Reduced Schiff Base Ligands Research Articles

Novel Copper (II) Complexes with Fluorine-Containing Reduced Schiff Base Ligands Showing Marked Cytotoxicity in the HepG2 Cancer Cell Line.

Several novel copper (II) complexes of reduced Schiff bases containing fluoride substituents were prepared and structurally characterized by single-crystal X-ray diffraction. The complexes exhibited diverse structures, with the central atom in distorted tetrahedral geometry. The biological effects of the products were evaluated, specifically their cytotoxicity, antimicrobial, and antiurease activities, as well as affinity for albumin (BSA) and DNA (ct-DNA). The complexes showed marked cytotoxic activities in the HepG2 hepatocellular carcinoma cell line, considerably higher than the standard cisplatin. The cytotoxicity depended significantly on the substitution pattern. The best activity was observed in the complex with a trifluoromethyl group in position 4 of the benzene ring-the dichloro[(±)-trans-N,N'-bis-(4-trifluoromethylbenzyl)-cyclohexane-1,2-diamine]copper (II) complex, whose activity (IC50 28.7 μM) was higher than that of the free ligand and markedly better than the activity of the standard cisplatin (IC50 336.8 μM). The same complex also showed the highest antimicrobial effect in vitro. The affinity of the complexes towards bovine serum albumin (BSA) and calf thymus DNA (ct-DNA) was established as well, indicating only marginal differences between the complexes. In addition, all complexes were shown to be excellent inhibitors of the enzyme urease, with the IC50 values in the lower micromolar region.

An insight into the non-covalent Cl•••Cl interaction in the solid state structure of carboxylate bridged trinuclear mixed valence cobalt(III/II/III) complexes with tetradentate N2O2 donor reduced Schiff base ligands

Two mixed-valence trinuclear cobalt(III)-cobalt(II)-cobalt(III) complexes, [CoII{(μ-L1)(μ-OOCC6H5NO2)CoIII(N3)}2] (1) and [CoII{(μ-L2)(μ-OOCC6H4NO2CH3)CoIII(N3}2] (2) have been synthesized using two tetradentate N2O2 donor 'reduced Schiff base' ligands, H2L1 {2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(4-chlorophenol}, and H2L2{2-hydroxy-1,3-propanediyl)bis(iminomethylene)bis(4-chlorophenol}, and 3-nitrobenzoic benzoic acid or 4-methyl 3-nitrobenzoic benzoic acid as anionic co-ligands. The complexes have been characterized by spectroscopic measurements and their solid state structures have been determined by single crystal X-ray diffraction analysis. The trinuclear cobalt(III)-cobalt(II)-cobalt(III) skeleton of both the complexes are linear and centrosymmetric. Both the central cobalt(II) and terminal cobalt(III) of both the complexes are hexa-coordinated. DFT calculations have been used to analysed some supramolecular assemblies of the complex that have been observed in the solid state, specifically the Cl···Cl interactions that result in the creation of a stable 2D supramolecular assembly in the solid state. QTAIM and NCI Plot computational tools have been used to characterize the interactions. Thermo-gravimetric (TG) analysis was used to examine the thermal behaviour of both complexes. The redox behaviors of both the complexes were studied by using Cyclic Voltammetry (CV).

Variation of carboxylate binding mode in self-assembled Ni(II) complexes with tridentate reduced Schiff base ligand: Syntheses, structural analysis

Variation of carboxylate binding mode in self-assembled Ni(II) complexes with tridentate reduced Schiff base ligand: Syntheses, structural analysis

Structural features and antiproliferative activity of Pd(II) complexes with halogenated ligands: a comparative study between Schiff base and reduced Schiff base complexes.

