Tetradentate Schiff Base Research Articles

Synthesis and characterization of new Cr(III) complex with a tetradentate Schiff base ligand for polymer composite application

Synthesis and characterization of new Cr(III) complex with a tetradentate Schiff base ligand for polymer composite application

Well Defined Phosphine Free Ni-Catalyzed Dehydrogenation of Secondary Alcohols for the Synthesis of Ketones and Ketazines.

In this work, we unveil a novel synthesis of bench stable Ni (II) complexes supported by tetradentate Schiff-base ligands and the complexes were devoid of any phosphine or phosphine-based ligand. These Ni-complexes were successfully applied for the dehydrogenation of secondary alcohols for ketone and ketazine syntheses. Secondary alcohols with different functional groups were well tolerated during catalytic cycle. Moreover, we successfully extended this protocol for the synthesis of biologically significant ketones and ketazines. On the basis of various control experiments, probable reaction pathway was proposed and an acceptorless alcohol dehydrogenation mechanism was suggested.

Ruthenium(III) unsymmetrical Schiff base complex supported on γ-Fe2O3 magnetic nanoparticles: A new heterogeneous nanocatalyst for efficient oxidation of hydrocarbons with tert-butyl hydroperoxide

In the present work, an unsymmetrical salen-type ruthenium(III) complex, Ru(salenac)Cl, where the unsymmetrical tetradentate Schiff base H2salenac = salicylideneiminoethyliminopentane-2-one, was synthesized and anchored on the surface of aminopropyl-functionalized silica-coated γ-Fe2O3 magnetic nanoparticles. The characterization of the resulting γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanoparticles was performed using XRD, FT-IR, VSM, TGA, ICP, TEM, BET, SEM and EDX methods. The prepared γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl magnetic nanoparticle was successfully employed as an efficient heterogeneous nanocatalyst for alkenes epoxidation and alkanes oxidation with tert-butyl hydroperoxide (tert-BuOOH, 70 % aqueous solution) as oxidant in acetonitrile at ambient temperature. In the mentioned catalytic system, the intended products were obtained with good to excellent yields along with high selectivity. The heterogeneous γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanocatalyst can be recovered easily using an external magnet and recycled six times with no notable decrease in catalytic activity. Moreover, FT-IR, XRD, SEM and EDX techniques were used to characterize the recovered γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanocatalyst and it was demonstrated that the catalyst maintained its structure intact following the recovery process.

Preparation and investigation of TbCrO3/montmorillonite-K10 nanocomposite electrode for electrochemical hydrogen storage application

The limited resources of fossil fuels and the increase in human’s demand for energy have made the use of alternative green energies like hydrogen very important. In this regard, achieving superior specific capacity and high-performance electrochemical hydrogen storage requires the structural design and development of highly active electrode material with cooperative influence of “spillover”, “redox”, and “physisorption” mechanisms. The aim of this report is to fabricate a binary TbCrO3/montmorillonite-K10 (TC/MMT) nanocomposite and to skillfully ensure its electrochemical ability for hydrogen storage in 2.0 M KOH electrolyte, for the first time. A facile sonochemical strategy was presented to successfully form uniform orthorhombic TC nanoparticles with varying tetradentate Schiff base ligands derived from salicylaldehyde and relative diamines as well as the molar ratio of H2Salbn to Tb3+. Characterization analyses displayed that the nucleation and growth process of TC samples can be well controlled by a molar ratio of H2Salbn:Tb3+ = 1:1 within the range of 17–72 nm. Furthermore, implementation of a well-organized MMT-based nanocomposite with various amounts of nano-TC perovskites was evaluated on the structural and electrochemical features. The greatly enhanced hydrogen storage capacity of TC/MMT nanocomposites was acquired as 734.3 mAh/g after 15 cycles, when 10.0 % of perovskite oxide is induced by MMT layers. Moreover, architecture of pristine TC and MMT electrodes possessed a 936.87 and 341.52 mAh/g discharge capacities at the same situation. These merits allow a promising potential application of the nanocomposite electrodes containing rare-earth chromite oxide and clay substrates in electrochemical energy-storage devices.

