Schiff Base Transition Metal Research Articles

Transition metal Schiff base complexes supported on layered double hydroxide: synthesis, characterization and catalytic activity for the oxidation of toluene

The catalytic oxidation of toluene was studied over Mn(III) and Fe(III) Schiff base complexes supported layered double hydroxide catalysts. The supported catalysts were synthesized by intercalation method and abbreviated as LDH-[NAPABA-M], {where M = Mn(III) and Fe(III)}. The obtained material was characterized by various physical techniques such as ICP-AES, EDX, XRD, FTIR, SEM, TEM, BET surface area, EPR, and TGA. The liquid-phase catalytic oxidation of toluene was studied using LDH-[NAPABA-M]/TBHP system. A maximum conversion of toluene (55.3%) and selectivity of benzaldehyde (86.1%) was observed with LDH-[NAPABA-Mn(Cl)]/TBHP system, when the reaction is carried out at toluene to tert-butylhydroperoxide (TBHP) molar ratio 1:3, temperature 373 K, and catalyst amount, 100 mg. The catalyst, LDH-[NAPABA-Mn(Cl)] gave excellent; conversion of toluene and selectivity of benzaldehyde in comparison to LDH-[NAPABA-Fe(Cl)] catalyst. The catalyst, LDH-[NAPABA-Mn(Cl)] showed good stability and reusability up to five cycles without significant loss of catalytic activity.

Design, synthesis and biological evaluation of heterocyclic methyl substituted pyridine Schiff base transition metal complexes

In recent years heterocyclic Schiff base metal complexes attract more attention in biological application and also showing interesting co-ordination chemistry. In this research article a novel heterocyclic methyl-substituted pyridine Schiff base transition metal complexes of Fe(III), Co(III), Cu(II), and Ni(II) have been design and synthesized by reacting metal acetate or metal salts (FeCl3, CoOAc, CuOAc, NiOAc), with substituted heterocyclic ligand. All newly synthesized metalcomplexes were characterized by spectroscopic data and screened for elemental analysis, FT-IR, ESR, Magnetic susceptibility and TGA. The Electronic spectra and magnetic susceptibility measurements indicates that square planer and octahedral geometry of these complexes also suggest their structure in which (N, O) group acts as bidentate ligand. The thermal stability, decomposition rate and thermodynamic parameters of synthesized metal complexes were calculated by Freeman Carroll method. Also the biostatistical data of antimicrobial and anti-oxidant activities of synthesized metal complexes indicates moderate to good results.Graphic abstract

Synthesis, Characterization and Electrochemical Sensor Based Upon Novel Schiff Base Metal Complexes Derived from the Non-Steroidal Anti-inflammatory Drug, Flufenamic Acid for the Determination of Uric acid and their Biological Applications

The current trend in coordination chemistry is the design and synthesis of new Schiff base transition metal complexes for therapeutic, diagnostic, and catalytic applications. For decades, it has been observed that special attention is being paid to the chemistry of Schiff base metal complexes because of their wide range of applications. Therefore the present paper involves the synthesis of Schiff base ligand by altering the functional group of the drug, Flufenamic acid. From that Schiff base ligand, four complexes, i.e., Co(II), Cu(II), Ni(II), and Zn(II) have been prepared (SB metal complexes). The synthesized SB metal complexes have been characterized using several spectral and analytical techniques. All the metal complexes show non-electrolytic behavior suggested by molar conductance measurements. Spectral studies suggest that all four metal complexes exhibit octahedral geometry. The modified SB-Co complex/GCE showed a greater electro-catalytic activity and lower potential towards the oxidation of uric acid (UA). The response of UA was linear over the concentration ranging from CV is 0.5–1.8 μmol/L, sensitivity for 131.85 μAμM-1cm-2, and detection limit for 0.16 μM (S/N=3). The modified GCE showed very good sensitivity along with good repeatability and reproducibility for the determination of UA. The pure drug, Schiff base ligand, and metal complexes, were also screened for anti-inflammatory and antibacterial activities. The observed results prove that the metal complexes exhibit greater activity than that of the original drug.

