Showing papers on "Schiff base published in 2007"
TL;DR: The crystal structures of the key complexes are elucidated by X-ray diffraction, which confirms that they are chiral, and analysis of the (1)H and (13)C NMR spectra unambiguously demonstrates that their conformations are so flexible that the chiral environment of the complexes cannot be maintained in solution at 25 degrees C and that the complexes are achiral under the polymerization conditions.
Abstract: Highly isotactic polylactide or poly(lactic acid) is synthesized in a ring-opening polymerization (ROP) of racemic lactide with achiral salen- and homosalen-aluminum complexes (salenH(2)=N,N'-bis(salicylidene)ethylene-1,2-diamine; homosalenH(2)=N,N'-bis(salicylidene)trimethylene-1,3-diamine). A systematic exploration of ligands demonstrates the importance of the steric influence of the Schiff base moiety on the degree of isotacticity and the backbone for high activity. The complexes prepared in situ are pure enough to apply to the polymerizations without purification. The crystal structures of the key complexes are elucidated by X-ray diffraction, which confirms that they are chiral. However, analysis of the (1)H and (13)C NMR spectra unambiguously demonstrates that their conformations are so flexible that the chiral environment of the complexes cannot be maintained in solution at 25 degrees C and that the complexes are achiral under the polymerization conditions. The flexibility of the backbone in the propagation steps is also documented. Hence, the isotacticity of the polymer occurs due to a chain-end control mechanism. The highest reactivity in the present system is obtained with the homosalen ligand with 2,2-dimethyl substituents in the backbone (ArCH==NCH(2)CMe(2)CH(2)N==CHAr), whereas tBuMe(2)Si substituents at the 3-positions of the salicylidene moieties lead to the highest selectivity (P(meso)=0.9(8); T(m)=210 degrees C). The ratio of the rate constants in the ROPs of racemic lactide and L-lactide is found to correlate with the stereoselectivity in the present system. The complex can be utilized in bulk polymerization, which is the most attractive in industry, although with some loss of stereoselectivity at high temperature, and the afforded polymer shows a higher melting temperature (P(meso)=0.9(2), T(m) up to 189 degrees C) than that of homochiral poly(L-lactide) (T(m)=162-180 degrees C). The "livingness" of the bulk polymerization at 130 degrees C is maintained even at a high conversion (97-98 %) and for an extended polymerization time (1-2 h).
365 citations
TL;DR: In this paper, the role of compartmental ligands, i.e. their ability to bind two or more metal ions in close proximity into two identical or different compartments, and their relevance in modulating the type and the extent of mutual interaction between the metal ions inside the adjacent chambers are reviewed.
341 citations
TL;DR: In this article, dissymmetric tridentate Schiff base ligands, containing a mixed donor set of ONN and ONO were prepared by the reaction of benzhydrazide with the appropriate salicylaldehyde and pyridine-2-carbaldehyde and characterized by FT-IR, 1H and 13C NMR.
269 citations
TL;DR: A series of transition metal complexes of Cu(II), Ni, Co, Mn, Zn, VO, Hg, and Cd have been synthesized from the Schiff base derived from 4-aminoantipyrine, 3-hydroxy-4-nitrobenzaldehyde and o-phenylenediamine.
Abstract: A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) and Cd(II) have been synthesized from the Schiff base (L) derived from 4-aminoantipyrine, 3-hydroxy-4-nitrobenzaldehyde and o-phenylenediamine. Structural features were obtained from their elemental analyses, magnetic susceptibility, molar conductance, mass, IR, UV-Vis, 1H NMR and ESR spectral studies. The data show that these complexes have composition of ML type. The UV-Vis, magnetic susceptibility and ESR spectral data of the complexes suggest a square-planar geometry around the central metal ion except VO(IV) complex which has square-pyramidal geometry. The redox behaviour of copper and vanadyl complexes was studied by cyclic voltammetry. Antimicrobial screening tests gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that Cu, Ni and Co complexes cleave DNA through redox chemistry whereas other complexes are not effective.
234 citations
TL;DR: The present method is complementary to the previously reported methods, and products were obtained in high syn-selectivity (>20:1), yield, yield, and enantioselectivity (98−83% ee).
Abstract: syn-Selective catalytic asymmetric nitro-Mannich reactions using a heterobimetallic Cu/Sm/Schiff base complex are described. The present method is complementary to the previously reported methods, and products were obtained in high syn-selectivity (>20:1), yield (99−62%), and enantioselectivity (98−83% ee). Both Cu and Sm metals, aligned suitably in a dinucleating Schiff base ligand, were essential to realize high syn-selectivity.