Development of mixed-ligand ruthenium complexes bearing phosphine and imine ligands for utilisation as catalysts in Suzuki-type C–C cross-coupling reactions

ABSTRACT Herein we report the development of two mixed-ligand ruthenium (II) complexes bearing phosphine and imine ligands, their thorough characterisation and their utilisation as homogeneous catalysts in Suzuki-type C–C cross-coupling reactions. Reactions of two tetradentate Schiff base ligands, derived from imidazole-2-carboxaldehyde and ethylenediamine (H2L1 ) or propylenediamine (H2L2 ), with [Ru(PPh3)3Cl2] in refluxing ethanol in the presence of NEt3 afforded two complexes of type [Ru(L1)(PPh3)2] and [Ru(L2)(PPh3)2], respectively. The solid-state structure of [Ru(L2)(PPh3)2] was determined by single crystal X-ray diffraction analysis. The molecular structure of [Ru(L1)(PPh3)2] was optimised by the DFT method. Electronic spectra of the complexes showed intense absorptions spanning over the visible and ultra-violet regions, the origin of which was probed with TDDFT calculations. Redox properties of the complexes were studied by cyclic voltammetry. These mixed-ligand ruthenium(II) complexes serve as efficient catalyst-precursors for Suzuki-type C–C cross-coupling reactions.

Photophysical Studies of a Zr(IV) Complex with Two Pyrrolide-Based Tetradentate Schiff Base Ligands.

The reaction of two equivalents of N,N'-bis(2-pyrrolylmethylidene)-1,2-phenylenediamine (H2bppda) with tetrabenzylzirconium provided the air- and moisture-stable eight-coordinate complex Zr(bppda)2. Temperature-dependent steady-state and time-resolved emission spectroscopy established weak photoluminescence (ΦPL = 0.4% at 293 K) by a combination of prompt fluorescence and thermally activated delayed fluorescence (TADF) upon visible light excitation at and around room temperature. TADF emission is strongly quenched by 3O2 and shows highly temperature-sensitive emission lifetimes of hundreds of microseconds. The lifetime of the lowest energy singlet excited state, S1, was established by transient absorption spectroscopy and shows rapid deactivation (τ = 142 ps) by prompt fluorescence and intersystem crossing to the triplet state, T1. Time-dependent density functional theory (TD-DFT) calculations predict moderate ligand-to-metal charge transfer (LMCT) contributions of 25-30% for the S1 and T1 states. A comparison of Zr(bppda)2 to related zirconium pyridine dipyrrolide complexes, Zr(PDP)2, revealed important electronic structure changes due to the eight-coordinate ligand environment in Zr(bppda)2, which were correlated to differences in the photophysical properties between the two compound classes.

Oxidovanadium(V) Schiff Base Complexes Derived from Chiral 3-amino-1,2-propanediol Enantiomers: Synthesis, Spectroscopic Studies, Catalytic and Biological Activity.

Oxidovanadium(V) complexes, [(+)VOL1-5] and [(-)VOL1-5], with chiral tetradentate Schiff bases, which are products of monocondensation of S(‒)-3-amino-1,2-propanediol or R(+)-3-amino-1,2-propanediol with salicylaldehyde derivatives, have been synthesized. Different spectroscopic methods, viz. 1H and 51V NMR, IR, UV-Vis, and circular dichroism, as well as elemental analysis, have been used for their detailed characterization. Furthermore, the epoxidation of styrene, cyclohexene, and two monoterpenes, S(‒)-limonene and (‒)-α-pinene, using two oxidants, aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP) in decane, has been studied with catalytic amounts of all complexes. Finally, biological cytotoxicity studies have also been performed with these oxidovanadium(V) compounds for comparison with cis-dioxidomolybdenum(VI) Schiff base complexes with the same chiral ligands, as well as to determine the cytoprotection against the oxidative damage caused by 30% H2O2 in the HT-22 hippocampal neuronal cells in the range of their 10-100 μM concentration.

Copper(II) Driven Fluorescence switch-on Detection of Ovalbumin and GSH Using a Pyridoxal 5'-phosphate Derived Tetradentate Schiff Base and its Applications.