Fluorimetric Detection of Phosphates in Water Using a Disassembly Approach: A Comparison of FeIII‐, ZnII‐, MnII‐ and MnIII‐salen Complexes

Details of the reaction sequence used for the fluorimetric detection of phosphates by disassembly of transition metal Schiff base complexes were investigated for [FeIII(salen)(H2O)]+, [ZnII(salen)], [MnII(salen)(H2O)2], and [MnIII(salen)(H2O)]+. The reactivity of these compounds towards phosphorus oxoanions of differing charge, number of donor atoms and steric hindrance was detected by UV/Vis and fluorescence spectroscopy in both aprotic organic and aqueous media. Selectivity of [FeIII(salen)(H2O)]+ towards pyrophosphate over all other tested phosphorus‐containing analytes was strongly supported. [ZnII(salen)] showed a faster reactivity but was much less selective. In contrast, [MnIII(salen)(H2O)]+ proved to be more stable than the iron complex but generally showed little reactivity towards phosphorus oxoanions. The influence of the charge of the central atom was investigated using the MnII analogue [MnII(salen)(H2O)2]. As expected, the reduced charge resulted in a reactivity comparable to the ZnII complex in organic solution but lead to hydrolysis of the complex in water. Finally, the reaction products of [FeIII(salen)(H2O)]+ with phosphates were characterized by IR spectroscopy and mass spectrometry, providing further insights into the reaction mechanism of the disassembly process.

A review of Titanium, Vanadium and Chromium transition metal Schiff base complexes with biological and catalytic activities

Schiff bases are compounds obtained from the condensation reaction of a primary amine and aldehyde or ketone They can be coordinated with metals especially the transition metals to form Schiff base complexes The objective of this work is to review the synthesis biological as well as catalytic activities of both Schiff base ligands and their transition metal complexes of titanium vanadium as well as chromium The methodology used for looking for the references were through the internet Biological activities that were considered in this review were mainly those of antibacterial and antifungal For the antibacterial both gram positive and gram negative strain were considered The results obtained from the study indicated that the Schiff base complexes Schiff bases as well as metal ions for the metals titanium vanadium and chromium were used by different researchers to investigate antimicrobial activities against bacteria fungi as well as anti tumour activity against breast cancer The antimicrobial literature studies showed that the metal ions were having lower inhibition capacity than the ligands but the complexes showed the highest inhibition capacity against the microbial The use of Mono and dioxide complexes showed anticancer activity against MCF breast cancer cells The cis Dioxido vanadium V complexes were also investigated for catalytic activity on the oxidation of cyclohexane and gave conversion of and selectivity of up to The paper is divided into five sections which include introduction methodology used in looking for references results and discussion acknowledgements and references The results obtained from the review show that the Schiff base complexes were more effective when screened as anti microbial compounds than their ligands The complexes also showed effectiveness when screened for their catalytic activity on organic chemistry reactions

Synthesis, Characterization and Biological Evaluation of Schiff Base Transition Metal Complexes Derived from 4-Nitrobenzene-1,2-diamine and 5-Chloroisatin

A series of transition metal complexes of the type [MLX2], where M = Mn(II), Fe(II), Co(II), Ni(II), X = Cl–/CH3COO– and L = Schiff base derived from 4-nitrobenzene-1,2-diamine and 5-chloroisatin have been synthesized and characterized by elemental analysis, molar conductance, IR, UV-visible, magnetic moments measurement, 1H & 13C NMR and mass spectral studies. On the basis of physico-chemical studies and spectral evaluation, an octahedral geometry have been proposed for all metal(II) complexes. The antimicrobial activity of ligand and its metal complexes have been additionally screened against bacteria and fungi. Metal(II) complexes show good activity as compared to ligand towards studied microorganisms and also metal complexes checked for their catalytic properties for benzoylation of phenol.

Synthesis, Characterization and DNA Binding Studies of N,N′-bis(2-Hydroxy-5-methylbenzylidene)- 2-hydroxy-propane-1,3-diamine Copper(II) and Nickel(II) Complexes

Two new Schiff base transition metal complexes [Cu(HL)]2.CH3CH2OH (1) and [Ni(HL)] (2) (L = N,N′-bis(2-hydroxy-5-methyl-benzylidene)-2-hydroxy-propane-1,3-diamine) were synthesized and characterized by different physico-chemical and spectroscopic techniques. Structure of complex 1 was determined by single crystal X-ray diffractometer. Both the complexes have distorted square planar geometry. The DNA binding study of two complexes was performed via electronic absorption, cyclic voltammetry, photoluminescence, and viscosity methods and found to be intercalative mode of binding.