In order to investigate the structural features and antiproliferative activity of Pd(II) complexes containing halogenated ligands with different flexibility, several Schiff base and reduced Schiff base Pd(II) complexes, namely X1X2PicPd, X1X2PyPd, X1X2Pic(R)Pd, and X1X2Py(R)Pd (where X1 = X2 = Cl, Br and I; Pic: 2-picolylamine; Py = 2-(2-pyridyl)ethylamine), were synthesized and characterized by spectroscopic methods and, in the case of Br2PyPd, Cl2Py(R)Pd and ClBrPy(R)Pd, also by X-ray crystallography. The results of the X-ray crystallography showed that in both series of complexes the Pd(II) ion has a distorted square-planar geometry, although the coordination modes of the two ligands are different. In the Schiff base-type complexes the ligand acts as a tridentate chelate with NN'O donor atoms, whereas in the reduced Schiff base-type complexes the ligand acts as a bidentate chelate with NN' donor atoms. In both series of complexes, the chloride ions occupy the residual coordination sites of the Pd(II) ion. TD-DFT calculations were performed for a better understanding of the UV-Vis spectra. From these calculations it was found that the signal appearing at ∼400 nm in the complexes with reduced Schiff base ligands (X1X2Pic(R)Pd and X1X2Py(R)Pd) is mainly due to a HOMO → LUMO transition, while for the Schiff base complex ClBrPyPd the signal is due to a HOMO → LUMO+1 transition. For the complex I2PicPd, combinations of HOMO-4 → LUMO and HOMO-2 → LUMO transitions were found to be responsible for that signal. In regard to the biological activity profile, all complexes were first investigated as proteasome inhibitors by fluorometric methods. From these enzymatic assays, it emerged that they are good inhibitors with IC50 values in the low-micromolar range and that their inhibitory activity is strictly related to the presence of the metal ion. Subsequently they were also subjected to cell-based assays (the resazurin method) to assess their antiproliferative properties by using two leukemic cell lines, namely the drug-sensitive CCRF-CEM cell line and its multidrug-resistant sub-cell line CEM/ADR5000. In this test they displayed IC50 values in the sub-micromolar and low-micromolar range determined for a selected metal complex (Br2Pic(R)Pd) and ligand (Cl2Pic(R)), respectively. Moreover, docking studies were performed on the two expected molecular targets, i.e. proteasome and DNA, to shed light on the mechanisms of action of these types of Pd(II) complexes.

The crucial role of hydrogen bonding in shaping the structures of zinc-based coordination polymers using tridentate N, N, O donor reduced Schiff base ligands and bridging acetates.

In this manuscript we report the synthesis and characterization of two new polynuclear zinc(ii) complexes, [Zn2L1(μ-OAc)3]n·H2O (1) and [Zn2L2(μ-OAc)3]n (2) using two tridentate ligands, HL1 {4-chloro-2-(((2-(methylamino)ethyl)amino)methyl)phenol} and HL2 {2,4-dibromo-6-(((3-(methylamino)propyl)amino)methyl)phenol}. The structures were confirmed by single-crystal X-ray diffraction analysis. Both complexes form 1D chains. The energy of H-bonding interaction in the solid state structures of the complexes has been estimated by DFT calculation and the crucial role of hydrogen bonding in shaping their structures has been highlighted.

Synthesis, structural characterization and magnetic studies of two Cu(II)-azide based one-dimensional polymeric chains derived from reduced Schiff base ligands

This article describes syntheses, structural characterizations and magnetic studies of two new Cu(II)-azido based coordination polymers. The complexes, [Cu4(L1)2(N3)6]∞ (1) and [Cu4(L2)2(N3)6]∞ (2) have been synthesized by using Cu(ClO4)2·6H2O, reduced Schiff base ligands (HL1−2) and NaN3 in 1:1:2 M ratios. HL1 and HL2 are the condensation products of salicylaldehyde with N-ethyl-1,2-ethylenediamine and N,N-dimethyl-1,3-propanediamine, respectively. Structural analysis shows that both complexes have similar tetrameric Cu(II) building units in which Cu(II) ions are linked by phenoxo oxygen atoms and two different bridging azido linkages (µ1,1-N3− and µ1,1,3-N3−). An azide co-ligand is also attached with one of the Cu centres through terminal mode. The Cu(II) ions occupy distorted penta-coordinated square pyramidal geometry in complexes 1 and 2. Magnetic susceptibility measurements in the range of 300 K–2 K exhibit the presence of antiferromagnetic interactions between Cu(II) centeres of both complexes 1 and 2.

