Structures of o-hydroxy Schiff-base copper(II) complexes derived from p-benzylamines

Nine copper(II) complexes of o-hydroxy Schiff bases derived from benzylamine, p-methoxybenzylamine, p-nitrobenzylamine, salicylaldehyde, 2-hydroxy-1-naphthalenecarboxaldehyde, and 3-hydroxy-2-naphthalenecarboxaldehyde were synthesized and characterized by chemical analysis, mass spectrometry, UV-Vis, infrared and electron paramagnetic resonance (EPR) spectroscopy, and seven X-ray crystal structures. The X-ray diffraction studies of these compounds showed that the geometry around the copper is square planar in six of the seven complexes. EPR studies of all the complexes in DMF solution at 77 K suggest that their geometries in solution are square planar as well.     

Nickel(II) complexes of fully and partially condensed Schiff-base ligands derived from tris(3–aminopropyl)amine and acetylpyridine

In the presence of nickel(II), 2–acetylpyridine condenses with tris(3–aminopropyl)amine in absolute MeOH to give the fully condensed Schiff-base complex [Ni(tptpy3)]2+. Although the ligand is potentially heptadentate, the metal atom is effectively six-coordinate, interaction with the bridgehead nitrogen being rather weak. However, when aqueous MeOH is used, the condensation is limited to a single step, and a complex of the pentadentate mono-Schiff base adduct is formed, [Ni(tptpy)(H2O)]2+, which was characterised by X-ray diffraction of its PF6– salt.     

Biologically active complexes of nickel(II), copper(II) and zinc(II) with Schiff-base ligand derived from the reaction of 2-aminopyridine and pyrrol-2-carboxaldehyde--their synthesis and characterisation.

A new Schiff-base ligand N-(2'-pyrrylmethylidene)2-aminopyrimidine derived from the reaction of 2-amino pyrimidine and pyrrol-2-carboxaldehyde and its nickel(II), copper(II) and zinc(II) complexes have been synthesised and characterised on the basis of elemental analysis, molar conductance, infrared, electronic and proton nuclear magnetic resonance (1H-NMR) and magnetic susceptibility data. The ligand and its complexes when screened for antibacterial activity against bacterial species such as, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. In all cases, the activity substantially increased on complexation with metals.     

Nickel(II) and copper(II) complexes of macrocyclic and acyclic Schiff-base ligands derived from new asymmetrical tripodal tetraamines and 2,6-diacetylpyridine

The asymmetrical tripodal 4,2,2-tetraamine N{(CH₂)₄NH₂}{(CH₂)₂NH₂}₂ bee, 3,2,2-tetraamine N{(CH₂)₃NH₂} {(CH₂)₂NH₂}₂ pee, and 3,3,2-tetraamine N{(CH₂)₃NH₂}₂{(CH₂)₂NH₂} ppe ligands have been prepared. In the presence of Cu^II or Ni^II ions, these ligands condense with 2,6-diacetylpyridine. In some cases, cyclization occurs and new isomers of CR-type with a pendant primary amine group are formed. In the other cases ring closure does not occur and coordinated acyclic hexadentate ligands have been isolated. At room temperature and in absolute methanol the latter acyclic complexes are usually the only products. I.r., u.v.–vis., reflectance spectra and magnetic moments for the complexes were recorded.     

Neutral pyridylmethylamide ligands and their mononuclear copper(II) complexes

Mononuclear copper(II) complexes of a family of pyridylmethylamide ligands HL, HL^Me, HL^Ph, HL^Me3 and HL^Ph3, [HL = N-(2-pyridylmethyl)acetamide; HL^Me = N-(2-pyridylmethyl)propionamide; HL^Ph = 2-phenyl-N-(2-pyridylmethyl)acetamide; HL^Me3 = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HL^Ph3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide], were synthesized and characterized. The reaction of copper(II) salts with the pyridylmethylamide ligands yields complexes [Cu(HL)₂(OTf)₂] (1), [Cu(HL^Me)₂](ClO₄)₂ (2), [Cu(HL)₂Cl]₂[CuCl₄] (3), [Cu(HL^Me3)₂(THF)](OTf)₂ (4), [Cu(HL^Me3)₂(H₂O)](ClO₄)₂ (5a and 5b), [Cu(HL^Ph3)₂(H₂O)](ClO₄)₂ (6), [Cu(HL)(2,2′-bipy)(H₂O)](ClO₄)₂ (7), and [Cu(HL^Ph)(2,2′-bipy)(H₂O)](ClO₄)₂ (8). All complexes were fully characterized, and the X-ray structures vary from four-coordinate square-planar, to five-coordinate square-pyramidal or trigonal-bipyramidal. The neutral ligands coordinate via the pyridyl N atom and carbonyl O atom in a bidentate fashion. The spectroscopic properties are typical of mononuclear copper(II) species with similar ligand sets, and are consistent their X-ray structures.     