Transition Metal Schiff Base Complexes Synthesis, Spectral Examination and used as a Catalyst in the Oxidation of Alcohols and C-C Coupling Reactions

In this correspondence, it reveals the formation of Co (II) and Cu (II) complexes consists of a Schiff base ligand having the four donar destinations 2NO. Co(II) and Cu(II) complexes were made ready by the response of 1:1 proportion of the MCl2 .6H2O (M = Co/Cu) with a Schiff base ligand prepared by the response of 2-hydroxynaphthaldehyde with orthophenylene diamine in ethanolic medium having the stoichimetric proportion of 2:1. The purged and arranged complexes were analytically explored. Catalytic efficacy was assessed for oxidation of alcohols and C-C coupling responses.

Synthesis, characterization and biological evaluation of novel 2,2′-((1,2-diphenylethane-1,2-diylidene)bis(azanylylidene))bis(pyridin-3-ol)and metal complexes: molecular docking and in silico ADMET profile

A novel series of bio vital Schiff base ligand and transition metal complexes was prepared from benzil, 2-amino-3-hydroxy pyridine and metal chlorides. The synthesized compounds were characterized by physicochemical measurements like elemental analysis, magnetic susceptibility, molar conductance and multispectral analysis like Fourier transform, electronic absorption, nuclear magnetic resonance, electron paramagnetic resonance, ESI-mass spectroscopy, XRD and scanning electron microscopy. Based on the spectral results, the synthesized compounds are in crystalline nature and copper complex has square planar geometry. Conversely, cobalt, nickel and zinc complexes have tetrahedral geometry. Furthermore, the biological potential of the synthesized compounds is analysed by DNA binding and cleavage analysis and antimicrobial, anticancer, apoptosis and antioxidant inspections. The DNA binding analysis was performed using UV absorption titration and hydrodynamic experiments, which unveiled that the prepared compounds could be interconnected with calf thymus DNA by the way of intercalative mode. The mode of intercalation is further supported by docking investigations with nucleic acid and Bowman-Birk inhibitor. The DNA cleaving analysis implied that Cu(II) complex has eminent cleaving ability to split up the pUC18 DNA with an oxidising agent. Additionally, the anti-pathogenic screening studies explained that the complexes have antimicrobial skill against selected microbes. The anti-carcinogenic talent of the compounds is scrutinized on human cancer cell lines, which revealed that the prepared compounds possess good anticancer proficiency. During Hoechst staining analysis, the synthesized compounds have undergone the morphological moderations and succeeding cell death. The free radical scavenging investigations display that the metal complexes hold the suited talent to hunt the OH radical effectively. The prediction of in silico ADMET belongings found out that synthesized compounds acquire substantial drug-likeness characters based on Lipinski’s rules.

RETRACTED ARTICLE: Three novel Schiff base transition metal(II) complexes induce gastric cancer cell death through ROS-mediated apoptotic pathway

We, the Editors and Publisher of the Journal of Coordination Chemistry, have retracted the following article: Xiu-Heng Qi, Zhen-Ming Wu, Shuai-Bing Wang, Bao-Xin Wang, Ling-Ling Wang, Haiyan Li & Qian Guo (2019) Three novel Schiff base transition metal(II) complexes induce gastric cancer cell death through ROS-mediated apoptotic pathway, Journal of Coordination Chemistry; 2019, VOL. 72, NO. 14, 2310–2325. DOI: 10.1080/00958972.2019.1647535 Since publication, concerns have been raised about the integrity of the data in the article. When approached for an explanation, the authors have been unable to address the concerns raised and have not been able to provide sufficient supporting information. As verifying the validity of published work is core to the integrity of the scholarly record, we are therefore retracting the article. The corresponding author listed in this publication has been informed. The authors do not agree with the retraction. We have been informed in our decision-making by our policy on publishing ethics and integrity and the COPE guidelines on retractions. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’.