The facile detection of glutathione (GSH) and ovalbumin (OVA) is of great importance in biological research. Herein, a tetradentate Schiff base N, N'-bis(pyridoxal-5-phosphate)-o-phenylenediamine (L) obtained by condensing two moles of pyridoxal 5'-phosphate (PLP) with one mole of 1,2-phenylenediamine was employed for the fluorescence switch-on detection of GSH and OVA. When excited at 389nm, receptor L showed a weak emission at 454nm in an aqueous medium. The addition of GSH to the solution of L caused a significant fluorescence enhancement at 454nm. Amino acids (leucine, glycine, serine, tryptophan, homocysteine, alanine, methionine, arginine and proline) and albumins (bovine serum albumin and OVA) failed to alter the fluorescence profile of L. Receptor L can be applied to detect GSH down to 1.16 µM. However, the fluorescence emission of L was quenched upon the formation of the L-Cu2+ complex. The addition of GSH and OVA to the in-situ formed L-Cu2+ complex restored not only the fluorescence emission of L but also a noticeable fluorescence enhancement observed at 454nm. The decomplexation of L-Cu2+, along with the interaction of L with GSH and OVA is expected to suppress the conformational flexibility of L that enhanced the fluorescent intensity at 454nm. Using L-Cu2+ complex, the concentration of OVA and GSH can be detected down to 0.31 µM and 0.20 µM, respectively. Molecular docking and dynamics simulation were performed to analyze the binding mode, conformational flexibility and dynamic stability of the L-Cu2+-OVA complex. Finally, the analytical novelty of L-Cu2+ was examined by detecting GSH/OVA in real biological samples, such as human blood serum, urine, and egg white.

Syntheses, crystal structures, and magnetic behaviors of phenoxo-bridged manganese compounds based on tetradentate Schiff bases

Six Mn(II)/Mn(III) coordination compounds with tetradentate Schiff bases, [Mn(L1)(N3)]2 (1), [Mn(L2)(N3)]2 (2), [Mn(L1)(SCN)]2 (3), [Mn(L2)(SCN)]2[Mn(L2)(SCN)(C2H5OH)]2 (4), [Mn(L1)(CH3OH)]2 (5), and [Mn3(L2)2(CH3COO)2] (6) [H2L1 = N,N'-bis(5-chloro-salicylaidimine)-1,2-diaminop-ropane), H2L2 = N,N'-bis(5-chloro-salicylaidimine)-2,2-dimethylpropane-1,3-diami- ne], were structurally and magnetically characterized by X-ray single crystal diffraction, powder X-ray diffraction (PXRD), elemental analysis, infrared (IR) spectroscopy and magnetic susceptibility measurement. Structural analysis reveals that each manganese center displays a typical Jahn-Teller distortion. Compounds 1, 2, 3 and 5 are binuclear systems in which two central manganese atoms are connected by di-u2-phenoxo-bridging from two inverse tetradentate ligands. The asymmetric unit of compound 4 contains two moieties, which is composed of a dimeric unit [Mn(L1)(SCN)]2 and two monomeric units [Mn(L1)(SCN)(C2H5OH)]. Compound 6 is a linear homo-trinuclear structure. Dc variable-temperature magnetic susceptibility measurements show that compounds 1, 2, 4 and 5 exhibit paramagnetic behaviors with J = +0.202 cm−1 for 1, J = +0.203 cm−1 for 2, J = +1.03 cm−1 for 4 and + 0.152 cm−1 for 5, respectively, whereas compounds 3 and 6 show a strong antiferromagnetic interaction between the high-spin metal centers. In addition, we investigated the relationship between the structures and magnetic behaviour.

Corrigendum to: Investigation of the Apoptosis Inducing and β-catenin Silencing by Tetradentate Schiff Base Zinc(II) Complex on the T-47D Breast Cancer Cells.

