Synthesis, characteristic and theoretical investigation of the structure, electronic properties and second-order nonlinearity of salicylaldehyde Schiff base and their derivatives

A series of asymmetric donor-acceptor substituted salen-type Schiff-bases have been synthesized and their structures, electronic properties and second order nonlinearities were investigated by DFT methods. In order to verify the stable of these Schiff-base derivates, the IR spectrum of these Schiff-base derivates were calculated, the result showed that these compounds are stable. The results of TD-DFT calculation indicate that the derivatives with the electron-donating group (CH3, OCH3 or N(C2H5)2) have a red shift absorption compared to derivatives with the electron-withdrawing group (NO2). The analysis of MOS indicates that the CN group has contribution to the LUMO orbital while the groups of OCH3, N(C2H5)2 and NO2 have contribution to the HOMO orbital. OCH3, N(C2H5)2 as electron rich groups, made the derivates have a larger first static hyperpolarizability. However, the compound (II) with a NO2 substituent, also has a large first static hyperpolarizability. This is probably because of the special transition model, namely the values of two oscillator strength f (fHOMO-1-LUMO=0.405, fHOMO-LUMO=0.321) are almost equal. In order to understand the influence of the energy gap (ΔE) between the HOMO and the LUMO orbitals on the first static hyperpolarizability, we calculated the energy gap (ΔE) of all Schiff-base compounds. The results show that the smaller the HOMO-LUMO energy gap is, the larger the first static hyperpolarizability is.     

Synthesis, crystal structure and spectroscopic properties of some cadmium(II) complexes with three polyamine and corresponding macroacyclic Schiff base ligands

Three Cd(II) macroacyclic Schiff base complexes [CdL⁴(NO₃)₂] (4), [CdL⁵(NO₃)₂] (5), [CdL⁶(NO₃)₂] (6) were prepared by template condensation of 2-pyridinecarboxaldehyde with N1-(2-nitrobenzyl)-N1-(2-aminoethyl)ethane-1,2-diamine (L¹), N1-(2-nitrobenzyl)-N1-(2-aminoethyl)propane-1,3-diamine (L²) or N1-(2-nitrobenzyl)-N1-(3-aminopropyl)propane-1,3-diamine (L³), in the presence of cadmium metal ion, respectively. Three Cd(II) complexes with L¹, L² and L³ were also synthesized. All complexes have been studied with IR, ¹H NMR, ¹³C NMR, DEPT, COSY, HMQC and microanalysis. Two of these complexes, [CdL⁴(NO₃)₂] (4) and [CdL¹(NO₃)₂] (1) have been characterized through X-ray crystallography. In complex 4, the Cd is in a six-coordinate environment comprised of the ligand N₄-donor set and two oxygen atoms of two nitrate groups. In the polyamine complexes (1, 2 and 3) Cd and ligand are in a ratio of 1:1. Supporting ab initio HF-MO calculations have been undertaken using the standard 3-21G^∗ and 6-31G^∗ basis sets.     

Synthesis, characterization, tautomerism and theoretical study of some new Schiff base derivatives

New Schiff base derivatives were prepared by the condensation of 5-chloro and 5-bromo salicylaldehyde with bis(o-aminophenol)ethers. Five bis(o-nitrophenol)ether compounds were synthesized using some ditosylate, 1,3-dibromopropane and 1,4-dibromobuthane with o-nitrophenol. These compounds were reduced to bis(o-aminophenol)ethers. The products have been characterized by elemental analysis, FTIR, 1H, 13C NMR, HETCOR and HMBC spectroscopic techniques. The tautomerisms of all of the Schiff bases compounds were determined in DMSO, CHCl3, C2H5OH and C6H12 solvents and in both acidic and basic media using the UV-vis spectrophotometric method. The heat of formation (ΔHf), enthalpy (ΔH), entropy (ΔS), Gibbs free energy (ΔGf and ΔG), stable isomers, conformations and tautomers of the synthesized compounds are calculated using the MOPAC2009 (PM6) program.     