Nickel(II) and copper(II) complexes with an asymmetric bidentate Schiff-base ligand derived from furfurylamine

New asymmetric bidentate Schiff-base ligand (5-bromo-2-hydroxybenzyl-2-furylmethyl)imine, (HL), and its nickel(II) and copper(II) complexes with the general composition ML₂ [M = Ni (1) and Cu (2)], were prepared. The ligand and the metal complexes were characterized by elemental analysis, FT-IR, and UV–Vis spectroscopy. In addition, ¹H-NMR and X-ray powder diffraction (XRD) were employed for characterization of ligand and metal complexes, respectively. Thermogravimetric analysis (TGA) of the ligand and metal complexes revealed the thermal stability and decomposition pattern of the species.     

Trinuclear copper(II) complexes derived from Schiff-base ligands based on a 6-amino-6-deoxyglucopyranoside: structural and magnetic characterization

The trinuclear copper(II) complexes ([CuL1)(mu-ac)Cu(mu-ac)CuL1) (1) and ([CuL2)(mu-ac)Cu(mu-ac)CuL2) (2) of the tridentate aminosaccharide-derived Schiff-base ligands H2L1 [6-N-(salicylidene)amino-6-deoxy-1,2,3-tri-O-methyl-alpha-D-glucopyranoside] and H2L2 [6-N-(3,5-di-tert-butylsalicylidene)amino-6-deoxy-1,2,3-tri-O-methyl-alpha-D-glucopyranoside] were synthesized and structurally characterized. The trinuclear complex units can be described as two terminal copper-ligand moieties bridged by a central copper acetate moiety, with the Cu centers arranged in a triangular fashion. IR and UV/vis spectroscopic studies strongly indicate that the trinuclear structure is maintained in a methanolic solution. The temperature dependence of the magnetic susceptibility of both complexes shows a moderate antiferromagnetic coupling and can be well interpreted by applying a symmetric Cua-Cub-Cua' model with linear spin topology. The fit of the magnetic data affords coupling constants J of -34 and -24 cm(-1) for 1 and 2, respectively [H = -J(SaSb + SbSa')]. For mu-alkoxo-mu-acetato-bridged copper(II) complexes with a large dihedral angle between the adjacent coordination planes, as found in 1 and 2, such an antiferromagnetic coupling is unusual. However, density functional theory calculations of 2 using BP86, B3LYP*, and B3LYP density functionals confirmed a symmetric doublet ground state.     

Catalytic asymmetric Henry reaction using copper(II) chiral tridentate Schiff-base complexes and their polymer-supported complexes

A series of chiral tridentate Schiff-base ligands and their polymer-supported ligands were conveniently prepared and introduced as copper(II) chiral complexes for the asymmetric Henry reaction. The structures of these ligands have been characterized by IR, ¹H NMR, ¹³C NMR and MS. The experimental results showed that the corresponding β-nitro alcohols were obtained in moderate to high yields (up to 98%) with up to 98% ee under mild conditions. The complex catalyst forming from copper(II) polymer-supported ligands could be recycled by a simple filtration and reused 6 times at least with similar good catalytic effect (about 94% yield and 90% ee).     