In situ reduction synthesis of quinoline-based copper(I) complexes: “Self-activating” chemical nuclease, antioxidation and anticancer activity

Two new Cu(І) complexes, [Cu2(L1)2(μ-Br)2] (1) and [Cu2(L1)2(μ-Cl)2] (2) were synthesized from Cu(II) halogen salts and the reduced Schiff base ligand. Stable Cu(І) complexes were obtained via in situ reduction of Cu(II) to Cu(I) and the CN was oxidize to C = N in the ligand. The structures of two complexes were characterized by X-ray single crystal diffraction analysis as well as IR and UV–Vis spectra. The two complexes have potential antioxidant capacity and exhibit efficiently self-activated DNA cleavage activity and hydroxyl radical ROS cleavage mechanism. MTT was used to assay cytotoxicity of the complexes toward a series of tumor cell and HUVEC cell lines. Both complexes exhibited higher selective cytotoxicity against tumor cells than normal cells, which is significantly superior to the positive control. The complexes could induce cell apoptosis via mitochondrial pathway by increase of ROS levels and decrease of mitochondrial membrane potential (Δψm). Furthermore, the complexes can obviously inhibit the migration and invasion of the quiz tumor cells, as well as inhibit the angiogenesis of HUVEC cells.

Metallomacrocycle or 1D chain: Synthesis, structures, and antifungal activities of zinc(II) and silver(I) complexes based on two reduced Schiff base ligands

Two reduced Schiff base ligands (L1 and L2) were synthesized from two Schiff base compounds containing pyridine-2,6-dicarboxamide skeletons. In the presence of Zn(II) or Ag(I) ions, five complexes, formulated as [ZnL1Cl2] (1), [AgL1NO3]·4CH3CN (2), {[AgL1]·NO3·DMSO}n (3), {[ZnL2Cl2]·2DMF·H2O}n (4), and [Ag2(L2)2(CH3CN)2]·2NO3·2CH3CN (5), were synthesized and further characterized via elemental analysis, FT-IR spectra and single-crystal X-ray diffraction. Complexes 1 and 2 exist as similar mononuclear [1+1] metallomacrocycles. Complexes 3 and 4 exist as 1D zig-zag chain polymers. Complex 5 exists as a centrosymmetric [2+2] metallamacrocycle. The structural differences of the complexes reveal two different configurations of the ligands in coordination with metal ions. Furthermore, antifungal measurements show that all of the three Ag(I) complexes exhibit good inhibiting effects against M. grisea and S. sclerotiorum.

In vitro cytotoxicity activity of copper complexes of imine and amine ligands: A combined experimental and computational study

Two new Cu(II) complexes [CuL1 (µ1,3-NCS)]2, 2ClO4 (A) and [CuL2 (NCS)2] (B) with Schiff base ligand L1 and reduced Schiff base ligand L2 have been synthesized and characterized by various spectroscopic and electrochemical methods along with single crystal XRD techniques. X-ray diffraction analysis confirms the formation of binuclear (A) and mononuclear (B) complexes. Hirshfeld surfaces analysis of the two complexes and their associated two-dimensional fingerprint plots are plotted. The metal complexes were optimized by using the density functional theory (DFT) comprising Becke’s three parameters exchange potential and Lee-Yang-Parr correlation functional (B3LYP) method, with 6-31G(d,p) basis set for the ligand atoms and LANL2DZ for the central metal ions. The synthesized binuclear Complex A and mononuclear Complex B were screened for their in vitro anticancer activity against human colon adenocarcinoma cells (HT-29) and human hepatoma cell line (Hep-G2) and HeLa cell line. Activity results proved that Complex A has excellent antiproliferative activity against colon carcinoma whereas Complex B is active against hepatocellular carcinoma and cervical cancer.

