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.     

Chirale Halbsandwich‐Pentamethylcyclopentadienyl‐Rhodium(III)‐ und Iridium(III)‐Komplexe mit Schiff‐Basen aus Salicylaldehyd und α‐Aminosäureestern [1]

Chiral Half‐sandwich Pentamethylcyclopentadienyl Rhodium(III) and Iridium(III) Complexes with Schiff Bases from Salicylaldehyde and α‐Amino Acid Esters [1] A series of diastereoisomeric half‐sandwich complexes with Schiff bases from salicylaldehyde and L‐α‐amino acid esters including chiral metal atoms, [(η⁵‐C₅H₅)(Cl)M(N,O‐Schiff base)], has been obtained from chloro bridged complexes [(η⁵‐C₅Me₅)(Cl)M(μ‐Cl)]₂ (M = Rh, Ir). Abstraction of chloride from these complexes with Ag[BF₄] or Ag[SO₃CF₃] affords the highly sensitive compounds [(η⁵‐C₅Me₅)M(N,O‐Schiff base]⁺X^? (M = Rh, Ir; X = BF₄, CF₃SO₃) to which PPh₃ can be added under formation of [(η⁵‐C₅Me₅)M(PPh₃)(N,O‐Schiff base)]⁺X^?. The diastereoisomeric ratio of the complexes ( 1 ‐ 7 and 11 ‐ 12 ) has been determined from NMR spectra.     

Preparation and characterization of some transition metal complexes of benzoic acid hydrazones of 2-aminonicotinaldehyde

Summary Cu^II, Ni^II, Co^II, Zn^II and Pd^II complexes of tridentate Schiff base ligands derived from the condensation of benzoic acid hydrazides with 2-aminonicotinaldehyde have been prepared and characterized. For M=Cu, Ni, Co and Zn the complexes were formulated as [M(ligand)(H₂O)X] (X=Cl, Br), with a distorted octahedral geometry and tridentate Schiff base ligands. The Pd complexes were formulated as Pd(ligand)Cl₂, with square planar geometries and bidentate Schiff base ligands. The e.s.r. spectra of the Cu^II complexes are discussed.     

Complexes of TiCl4, VCl4 and SnX4 (X = Cl or Br) with Schiff bases derived from 2-aminobenzimidazole

Summary The reactions of anhydrous titanium(IV), tin(IV) and vanadium(IV) halides with Schiff bases derived from 2-aminobenzimidazole and 4-methylbenzaldehyde (abimbz) and salicylaldehyde (abisal), yield hexacoordinated complexes M(abimbz)Cl₄ and M(abisal)₂X₄ (M = Ti, Sn or V; X = Cl or Br).The compounds have been characterized by elemental analyses, magnetic measurements, e.p.r., electronic and i.r. spectral studies. I.r. spectra suggest that the Schiff base (abimbz) is coordinated as a bidentate ligand with the metal ion and the (abisal) base acts as a monodentate ligand.     

Complexes of divalent nickel and copper with the Schiff base derived from 2-(2-aminophenyl)benzimidazole and benzaldehyde

Summary The reactions of divalent nickel and copper salts with the Schiff base derived from 2-(2-aminophenyl)benzimidazole and benzaldehyde, L, yield complexes of general formulae [CuL₂X₂] (X=Cl, Br, or ClO₄), [CuL(SO₄)], [CuL(SO₄)] · 4H₂O, and NiLX₂ (X=Cl, Br, or NCS).All the complexes have been characterized by elemental analyses, magnetic measurements, e.s.r. electronic and i.r. spectral studies. The results show that the Schiff base acts as bidentate ligand through the pyridine-like imine nitrogen of imidazole ring and the azomethine nitrogen. Tentative structures of the complexes are suggested.     

Synthesis and characterization of copper(II) and nickel(II) complexes of the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde

Summary Copper(II) and nickel(II) complexes with the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde, L, have been prepared. They are of the general types ML₂X₂ (M = Ni or Cu and X = Cl, Br, NO₃ or ClO₄) and NiL(NCS)₂.The compounds have been characterized by elemental analyses, magnetic measurements, e.s.r., electronic and i.r. spectra studies. The i.r. spectra suggest that the molecule, and not the anion, of the Schiff base is coordinated as a bidentate ligand with the metal ion. Possible structures for the complexes have been proposed.     