209 citations
TL;DR: The metal complexes have higher antimicrobial effect than the free ligands and have been screened in vitro against the three Gram-positive and two Gram-negative organisms.
172 citations
TL;DR: A series of aluminum ethyls and isopropoxides based upon N,N,O,O-tetradentate Schiff base ligand framework have been prepared.
Abstract: A series of aluminum ethyls and isopropoxides based upon N,N,O,O-tetradentate Schiff base ligand framework have been prepared. X-ray diffraction analysis and H-1 NMR confirmed that these Schiff base aluminum ethyls and isopropoxides were all monomeric species with a five-coordinated central aluminum in their solid structures. Compared to the aluminum ethyls which all retain their monomeric structure in the solution, the dinucleating phenomenons of aluminum isopropoxides with less steric hindered substituents in the solution have also been observed. The activities and stereoselectivities of these complexes toward the ring-opening polymerization of rac-lactide have been investigated. Polymerization experiments indicated that (SB-2d)(AlOPr)-Pr-i [(SB-2d) = 2,2-dimethyl-1,3-propylenebis(3,5-di-tert-butylsalicylideneiminato)] exhibited the highest stereoselectivity and (SB-3b)(AlOPr)-Pr-i [(SB-3b) = 2,2-dimethyl-1,3-propylenebis(3,5-dichlorinesalicylideneiminato)] possessed the highest activity among these aluminum isopropoxides. The substituents and the mode of the bridging part between the two nitrogen atoms both exerted significant influences upon the progress of the polymerizations, influencing either the tacticity of isolated polymers or the rate of polymerization.
167 citations
TL;DR: The binding site size, thermal melting, and viscosity data suggest DNA surface and/or groove binding nature of the complexes, which show efficient DNA cleavage activity on irradiation with UV-A light of 365 nm via a mechanistic pathway involving formation of singlet oxygen as the reactive species.
Abstract: Oxovanadium(IV) complexes [VO(salmet)(B)] (1−3) and [VO(saltrp)(B)] (4−6), where salmet and saltrp are N-salicylidene-l-methionate and N-salicylidene-l-tryptophanate, respectively, and B is a N,N-donor heterocyclic base (viz. 1,10-phenanthroline (phen, 1, 4), dipyrido[3,2-d:2‘,3‘-f]quinoxaline (dpq, 2, 5), and dipyrido[3,2-a:2‘,3‘-c]phenazine (dppz, 3, 6)) are prepared and characterized and their DNA binding and photoinduced DNA cleavage activity studied. Complexes 1, 2, and 4 are structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in the VO3N3 coordination geometry. The dianionic α-amino acid Schiff base acts as a tridentate O,N,O-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of bonding with a N-donor site trans to the oxo group. The complexes show a d−d band in the range of 680−710 nm in DMF with a shoulder near 840 nm. They exhibit an irreversible oxidative cyclic voltamm...
151 citations
TL;DR: In this paper, three dinuclear Zn(II) complexes [Zn(L)(μ1, 1-N3)Zn (L)(N3)]· 1.5H2O (1),[Zn[L]-(OCH3)(OH)C6H3CHN(CH2)2 N(CH3)2], which is the condensation product of o-vanillin and 2-dimethylaminoethylamine have been synthesized from a potentially tetradentate N2O2-donor Schiff base
149 citations
TL;DR: In this paper, eight chromium(III) complexes of tetradentate Schiff bases have been prepared in situ by condensing of a substituted salicylaldehyde compound with ethylenediamine.
149 citations
TL;DR: In this paper, three new Schiff bases, viz., N,N′-ethylen-bis (salicylidenimine) [S1], N, N′-isopropylien-bis [S2], and N-acetylacetone imine [S3] have been investigated as corrosion inhibitors for mild steel in 0.5 m H2SO4 using Tafel polarization and electrochemical impedance spectroscopy (EIS).
TL;DR: A new hydrazone ligand, HL, was prepared by the reaction of 7-chloro-4-hydrazinoquinoline with o-hydroxybenzaldehyde and it is clear that 8-OHqu behaves as monoprotic bidentate ligand in such mixed ligand complexes.
TL;DR: In this paper, the nano-pores of zeolite-Y have been characterized by metal analysis, spectroscopic (IR and electronic) studies, scanning electron micrographs, thermal analysis and X-ray diffraction patterns.