Redox, thermodynamic and spectroscopic of some transition metal complexes containing heterocyclic Schiff base ligands

Complexes of two series of Schiff base ligands, H₂L_a and H₂L_bderived from the reaction of 2,6-diacetyl pyridine with semicarbazide, H₂L_a and thiosemicarbazide, H₂L_b, with the metal ions, Co(II), Ni(II), Cu(II), VO(IV) and UO₂(VI) have been prepared. The ligands are characterized by elemental analysis, IR, UV–vis and ¹H NMR. The structures of the complexes are investigated with the IR, UV–vis, X-band ESR spectra, ¹H NMR and thermal gravimetric analysis as well as conductivity and magnetic moment measurements. The IR-spectra reveal the presence of variable modes of chelation for the investigated ligands. A variety of binuclear or mononuclear complexes were obtained with the two ligands in tri-, tetra or pentadentate forms. The bonding sites are the pyridine nitrogen, two azomethine nitrogen atoms and ketonic oxygen in case of H₂L_a or sulphur atoms in case of H₂L_b. The Coats–Redfern equation has been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. Cyclic voltammograms of Co(II) and Ni(II) show quasi-reversible peaks. The redox properties and the nature of the electro-active species of the complexes have been characterized.     

Synthesis of bromine- or aryl-substituted ditopic Schiff base ligands and their bimetallic iron(II) complexes: electronic and magnetic properties

Syntheses of three new ditopic Schiff base ligands bearing bromine, phenyl or 2-thienyl substituents are described. Bimetallic iron(II) complexes were prepared from these ligands and were characterized. Electrochemical measurements suggest no measurable electronic coupling between the metal ions in each complex. Variable temperature magnetic susceptibility measurements indicate gradual spin-crossover is operative in the complexes studied, with the low-spin state as the ground state in all cases. Density functional theory calculations corroborate these experimental observations. Attempts to electropolymerize the 2-thienyl-substituted complexes were not successful.     

Relationships between structure, retention and biological activity of some Schiff base ligands and their complexes

The lipophilicity of a series of Schiff base ligands and their complexes with nickel(II) and copper(II) has been determined by reversed-phase thin-layer chromatography using binary dioxane-water mobile phase. Chelate ligands were prepared by condensation of diamine and the corresponding beta-diketone. Copper(II) and nickel(II) complexes with chelate ligands containing ethane-1,2-diamine or propane-1,2-diamine as the amine part and pentane-2,4-dione and/or 1-phenylbutane-1,3-dione, pentane-2,4-dione and/or 1,1,1-trifluoropentane-2,4-dione, or 1,1,1-trifluoropentane-2,4-dione and/or 1-phenylbutane-1,3-dione as the beta-diketone part were synthesized. Some of investigated compounds were screened for their in vitro antifungal activity against Sacharomyces cerevisiae and antibacterial activity against Escherichia coli. Chromatographically obtained lipophilicity parameters were correlated both with calculated n-octanol-water partition coefficient C log P and antimicrobial activities. Satisfactory correlations were obtained. Chromatographic data proved to be reliable parameters for describing the lipophilic properties of the investigated compounds. Additionally, the principal components analysis was performed on the data chromatographically obtained. This statistical method was useful for distinguishing compounds and objective comparison of their lipophilicity parameters.     

Synthesis,structure and properties of some copper(II) complexes containing an ONO donor Schiff base and substituted imidazole ligands

Five new mixed ligand coper(II) complexes, viz. [Cu(SAA)(H₂O)] (1), [Cu(SAA)(MeImH)] (2), [Cu(SAA)(EtImH)] (3), [Cu(SAA)(BenzImH)] (4) and [Cu(SAA)(MebenzImH)] (5), where SAA = salicylideneanthranilic acid, MeImH = 2-methylimidazole, EtImH = 2-ethylimidazole, BenzImH = benzimidazole, MebenzImH = 2-methylbenzimidazole, have been synthesized and characterized by means of elemental analysis, FAB mass spectrometry, magnetic susceptibility, X-band EPR, electronic spectroscopy, IR and cyclic voltammetry. The frozen solution EPR spectra of the complexes have shown axial features. Single crystal X-ray analysis of 2 and 3 has revealed the presence of a distorted square planar geometry (N₂O₂) in the complexes. The superoxide dismutase (SOD) activity of the present complexes has also been measured and discussed.     

