Unsymmetrical Schiff Base Ligand Research Articles

Syntheses, crystal structure, and photocatalytic property of two new complexes of an unsymmetrical Schiff base ligand

The reaction of Zn(NO3)2·6H2O with an unsymmetrical Schiff base ligand 2,4-dihydroxybenzaldehyde nicotinoylhydrazone (H2dbp) gave [Zn(dbp)(H2O)·2DMF]n (1), while the reaction of Ni(Ac)2·4H2O with H2dbp in the presence of 1,10-phenanthroline generated [Ni(dbp)(phen)·2CH3OH·0.5H2O]n (2) (phen=1,10-phenanthroline). X-ray single-crystal analyses reveal that 1 contains a 2D layer with 1D open channel, while 2 shows 1D ladder-like chain, which are extended into 2D supramolecular sheet. Furthermore, the photocatalysis properties of 1–2 for degradation of the methyl violet (MV) and Rhodamine B (RhB) have been examined.

Synthesis, crystal structure and properties of a new 3D supramolecular unsymmetrical tetradentate Schiff bases copper (II) framework with stable tunnels

Flexible unsymmetrical Schiff base ligand (L) which is derived from the half unit Y=C6H5COCH2C(NCH2C6H4NH2)CH3 (obtained from the reaction of benzoylacetone and 2-aminobenzylamine) and 2- quinolinecarboxaldehyde have been successfully co-assembled with Cu(ClO4)2 to give out the [Cu(L)]ClO4 complex. The complex crystallizes in two different space groups; P21/n and P-1. The crystal structure of the P-1 phase indicates the presence of tunnels; the volume of these tunnels is 157 Å3 which is big enough to accommodate solvent molecules. The X-ray data indicates that these tunnels are most probably filled by highly disordered solvent molecules or solvent molecules with partial occupancy. The tunneled structure is stabilized via π–π stacking interactions to give a supramolecular MOF with 1D rhomboidal tunnels array. The copper(II) atom assumes a distorted-square pyrimidal coordination geometry where the perchlorate is located on the apex of the pyramide. In addition, this work presents and discusses the spectroscopic (IR, UV/vis), electro-chemical (cyclic voltammetry) behavior of the Cu(II) complexes. The Cu(II) oxidation state is stabilized by the novel tetradentate ligands, showing Cu(I/II) couple around 0.1 vs. Cp2Fe/Cp2Fe+.

Experimental and Computational Study of the Thermodynamic Properties of Trivalent Cobalt Schiff Base Complexes with Cyclic Amines

Some cobalt(III) complexes with a potentially tetradentate unsymmetrical NNOS Schiff base ligand have been synthesized and characterized using IR, 1HNMR, UV-Vis spectroscopy and elemental analysis. The equilibrium constants were measured spectrophotometrically for 1:1 adduct formation of the cobalt(III) complexes with some cyclic amines in acetonitrile as solvent at constant ionic strength (I = 0.1 M NaClO4), and at various temperatures. In addition, the ground state geometries of the complexes were optimized using density functional theory (DFT) at B3LYP/6-311G** level. Binding energy, thermodynamic parameters, structural parameters and electronic structures of complexes are investigated. The theoretical investigations were done for comparing with the experimental results. Our comparison between the computational and experimental results revealed that the cobalt(III) complexation process is spontaneous, exothermic and entropically unfavorable.

Synthesis, characterization and catecholase-like activity of new Schiff base metal complexes derived from visnagin: Theoretical and experimental study

A new tetradentate, unsymmetrical Schiff base ligand (H2L) containing a donor set of N2O2 and its mononuclear Cu(II) and Fe(II) complexes ([CuL] and [FeL]), were synthesized and characterized on the basis of their elemental analysis, FT-IR, Raman, 1H and 13C NMR spectra, electronic and mass spectra, molar conductivity and magnetic susceptibility measurements. Density functional theory (DFT) calculations were performed in order to clarify molecular structures, 1H NMR and 13C NMR chemical shift values, frontier molecular orbitals (FMOs), nonlinear optical properties and map of molecular electrostatic potential (MEP) of the title molecules. In agreement with trials, the results provide a full explanation of the highest efficiency observed for the compounds in relation to the electronic and the structural characteristics. The catecholase-like activity of the complexes toward the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the corresponding quinone showed that both complexes have moderate catalytic activity. [FeL] shows higher activity (kcat = 26.4 h−1) than that of [CuL] (kcat = 23.4 h−1).