Synthesis, Characterization and Biological Evaluation of Fe (III), Co (II), Ni(II), Cu(II), and Zn(II) Complexes with Tetradentate Schiff Base Ligand Derived from Protocatechualdehyde with 2-Aminophenol

Schiff base ligand (H₃L) was prepared from the condensation reaction of protochatechualdehyde (3,4-dihydroxybenzaldhyde)with 2-amino phenol. From the direct reaction of the ligand (H₃L) with Co(II), Ni(II) and Cu(II) chlorides, and Fe(III)and Zn(II)nitrates in 2?M/1?L molar ratio, the five new neutral complexes were prepared. The characterization of the newly formed compounds was done by ¹H NMR, UV?CVis, and IR spectroscopy and elemental analysis. The in vitro antibacterial activity of the metal complexes was studied and compared with that of free ligand.     

Synthesis,Electrochemical and Luminescence Studies of Nickel and Vanadium Complexes Containing Tetradentate Schiff Base Ligand with N2O2 Donor Atoms

A symmetrical tetradentate Schiff base ligand was derived by the condensation of ortho‐vanillin and thiourea in 2:1 molar ratio and adjusted pH. Nickel and vanadyl complexes were obtained using the template method by the reaction of ortho‐vanillin and thiourea with Ni(OAc)₂. 4H₂O and VO(acac)₂ (2:1:1 molar ratio) in absolute ethanol and adjusted pH. The Schiff base ligand and its complexes have been characterized by FT‐IR, ¹H NMR, UV/Vis, elemental analysis and conductometry measurements. In nickel and also vanadyl complexes the ligands were coordinated to the metals via the imine N and enolic O atoms. The complexes have been found to possess 1:1 metal to ligand stoichiometry and the molar conductance data revealed that the metal complexes were non‐electrolytes. The nickel and vanadyl complexes exhibited tetrahedral and square pyramidal coordination geometry, respectively. The emission spectra of the ligand and its complexes were studied in DMSO. Electrochemical properties of the ligand and its complexes were also investigated in the DMF solvent at the 150 mVs^‐1 scan rate. The ligand and its complexes showed irreversible processes at this scan rate.     

Spectroscopic,thermal, biological activity,molecular docking and density functional theoretical investigation of novel bis Schiff base complexes

New Schiff base ligand (H₂L, 1,2‐bis[(2‐(2‐hydroxyphenylimino)‐methyl)phenoxy]ethane) came from condensation reaction of bisaldehyde and 2‐aminophenol was synthesized in a molar ratio 1:2. Metal complexes and the ligand were completely discussed with spectroscopic and theoretical mechanism. The complexes with Fe(III), Cr(III), Mn(II), Co(II), Cu(II), Ni(II), Th(IV) and Zn(II) have been discussed and characterized by elemental analyses, molar conductance, IR, mass spectroscopy, thermal, magnetic measurements, and ¹H NMR. The results proved that the Schiff base was a divalent anion with hexadentate O₄N₂ donors came from the etheric oxygens (O1, O2), azomethine nitrogens (N1, N2) and deprotonated phenolic oxygens (O3, O4). Density Functional Theory using (B3LYP/6‐31G*) level of theory were implemented to predict molecular geometry, Mulliken atomic energetic and charges of the ligand and complexes. The calculation display that complexes had weak field ligand. The binding energy ranged from 650.5 to 1499.0 kcal/mol for Mn(II) and Th(IV) complexes, respectively. The biological behavior of the Schiff base ligand and its metal complexes were displayed against bacteria and fungi organisms. Fe(III) complex gave remarkable biological activity in comparison with the parent bis Schiff base.     