Corrosion Inhibition of Carbon Steel in 0.5 M H2SO4 by New Reduced Schiff Base Ligand

Corrosion Inhibition of Carbon Steel in 0.5 M H2SO4 by New Reduced Schiff Base Ligand

Large interaction energy for the homodimer and the heterodimer extracted from the supramolecular chain of a bent trinuclear zinc(ii) complex with a reduced Schiff base ligand

The coordinated amino groups in a trinuclear zinc complex participate in strong H-bonding interactions that have been analysed. The dimerization energy is very large for both the homodimer and the heterodimer in the 1D supramolecular chain.

Solid-State Thermolysis of 1D and 3D Cd-Coordination Polymers of l-methionine Derived Ligand to CdS Nanospheres: Facile Synthesis, Charecterization and Dye degredation Studies

• This article represents synthesis of coordination polymers 1/2 possessing one-dimensional (1D) and three-dimensional (3D) framework respectively. • The coordination polymers were characterized by various spectroscopic and analytical techniques as well as single crystal X-ray diffraction study. • CdS nanospheres ( CdS-1/2 ) were prepared by controlled solid-state thermolysis using of 1 and 2 as precursors. • The photocatalytic activities of 1, 2, CdS-1 , and CdS-2 were evaluated for degradation of methylene blue under visible light. • In comparison to coordination polymers, the NPs have greater photocatalytic efficiency. Two coordination polymers [Cd(L) 2 (H 2 O) 2 ] n ( 1 ) and [Cd(L)-µ 2 Cl] n ( 2 ) are synthesized from a l -methinone based reduced Schiff base ligand and characterized by various spectrochemical and analytical methods along with single-crystal X-ray analysis. The crystal structures indicate formation of a one-dimensional (1D) and a three-dimensional (3D) framework for 1 and 2 respectively. Controlled solid-state thermolysis of 1 and 2 , resulted size specific CdS nanospheres ( CdS-1/2 ) having hexagonal wurtzite structure with excellent optical properties. The photocatalytic activities of coordination polymers ( 1 / 2 ) as well as nanoparticles ( CdS-1/2) are evaluated in degradation of methylene blue (MB) solution in presence of visible light which shows enhanced catalytic efficiency of nanoparticles over coordination polymers. Catalytic efficacy and reusability suggest the synthesized nanospheres can be used as potential photocatalysts for removal of hazardous organic wastes from water.

Highly Active Homoleptic Zinc and Magnesium Complexes Supported by Constrained Reduced Schiff Base Ligands for the Ring-Opening Polymerization of Lactide.

New homoleptic zinc and magnesium complexes containing constrained reduced Schiff base ligands based on substituted 7-hydroxy-1-indanone were successfully synthesized and used as a catalyst for the polymerization of lactide. The ligands contain a side arm having different basicity because dimethylamino, pyridyl, and furfuryl groups are shown to greatly affect the polymerization rates. The homoleptic zinc complex containing constrained reduced Schiff base ligands and a dimethylamino side arm was highly active, giving a 92% conversion of l-lactide in 3 min using [LA]:[Zn]:[BnOH] = 500:1:2 at room temperature. The polymerization is pseudo-first-order dependent on the LA concentration. Well-controlled and living behavior of the zinc complex was observed and demonstrated in the preparation of stereodiblock and triblock copolymers of l-, d-, and rac-lactide in a one-pot sequential synthesis with a predictable block length, block sequence, and narrow dispersity rapidly in 10 min. Stereocomplex formation was observed for PLA made sequentially from 100 l-LA, 100 rac-LA, and 100 d-LA having a high Tm of up to 220 °C.

Catecholase-like activity in 2D MOFs: Oxidation of 3,5-DTBC by two Cu(II) 2D MOFs of reduced Schiff base ligands

