Showing papers on "Schiff base published in 2000"
TL;DR: Considering the magnetic and structural data obtained for various dinuclear (Cu-Gd) complexes leads to a correlation between the magnitude of the magnetic interaction and the exponential of the dihedral angle between the two halves of the CuO2Gd bridging core.
Abstract: The monometallic precursor L1Cu (L1H2 standing for 1,3-bis((3-methoxysalicylidene)amino)-2,2'-dimethylpropane) reacts with GdC13 x 6H2O to afford a dinuclear complex which crystallizes in the orthorhombic space group Pca2(1) (No. 29) in a cell having the dimensions a = 9.0246(11) A, b = 16.5198(14) A, c = 20.286(2) A, and Z = 4. Analysis of the structural data shows that it may be formulated as [L1CuCl2Gd(H2O)4]Cl x 2H2O. The cationic dinuclear unit possesses a CuO2Gd bridging core which is almost planar. The complex displays a ferromagnetic interaction (10.1 cm(-1) which is the largest yet reported for a structurally characterized dinuclear (Cu-Gd) complex. Lower magnetic interactions are observed for neutral L1CuGdX3 x H2O complexes (X = N3C2, CF3COO). Consideration of the magnetic and structural data obtained for various dinuclear (Cu-Gd) complexes leads to a correlation between the magnitude of the magnetic interaction and the exponential of the dihedral angle between the two halves of the CuO2Gd bridging core.
286 citations
TL;DR: In this paper, rare earth-containing metallomesogens with 4-alkoxy-N-alkyl-2-hydroxybenzaldimine ligands are reported and the stoichiometry of the complexes is [Ln(LH)(3)(NO3)(3)], where Ln is the trivalent rare earth ion;(Y, La, and Pr to Lu, except Pm) and LH is the Schiff base.
Abstract: Rare-earth-containing metallomesogens with 4-alkoxy-N-alkyl-2-hydroxybenzaldimine ligands are reported. The stoichiometry of the complexes is [Ln(LH)(3)(NO3)(3)], where Ln is the trivalent rare-earth ion;(Y, La, and Pr to Lu, except Pm) and LH is the Schiff base. The Schiff base ligands are in the zwitterionic form and coordinate through the phenolic oxygen only. The three nitrate groups coordinate in a bidentate fashion. The X-ray single-crystal structures of the nonmesogenic homologous complexes [Ln(LH)(3)(NO3)(3)]where Ln = Nd(III), Tb(III), and Dy(III) and LH = CH3OC6H3(2-OH)CH=NC4H9, are described. Although the Schiff base Ligands do not exhibit a mesophase, the metal complexes do (SmA phase). The mesogenic rare-earth complexes were studied by NMR, IR, EPR, magnetic susceptibility measurements, X-ray diffraction,and molecular modeling. The metal complexes in the mesophase have a very large magnetic anisotropy, so that these magnetic liquid crystals can easily be aligned by an external magnetic field.
242 citations
TL;DR: The experimental results show that the chromium(III) complexes bind to DNA by non-intercalative mode and major groove binding is the preferred mode of interaction for these Schiff base complexes of chromium (III).
217 citations
TL;DR: In this article, the atomic structures of the BR state and M photo-intermediate of the E204Q mutant were mined to 1.7 and 1.8 Aresolution, respectively, to understand how isomerization of the retinal drives uni- directional transmembrane ion transport in bacteriorhodopsin.
207 citations
186 citations
TL;DR: Gel electrophoresis of plasmid DNA in the presence of the Cr(III) complex shows that the complex brings about nicking of the DNA.
155 citations
TL;DR: In this paper, a model of the early part of the photocycle of bacteriorhodopsin was presented, based on the ground state and M intermediate structures, including a novel model which proposes that bacterion pumps hydroxide (OH(-)) ions from the extracellular to the cytoplasmic side.
137 citations
TL;DR: Four new coordination polymers are prepared by solution reactions and fully characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction, generating two new types of building blocks that are distinctly different from the common "T-shaped" building block generated from the same (MN3O4) coordination environment reported previously.