Synthesis and spectroscopic characterization of asymmetric Schiff bases derived from 4′-formylbenzo-15-crown-5 containing recognition sites for alkali and transition metal guest cations

Asymmetric salen-type Schiff base ligands have been synthesized via a stepwise approach. In the first step, mono-Schiff base compounds were prepared by condensation of salicylaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde and 2-hydroxy-1-naphthaldehyde with hydrazine hydrate. These compounds were then reacted with 4′-formylbenzo-15-crown-5 to prepare asymmetric ligands. ¹H-NMR spectra indicate that the mono- and asymmetric bis-Schiff base compounds exist in both (E) and (Z) isomeric forms in CDCl₃ solution. The asymmetric crown compounds form crystalline 1:1 (Na⁺:ligand) complexes with sodium perchlorate. Homo-metallic Ni(II) and Zn(II) complexes with 1:2 (metal:ligand) stoichiometries have also been synthesized. The results indicate that the Schiff base ligands coordinate through the azomethine nitrogen and phenolic oxygen.     

New nanobidentate Schiff base ligand of 2-aminophenol with 2-acetyl ferrocene with some lanthanide metal ions: synthesis,characterization and Hepatitis A,B, C and breast cancer docking studies

Three lanthanide complexes (La(III), Er(III), and Yb(III)) derived from ferrocene-based Schiff base ligand (HL) were synthesized from condensation of 2-aminophenol with 2-acetylferrocene. The ligand and metal complexes were characterized based on elemental analyses, IR, ¹H NMR, molar conductance, SEM and thermal analyses (TG, DTG). The molar conductance revealed that all the metal chelates were electrolytes having the general composition [M(L)(Cl)(H₂O)₃]Cl·4H₂O. HL and its complexes were screened for their antibacterial and antifungal activity by agar diffusion method. The results of these studies showed that the metal complexes are more effective antibacterial and antifungal agents as compared with the free ligand. The anticancer activity was screened against human breast cancer cell line (MCF-7). Results indicated that metal complexes showed an increased cytotoxicity in proliferation to cell lines as compared to free ligand. Molecular docking studies were performed to identify the binding orientation or conformation of a complex in the active site of the protein. HL and its complexes were docked with crystal structure of DDB1 of breast cancer, crystal structure of HCV, RNA-dependent RNA polymerase, receptors of HBV core protein, crystal structure of the Fab fragment of anti-HAV.     

Synthesis,spectroscopic and the biological activity studies of thiosemicarbazones containing ferrocene and their copper(II) complexes

Two Schiff bases, 1-acetylferrocene thiosemicarbazone (HL¹) and 1,1′-diacetyl-ferrocene dithiosemicarbazone (H₂L²) and their copper(II) complexes were prepared and characterized by elemental analysis, magnetic susceptibility, conductivity, and spectral (IR, UV–Vis, ESR) measurements The IR spectra showed that HL¹ acts as neutral or monobasic bidentate ligand, coordinating to copper(II) through either thiono- or thiolo-sulphur and azomethine-N atoms, whereas H₂L² is a neutral or dibasic mononucleating or binucleating quadridentate ligand coordinating through the same atoms. Other spectral measurements indicate that complexes [(L¹)₂Cu], [(L²)Cu] and [(HL¹)₂Cu]X₂, X?=?Cl, Br or ClO₄ have square-planar geometry around copper(II) while [(HL¹)CuX₂] and [(H₂L²)Cu₂X₄], X?=?Cl or Br, have distorted tetrahedral geometry. The biological activity studies of the complexes and the free ligands towards two gram positive and two gram negative bacteria and one fungal species have been studied and the potential is related to the nature and structure of the tested compounds.     

Syntheses,characterization and biological studies of zinc(II), copper(II) and cobalt(II) complexes with Schiff base ligand derived from 2‐hydroxy‐1‐naphthaldehyde and selenomethionine

Novel zinc(II), copper(II), and cobalt(II) complexes of the Schiff base derived from 2‐hydroxy‐1‐naphthaldehyde and D, L ‐selenomethionine were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements and powder XRD. The analytical data showed the composition of the metal complex to be ML(H₂O), where L is the Schiff base ligand and M = Co(II), Cu(II) and Zn(II). IR results confirmed the tridentate binding of the Schiff base ligand involving azomethine nitrogen, naphthol oxygen and carboxylato oxygen atoms. ¹H NMR spectral data of lithium salt of the Schiff base ligand [Li(HL)] and ZnL(H₂O) agreed with the proposed structures. The conductivity values of complexes between 12.50 and 15.45 S cm² mol^?1 in DMF suggested the presence of non‐electrolyte species. The powder XRD studies indicated that Co(II) complex is amorphous, whereas Cu(II) and Zn(II) complexes are crystalline. The results of antibacterial and antifungal screening studies indicated that Li(HL) and its metal complexes are active, but CuL(H₂O) is most active among them. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies on Co(II) and Cu(II) complexes of a ligand derived from 1,3-phenylenediamine and 5-bromosalicylaldehyde synthesis, characterisation, thermal properties and use as new precursors for preparation cobalt and copper oxide nano-particles