二氮杂芴酮Schiff碱两亲配体分子的自组织特性

本文研究了四种合成的二氮杂芴酮Schiff碱两亲配体分子C~1~1N~2H~6NC~nH~2~n~+~1(n=18,16,14,12)所形成的单分子膜,双分子膜的特性,并用透射电镜,紫外- 可见光谱及微量差示扫描量热观察了在所形成的囊泡中分子的聚集形式与相变过程.结果表明,该系列两亲配体分子所形成的单分子膜和双分子膜具有良好的稳定性,在稀溶液中能自组织成双层结构的囊泡     

Synthesis, characterization and catalytic activity of three palladium(II) complexes containing Schiff base ligands

Three new Pd(II) complexes of Schiff base ligands, namely, [Pd₄(L¹)₄] (1), [Pd₂(L²)₂Cl₂] (2) and [Pd(L³)₂Cl₂] (3) [HL ¹ ?=?N-(benzylidene)-2-aminophenol; L ² ?=?N-(2,4-dichlorobenzylidene)-2,6-diethylbenzenamine, L ³ ?=?4-(2,4-dichlorobenzylide-neamino)phenol] have been synthesized using solvothermal methods and characterized by elemental analysis, spectroscopy and single crystal X-ray diffraction. The crystal structures of the free ligands were also determined. The ??-oxygen-bridged tetranuclear cyclometallated Pd(II) complex (1) contains four nearly planar units, in which Pd^II is four-coordinate. Complex 2 is a ??-chloro-bridged dinuclear cyclometallated Pd(II) complex, whereas complex 3 is mononuclear. The Heck reactions of bromobenzene with acrylic acid catalyzed by complexes 1?C3 have also been studied.     

Kinetic investigation of aquation of some Fe(II) Schiff base amino acid complexes

Kinetics of aquation of some Fe(II) Schiff base amino acid complexes was followed spectrophotometrically. The Schiff base ligands were derived from salicylaldehyde and isoleucine, leucine, serine, methionine, tryptophan, or histidine. The reaction was studied in aqueous media, aqua–propanol mixtures, and in the presence of different concentrations of KBr. Moreover, the activation parameters were calculated and discussed for structures and other physical properties observed. The reaction was acid catalyzed and the general rate equation was suggested as follows: rate = k_obs [complex], where k_obs = k₂ [H⁺]. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 372–379, 2010     

Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato-κ²N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN₂O₂] coordination geometry with trans-N–Cu–N = 159.4(2)° and trans-O–Cu–O = 151.7(3)° for the 1-phenylethyl complex and trans-N–Cu–N = 157.9(3)° and trans-O–Cu–O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d–d band at 16 000–20 000 cm⁻¹ and remarkable shift of the π–π* band at 24 000–28 000 cm⁻¹, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted ‘photochromic solute-induced solvatochromism’ by a system of bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato-κ²N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d–d and π–π* bands of the complex in the absorption spectra caused by cis–trans photoisomerization of 4-hydroxyazobenzene.     

Experimental and theoretical investigation of the spectral and luminescent properties of some acridine compounds

Complex (experimental and quantum-chemical) investigation of the spectral and luminescent properties of acridine, 9-aminoacridine, 2,7-dimethyl-9-ditolylaminoacridine, and their protonated forms was performed. The electronic absorption and fluorescence spectra of the acridine dyes were studied at room temperature in ethanolic solutions at different pH values and in other solvents of different chemical nature and polarity. The energies of the excited states, the deactivation rate constants for the excited states, and the dipole moments are presented, which were obtained by calculations using the method of intermediate neglect of the differential overlap with special spectroscopic parameterization.     