Abstract: Oxovanadium(IV), copper(II) and nickel(II) complexes of Schiff base derived from salicylaldehyde and o -aminobenzyl alcohol (H 2 sal-oaba) have been encapsulated in the nano-pores of zeolite-Y by flexible ligand method and characterised by metal analysis, spectroscopic (IR and electronic) studies, scanning electron micrographs, thermal analysis and X-ray diffraction patterns. The encapsulated complexes abbreviated here as [VO(sal-oaba)(H 2 O)]-Y, [Cu(sal-oaba)(H 2 O)]-Y and [Ni(sal-oaba)(H 2 O) 3 ]-Y catalyse the oxidation of styrene, cyclohexane and methyl phenyl sulfide using H 2 O 2 as oxidant in good yield. Styrene catalysed by [VO(sal-oaba)(H 2 O)]-Y, [Cu(sal-oaba)(H 2 O)]-Y under optimised reaction conditions gave five reaction products namely, styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol, benzoic acid and phenylacetaldehyde, while [Ni(sal-oaba)(H 2 O) 3 ]-Y gave benzaldehyde selectively. In the presence of tert -butylhydroperoxide all catalysts gave styrene oxide in major yield, though overall conversion has been found low (10–30%). The oxidation products of cyclohexane are cyclohexanone and cyclohexanol. A maximum of 93.2% conversion of methyl phenyl sulfide has been achieved with [VO(sal-oaba)(H 2 O)]-Y using H 2 O 2 as oxidant, where selectivity of sulfoxide was 96.9%. Other catalysts were inactive towards the oxidation of methyl phenyl sulfide while neat complex [VO(sal-oaba)] has been found to be equally active.
TL;DR: The active role of the metal in determining the NLO properties of the complexes was shown through an analysis of their UV-vis spectra, which revealed the presence of metal-to-ligand (in closed-shell complexes) and ligand- to-metal (in open- shell complexes) charge-transfer bands together with intra-ligands charge- transfer transitions.
Abstract: New unsymmetrical [N2O2] tetradentate Schiff base complexes of Ni(II), Cu(II), Zn(II), and VO(II) were synthesized by template condensation of the tetradentate precursor 1-phenylbutane-1,3-dione mono-S-methylisothiosemicarbazone with o-hydroxybenzaldehyde or its 5-phenylazo derivative. They were characterized by elemental analysis, IR, UV−vis, electron spin resonance, and NMR spectroscopy, mass spectrometry, and magnetic measurements. The crystal structures of five of them have been determined by X-ray diffraction using, in some cases, synchrotron radiation. These compounds are characterized by a large thermal stability; their decomposition temperatures range from 240 up to 310 °C. Complexes with the phenylazo substituent were found to possess a large second-order nonlinear optical (NLO) response, as determined both by measurements of solution-phase direct current electric-field-induced second harmonic generation and by theoretical time-dependent density functional theory (TDDFT) calculations. The molecul...
TL;DR: Magnetic characterization shows that the mu1,3-bridging azide ion proves to mainly transmit antiferromagnetic interaction between MnIII ions, but these three complexes exhibit various magnetic behaviors at low temperatures.
Abstract: By changing ancillary tetradentate Schiff base ligands (L), two new one-dimensional azide-bridged manganese(III) coordination complexes [MnIII(L)(μ1,3-N3)]n [L = 5-Fsalen (1), 5-OCH3 (2); salen = N,N‘-bis(salicylidene)-1,2-diaminoethane] as well as a mononuclear complex [MnIII(salophen)(N3)] (3) [salophen = N,N‘-bis(salicylidene)-o-phenylenediamine] have been successfully obtained All of them have been structurally and magnetically characterized In the structures of 1−3 each MnIII ion is in a distorted octahedral geometry with an obvious Jahn−Teller effect, where the tetradentate L ligands all bind in the equatorial mode, whereas in the axial direction, the N3- ion acts as an end-to-end bridge in 1 and 2 while a terminal group in 3 with a methanol molecule at the other end Magnetic characterization shows that the μ1,3-bridging azide ion proves to mainly transmit antiferromagnetic interaction between MnIII ions, but these three complexes exhibit various magnetic behaviors at low temperatures Noteworthi
TL;DR: In this paper, six transition metal complexes with Schiff base were synthesized and crystallographically characterized, and their urease inhibitory activities were evaluated, and three of them showed potent inhibitions against jack bean ureases.
TL;DR: The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats-Redfern equation and it was found that the thermal decomposing of the complexes follow second order kinetics.
TL;DR: In this paper, the authors used oxovanadium(IV) exchanged zeolite-Y with the Schiff base derived from salicylaldehyde and 2-aminomethylbenzimidazole (Hsal-ambmz) in refluxing methanol followed by aerial oxidation leads to the formation of encapsulated dioxovanadium (V) complex, [VO2(sal-ambermz)]-Y(1).