Synthesis and Characterization of a New Unsymmetrical Potentially Pentadentate Schiff Base Ligand and Related Complexes with Manganese(II), Nickel(II), Copper(II), Zinc(II) and Cadmium(II)

New unsymmetric thioether Schiff base amine, 2-(2-aminoethylthio)-N-(thiophene-2-ylmethylene)aniline was prepared by reaction of 2-aminothiophenol with N-(2-bromoethyl)phthalimide and then by thiophene-2-carbaldehyde. Then, the phthalimide group converted to the amine by hydrazine hydrate. The new potentially pentadentate N3S2 donor unsymmetrical Schiff base ligand, 2-(2-(pyridine-2-ylmethyleneamino)ethylthio)-N-(thiophene-2-ylmethylene)aniline (L) was prepared via [1 + 1] condensation of pyridine-2-carbaldehyde with this amine. Manganese(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of this ligand were prepared by adding metal salts to an ethanolic solution in this ligand. The thioether amine, ligand (L) and unsymmetric Schiff base complexes are characterized by the appropriate spectroscopic methods such as infrared (IR), UV-Vis, 1H nuclear magnetic resonance (NMR), 13C NMR studies, X-ray, microanalysis and mass spectrometry.

Synthesis, characterization, electrical and catalytic studies of some coordination compounds derived from unsymmetrical Schiff base ligand

New unsymmetrical tetradentate Schiff base ligand derived from 5-chloro-2-hydroxyacetophenone, 2-hydroxy-5-methyl-3-nitro acetophenone and carbohydrazide and its complexes with VO(IV), Cr(III), Mn(III), Fe(III), MoO2(VI), WO2(VI), Zr(IV) and UO2(VI) have been prepared. They were characterized by elemental analysis, IR and electronic spectra, magnetic susceptibility measurements and thermal analyses. The Schiff base ligand has also been characterised by 1H-NMR spectroscopy. The thermal behaviour of metal complexes shows that the hydrated complexes lose water molecules of hydration in the first and then is immediately followed by decomposition of ligand molecule in the subsequent steps. The IR spectra suggest that ligand acts as dibasic tetradentate nature and coordination takes place through azomethine nitrogen and phenolate oxygen. The crystalline nature of the VO(IV) complex was conformed through the powder XRD analysis. The catalytic activity of the VO(IV) and Mn(III) complexes have been tested in the epoxidation reaction of styrene and conversion of styrene were 11.14-24.35% and 9.64-23.42%, respectively. The solid state electrical conductivity of ligand and its complexes were measured, which could obeyed the relation s = s0 exp (Ea/KT) over the temperature range 313-413 K. KEY WORDS: Schiff base, Metal complexes, TGA, Electrical conductivity, XRD, Oxidation of styrene Bull. Chem. Soc. Ethiop. 2015, 29(3), 387-397. DOI: http://dx.doi.org/10.4314/bcse.v29i3.6

New asymmetric Schiff base ligand derived from allylamine and 2,3-dihydroxybenzaldehyde and its molybdenum(VI) complex: Synthesis, characterization, crystal structures, computational studies and antibacterial activity together with synergistic effect against Pseudomonas aeroginosa PTTC 1570