Electrochemical behavior, structural, morphological, Calf Thymus-DNA interaction and in-vitro antimicrobial studies of synthesized Schiff base transition metal complexes

New tetradentate Schiff base transition metal complexes have been derived from salicylidene-4-imino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and histidine were characterized by CHN analysis, magnetic susceptibility measurements, molar conductance, FAB-MS, IR, 1H-NMR, UV, CV, EPR, Fluorescence emission, AFM and Powder XRD techniques. AFM images and Powder XRD data endure that the complexes are nano-size grains with polycrystalline structure. The spectral evidences showed that all the metal chelates are square planar geometry except [VOL] complex which exist square-pyramidal geometry. Electrochemical data (CV) for [CuL] and [VOL] complexes in acetonitrile solution indicates that the redox potential of metal ions is affected by the coordinated ligand. Electron Spin Resonance (ESR) spectra of [CuL] and [VOL] complexes were well coinciding with proposed geometries and other reported complexes. CT-DNA interaction studies of [CuL] complex reveals that an intercalation binding mode occurs between complex and DNA base pairs. The in vitro antimicrobial activity of complexes has been tested against the growth of some fungal and bacterial species persist that chelates have better control than ligand.

Synthesis, Crystal Structures, and Anti‐cervical Cancer Activity Evaluation of Three Trinuclear Transition Metal(II) Complexes with N,O‐Donor Schiff Base Ligand

A new bi‐nucleating Schiff base ligand, 2‐(((3‐(dimethylamino)propyl)imino)methyl)‐6‐methoxyphenol (HL1) was prepared by a one‐pot condensation reaction, which was further used in the construction of three trinuclear Schiff base transition metal(II) complexes [Cu3(L1)2(OH)2(H2O)2](NO3)2 (1), [Co3(L1)2(OH)2(H2O)2](NO3)2 (2), and [Cu3(L1)2(N3)4] (3). Furthermore, a green hand grinding technique was implemented to reduce the particle size of the coordination complexes to generate the nanoscale compounds. The SEM studies reveal the formation of square and spherical particles for nano 1 and 2, and nanorod for nano 3. In addition, the anti‐proliferation activity of nano 1–3 was detected on the human cervical cancer Hela cells with CCK‐8 assay. The cell viability curves and IC50 values indicated that only nano 1 has anti‐proliferation activity on Hela cells. To further investigate the mechanism of nano 1 induced Hela cell death, the Annexin V‐FITC/PI double staining assay, western blot assay, and ROS level detection was conducted.

Supported transition metal catalysts of Cu(II), Mn(II) and Co(II): synthesis, characterization, and catalytic behavior

A variety of heterogeneous transition metal Schiff base complexes have been prepared by their intercalation in layered double hydroxide, abbreviated as LDH-[SALABA-M] {where M is Cu, Mn and Co}. The synthesized catalysts are characterized by various analytical techniques like X-ray diffraction, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, inductive coupled plasma-atomic emission spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller surface area etc. The aforesaid catalysts are employed for the oxidation of cyclohexene. Effect of various metals, substrate to oxidant molar ratio, temperature, and catalyst amount etc. have been studied so as to derive optimum conditions for obtaining maximum conversion. Tert-butyl hydroperoxide has been used as an oxidant in acetonitrile solvent. The oxidation products obtained are 2-cyclohexene-1-ol and 2-cyclohexene-1-one. The catalyst, LDH-[SALABA-Cu(II)] is recycled ten times in consecutive runs. Additionally, mechanism of reaction is found out using quenching study.

Enhanced electrochemical performance of salen-type transition metal polymer with electron-donating substituents