A typographical error appeared in the author affiliation titled "Investigation of the Apoptosis Inducing and β-catenin Silencing by Tetradentate Schiff Base Zinc(II) Complex on the T-47D Breast Cancer Cells", published in Anti-Cancer Agents in Medicinal Chemistry, 2023, 23(15) [1]. Details of the error and a correction are provided here. Original: Author Affiliation: 2Department of Breast Medicine, Cancer Hospital Chinese Academy of Medical Science, Liaoning Provincial Cancer Hospital, Shenyang, Liaoning, 110042, China Corrected: Author Affiliation: 2Department of Breast Medicine, Cancer Hospital of China Medical University, Liaoning Cancer Hospital, Shenyang, China We regret the error and apologize to readers. The original article can be found online at https://www.eurekaselect.com/article/131718.

Oxidovanadium(V) complexes with chiral tetradentate Schiff bases: Synthesis, spectroscopic characterization, catalytic and biological activity

New mononuclear oxidovanadium(V) complexes, [(−)VOL1–10] and [(+)VOL1–4], with chiral tetradentate Schiff bases have been obtained by monocondensation of salicylaldehyde derivatives and optically active amino alcohols, i.e. 1R,2R-(−)-2-amino-1-phenyl-1,3-propanediol or 1S,2S-(+)-2-amino-1-phenyl-1,3-propanediol. All complexes have been characterized by elemental analysis, circular dichroism, UV–vis, IR, 1D (1H, 51V) and 2D (COSY, NOESY) NMR spectroscopy. The catalytic activity studies have also been performed for all complexes in the epoxidation of styrene, cyclohexene and two monoterpenes, i.e. S(−)-limonene and (−)-α-pinene, using aqueous 30 % H2O2 or tert-butyl hydroperoxide (TBHP) as the terminal oxidant. In addition, biological properties of these chiral oxidovanadium(V) compounds, as well as cis-dioxidomolybdenum(VI) complexes with the same chiral Schiff bases, were studied in relation to their cytoprotective activity against the oxidative damage generated exogenously by 30 % hydrogen peroxide in the HT-22 hippocampal neuronal cells. The latter compounds have revealed distinct cytoprotective properties causing the highest increase in the viability of HT-22 cells. Concentration dependent effect in the range of 10-100 μM concentration of the investigated compounds has also been observed.

Synthesis, Structural Characterization, Reactivity and Bioactivity Studies of Some Binuclear Salen Type Schiff Base Complexes of Manganese(III)

Four new phenoxy bridged binuclear Salen type Schiff base complexes of manganese(III), [MnLX]2 with tetradentate Schiff base, H2L [H2L = N,N′-O-phenylene bis(salicylaldimine)] containing anionic co-ligands, X (X = benzoate, p-hydroxy benzoate, p-aminobenzoate, 3,5-dinitrobenzoate) have been synthesized from manganese(II) acetate, Schiff base (H2L) and the corresponding co-ligands in methanol medium. Schiff base ligand (H2L) was obtained in situ by condensation of salicylaldehyde and o-phenylenediamine in aqueous methanol. Elemental analyses, FT-IR, molar conductance, UV-visible spectroscopic studies and magnetic moment measurements at room temperature were used to characterize the binuclear Schiff base complexes. The IR spectra of [MnLX]2 (X = benzoate, p-hydroxy benzoate, p-aminobenzoate, 3,5-dinitrobenzoate) complexes showed the characteristic absorptions due to coordinated azomethine nitrogen and phenolic oxygen atoms of the Schiff base. In addition, IR spectra of the compounds also suggest coordination of the co-ligands namely benzoate, p-hydroxy benzoate, p-aminobenzoate, 3,5-dinitrobenzoate in the respective complexes. A consistent presence of a band at ca. 755 cm-1 in all the binuclear complexes arises due to (Mn-O-Mn) moiety originated from interactions of phenoxy oxygen and manganese atoms, resulted in dimeric structure of the compounds. The magnetic moment values ranging from 4.74-4.91 B.M. per manganese centre for the complexes suggest presence of Mn(III) ion in the complexes. The overall coordination geometry around the manganese centres is distorted octahedral. Redox behaviour of the synthesized complexes was ascertained from cyclic voltametric studies. The Schiff base complexes, [Mn(L)X]2 (X = p-aminobenzoate, 3,5-dinitrobenzoate) have demonstrated their catalytic potentials in oxidizing selective organic substrates namely cyclohexene and styrene by hydrogen peroxide as oxidant. The oxidized products were characterized as trans-cyclohexane 1,2-diol and styrene epoxide, respectively. Complex 4 demonstrated a considerable level of effectiveness against a wide variety of pathogenic microorganisms.