A new unsymmetrical Schiff base ligand (H2L) was derived from the 1:1M condensation of 2,3-dihydroxybenzaldehyde with allylamine. Molybdenum(VI) complex, MoO2L2, was synthesized from the reaction of MoO2(acac)2 with the Schiff base ligand in a 1:2 ratio in methanol at ambient temperature. The Schiff base ligand and its Mo(VI) complex were characterized by elemental analyses, FT-IR, 1H NMR, 13C NMR and UV–Vis spectroscopies and single crystal X-ray analysis. The molecular structure of schiff base ligand and Mo(VI) complex showed pseudo-scorpionate structure in solid state. The MoO2L2 complex adopts an octahedral environment around the Mo center with a cis-oxo configuration. The other coordination sites are occupied by the hydroxyl oxygen atoms of the two Schiff base ligands. The pseudo-scorpionate interaction in ligand was investigated by theoretical calculation. The Schiff base ligand and its Mo(VI) complex were also tested for their in vitro antimicrobial activity against Staphylococcus aureus (ATCC 29737) and Pseudomonas aeroginosa (PTTC 1570) as examples of Gram-positive and Gram-negative bacterial strains, respectively, by disc diffusion method. The results indicated that the Schiff base ligand had a better antibacterial activity than its Mo(VI) complex and surprisingly, they were synergistic when used against P. aeroginosa PTTC 1570.

Synthesis, characterization and biological activity of some unsymmetrical Schiff base transition metal complexes

In this study, several unsymmetrical Schiff bases and their cobalt and manganese complexes have been synthesized and characterized. The unsymmetrical Schiff bases were prepared from reaction of o-phenylendiamine derivatives with 1-hydroxy-2-acetonaphthone and then the product was reacted with the following aldehydes: salicyaldehyde, 2-hydroxynaphthaldehyde, 2-pyridinecarboxaldehyde and 2-qinolinecarboxaldehyde to produce the desired tetradentate unsymmetrical Schiff base ligands H2SL, H2NL, HPYL and HQN, respectively. Reaction of these ligands with cobalt and manganese salts produced complexes of the general formula [M(SL)], [(NL)], [M(PYL)] and [M(QL)]. All the complexes were characterized by elemental analysis, infrared spectroscopy, UV-visible spectroscopy, electrical conductivity and magnetic susceptibility measurements. The prepared complexes were examined for their anti-bacterial activity using gram-positive and gram-negative pathogens. The following complexes showed strong antibacterial activity against Staphylococcus aureus: MnSL1, MnSL2 and MnSL3. The genotoxic activity of four complexes, which are MnNL1, MnSL1, CoNL1 and CoSL1, were examined using 8-hydroxy-2-deoxy guanosine (8-OHdG) assay in cultured human blood lymphocytes. All examined complexes were found to be genotoxic at examined concentrations (0.1–100 µg/mL), but with variable magnitudes (p < 0.05). The levels of 8-OHdG induced by MnNL1 and MnSL1 were significantly higher than that induced by CoNL1 and CoSL1 ones. In general, the order of mutagenicity of the compounds is MnSL1 > MnNL1 > CoSL1 > CoNL1. In conclusion, some of the prepared complexes showed some biological activities that might be of interest for future research.

Unsymmetrical Schiff base (ON) ligand on complexation with some transition metal ions: Synthesis, spectral characterization, antibacterial, fluorescence and thermal studies

A series of eight metal Schiff base complexes were synthesized by the thermal reaction of Cu(II), Ni(II), Fe(III), Co(II), Zn(II), Hg(II), La(III) or Sm(III) with a Schiff base “L” produced by the condensation of furfuraldehyde and 1,2-diaminobenzene. These compounds were characterized by elemental analysis, UV–Vis, FT-IR, molar conductance, mass spectrometry, thermal and fluorescence studies. The studies suggested the coordination of the ligand L to metal through azomethine imine nitrogen and furan oxygen atoms of Schiff base moiety. Thermogravimetric (TG/DTG) analyses data were studied and indicated high stability for all complexes and suggested the presence of lattice and/or coordinated water molecules in the complexes. Coats–Redfern method has been used to calculate the kinetic and thermodynamic parameters of the metal complexes. The spectral and thermal analysis reveal that all complexes have octahedral geometry except Cu(II) and Ni(II) complexes which can attain a square planner arrangements. The ligand and its complexes exhibited intraligand (π–π∗) fluorescence and can potentially serve as photoactive materials. Both the ligand and its complexes have been screened for antibacterial activities.