Two-dimensional metal-organic frameworks (2D MOFs) materials have been explored extensively for their interesting properties and applications, but not so much for Catecholase-like catalytic activity. We describe here two Cu(II) 2D MOFs of reduced Schiff base ligands for their Catecholase-like activity. These were synthesized and characterized by spectroscopic analyses. The solid state structure of [Cu2(NglyR)2] (where NglyR is a reduced Shiff base ligand derived from 2-hydroxy-1-naphthaldehyde and glycine) (1) consistes of two Cu(II) atoms bridged by two phenalato groups and further chelated by oxygen and nitrogen atoms of the glycine part of NglyR ligand. These dimers are further linked by the terminal carboxylato oxygen atoms to possess a 2D sheet structure. In the absence of solid-state structure of [Cu2(NSchR)2] (2) (where NSchR is a reduced Schiff base ligand derived from 2-hydroxy-1-naphthaldehyde and 1-amino-1-cyclohexanecarboxylic acid), the dinuclear core with bridging phenolate ligands has been proposed from physicochemical and spectroscopic methods. The MOFs have also been investigated for their catecholase-like activities with 3,5-di-tert-butylcatechol (3,5-DTBC). Hyperbolic inhibition was observed for 1 in the following solvent systems: MeOH, MeOH:DMF (95:5, v/v) and (90:10, v/v), but not for 2. Moreover, catalytic activities are found to be heavily influenced by v/v ratio of the mixed solvent systems and solvent nucleophilicity.

Phenoxo-bridged dinuclear mixed valence cobalt(III/II) complexes with reduced Schiff base ligands: synthesis, characterization, band gap measurements and fabrication of Schottky barrier diodes.

Two homometallic class-I dinuclear mixed valence cobalt complexes, [(N3)CoIIIL1(μ-C6H4(NO2)CO2)CoII(N3)] (1) and [(N3)CoIIIL2(μ-C6H4(NO2)CO2)CoII(N3)] (2), have been synthesized using multisite N2O4 coordination ligands, H2L1 {where H2L1 = (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol) and H2L2 = (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)}. Each complex has been structurally characterized by single crystal X-ray diffraction and spectral analysis. Both the cobalt centers in these dinuclear complexes adopt a distorted-octahedral geometry, where the cobalt(iii) center resides at the inner N2O2 cavity and the cobalt(ii) center resides at the outer O4 cavity of the reduced Schiff base. Both of them show good electrical conductivity, which has been rationalized by band gap measurements. The band gap in the solid state has been determined by experimental and DFT calculations and it confirms that each of the two complexes behaves as a semiconductor. The space-charge-limited current (SCLC) theory is employed to evaluate the charge transport parameters such as effective carrier mobility and transit time for both complexes. The difference in the conductivity values of the complexes may be correlated with the strengths of extended supramolecular interactions in the complexes. Bader's quantum theory of atoms-in-molecules (QTAIM) is applied extensively to get quantitative and qualitative insights into the physical nature of weak non-covalent interactions. In addition, the non-covalent interaction reduced density gradient (NCI-RDG) methods well support the presence of such non-covalent intermolecular interactions.

Heterometallic Complexes Containing the NiII-LnIII-NiII Moiety—Structures and Magnetic Properties

This review summarizes the structural characteristics and magnetic properties of trinuclear complexes containing the NiII-LnIII-NiII moiety and also oligonuclear complexes and coordination polymers containing the same trinuclear moiety. The ligands used are mainly polydentate Schiff base ligands and reduced Schiff base ligands and, in some cases, oximato, β-diketonato, pyridyl ketone ligands and others. The compounds reported are restricted to those containing one, two and three oxygen atoms as bridges between the metal ions; examples of carboxylato and oximato bridging are also included due to structural similarity. The magnetic properties of the complexes range from ferro- to antiferromagnetic depending on the nature of the lanthanide ion.

Dinuclear mixed valence cobalt(II/III) and hetero-tetranuclear cobalt(III)/Na complexes with a compartmental ligand: Synthesis, characterization and use as catalysts for oxidative dimerisation of 2-aminophenol

