation the crystallinity was lost. The fluorescence spectra of the ligand and its metal complexes in DMSO were also recorded. The ligand and the metal complexes were screened for their antimicrobial activities, and it was observed that the metal complexes are more active than the ligand. The α‐amylase inhibitory activity and the DNA cleavage activity of the ligand and the metal complexes were also examined. in vitro antitumor activity of the copper(II) complex was assayed against human cervical carcinoma cells (HeLa cell line), showing that the complex exhibited promising antitumor activity on the HeLa cell line.     

Stereochemistry of new nitrogen containing heterocyclic aldehyde. Part XI. Novel ligational behaviour of quinoline as chelate ligand toward transition metal ions

Novel complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and UO2(II) with a new Schiff base derived from 8-hydroxy-7-quinolinecarboxaldehyde and 2-aminoethanethiol (LH2) (system name: 2-(8-hydroxy-7-carboxalimino)ethanethiol.) have been prepared and characterized on the basis of analytical, thermal, magnetic moment, infrared, electronic, NMR and EPR spectral data. From the analytical, NMR and thermal data and stoichiometry of the complexes indicate that LH2 act as a dibasic tridentate ligand with ONS donors towards all the metal ions. The magnetic moment, electronic and EPR spectral data commensurate that the Mn(II), Fe(II), Ni(II) and UO2(II) complexes are dimeric with octahedral configuration while the Cu(II) and Zn(II) complexes are monomeric with square-planar and tetrahedral geometries, respectively. Various ligand field parameters Dq, B and beta for complex 5 was calculated. The complexes 3+4 have lower symmetries and the amount of distortion in terms of DT/DQ applying NSH "Hamiltonian Theory" has been evaluated which indicate that the complexes are moderately distorted.