Syntheses and characterization of copper(II) complexes with Schiff-base ligands derived from ethylenediamine,diphenylethylenediamine and nitro,bromo and methoxy salicylaldehyde

Copper(II) quelates with Schiff bases derived from ethylenediamine, 1R,2R-(+)- or 1S,2S-(−)-1,2-diphenylethylenediamine and 5-X-salicylaldehyde (X=OCH₃, H, Br, NO₂) have been synthesized and characterized by elemental analysis and IR and UV-visible spectroscopies. The ORD and CD spectra of the chiral ligands and their related complexes have also been measured. The absorption and CD spectra of the metal complexes in the visible region are consistent with near square planar coordination geometries. Trends in absorption spectra over the series of complexes can be correlated with electronic effects of the substituents at position 5 of the salicylaldehyde. The sign patterns of the CD spectra in both UV and visible regions suggest the prevalence of δ and λ conformations for the chelate ring in the complexes of Schiff bases derived, respectively, from R,R- and S,S-diamines. Specific features of the CD spectra of the metal complexes are discussed in terms of the exciton chirality method.     

Copper(II) complexes of peptide-group-containing amino acids bis(N-acetyl-l-alaninate)copper(II) complexes and their amine adducts

The bis(N-acetyl-l-alanine)copper(II) monohydrate for which magnetic data and electronic and IR spectra suggest a copper-acetate monohydrate type structure, was prepared. Substitution of the water molecule by some amines was made to investigate their effect on the amino acid coordination and on the geometry around the copper ion. For the adducts of monodentate heterocyclic amines such as N-methylpiperazine, piperidine, morpholine, pyridine, 3- and 4-methylpyridine (CuL₂B₂) and of bidentate amines such as piperazine, ethylenediamine, 2,2′- and 4,4′-bipyridine (CuL₂B) in the solid state or chloroform solution, magnetism, electronic spectra (one d-d band in the 14,500–18,700 cm⁻¹ spectral region, depending on the bascity or steric interference of the amines) and IR spectra suggest a square-planar or strongly distorted tetragonal arrangement around the copper ion with a CuN₂O₂ or CuN₄ chromophore. For the Cu(N-acll-ala)₂B₂ (B  N-methylpiperazine, piperidine and morpholine) adducts in chloroform solution in the presence of excess amine, electronic (two d-d bands) and IR spectra indicate tetragonal arrangement around the copper ion with CuN₄O₂ chromophore, while for the Cu(N-ac-l-ala)₂ · o-phen adduct in the solid state and chloroform solution they suggest the presence of 6-coordinate cis-octahedral species, with CuN₂O₄ chromophores. In all the adducts studied the IR spectra exclude any interaction between the peptide group and the metal ion.     

Highly enantioselective nitroaldol reactions catalyzed by copper(II) complexes derived from substituted 2-(pyridin-2-yl)imidazolidin-4-one ligands

Ten optically pure substituted 2-(pyridin-2-yl)imidazolidin-4-ones, 1a-d, 2a-4a, and 2b-4b, were prepared and characterized. The absolute configurations of individual ligands were determined by X-ray analysis or NOESY experiments. The Cu(II) complexes of the respective ligands were studied as enantioselective catalysts of the nitroaldol (Henry) reaction of aldehydes with nitromethane, giving the corresponding substituted 2-nitroalkanols. In the case of an anti arrangement of the imidazolidin-4-one ring, the obtained result was 91-96% ee, whereas in the case of syn arrangement, a significant drop to 25-27% ee was observed.     

Dinuclear Schiff-base copper(II) complexes with various bridging groups

Three new centrosymmetric dinuclear copper(II) complexes, [Cu₂Cl₂(L¹)₂] (1), [Cu₂(μ _1,3-NCS)₂(L²)₂] (2), and [Cu₂(μ _1,1-N₃)₂(L³)₂] (3), where L¹, L², and L³ are the deprotonated forms of the Schiff bases 1-[(2-propylaminoethylimino)methyl]naphthalen-2-ol (HL¹), 1-[(3-methylaminopropylimino)methyl]naphthalen-2-ol (HL²), and 2-[(2-isopropylaminoethylimino)methyl]phenol (HL³), respectively, have been prepared and characterized by elemental analysis, IR spectra, and single-crystal X-ray crystallography. Each Cu is coordinated by the three donors of the Schiff bases and by two bridging groups, forming a square-pyramidal geometry.     