Abstract: The coordination chemistry of the long conjugated bidentate Schiff-base ligands 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (L1) and 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene (L2) with cadmium and cobalt nitrate hydrates is investigated. Four new coordination polymers are prepared by solution reactions and fully characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. [Cd(NO3)2(L1)1.5·0.5(L1)]n (1; monoclinic, P21/c; a = 7.7729(16) A, b = 19.049(4) A, c = 17.865(4) A, β = 93.13(3)°, Z = 4) is obtained by combination of L1 with Cd(NO3)2·4H2O in a benzene/methanol or THF/methanol mixed-solvent system. The structure features two-dimensional brick wall sheets that are cross-linked by weak noncovalent π−π interactions (alternating face-to-face stacking of coordinated and uncoordinated L1 molecules) to generate a novel three-dimensional network. [Co(NO3)2(L1)1.5·H2O]n (2; orthorhombic, Ccca; a = 19.031(4) A, b = 33.627(7) A, c = 14.299(3) A, Z...
135 citations
TL;DR: In this article, the first copper complexes from benzilbisthiosemicarbazone (L1H6) and from the cyclic 6-methoxi-1,6-diphenyl-4-thio-3,4,9,10-tetraphenyl, 1,2,5,6,8,11,11-hexaazacyclododeca-7,12-dithione-3.4, 9,10,10-, 10,10)-tetraene (
130 citations
TL;DR: Several new complexes of a tridentate ONS Schiff base derived from the condensation of S-benzyldithiocarbazate with salicylaldehyde have been characterised by elemental analyses, molar conductivity measurements and by i.r. and electronic spectra as discussed by the authors.
Abstract: Several new complexes of a tridentate ONS Schiff base derived from the condensation of S-benzyldithiocarbazate with salicylaldehyde have been characterised by elemental analyses, molar conductivity measurements and by i.r. and electronic spectra. The Schiff base (HONSH) behaves as a dinegatively charged ligand coordinating through the thiolo sulphur, the azomethine nitrogen and the hydroxyl oxygen. It forms mono-ligand complexes: [M(ONS)X], [M=NiII, CuII, CrIII, SbIII, ZnII, ZrIV or UVI with X = H2O, Cl]. The ligand produced a bis-chelated complex of composition [Th(ONS)2] with ThIV. Square-planar structures are proposed for the NiII and CuII complexes. Antimicrobial tests indicate that the Schiff base and five of the metal complexes of CuII, NiII, UVI, ZnII and SbIII are strongly active against bacteria. NiII and SbIII complexes were the most effective against Pseudomonas aeruginosa (gram negative), while the CuII complex proved to be best against Bacillus cereus (gram positive bacteria). Antifungal activities were also noted with the Schiff base and the UVI complex. These compounds showed positive results against Candida albicans fungi, however, none of them were effective against Aspergillus ochraceous fungi. The Schiff base and its zinc and antimony complexes are strongly active against leukemic cells (CD50 = 2.3–4.3 μg cm−3) while the copper, uranium and thorium complexes are moderately active (CD50 = 6.9–9.5 μg cm−3). The nickel, zirconium and chromium complexes were found to be inactive.
122 citations
TL;DR: The results from the present study suggest the importance of the bulky residue of Trp-86 in the isomerization process, in both ground and excited states of the chromophore, and in fine-tuning of the pK(a) of the retinal protonated Schiff base in bacteriorhodopsin.
TL;DR: Two new Schiff bases (1a)-(2a) derived from 2,3-diaminopyridine (DAPY) with pyrrole-2-carboxaldehyde (Pyrr) and 2-hydroxy-1-naphthaldehyde (NaphH) were synthesized by a combination of elemental analyses, magnetic susceptibility measurements, IR and NMR spectra as discussed by the authors.