Synthesis, Physiochemical, Thermal, Catalytic and Electrical Studies of Mn(III) VO(IV), MoO2(VI) and UO2(VI) Complexes with Unsymmetrical Schiff Base Ligand

The solid complexes of Mn(III), VO(IV), MoO2(VI) and UO2(VI) with unsymmetrical dibasic tetradentate ONNO donor Schiff base derived from the condensation of salicylaldenyde, o-hydroxy acetophenone and ethylene diamine have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements, IR and reflectance spectra. The thermal dehydration and decomposition of these complexes were studied kinetically using the Horowitz- Metzger method. The solid state electrical conductivity of complexes has been measured in the temperature range 313 K≤ T ≥403 K and the complexes exhibited semiconducting behavior. Scanning electron micrograph has also been reported and suggested homogeneous phase material. Complexes were used for the catalytic oxidation of styrene.

Some quantum chemical study on the structural properties of three unsymmetrical Schiff base ligands

In this studythree Schiff base ligands derived of 2-hydroxybenzaldehyde: H2L1, H2L2 and H2L3 have been subjected to theoretical studies by using density functional theory (DFT) calculations. The electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy, HOMO-LUMO gap energy, RHF energy, some of important bond lengths and angles, dipole moment and molecular densities have been investigated. Also the calculated IR spectra of these ligands are in good consistency with the experimental results. KEY WORDS: Schiff base, 2-Hydroxybenzaldehydeand, 2-Aminoethanthiol, HOMO, LUMO, Band gap Bull. Chem. Soc. Ethiop. 2014, 28(2), 265-270.DOI: http://dx.doi.org/10.4314/bcse.v28i2.10

Synthesis, crystal structure, and electrochemical properties of Ni(II) and Cu(II) complexes with two unsymmetrical N2O2 Schiff base ligands

Nickel(II) and copper(II) complexes of two unsymmetrical tetradentate Schiff base ligands [Ni(Me-salabza)] (1), [Cu(Me-salabza)] (2) and [Ni(salabza)] (3), {H2salabza = N,N′-bis[(salicylidene)-2-aminobenzylamine] and H2Me-salabza = N,N′-bis[(methylsalicylidene)-2-aminobenzylamine]}, have been synthesized and characterized by elemental analysis and spectroscopic methods. The crystal structures of 2 and 3 complexes have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry in [Cu(Me-salabza)] and [Ni(salabza)] complexes. The cyclic voltammetric studies of these complexes in dichloromethane indicate the electronic effects of the methyl groups on redox potential.

Synthesis, X-ray crystal structure, and electrochemistry of polynuclear azido-bridged manganese(III) and copper(II) Schiff base complexes

Abstract New azido-bridged [MnIII(salabza)(μ-1,3-N3)]n (1), and [CuII4(salabza)2(μ-1,1-N3)2(N3)2(HOCH3)2],(2) complexes with an unsymmetrical Schiff base ligand, {H2salabza = N,N’-bis(salicylidene)-2-aminobenzylamine}, have been synthesized, characterized by spectroscopic and electrochemical methods, and their crystal structures have been determined by X-ray diffraction. In complex 1, each manganese(III) atom is coordinated with N2O2 donor atoms from salabza and two adjacent Mn(III) centers are linked by an end-to-end (EE) azide bridge to form a helical polymeric chain with octahedral geometry around the Mn(III) centers. Complex 2 is a centrosymmetric tetranuclear compound containing two types of Cu(II) centers with square pyramidal geometry. Each terminal copper atom is surrounded by N2O2 atoms of a salabza ligand, and the oxygen atom of the methanol molecule. Each central copper(II) ion is coordinated with two phenoxo oxygen atoms from one salabza, one terminal azido, and two end-on (EO) bridging azido ligands. The central copper(II) ions are linked to each other by the two end-on (EO) azido groups.