Non-covalent interactions in molecular architectures and solvent-free catalytic activity towards CO2 fixation of mononuclear Co(III) complexes installed on modified Schiff base ligands.

A set of mononuclear cobalt(III) octahedral complexes {[Co(LH)(acac)] (Co-1H), [Co(LBr)(acac)] (Co-1Br), and [Co(LNO2)(acac)] (Co-1NO2)} were synthesized using new-generation N/O donors, maleonitrile-tethered, tetradentate heteroscorpionate half-reduced Schiff base ligands, 2-((E)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LH), 2-((E)-(5-bromo-2-hydroxybenzylidene)amino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (H2LBr), and 2-((E)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LNO2). All the compounds were well characterized spectroscopically and structurally. The non-covalent interactions present in the lattice of Co-complexes were studied in detail to explain the molecular architecture using the Hirshfeld surface (HS) analysis. The catalytic activity of CO2 fixation towards epoxides under mild and solvent-free conditions was demonstrated. The synthesized complexes are catalysts that are well-active towards the CO2 activation under ambient conditions, whereas most of the reported catalysts require harsh conditions.

Insight into the conformational selectivity of cobalt(iii) complexes with a tetradentate salen-type Schiff base ligand and their biorelevant catalysis: a combined experimental and theoretical study

A series of mononuclear CoIII complexes showing conformational selectivity (stepped vs. umbrella) and biomimetic catalytic activities are reported.

THE FIRST STRUCTURAL CHARACTERIZATION OF A NI(NCS)64– BRIDGED HOMOMETALLIC NI(II) CHAIN DERIVED FROM A N3O DONOR SCHIFF BASE LIGAND

Thiocyanate bridged homometallic Ni(II) chains have potential applications in areas such as molecular magnetism and spintronics due to their tunable magnetic properties. The magnetic properties of these chains are of particular interest and can lead to intriguing magnetic behaviors, such as antiferromagnetic or ferromagnetic interactions. In this context, we have successfully synthesized a Ni(NCS)64– bridge Ni(II) chain complex [Ni2(H2L)2(m1,3-NCS)2(NCS)4]n∙2nCH3CN (1), derived from a tetradentate N3O donor Schiff base ligand (HL). It has been thoroughly characterized by the help of elemental analysis and IR spectroscopy. Single crystal X-ray crystallography has confirmed the geometry of the chain complexes. Both Ni1 and Ni2 centers exhibit hexa-coordination with slightly distorted octahedral geometries, and their coordination environments differ significantly (NiN2O2S2 for Ni1 and NiN6 for Ni2). Within the solid-state structure of the complex, a noteworthy two-dimensional network of hydrogen bonding is observed. The present complex showing a unique example in the realm of single thiocyanato-bridged Ni(II) chains.

Chiral spin-crossover complexes based on an enantiopure Schiff base ligand with three chiral carbon centers.

The preparation of Fe(II) complexes combining monodentate NCX- (X = S or Se) and the tetradentate Schiff base chiral ligands RR-L1 and SS-L1 = (RR- or SS-L1 = 1R,2R or 1S,2S)-N1,N2-bis(pyridin-2-ylmethylen)cyclohexane-1,2-diamine in acetone results in an unexpected reaction. Thus, four enantiomerically pure compounds of formulas [Fe(RR-S-L2)(NCX)2] and [Fe(SS-R-L2)(NCX)2] (X = S or Se) are formed by the new asymmetrical ligand L2. In L2, one acetone solvent molecule is incorporated into the ligand forming a bond with the C atom of one of the two CN imine groups of L1, which is transformed into an amine (Mannich reaction). This reaction is diastereoselective as the incorporation of acetone leads to an asymmetric C adjacent to the NH group with opposite chirality S- or R- to that of the cyclohexane carbons (RR- or SS-, respectively). Therefore, L2 contains three C chiral centers. Structural and magnetic characterization of these compounds demonstrates that they show in the bulk a gradual spin-crossover behavior and LIESST effect. Interestingly, the presence of an intramolecular hydrogen bond between the integrated acetone molecule and the NH group can trigger a secondary stimuli-responsive behavior in the system. Therefore, by changing the solvent polarity, the color of the complex in solution can be easily tuned.