A symmetric tetradentate Schiff base ligand, N,N′-bis(5-bromosalicylaldehyde)-1,3-phenylenediamine [(Brsal)₂-1,3-phen) and its Cu(II) and Co(II) complexes with general formula M₂((Brsal)₂-1,3-phen)₂, where M=Co (1) and Cu (2)], have been synthesized and characterized by elemental analyses and FTIR spectroscopy. In addition, Schiff base ligand has been characterized by ¹HNMR spectroscopy. Thermogravimetric analysis of the ligand and its metal complexes reveals their thermal stability and decomposition pattern.     

Biomolecular docking,antimicrobial and cytotoxic studies on new bidentate schiff base ligand derived metal (II) complexes

Three new metal complexes [Cu(L)₂] (1), [Co(L)₂] (2) and [Zn(L)₂] (3) have been prepared by the reaction of hydrated salts of metal (II) acetate with new Schiff base ligand HL, [2‐((4‐(dimethylamino)phenylimino)methyl)‐4,6‐di‐t‐butylphenol] and characterized by different physico‐chemical analyses such as elemental analysis, single XRD, ¹H NMR, FTIR and UV–Vis spectroscopic techniques. Their biomolecular docking, antimicrobial and cytotoxicity studies have also been demonstrated. The proposed structure of Schiff base ligand HL and complex 2 are confirmed by Single crystal X‐ray crystallography study. This analysis revealed that metal (II) complexes remain in distorted tetrahedral coordination environments. The electronic properties such as HOMO and LUMO energies are carried out by gaseous phase DFT/B3LYP calculations using Gaussian 09 program. Complex 1 showed a good binding propensity to the DNA and HSA, during the assessment of docking studies. Schiff base ligand HL and its metal (II) complexes, 1–3 screened for their in vitro antimicrobial activities using the disc diffusion method against selected microbes. Complex 1 shows higher antimicrobial activity than complexes 2, 3 and Schiff base ligand HL. According to the results obtained from the cytotoxic studies, Schiff base ligand HL and its metal (II) complexes 1–3 have better cytotoxicity against MCF‐7 cell lines with potency higher than the currently used chemotherapeutic agent cyclophosphamide.     

Conductivity and band gap of oligo-2-[(4-fluorophenyl) imino methylene] phenol and some of its oligomer-metal complexes

Schiff base oligomer of 2-[(4-fluorophenyl) imino methylene] phenol (FPIMP) was synthesized via oxidative polycondensation reaction in an alkaline medium. Oligomer-metal complex compounds were synthesized from the reactions of oligo-2-[(4-fluorophenyl) imino methylene] phenol (OFPIMP) with Co⁺², Ni⁺² and Cu⁺² ions. The synthesis was achieved by oxidative coupling based on air oxygen as an oxidant. While synthesized Schiff base oligomer was soluble in most common organic solvents, its metal complexes were only soluble in dimethylsulfoxide. Electrochemical HOMO and LUMO band gap (E_g) of monomer, oligomer and its metal complexes were calculated from oxidation and reduction onset values. According to cyclic voltammetry (CV) and UV-vis measurements, electrochemical energy gaps and optical band gap (E_g) values of monomer and oligomer were found to be 3.26 and 3.10; 3.15 and 2.96 eV, respectively. Conductivity measurements of doped and undoped Schiff base oligomer and its metal complexes were carried out by electrometer at a room temperature and atmospheric pressure and were calculated from four-point probe technique. When iodine was used as doping agent, conductivity of this oligomer and its metal complexes were observed to be increased.     