Synthesis, spectroscopic, electrochemical, magnetic properties and super oxide dismutase activity of nickel (II) complexes with unsymmetrical Schiff base ligands

s: Five new mixed-ligand nickel (II) complexes; viz; [Ni (BHM)(PMDT)]1; [Ni(BHM)(dien)] 2; [Ni(BHM)(L 1 )]3; [Ni(BHM)(L 2 )] 4, [Ni(BHM)(L 3 )] 5; where H2BHM= N ’ -(1E)-(5-bromo-2-hydroxyphenyl) methylidene] benzoylhydrazide, PMDT= N,N,N’,N, ” N ” -Pentamethyldiethylenetriamine; dien= diethylenetriamine; L 1 = N,Ndimethyl-N’ (Pyrid-2-yl-methyl) ethylenediamine; L 2 = N-methyl-N’-(pyrid-2ylmethyl)ethylenediamine; L 3 = N,N-dimethyl-N’-(6-methyl)pyrid-2-ylmethyl) ethylenediamine, have been synthesized and characterized by using elemental analyses, FAB (fast atomic bombardment), magnetic measurements, electronic absorption , conductivity measurements, cyclic voltammetry (CV) and IRspectroscopy . All the complexes yielded an irreversible couple that can be assigned to a Ni II → Ni I redox process. Infrared spectra, ligand field spectra and magnetic susceptibility measurements agree with the observed octahedral environment. H2BHM is a diprotic tridentate Schiff base ligand (ONO donor atom) whereas L 1 -L 3 possessing N3 coordination sites. The SOD activities have been measured using alkaline DMSO as a source of superoxide radical (O2 – ) and nitro blue tetrazolium (NBT) as O2 – scavenger.

Titanium(IV) Complexes of Unsymmetrical Schiff Bases Derived from Ethylenediamine and o‐Hydroxyaldehyde/Ketone and Their Anti‐microbial Evaluation

AbstractThe titanium(IV) complexes of the unsymmetrical Schiff base ligands (L) of ethylenediamine and salicylaldehyde, o‐hydroxyacetophenone, o‐hydroxynapthaldehyde have been prepared and characterized when unsymmetrical ligands are synthesized through in situ partial displacement of the symmetrical bis‐Schiff bases. Compounds have been characterized by elemental analysis, electronic, (Infra‐red) IR, 1H NMR spectral data, magnetic susceptibility measurement and molar conductance and eight coordinated geometry of the complexes was proposed. The complexes have been found to posses 1:2:1 (M:L:B) stoichiometry (B is the secondary ligand). The bio‐efficacy of the prepared complexes has been examined against the growth of bacteria and fungi in vitro to evaluate their anti‐microbial potential.

Ruthenium(II) Carbonyl Complexes Containing Unsymmetrical Schiff Bases: Synthesis, Characterization, and Catalytic Applications

Unsymmetrical Schiff base complexes of general formula [Ru(CO)(B)(L)] (B = PPh3, AsPh3, or Py; L = dianion of unsymmetrical Schiff base ligand) have been synthesized from the reaction of [RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3, or Py) with unsymmetrical Schiff bases. The new synthesized complexes were characterized by using elemental analysis, IR spectra, electronic spectra, 1H-NMR, 13C-NMR, and 31P-NMR spectra. All the complexes were tentatively assigned an octahedral geometry. The catalytic activities of the synthesized complexes have been studied and found that the complexes showed efficient catalytic activity for oxidation of alcohols and reduction of ketones.