Abstract: Interaction of oxovanadium(IV) exchanged zeolite-Y with the Schiff base derived from salicylaldehyde and 2-aminomethylbenzimidazole (Hsal-ambmz) in refluxing methanol followed by aerial oxidation leads to the formation of encapsulated dioxovanadium(V) complex, [VO2(sal-ambmz)]-Y(1). Similar reaction with copper(II) exchanged zeolite-Y followed by its treatment with aqueous NaCl gave encapsulated copper(II) complex, [Cu(sal-ambmz)Cl]-Y(2). These encapsulated complexes have been characterized by spectroscopic studies, thermal analysis and scanning electron micrographs (SEMs) as well as X-ray diffraction patterns. 3D model structure generated for neat complex [VO2(sal-ambmz)] suggests that zeolite-Y can accommodate these complexes in its nano-cavity without any strain. The encapsulated materials are active catalysts for the oxidation of phenol, styrene and methyl phenyl sulfide using H2O2 as an oxidant. Under the optimised reaction conditions about 42% conversion of phenol was obtained with these catalysts where the selectivity of catechol varied in the order: 2 (73.9%) >1 (65.2%). With the conversion of 97.0% with 1 or 56.7% with 2, the oxidation of styrene gave styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde as major products. A maximum of 96.1% (with 1) conversion of methyl phenyl sulfide was observed in which the selectivity of major product methyl phenyl sulfoxide was found to be ca. 98%.
TL;DR: In this article, a new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt, copper, nickel and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements.
Abstract: A new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements. The spectral data indicated the Schiff base ligands (L1–L5) derived by condensation of salicylaldehyde with glycine, alanine, phenylalanine, methionine and cysteine, to act as tridentate towards divalent metal ions (cobalt, copper, nickel and zinc) via the azomethine-N, deprotonated carboxyl group of the respective amino acid and deprotonated oxygen atom of salicylaldehyde by a stoichiometric reaction of M:L (1:2) to form complexes of the type K2[M(L)2] [where M = Co(II), Cu(II), Ni(II) and Zn(II)]. The magnetic moments and electronic spectral data suggested that all complexes have an octahedral geometry. Elemental analyses and NMR spectral data of the ligands and their Zn (II) complexes agree with their proposed structures. The synthesized ligands, along with their metal complexes, were screened for their in-vitro antibacterial activity against four Gram-negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in-vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against one or more species as compared with the uncomplexed Schiff base ligands. The brine shrimp bioassay was also carried out to study their in-vitro cytotoxic properties. Only three compounds (2, 11 and 17) displayed potent cytotoxic activity as LD50 = 8.196 × 10−4, 7.315 × 10−4 and 5.599 × 10−4M/ml respectively, against Artemia salina. Copyright © 2007 John Wiley & Sons, Ltd.
TL;DR: The TGA curves show that the decomposition takes place in three steps for all complexes, and the antimicrobial activity properties of the ligands and their mono- and binuclear complexes have been studied against the bacteria and fungi.
TL;DR: The isotropic shifts of protons in the complexes proved to be suitable tools for following a spin transition in solution for the pure high-spin iron(II) complexes close to ideal Curie behavior.
Abstract: The 1H NMR spectra of a series of mono- and dinuclear pyridine complexes [FeL1(R1/R2)(py)2] and [Fe2L2(R1/R2)(py)4] have been investigated in a mixed toluene-d8/pyridine-d5 solution. The equatorial tetradentade Schiff base like ligands L1(R1/R2) and L2(R1/R2) with a N2O22- coordination sphere for each metal center have been obtained by condensation of a substituted malonodialdehyde (R1/R2 are Me/COOEt, Me/COMe, or OEt/COOEt) with o-phenylenediamine (L1(R1/R2)) or 1,2,4,5-tetraaminobenzene (L2(R1/R2)). The 1H NMR resonances were assigned by comparison of differently substituted complexes in combination with a line-width comparison. The 1H NMR shifts from 188 to 358 K show a strong influence of the spin state of the iron center. The behavior of the pure high-spin iron(II) complexes is close to ideal Curie behavior. Analysis of the resonance shifts of the spin-transition complexes can be used for determining the high-spin mole fraction of the complex in solution at different temperatures. Magnetic susceptibi...
TL;DR: Four platinum(II) complexes of Schiff bases derived from salicylaldehyde and 2-furaldehyde with o- and p-phenylenediamine were reported and characterized based on their elemental analyses, IR and UV-vis spectroscopy and thermal analyses (TGA) and activity data show that the platinum( II) complexes are more potent antimicrobials than the parent Schiff base ligands against one or more microorganisms.