Salen-type Schiff base transition metal monomers with substituents Ni (CH3-salen), Ni (CH3O-salen), and Ni (Cl-salen) have been synthesized and electro-polymerized onto the indium tin oxide substrate electrodes. The effect of electron-donating groups on the electrochemical performance of the polymer is studied. Electron-donating groups enhance the electrochemical activity of the salen-type Schiff base during the electropolymerization process. SEM images show that the morphology of poly [Ni (CH3O-salen)] is nanobelt with a width of 200–500 nm. The cyclic voltammetry plots indicate that the strong electron-donating methoxy group facilitates the polymerization of the salen-type Schiff base. Thus, Ni (CH3O-salen) shows a higher doping level than other three polymers. XPS measurement is conducted to investigate the polymerization process and the mechanism of energy storage. It is proved that the azomethine nitrogen group (−N=CH−) matters a lot in the polymerization and energy storage process. In brief, the azomethine nitrogen group was affected by the introduction of the electron-donating group so that extra redox peaks appear in the cyclic voltammetry plots. There is no chemical valence change of nickel, and the nickel atom worked as a bridge in the system. The electro-donating substituent group activates the benzene ring of the polymer and facilitates the charge transfer and leads to poly [Ni(CH3O-salen)] that exhibits the highest doping level, charge-transfer ability, and electrochemical capacity characteristics than the polymer with weaker electro-donating or electro-withdrawing substituents (polyNi(Cl-salen)). At the current density of 0.1 mA cm−2, the specific capacitance of poly [Ni(CH3O-salen)] is 270.1 F g−1, higher than that of poly [Ni(salen)](136.7 F g−1), poly [Ni(CH3-salen)](148.1 F g−1), and poly [Ni(Cl-salen)](106.0 F g−1).

Bioactive Salen-type Schiff Base Transition Metal Complexes as Possible Anticancer Agents.

Although metal-based anticancer drugs have been recognized as the most effective agents over the organic compounds, non-selectivity and high toxic effects have limited their applications in a way that only three Pt-analogues have progressed into clinical use. These problems have spurred chemists to develop different strategies based on alternative targets. This work focuses on predicting potency and mode of interactions of a series of salen type Schiff base transition metal complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine, over some proteins (HDAC7, HDAC2, CatB, B-RAF kinase, TopII, RNR, TS, and rHA) using computational docking method, to be later considered as possible anticancer agents. The obtained results showed that all complexes exhibited higher affinity for HDAC7 than the other targets. Moreover, the bromo-derivatives of the copper compounds were more active on HDAC7 than the other derivatives. Such bromo compounds showed considerable interactions with Kinase, RNR, TS, and CatB. Contrary to Histone deacetylase (HAD)C7; HDAC2 was predicted to be relatively poor target. As expected, formation of the hydrophobic interactions between the metal complexes and the protein targets were essential for activity of the metal compounds. This study provides some more information for further optimizations and development of new metallodrugs as enzyme inhibitors for potential therapeutic agents.

Installation of internal electric fields by non-redox active cations in transition metal complexes.

Local electric fields contribute to the high selectivity and catalytic activity in enzyme active sites and confined reaction centers in zeolites by modifying the relative energy of transition states, intermediates and/or products. Proximal charged functionalities can generate equivalent internal electric fields in molecular systems but the magnitude of their effect and impact on electronic structure has been minimally explored. To generate quantitative insight into installing internal fields in synthetic systems, we report an experimental and computational study using transition metal (M1) Schiff base complexes functionalized with a crown ether unit containing a mono- or dicationic alkali or alkaline earth metal ion (M2). The synthesis and characterization of the complexes M1 = Ni(ii) and M2 = Na+ or Ba2+ are reported. The electronic absorption spectra and density functional theory (DFT) calculations establish that the cations generate a robust electric field at the metal, which stabilizes the Ni-based molecular orbitals without significantly changing their relative energies. The stabilization is also reflected in the experimental Ni(ii/i) reduction potentials, which are shifted 0.12 V and 0.34 V positive for M2 = Na+ and Ba2+, respectively, compared to a complex lacking a proximal cation. To compare with the cationic Ni complexes, we also synthesized a series of Ni(salen) complexes modified in the 5' position with electron-donating and -withdrawing functionalities (-CF3, -Cl, -H, -tBu, and -OCH3). Data from this series of compounds provides further evidence that the reduction potential shifts observed in the cationic complexes are not due to inductive ligand effects. DFT studies were also performed on the previously reported monocationic and dicatonic Fe(ii)(CH3CN) and Fe(iii)Cl analogues of this system to analyze the impact of an anionic chloride on the electrostatic potential and electronic structure of the Fe site.