A N2O4 donor compartmental reduced Schiff base ligand, H2L [(2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol)], obtained on 1:2 condensation of 2,2-dimethyl-1,3-propanediamine with ortho-vanillin followed by reduction with NaBH4 in methanol solution, has been used to prepare two cobalt complexes, [(N3)CoIIIL(µ-OAc)CoII(N3)] (1) and [(μ-N3)2{(AcO)CoIIILNa(CH3OH)}2]·2CH3OH (2). Complex 1 is a dinuclear mixed valence cobalt(III)/cobalt(II) complex with CoIIIO2CoII core. Complex 2, on the other hand, is a tetranuclear cobalt(III)/sodium complex with CoO2Na(N3)2NaO2Co core. Formation of complex 1 or 2 is mainly governed by the amount of cobalt(II) precursors present in the reaction mixture. Each complex has been characterized by elemental and spectral analysis. X-ray diffraction analysis has confirmed their structures. Complex 1 crystallized in a chiral space group Pna21 where both the cobalt(III) and cobalt(II) centers adopt six-coordinate distorted octahedral geometry with cobalt(III) and cobalt(II) centers residing respectivelyat inner N2O2 and outer O4 cavities of the reduced Schiff base. Complex 2 crystallized in triclinic system with P1-space group, where both cobalt(III) and sodium centers adopt distorted octahedral geometry. Oxidation states of cobalt centers have been confirmed by bond length consideration, BVS calculations as well as from room temperature magnetic moment measurement. Both complexes 1 and 2 show phenoxazinone synthase mimicking activity with kcat values 250.21 and 493.73 h−1 respectively.

Synthesis, structure and magnetic property of a dinuclear cobalt(II/III) complex with a reduced Schiff base ligand

A dinuclear mixed valence cobalt(II/III) complex, [(N3)CoIIIL(µ-CH3COO)CoII(N3)]∙CH3OH with a N2O4 donor compartmental reduced Schiff base ligand, H2L [(1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)], has been synthesized and characterized by spectral and elemental analyses. Cobalt(III) is placed in the inner N2O2 compartment whereas cobalt(II) is present in the outer O4 compartment of the ligand. Structure of the complex is confirmed by single crystal X-ray crystallography. The magnetic susceptibility measurement confirms that the complex belongs to localized class-I mixed valence system with isolated S = 3/2 ion and shows Curie-Weiss paramagnetism.

An acetate bridged centrosymmetric zinc(II) complex with a tetradentate reduced Schiff base ligand: Synthesis, characterization and ability to sense nitroaromatics by turn off fluorescence response

A unique trinuclear centrosymmetric zinc(II) complex, [Zn3L2(CH3CO2)2(DMSO)2] has been synthesized and characterized by using a reduced Schiff base ligand H2L {H2L = 1,3-bis(2-hydroxybenzylamino)2,2-dimethylpropane}. The complex has been characterized by spectral and elemental analysis. Single crystal X-ray diffraction analysis has confirmed the structure of the complex. The complex has showed strong fluorescence, which may be quenched in presence of different nitroaromatic substances. The complex thus used as a sensor for the detection of nitroaromatics in DMF via turn-off fluorescence response.

Application of two Cu(II)-azido based 1D coordination polymers in optoelectronic device: Structural characterization and experimental studies

Two new azido bridged 1D polymeric Cu(II) chains, [Cu(L1)(μ1,3-N3)]∞ (1) and [Cu2(L2)2(μ1,1-N3)(μ1,3-N3)]∞ (2) have been synthesized by using two different N2O donor tridentate reduced Schiff base ligands, HL1 = 2-[(2-dimethylamino-ethylamino)-methyl]-4-nitrophenol, HL2 = 2-[(2-diethylamino-ethylamino)-methyl]-4-nitrophenol and both are structurally characterized. Cu(II) ions in both complexes occupy distorted pentacoordinated square pyramidal geometry. Both structures form polymeric chains, in 1, via μ1,3-N3− while in 2via both μ1,1-N3− and μ1,3-N3− bridges. The band gaps of the complexes (2.91 eV for 1 and 2.89 eV for 2) suggest that both polymeric chains are semiconducting and thus possess the potential for uses in devices. A detail I–V analysis was performed to measure device related parameters i.e. effective carrier mobility, transit time, carrier concentration, diffusion length and ideality factor. The results show that both polymeric chains behave as Schottky barrier diodes (SBD) and could be used in opto-electronic device. Between the two complexes, 2 performs better than 1 in terms of applicability as indicated by the calculated parameters.