Abstract: Two new Schiff bases (1a)-(2a) derived from 2,3-diaminopyridine (DAPY) with pyrrole-2-carboxaldehyde (Pyrr) and 2-hydroxy-1-naphthaldehyde (NaphH), and new copper(II), iron(III), nickel(II), ruthenium(II) and zinc(II) complexes (1b)-(1e), (2b)-(2f) and (3b)-(3d) derived from these two new Schiff bases, and the bis-condensed Schiff base of 2,3-diaminopyridine and salicylaldehyde (SalH) were synthesized. They were characterized by a combination of elemental analyses, magnetic susceptibility measurements, IR and NMR spectra. The two new Schiff bases and some of the metal complexes show antibacterial activity. The iron(III) and Ru(II) complexes display catalytic activity in the oxidation of alcohols in the presence of N-methylmorpholine-N-oxide as co-oxidant.
TL;DR: A tridentate Schiff base ligand (LH) has been synthesized from 2-hydroxyacetophenone and 2-dimethylaminoethylamine as discussed by the authors, which forms the neutral complexes [Co(L)(N3){o-(CH3CO)C6H4O}] (1) and [Co[L)(SCN]·1/2H2O (2) in presence of equivalent amount of Co(II) acetate, and sodium azide for 1 and sodium thiocyanate for 2).
TL;DR: In this paper, a chiral and optically active trinucleating 3 + 3 condensed hexaaza triphenolic Schiff base macrocycle H3L1I with transition metal ions (Zn, Cu, Ni, Co, Fe and Mn) in 1∶3 molar ratio in methanol under reflux conditions resulted in complexes.
Abstract: Reaction of a new chiral and optically active trinucleating 3 + 3 condensed hexaaza triphenolic Schiff base macrocycle H3L1I with transition metal ions (Zn, Cu, Ni, Co, Fe and Mn) in 1∶3 molar ratio in methanol under reflux conditions resulted in complexes. Analytical data reveal the formation of 2 + 2 condensed dinuclear macrocyclic Schiff base complexes, instead of the expected trinuclear macrocyclic complexes. X-Ray crystallographic studies on three of these complexes established their dinuclearity. On the other hand, reaction of I with metal ions (Zn, Cu, Fe and Mn) in 1∶3 molar ratio in methanol at room temperature for 2 h resulted in one-side condensed mononuclear acyclic complexes. This is confirmed by the crystal structure of the manganese complex. Second-order non-linear properties are discussed.
TL;DR: In this paper, three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands were studied by cyclic voltammetry and chronoamperometry in N,N′-dimethylformamide and (CH3)2SO.
TL;DR: A series of substituted ferrocenyl compounds where one of the cyclopentadienyl rings is linked to an aromatic Schiff base, have been synthesized and analyzed for their second-order nonlinearity as discussed by the authors.
TL;DR: The Schiff base ligand (1) and its Zn(II) complex (2) have been synthesized and their crystal structures have been determined as mentioned in this paper, and they have been shown to be in tautomeric equilibria (phenol-imine, O-H⋯N keto-amine, O ⋯H-N forms), as supported by 1H NMR and UV visible data.
TL;DR: In this paper, the synthesis and characterisation of four monomeric cis-dioxomolybdenum(VI) complexes involving Schiff base ligands is described, which act as inhibitors in the oxidation of aldehydes by oxygen.
TL;DR: In this article, the authors showed that the two ZnII centers have a distorted tetrahedral coordination sphere with two-wrapped ligands and showed that these unprecedented helical motifs in the solid state and solution seem to be induced by the geometrical preference for octahedral coordination mode of the zinc ion and the interligand π-stacking interactions between the spacer groups of L16 and L17.