Carbonyl amine/Schiff base ligands in manganese complexes: theoretical study on the mechanism, capability of NO release

A compound having the capability of releasing NO upon exposure to visible or near-infrared (vis or NIR) light could be a potential candidate for photodynamic therapy (PDT), which is significant for humans. Here, we investigated a series of Mn(II) complexes (a-d) based on density functional theory (DFT) to illuminate the mechanism of their behavior of releasing NO. Their structural, spectroscopic, and photodissociable properties were calculated by quantum theoretical methods to give a detailed and warranted explanation of the performance of releasing NO. The results indicate that, for a-d, releasing NO was attributed to the electron transfer from d(yz)/d(xz)(Mn) orbitals to π*(NO) orbitals at the second excited triplet state (T(2)). Importantly, we confirmed the finding in the experiment that d could release NO upon exposure to the NIR region and, thus, may be a best candidate for PDT in a-d. Therefore, to take d for example, the analyses of the potential energy curves (PECs) of difference states and electron density difference between the T(2) and the ground state (S(0)) were performed to further provide evidence of ligand dissociation and release of NO at the T(2) state. Finally, we hope that our discussion can provide assistance to understand the behavior of the release of NO and design novel photodissociable transition metal nitrosyls for PDT applications.     

Synthesis,characterization and antimicrobial activity of triorganotin(IV) derivatives of some bioactive Schiff base ligands

Triorganotin(IV) complexes of the type Me₃Sn[OC(R¹):CH(CH₃)C:NR²OH] and Ph₃Sn[OC(R′):CH(CH₃)C:NR″OH] (R′ = ─CH₃, ─C₆H₅; R″ = ─(CH₂)₂─, ─(CH₂)₃─) have been synthesized by the reactions of trimethyl/phenyltin(IV) chloride with the sodium salt of corresponding Schiff base ligands in unimolar ratio in refluxing tetrahydrofuran. All these compounds have been characterized using elemental analyses and their probable structures have been proposed on the basis of infrared, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR and mass spectroscopic studies. In the trimethyltin(IV) derivatives the central tin atom is tetracoordinated, whereas in the analogous triphenyltin(IV)derivatives the central tin atom is pentacoordinated. All these ligands, metal precursors and corresponding triorganotin(IV) complexes have been screened for antimicrobial activities. A comparison of activities of the ligands and their corresponding triorganotin(IV) derivatives has been made. Attempts have also been made to relate the activity to the structure of these compounds.     

Synthesis and characterization of some new Schiff base polymers

Seven Schiff base polymers poly 5,5^′-methylenebis(2-hydroxyacetophenone)semicarbazone (PHASC), poly-5,5^′-methylenebis(2-hydroxyacetophenone)thiosemicarbazone (PHATS), poly 6,6^′-methylenebis(2-hydroxynaphthaldehyde)1,2-propylenediimine (PHNPn), poly 6,6^′-methylenebis (2-hydroxynaphthaldehyde)1,3-propylenediimine (PHNPR), poly 6,6^′-methylenebis (2-hydroxy-naphthaldehyde)thiosemicarbazone (PHNTS), poly 6,6^′-methylenebis(2-hydroxy-naphthaldehyde)urea (PHNU) and poly-6,6^′-methylenebis(2-hydroxynaphthaldehyde)semicarbazone (PHNSC) were prepared by polycondensation of 5,5^′-methylenebis(2-hydroxyacetophenone) (MHA) or 6,6^′-methylenebis(2-hydroxynaphthaldehyde) (MHN) with semicarbazide, thiosemicarbazide, 1,2-propylenediamine, 1,3-propylenediamine or urea. The polymers were characterized by elemental micro-analysis, infrared and ultraviolet spectroscopy and viscosity measurements. The reduced viscosity of the polymers measured in dimethylformamide (DMF) was observed in the range 0.32-0.63 dl/g.     