Catalytic Copolymerization of Carbon Dioxide and Cyclohexene Oxide by a Trinuclear Cyclohexane-bridged Tetradentate Schiff Base Chromium Complex

The development of catalytic systems is a central area of research in carbon dioxide (CO2) and epoxy copolymerization. A novel trinuclear cyclohexane-bridged tetradentate Schiff base chromium complex 1 was synthesized...

Promising in vitro and in silico biological activity of tetradentate Schiff base copper(ii) complexes with a propylenediamine bridge

Analyzed tetradentate Schiff base copper(ii) complexes (with a propylenediamine bridge) show promising antioxidant and antiproliferative activity and the ability to bind to macromolecular targets such as HSA and DNA.

Unusual Ni⋯Ni interaction in Ni(ii) complexes as potential inhibitors for the development of new anti-SARS-CoV-2 Omicron drugs.

Two nickel(ii) coordination complexes [Ni(L)]2(1) and [Ni(L)]n(2) of a tetradentate Schiff base ligand (H2L) derived from 2-hydroxy-1-naphthaldehyde with ethylenediamine were synthesized, designed, and characterized via spectroscopic and single crystal XRD analyses. Both nickel(ii) complexes exhibited unusual Ni⋯Ni interactions and were fully characterized via single-crystal X-ray crystallography. Nickel(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) crystallize in monoclinic and triclinic crystal systems with P21/c and P1̄ space groups, respectively, and revealed square planar geometry around each Ni(ii) ion. The structure of both the complexes have established the existence of a new kind of metal system containing nickel(ii)-nickel(ii) interactions with a square planar-like geometry about the nickel(ii) atoms. Both square planar Ni(ii) complexes were often stacked with relatively short Ni⋯Ni distances. The non-bonded Ni-Ni distance (Ni⋯Ni separation) seems to be 3.356 Å and 3.214 Å from the nickel atoms of [Ni(L)]2(1) and [Ni(L)]n(2), respectively. These distances are shorter than the sum of their van der Waals radii (4.80 Å) but longer than the sum of their covalent radii (2.50 Å), indicating that there is a Ni⋯Ni interaction but not a Ni-Ni bond. The discrete molecules are π-stacked and connected via weak intermolecular interactions (C-H⋯O and C-H⋯N). Cyclic voltammetry measurements were obtained for both the complexes, and their pharmacokinetic and chemoinformatics properties were also explored. Detailed structural analysis and non-covalent supramolecular interactions were investigated using single-crystal structure analysis and computational approaches. Both the unique structures show good inhibition performance for the Omicron spike proteins of the SARS CoV-2 virus. To gain insights into potential SARS-CoV-2 Omicron drugs and find inhibitors against the Omicron variants of SARS-CoV-2, we examined the molecular docking of the nickel(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) with the SARS-CoV-2 Omicron spike protein (PDB ID: 7WK2 and 7WVO). A strong binding was predicted between Ni(ii) coordination complexes [Ni(L)]2(1) and [Ni(L)]n(2) with the SARS-CoV-2 Omicron variant receptor protein through the negative value of binding affinity. Molecular docking of Nil(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) with a DNA duplex (PDB ID: 7D3T) and RNA (PDB ID: 7TDC) binding protein was also studied. Overall, this study suggests that Ni(ii) complexes can be considered as drug candidates against the Omicron variants of SARS-CoV-2.

Synthesis, characterization, electrochemical and biological activity studies of tetradentate Schiff base and its Mn(IV) complexes

Synthesis, characterization, electrochemical and biological activity studies of tetradentate Schiff base and its Mn(IV) complexes