Nanographene Sheet Immobilized Transition Metal Complexes for C-C Coupling Reactions

Transition metal Schiff base complexes covalently immobilized on the surface of amino functionalized graphene sheet to catalyze C-C coupling reaction is reported. Graphene sheet which synthesized using mechanical exfoliation and then by differential oxidative reduction phenomenon of graphite. The schiff base ligand is prepared using aldehyde and amino groups containing compounds which further treated with metal salts to form metal complexes. The as-synthesized metal complexes was then incorporated into amino functionalized nanosheets which are characterized using different spectrochemical techniques. The catalytic investigation of the as-prepared catalyst were done by the cross coupling of aryl halides and aryl boronic acids to form biaryls as product in C-C cross coupling reaction. The yield of the products were high and selective which were analyzed using Gas chromatography technique. The advantage of this catalyst is high stability, recyclability easy recovery of catalyst, environmentally benign and mild reaction condition.

Exploring the DNA interactions, FGF growth receptor interaction and biological screening of metal(II) complexes of NNN donor ligand derived from 2‑(aminomethyl)benzimidazole

This work deals with a series of biologically important novel transition metal(II) Schiff base chelates containing terpyridine. Benzimidazole, a moiety found in broad spectrum of drugs is espoused in a Schiff base ligand system. Eight such metal(II) complexes are designed, synthesized and characterized. An octahedral geometry has been envisaged for all the complexes. DNA-binding behaviours are studied by absorption titration, electrochemical, viscosity, fluorescence and circular dichroism methods. The DNA cleavage ability is also evaluated by agarose gel electrophoresis method. These studies reveal that the complexes show an intercalative mode of binding to CT-DNA and also effectively cleave the supercoiled pBR322 DNA. The molecular docking studies of the complexes against FGF growth receptors indicate that they bind through electrostatic, van der Waals, hydrogen bonding and π-π interactions. The ligand and its complexes are screened for in vitro antimicrobial activities against a few microorganisms. The data exhibit that they are better antimicrobial agents than the ligand. The cytotoxic activity of the complexes is probed in four cell lines wherein the complex 5 has good cytotoxic activity and is partial to MCF-7 cell line which is comparable with the cisplatin drug which can be attributed to the presence of planar terpyridine co-ligand.

Synthesis and characterization of transition metal complexes with a Schiff base derived from cephalexin and 1,2–diaminobenzene. antibacterial activity

From the reaction of 1,2-diaminobenzene 1 with cephalexin 2 antibiotic a cephalexin–based Schiff base (HL) 3, was obtained and the transition metal Schiff base complexes were synthesized. The products were characterized by physical and spectral techniques, namely, UV–Vis, FT-IR, 1H-NMR, EPR, MALDI mass spectrometry, magnetic susceptibility, molar conductance, molecular modeling, together with elemental and thermal analysis. The general composition [M(L)(OAc)(H2O)2], M(II) = Mn2+ 4, Co2+ 5, Ni2+ 6, Cu2+ 7, Zn2+ 8, where L represents deprotonated tridentate NNO Schiff base, have been assigned to the adducts. Direct calcinations of the complexes 6 and 8 at 700 °C resulted high-quality metal oxide (MO) nanoparticles. Paper disc diffusion method was used to test the bactericidal activity of the synthesized products.

Synthesis of pyrimidine Schiff base transition metal complexes: characterization, spectral and electrochemical analyses, and photoluminescence properties

This study includes the synthesis, characterization, electrochemical analysis and photoluminescence properties of a Schiff base ligand bearing a pyrimidine ring and its Co(II), Ni(II), Cu(II) and Pd(II) metal complexes. The Schiff base ligand was derived from the condensation reaction of a pyrimidine amine with 2-hydroxy-1-naphthaldehyde. The structures were characterized using FT-IR, UV–Vis, elemental analysis, magnetic susceptibility and electrolytic conductivity. The ligand and its metal complexes displayed strong violet emissions upon UV exposure. The photoluminescence quantum yield and excited-state decay were measured for the ligand and its complexes. The excited-state lifetime for the ligand was 3.70 ns and its quantum yield of luminescence was found to be 0.40. A reduction in photoluminescence intensity and quantum yield was observed upon metal ion complexation. The compounds synthesized were studied by cyclic voltammetry to probe the existence of electrochemical reduction and oxidation processes.