Abstract: Zinc(II)-assisted self-assembly of a new bis-N,O-bidentate Schiff base ligand, (N-salicylidene-4,4′-diaminodiphenyl)methane (L16) with two chelating sites linked by a spacer group (-C6H4CH2C6H4-), afforded in high yield the double-helical dinuclear complex (L16 : ZnII = 2∶2). Single-crystal X-ray analyses demonstrated clearly that the two ZnII centers have a distorted tetrahedral (Td) coordination sphere with two-wrapped ligands. The analogous Schiff base, bis[4-(2-pyridylmethyleneaminophenyl]methane (L17) was also designed to self-assemble in the presence of metal ions, leading to a triple-helical dinuclear (L17∶ZnII = 3∶2) supramolecular motif. Each zinc ion has six-coordinate octahedral geometry with six nitrogens from three ligands. These unprecedented helical motifs in the solid state and solution seem to be induced by the geometrical preference for octahedral or tetrahedral coordination mode of the ZnII ion and the interligand π-stacking interactions between the spacer groups of L16 and L17. Electrospray mass spectrometry proved a very useful characterisational tool in detecting the distribution of supramolecular species in solution. Use of a N,N′-bis(2-pyridylmethylene)-1,4-diaminobenzene (L35) with a rigid phenylene spacer in its center resulted in the one-dimensional zigzag polymeric structure ((L35∶ZnII)∞ = (1∶1)∞) where the multiple π-stacking interactions operate between the aromatic rings of linking ligands. Each zinc ion is octahedrally coordinated by two N,N-bidentate arms of two different ligands and two cis oxygens from N,N-dimethylformamide as coordinating solvent.
TL;DR: A new switching molecular array that interconverts reversibly either by thermal means (valence tautomerism) or by a reversible oxidation process has been established.
Abstract: A new switching molecular array that interconverts reversibly either by thermal means (valence tautomerism) or by a reversible oxidation process has been established. Such an array is based on the rich electrochemical behavior of the cobalt Schiff base complex 2. The Schiff base ligand can exist in different oxidation forms that interconvert reversibly by means of redox processes and that can be used to obtain stable coordination complexes.
TL;DR: In this article, a second-order polynomial relationship of the form x/([A 0] − x)[A0] = k 2t + k2t2.
TL;DR: Two tridentate Schiff bases having ONS and NNS donor sequences were prepared by condensing S-benzyldithiocarbazate (NH2NHCSSCH2Ph) with pyridine-2-carboxaldehyde and salicylaldehyde, respectively.
Abstract: Two tridentate Schiff bases having ONS and NNS donor sequences were prepared by condensing S-benzyldithiocarbazate (NH2NHCSSCH2Ph) (SBDTC) with pyridine-2-carboxaldehyde and salicylaldehyde, respectively. Complexes of these ligands with NiII, ZnII, CrIII, CoII, CuII, and SnII were studied and characterized by elemental analyses and various physico-chemical techniques. NiII, CuII, ZnII and SnII complexes were four-coordinate while the CrIII, SrIII and CoIII complexes were six-coordinate. The ONS Schiff base was moderately active against leukemia, while its zinc, antimony and cobalt complexes were strongly active against leukemic cells with DC50 = 0.35–5.00.
TL;DR: In the presence of titanium tetraisopropoxide, tridentate salen ligands derived from cis-1-amino-2-indanol have been utilized in the asymmetric addition of trimethylsilylcyanide to benzaldehyde, which gave the cyanohydrins in up to 85% ee as discussed by the authors.
TL;DR: In this article, the Ni(II) complex of the Schiff base of glycine with o-[N-α-picolylamino]acetophenone, as a nucleophilic glycine equivalent, and N-(trans-enoyl)oxazolidin-2-ones, as derivatives of an α,β-unsaturated carboxylic acid, were found to be the substrates of choice featuring geometric/conformational homogeneity and high reactivity.
Abstract: Via the rational design of a single-preferred transition state, stabilized by electron donor−acceptor-type attractive interactions, structural and geometric requirements for the corresponding starting compounds have been determined. The Ni(II) complex of the Schiff base of glycine with o-[N-α-picolylamino]acetophenone, as a nucleophilic glycine equivalent, and N-(trans-enoyl)oxazolidin-2-ones, as derivatives of an α,β-unsaturated carboxylic acid, were found to be the substrates of choice featuring geometric/conformational homogeneity and high reactivity. The corresponding Michael addition reactions were found to proceed at room temperature in the presence of catalytic amounts of DBU to afford quantitatively the addition products with virtually complete diastereoselectivity. Acidic decomposition of the products followed by treatment of the reaction mixture with NH4OH gave rise to the diastereomerically pure 3-substituted pyroglutamic acids.