TL;DR: In this article, three Schiff base ligands have been prepared by condensation of 3-methyl, 4-methyl and 5-methyl salicylaldehyde with 4,4′-diaminoazobenzene (1 ), respectively.
TL;DR: The antimicrobial activity of the obtained products, which indicate that in some cases metallation increase activity than the ligand, and the low molar conductance values suggest the non-electrolytic nature of these complexes.
TL;DR: Schiff base metal complexes are a class of compounds that have been studied extensively because of their attractive chemical and physical properties, and their wide-ranging applications in numerous scientific areas as discussed by the authors.
Abstract: Schiff base metal complexes are a class of compounds that have been studied extensively because of their attractive chemical and physical properties, and their wide-ranging applications in numerous scientific areas. Researchers have incorporated Schiff base complexes into polymers, generating new materials with useful mechanical, thermal, chemical, and electronic properties. This work comprehensively reviews the developments in macromolecules containing Schiff base metal complexes, emphasizing new synthetic strategies and characterization techniques that were used to prepare and study these polymers.
TL;DR: In this article, six transition metal complexes (M =Cu(II), Ni(II) and Mn(III)) of tridentate (H2L1, HL2) and/or bidentate(HL3, HL4) Schiff-base ligands, obtained from the condensation of salicylaldehyde with glycine, N-(2-aminoethyl)morpholine, 4-(2amino methyl)phenylic acid and 4-( 2-aminosulfamide, respectively, were synthesized and structurally determined by single-crystal X
TL;DR: A novel series of hydrogen-bonded, polycrystalline 1:1 complexes of Schiff base models of the cofactor pyridoxal-5'-phosphate with carboxylic acids that mimic the co Factor in a variety of enzyme active sites and an interesting coupling of the two "functional" OHN hydrogen bonds was observed.
Abstract: We present a novel series of hydrogen-bonded, polycrystalline 1:1 complexes of Schiff base models of the cofactor pyridoxal-5‘-phosphate (PLP) with carboxylic acids that mimic the cofactor in a variety of enzyme active sites. These systems contain an intramolecular OHN hydrogen bond characterized by a fast proton tautomerism as well as a strong intermolecular OHN hydrogen bond between the pyridine ring of the cofactor and the carboxylic acid. In particular, the aldenamine and aldimine Schiff bases N-(pyridoxylidene)tolylamine and N-(pyridoxylidene)methylamine, as well as their adducts, were synthesized and studied using 15N CP and 1H NMR techniques under static and/or MAS conditions. The geometries of the hydrogen bonds were obtained from X-ray structures, 1H and 15N chemical shift correlations, secondary H/D isotope effects on the 15N chemical shifts, or directly by measuring the dipolar 2H−15N couplings of static samples of the deuterated compounds. An interesting coupling of the two “functional” OHN hy...
TL;DR: Schiff base complexes of cobalt, nickel, copper, and zinc with 3-ethoxysalicyliden-p-aminoacetophenoneoxime (HL) were prepared and characterized on the basis of elemental analyses, IR, 1H- and 13C-NMR, electronic spectra, magnetic susceptibility measurements, molar conductivity and thermogravimetric analyses as discussed by the authors.
Abstract: Schiff-base complexes of cobalt(II), nickel(II), copper(II) and, zinc(II) with 3-ethoxysalicyliden-p-aminoacetophenoneoxime (HL) were prepared and characterized on the basis of elemental analyses, IR, 1H- and 13C-NMR, electronic spectra, magnetic susceptibility measurements, molar conductivity and thermogravimetric analyses (TGA). A tetrahedral geometry has been assigned to the complexes.
TL;DR: The effect of three Schiff base compounds with increasing number of coordination sites, namely, 2-{(E)-[(2-hydroxyethyl)imino]methyl} phenol (I), 2-E)-({2]-( 2-hydroxyl methyl)amino]ethylimino)methyl]phenol (II) and 2,2′-{iminobis[ethane-2,1-diylnitrilo(E)methylylidene]}diphenol (III) have been investigated at 298
TL;DR: In this article, three di-Schiff-base ligands, N,N′-bis(salicylidene)-1,3-propanediamine (H2Salpn), N, N′-bi-bis-1, 3-pentanediamine, H2Salpen, and H 2Salen, react with Ni(SCN)2· 4H2O in 2:3 molar ratios to form the complexes; mononuclear [Ni(HSalpn)(NCS), trinuclear [{Ni