Coordination properties of hydralazine Schiff base Synthesis and equilibrium studies of some metal ion complexes

In the present study, a new ligand is prepared by condensation of hydralazine (1-Hydralazinophthalazine) with 2-butanon-3-oxime. The acid-base equilibria of the schiff-base and the complex formation equilibria with the metal ions as Cu(II), Ni(II), Co(II), Cd(II), Mn(II) and Zn(II) are investigated potentiometrically. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties as atomic number, ionic radius, electronegativity and ionization potential are investigated. The isolated solid complexes are characterized by conventional chemical and physical methods. The potential coordination sites are assigned using the i.r. and (1)H NMR spectra. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies.     

Synthesis,characterization and magnetostructural correlation studies on three binuclear copper complexes of pyrimidine derived Schiff base ligands

Three binuclear Cu(II) complexes of two pyrimidine derived Schiff base ligands, 2-S-methyl-6-methyl-4-formyl pyrimidine-N(4)-ethyl thiosemicarbazone (HL₁) and salicyl hydrazone of 2-hydrazino-4,6-dimethylpyrimidine (HL₂), have been prepared. HL₁ produces a bis(μ-thiolato) Cu(II) complex co-crystallizing with its mononuclear analog, [Cu₂(L₁)₂(NO₃)₂][Cu(L₁)(NO₃)] (1). On the other hand HL₂ shows versatility by producing two different classes of binuclear Cu(II) complexes, a bis(μ-phenoxo) complex [Cu₂(L₂)₂(NO₃)₂] (2) and another a (μ-4,4′-bipyridyl) complex, [Cu₂(L₂)₂(μ-4,4′-bipyridyl)(NO₃)₂] (3) under suitable conditions. All the three complexes show distorted square pyramidal geometry around each Cu atom but to a varied extent. Magnetic behavior of complex 1 shows that it is strongly ferromagnetic in nature whereas compounds 2 and 3 are weakly antiferromagnetic in nature. A magnetostructural correlation study combined with molecular modelling on complexes 1 and 2 has thrown light on the difference on magnetic interaction between the Cu atoms in these two complexes. Various factors that may be responsible for such differences are also explored. A novel and potentially useful pH dependant conversion of 3 to 2 has also been noticed.     

Syntheses and mesomorphic properties of new oxygen-bridged dicopper complex homologous derived from azo-containing salicylaldimine Schiff base ligands

The synthesis, characterization and liquid crystal properties of a homologous series of new tridentate 5-((4-ⁿalkoxyphenyl) azo)-N-(3-ydroxypropyl) salicylaldimine ligands (alkoxy = octloxy, decyloxy, dodecyloxy and tetradecyloxy) and their dicopper(II) complexes are reported. These ligands were prepared by the condensation of the 5-((4-ⁿalkoxyphenyl)azo)salicylaldehydes homologous with 3-amino-1-propanol. The ligands and their dicopper complexes have been characterized by IR, ¹H NMR, mass spectroscopy and elemental analyzes. The liquid crystalline properties of the ligands and the related dicopper complexes were studied by differential scanning calorimetry (DSC) and by using a polarizing microscope equipped with a heating and cooling stage. None of the free ligands exhibit liquid crystalline behavior but all of the dicopper complexes demonstrate a smectic A mesophase.     

An experimental and theoretical investigation on adsorption properties of some diphenolic Schiff bases as corrosion inhibitors at acidic solution/mild steel interface

The effect of novel synthesized three Schiff bases, namely, 1,3-bis[2-(2-hydroxy benzylidenamino) phenoxy] propane (P1), 1,3-bis[2-(5-chloro-2-hydroxybenzylidenamino) phenoxy] propane (P2), and 1,3-bis[2-(5-bromo-2-hydroxybenzylidenamino) phenoxy] propane (P3), on the corrosion of mild steel in 0.1 M HCl was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy methods. Polarization measurements suggest that P1 acts as mixed type inhibitor while P2 and P3 behave as mainly cathodic inhibitors for acidic corrosion of steel. All electrochemical measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on steel surface. Adsorption of these inhibitors follows Temkin adsorption isotherm. The correlation between the adsorption ability of inhibitors and their molecular structures has been investigated using quantum chemical parameters obtained by MNDO semi-empirical method. Calculated quantum chemical parameters indicate that Schiff bases adsorbed on steel surface by chemical mechanism.