Synthesis,structural characterization and in vitro cytotoxicity of diorganotin complexes with Schiff base ligands derived from 3‐hydroxy‐2‐naphthoylhydrazide

A series of diorganotin complexes with Schiff base ligands, (E)‐N′‐(5‐bromo‐2‐hydroxybenzylidene)‐3‐hydroxy‐2‐naphthohydrazide, H₂L1, and (E)‐N′‐(5‐chloro‐2‐hydroxybenzylidene)‐3‐hydroxy‐2‐naphthohydrazide, H₂L2, were synthesized and characterized by elemental analysis, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The molecular structures of the complexes, [(5‐bromo‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]di(o‐chlorobenzyl)tin(IV) 6 and [(5‐chloro‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dibutyltin(IV) 9, were determined through single‐crystal X‐ray diffraction and revealed a distorted trigonal‐bipyramidal configuration. The in vitro cytotoxic activity of the Schiff bases and their diorganotin complexes was also evaluated against several human carcinoma cell lines, namely HT29 (human colon carcinoma cell line), SKOV‐3 (human ovarian cancer cell line), MCF7 (hormone‐dependent breast carcinoma cell line) and MRC5 (non‐cancer human fibroblast cell line). [(5‐Bromo‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dibutyltin(IV) 2 and [(5‐bromo‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dibenzyltin(IV) 5 were the most active diorganotin complexes of H₂L1 ligand. Among the diorganotin complexes of H₂L2 ligand, [(5‐chloro‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dicyclohexyltin(IV) 11 showed good cytotoxic activity against all the tested cell lines. As such, the above compounds can be considered agents with potential anticancer activities, and can therefore be investigated further in in vitro or in vivo anticancer studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis, characterization and computational studies of zinc(II)-halide complexes with a bidentate schiff base ligand (2,5-MeO-ba)2En: The crystal structure of (2,5-MeO-ba)2En

In this study four coordinated complexes of zinc(II) halides with a new symmetrical bidentate Schiff base ligand (2,5-MeO-ba)₂En are synthesized and characterized. The metal to ligand ratio of the complexes is found to be 1:1 with the formula of Zn((2,5-MeO-ba)₂En)X₂ (X = Cl (1), Br (2), I (3)). The crystal structure of the Schiff base ligand (2,5-MeO-ba)₂En is determined by X-ray crystallography from single crystal data. Also, the optimized geometries of the Schiff base ligand (2,5-MeO-ba)₂En and its zinc(II) complexes are calculated using the density functional theory method (B3LYP/6-31G). The obtained structural parameters of (2,5-MeO-ba)₂En are in agreement with the experimental data.     

Ge2H2 a π-ligand in organometallic chemistry

η² π-Complexes of Ge₂H₂ with the organometallic fragments V(PH₃)₂(I)(CO)₂, Cr(CO)₄, Co(PH₃)₂(Cl) and M(PH₃)₂ (M = Ni, Pd, Pt) have been studied at the B3LYP level using the SBKJC relativistic effective core potentials and their associated basis sets on metals and iodine, and the 6-31G(d) basis set on all other elements. The transition metal fragments of V, Cr, Co, Ni, Pd and Pt were chosen based on known alkyne compounds. All the complexes are local minima for both the HGeGeH and GeGeH₂ isomers of the Ge₂H₂ ligand. The complexes containing GeGeH₂ isomer as a ligand are lower in energy than those with the HGeGeH ligand (except in the V complex in which the difference is only 1.0 kcal/mol). There is a net charge transfer from ligand to metal in complexes V-Co and from metal to ligand in late transition metal complexes (Ni-Pt).     

A Kinetic Study of Phenolic Oxidation by H2O2 Using the Schiff Base Complexes As Mimetic Peroxidases

The Schiff base complexes containing a transition metal ion, Co^II and Cu^II, were used as mimetic peroxidase in the catalytic oxidation of phenol by H₂O₂. The characteristic spectra of the Schiff base complexes in H₂O₂-buffered solution were recorded and analyzed, respectively. The mechanism and the kinetic mathematic model of the phenol catalytic oxidation were studied. The results showed that the Schiff base complexes containing the transition metal ion, Co^II and Cu^II, as peroxidase mimics exhibited good catalytic activity and the character of the peroxidase in the catalytic oxidation of phenol by H₂O₂ under different conditions.