Crystal structure and biological activities of water-soluble nickel(II) and copper(II) complexes of a Schiff-base derived from paeonol

Water-soluble Ni(II) and Cu(II) complexes of a flexible Schiff-base ligand have been synthesized, and the Ni(II) complex was characterized by X-ray crystallography. The interactions of the two complexes with calf thymus DNA were investigated by spectroscopic and viscosity measurements in water. The results suggest that the two complexes bind to DNA within the groove. Antioxidant experiments against OH^• and O₂^−• show that these two complexes have excellent ability to scavenge O₂^−•, and the Cu(II) complex exhibits better activity than the Ni(II) complex.     

Compartmental Schiff-base ligands as selective double-loaded extractants for copper(II)

The Robson compartmental macrocyclic ligand derived from the condensation of derivatives of 2,6-diformylphenol and diamines has been prepared for the first time in its free ligand form; competitive three-phase transport and two-phase extraction studies confirm high double-loaded selectivity for the binding and delivery of Cu(II).     

Magnetostructural studies on ferromagnetically coupled copper(II) cubanes of Schiff-base ligands

Three cubane copper(II) clusters, namely [Cu(4)(HL')4] (1), [Cu4L2(OH)2] (2), and [Cu4L2(OMe)2] (3), of two pentadentate Schiff-base ligands N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine) (H3L') and N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H3L), are prepared, structurally characterized by X-ray crystallography, and their variable-temperature magnetic properties studied. Complex 1 has a metal-to-ligand stoichiometry of 1:1 and it crystallizes in the cubic space group P43n with a structure that consists of a tetranuclear core with metal centers linked by a mu(3)-alkoxo oxygen atom to form a cubic arrangement of the metal and oxygen atoms. Each ligand displays a tridentate binding mode which means that a total of eight pendant binding sites remain per cubane molecule. Complexes [Cu4L2(OH)2] (2) and [Cu4L2(OMe)2] (3) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self-assembly of two {Cu2L}+ units. The variable-temperature magnetic susceptibility data in the range 300-18 K show ferromagnetic exchange interactions in the complexes. Along with the ferromagnetic exchange pathway, there is also a weak antiferromagnetic exchange between the copper centers. The theoretical fitting of the magnetic data gives the following parameters: J1 = 38.5 and J2 = -18 cm(-1) for 1 with a triplet (S = 1) ground state and quintet (S = 2) lowest excited state; J1 = 14.7 and J2 = -18.4 cm(-1) for 2 with a triplet ground state and singlet (S = 0) lowest excited state; and J1 = 33.3 and J2 = -15.6 cm(-1) for 3 with a triplet ground state and quintet lowest excited state, where J1 and J2 are two different exchange pathways in the cubane {Cu4O4} core. The crystal structures of 2 * 6 H2O and 3 * 2 H2O * THF show the presence of channels containing the lattice solvent molecules.     

New acyclic Schiff-base copper(II) complexes and their electrochemical,catalytic, and antimicrobial studies

A new series of acyclic mononuclear copper(II) complexes have been prepared by Schiff-base condensation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylenetetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and copper perchlorate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show a d–d transition in the range 500–800?nm, electrochemical studies of the complexes show irreversible one-electron-reduction process around ?1.10 to ?1.60?V. The reduction potential of the mononuclear copper(II) complexes shifts toward anodic direction upon increasing the chain length of the imine compartment. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ _eff?=?1.72–1.76?BM, close to the spin-only value of 1.73?BM. Electrochemical and catalytic studies of the complexes were compared on the basis of increasing the chain length of the imine compartment. All the complexes were screened for antifungal and antibacterial activities.     

Synthesis and characterization of manganese(II), nickel(II), copper(II) and zinc(II) Schiff-base complexes derived from 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine

The synthesis of a new Schiff base containing 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine is described. The reaction of 1,10-phenanthroline-2,9-dicarboxaldehyde with 2-mercaptoethylamine leads to 2,9-bis(2-ethanthiazolinyl)-1,10-phenanthroline (I) which undergoes rearrangement when reacted with manganese, nickel, copper or zinc ions to produce complexes of the tautomeric Schiff base 2,9-bis[2-(2-mercaptoethyl)-2-azaethene]-1,10-phenanthroline (L). The [M(L)Cl₂] complexes [where M = Mn(II), Ni(II), Cu(II) and Zn(II) ions] were characterized by physical and spectroscopic measurements which indicated that the ligand is a tetradentate N₄ chelating agent.