TL;DR: In this paper, an octahedral geometry around the metal with the Schiff base in the equatorial plane acting as tetradentate and solvent molecules in the axial positions was shown.
TL;DR: In this paper, the copper complex with Schiff bases obtained by condensation of 5-phenylazo salicylaldehyde with di-or tri-amines has been synthesized and characterized by their infrared spectra and elemental analysis.
TL;DR: A Ni(II) complex of the Schiff base of glycine with o-[N-α-picolylamino]benzophenone or -acetophenone as a nucleophilic glycine equivalent, and N-trans-enoyloxazolidinones, as a derivative of an α,β-unsaturated carboxylic acid, were found to be the substrates of choice in the corresponding Michael addition reactions.
TL;DR: In this paper, phase-transfer catalysis of the rationally designed C2-symmetric chiral quaternary ammonium salts was used for asymmetric synthesis of l-Dopa and related amino acid esters.
TL;DR: In this paper, the Schiff base, 4-(2-pyrrolylmethylideneamino)antipyrine (HPAP), and its copper(II) complexes were synthesized and characterized by elemental analysis and by physical and spectral methods such as i.m., u.m.n.r. and e.s.
Abstract: The Schiff base, 4-(2-pyrrolylmethylideneamino)antipyrine (HPAP), (1), and its copper(II) complexes were synthesized and characterized by elemental analysis and by physical and spectral methods such as i.r., u.v.–vis., 1H-n.m.r., 13C-n.m.r. and e.s.r. as well as by molar conductance and magnetic moment determinations. Both the bis-ligand, [(HPAP)2Cu]X2
(4, 5), [(PAP)2Cu] (6), and the dimer, [(PAP)Cu]2X2
(2, 3), complexes were isolated. In these complexes, the Schiff base acts as a bidentate or tridentate neutral or monobasic ligand. Interaction of the isolated [(PAP)Cu]2Cl2
(2), with strong coordinating organic bases was studied and the resultant adducts, [(PAP)CuLs]Cl; Ls = pyridine (7), α-picoline (8), β-picoline (9), γ-picoline (10) or n-propylamine (11), were isolated and characterized. Biological activity screening was studied and an activity correlation coefficients matrix was constructed for HPAP and the copper(II) complexes against gram-positive, gram-negative and fungi species. The copper content, structure of the complex as well as the degree of exposure of the metal center control the biological activity of the isolated complexes.
TL;DR: In this paper, a diversity of reaction products have been found in the reactions of two related unsymmetrical Schiff base dinucleating ligands, HL1 and HL2, derived from 3-chloromethyl-5-methylsalicylaldehyde 1, with copper(II) and nickel (II) salts.
Abstract: A diversity of reaction products have been found in the reactions of two related unsymmetrical Schiff base dinucleating ligands, HL1 and HL2, derived from 3-chloromethyl-5-methylsalicylaldehyde 1, with copper(II) and nickel(II) salts. The ligands remain intact in the copper(II) complexes to give the homodinuclear complexes [Cu2L1Br3] 2 and [Cu2L2(OH)(ClO4)]ClO43, the crystal structures of which have been solved. The reactions of HL1 and HL2 with nickel perchlorate led to hydrolysis of the imine bond. With HL1 the homodinuclear complex [NiLA(OH2)]2[ClO4]2·4H2O was formed and with HL2 hydrolysis was followed by elimination of C2H4 from the terminal NEt2 of the iminic side arm to leave an NHEt group and the dinuclear complex [NiLC(OH2)]2[ClO4]2·3CH3OH. The crystal structures of the two nickel complexes are also reported.