Synthesis, spectral, thermal, catalytic and biological studies of some transition metal complexes with unsymmetrical Schiff base ligand

Synthesis, spectral, thermal, catalytic and biological studies of some transition metal complexes with unsymmetrical Schiff base ligand

Stereochemical Consequences of Oxygen Atom Transfer and Electron Transfer in Imido/Oxido Molybdenum(IV, V, VI) Complexes with Two Unsymmetric Bidentate Ligands

Two equivalents of the unsymmetrical Schiff base ligand (L(tBu))(-) (4-tert-butyl phenyl(pyrrolato-2-ylmethylene)amine) and MoCl(2)(NtBu)O(dme) (dme = 1,2-dimethoxyethane) gave a single stereoisomer of a mixed imido/oxido Mo(VI) complex 2(tBu). The stereochemistry of 2(tBu) was elucidated using X-ray diffraction, NMR spectroscopy, and DFT calculations. The complex is active in an oxygen atom transfer (OAT) reaction to trimethyl phosphane. The putative intermediate five-coordinate Mo(IV) imido complex coordinates a PMe(3) ligand, giving the six-coordinate imido phosphane Mo(IV) complex 5(tBu). The stereochemistry of 5(tBu) is different from that of 2(tBu) as shown by NMR spectroscopy, DFT calculations, and X-ray diffraction. Single-electron oxidation of 5(tBu) with ferrocenium hexafluorophosphate gave the stable cationic imido phosphane Mo(V) complex [5(tBu)](+) as the PF(6)(-) salt. EPR spectra of [5(tBu)](PF(6)) confirmed the presence of PMe(3) in the coordination sphere. Single-crystal X-ray diffraction analysis of [5(tBu)](PF(6)) revealed that electron transfer occurred under retention of the stereochemical configuration. The rate of OAT, the outcome of the electron transfer reaction, and the stabilities of the imido complexes presented here differ dramatically from those of analogous oxido complexes.

Synthesis, X-ray crystal structure, and electrochemistry of copper(II) complexes of a new tridentate unsymmetrical Schiff base ligand and its hydrolytically rearranged isomer

A new unsymmetrical Schiff base ligand HL1, HBacabza, and its copper(II) complexes [Cu2L12(OAc)2] (1) and [Cu2L22(N3)2]·2H2O (2) with HBacabza=3-(2-aminobenzylimino)-1-phenylbutan-1-one as HL1 and its hydrolytically rearranged isomer 3-(2-aminomethylphenyleneimino)-1-phenylbutan-1-one as HL2, have been synthesized and characterized by elemental analyses and spectroscopic methods. The rearrangement of HL1 to HL2 occurs in a hydrolysis-recondensation process in the reaction of HL1 with Cu(ClO4)2·6H2O and NaN3. The crystal structures of the ligand and its complexes have been determined by single crystal X-ray diffraction. The deprotonated Bacabza− coordinates to the metal center as a tridentate ligand. The acetate anion coordinates through one oxygen atom in complex 1 leading to a mono-atomic acetate oxygen-bridging dimeric copper(II) complex. Similarly, the azide anion coordinates through one nitrogen atom in complex 2 leading to a mono-atomic azide nitrogen-bridging dimeric copper(II) complex. The copper(II) ions adopt a distorted square pyramidal (4+1) coordination in these two complexes. The cyclic voltammetric studies of these complexes in N,N-dimethylformamide indicate that the reduction process corresponding to CuII/CuI is electrochemically irreversible in complex 1, presumably due to the structural changes during the course of redox reaction, and quasi-reversible in complex 2.

Synthetic, characterization and catalytic studies of some coordination compounds derived from unsymmetrical quadridentate Schiff base ligand

The stable complexes of VO(IV), Cr(III), Mn(III), Fe(III), MoO2(VI), and WO2(VI), with an unsymmetrical tetradentate Schiff base ligand derived from 2-hydroxy-5-methylacetophenone, 2-hydroxy-5-chloroacetophenone and carbohydrazide were synthesized and characterized by the elemental analysis, UV-Vis and IR spectroscopy, magnetic measurements and thermal analysis. The VO(IV) and Mn(III) complexes were tested for the catalytic oxidation of styrene. The conversion of styrene increases with use of VO(IV) catalyst and decreases with use of Mn(III) catalyst.