Neutral Tridentate Ligand Research Articles

Targeted synthesis, structural elucidation, density functional theory, and molecular docking studies of transition metal(II)/(III) complexes of levofloxacin‐based Schiff base for promising their antioxidant and antibacterial applications

Levofloxacin and 4‐aminoantipyrine undergo a condensation process to synthesize a novel Schiff base ligand (L). Metal complexes containing Co(II), Cu(II), Cd(II), Mn(II), Zn(II), Cr(III), Ni(II), and Fe(III) metal ions are prepared using this Schiff base ligand. The new ligand and its complexes are characterized by elemental analyses, Fourier transform infrared, mass spectrometry, ultraviolet–visible, magnetic moment, 1H‐NMR, molar conductivity, and powder X‐ray diffraction, and further thermogravimetric analysis (TG, DTA) verifies their thermal stability. The metal to ligand ratio is 1:1, according to the analytical results. Spectroscopic methods reveal that metal complexes are expected to have an octahedral geometry and demonstrate a neutral tridentate ligand behavior. It also becomes apparent from the molar conductivity values that all metal complexes are electrolytic in nature except zinc(II) and cadmium(II) complexes which are non‐electrolytes. Moreover, the bioactivity of the compounds are investigated. The antibacterial activity is investigated in relation to various Gram‐positive and Gram‐negative bacteria. The results give good indication for higher activity of the prepared compounds than the standard antibiotic drug. Also, the antioxidant activity of the newly prepared ligand and its complexes has been investigated via 2,2‐diphenyl‐1‐picrylhydrazyle (DPPH) free radical scavenging assay. The findings show that Schiff base complexes exhibit good antioxidant activity. Finally, theoretical density functional theory using density functional theory/B3LYP method and molecular docking studies with two receptors of 3T88 and 3Q8U are calculated for the investigated compounds.

Novel hydroxy-tagged bis-dihydrazothiazole derivatives: Synthesis, antimicrobial capacity and formation of some metal chelates with iron, cobalt and zinc ions

Until today, microbialinfectionsepitomize a seriousuniversal health threat. Subsequently, developing a potential antimicrobialprototype remains an urgent, global necessity. Despite several reports discussing the biological utility of some bis-thiazoles, the use of bis-dihydrazothiazoles and their corresponding metal chelates as potent antimicrobials, is yet to be explored. The current report outlines an attempt to fill that void by representing a successful synthesis of a new class of bis-dihydrazothiazoles as well as three of their transition metal chelates and their use as potential antimicrobials. This report presents the design of some novel hydroxy-tagged bis-dihydrazothiazoles 6a-e and bis-dihydrazothiazolones 9a-evia the reaction of a bis-aldehyde thiosemicarbazone 3, as a common synthetic precursor, with two groups of hydrazonoyl halide derivatives 4a-e and 7a-e. The chelation affinity of these novel bis-dihydrazothiazoles to behave as neutral tridentate ligands coordinating to the metal ions; Fe(III), Co(II), or Zn(II) through azomethine-N, thiazole-S, and azo-N atoms to form metal complexes with a metal/ligand ratio of 2:1 was confirmed. In-vitro, antimicrobial screening of the novel hydroxy-tagged bis-dihydrazothiazole derivatives, as well as a selected group of their transition metal chelate complexes [M2L], was inspected, and the data weremeasured incomparisonto those of ketoconazole and gentamycin as antimicrobial reference standards. Most bis-dihydrazothiazoles 6a-e and bis-dihydrazothiazolones 9a-e showed decent to excellent antimicrobial activities against the screened microbes, but the chloro-substituted bis dihydrazothiazole derivatives 6c and 9c showed exceptional inhibition of Bacillus subtilis (20 mm), Escherichia coli (25 mm), and Candida albicans (19 mm), and Salmonella typhimurium (19 mm), respectively. Additionally, amongst the three synthesized metal complexes [M2L], only the zinc complex, [Zn2L] showed remarkable inhibition of both Staphylococcus aureus (21 mm) and Salmonella typhimurium (19 mm) compared to the reference standard Gentamycin, and was more potent than the free ligand, 6a itself (no activity and 11 mm respectively). Antimicrobial inspection was assessed by the agar well diffusion assay method against all bacterial and fungal strains. Magnetic moment, diffused reflectance, FT-IR, 1H NMR, molar conductivity, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscope(SEM) were among the many techniques used to elucidate the structures of all novel hydroxy-tagged bis-heterocyclic ligands and their metal chelate complexes.

Innovative bis-dihydrazothiazolone derivatives with a 1,4-xylenyl spacer: Design, antimicrobial prospective and construction of several transition metal chelates with iron, cobalt and zinc

Several new xylenyl-spaced bis-dihydrazothiazoles 6a-e and bis-dihydrazothiazolones 9a-e were synthesized by the simple reaction between bis-thiosemicarbazone 3 as a common synthetic scaffold, with two series of hydrazonoyl halides derivatives 4a-e and 7a-d. The chelation ability of these novel bis-dihydrazothiazole derivatives to perform as neutral tridentate ligands and coordinate to transition metal ions; Fe(III), Co(II), or Zn(II) through azomethine-N, thiazole-S, and azo-N atoms to form metal complexes with a metal/ligand ratio of 2:1 was elucidated. Diffused reflectance, magnetic moment, 1HNMR, FT-IR, TGA, and molar conductivity, were used to interpret the structures of all new xylenyl-spaced bis-heterocyclic compounds and their metal chelates. In-vitro, antibacterial and antiviral screening of these innovative xylenyl-spaced bis-dihydrazothiazole derivatives, as well as a selected group of their transition metal chelate complexes [M2L], were inspected, and the data was evaluated in comparison to those of Ketoconazole and Gentamycin as antimicrobial control standards using the agar well diffusion assay protocol against a selected group of fungal and bacterial species. Several compounds displayed respectable to great antimicrobial behavior against the examined microbial species. Bis-dihydrazothiazole 6c, particularly, showed exceptional inhibition of both C. albicans and E. coli. However, bis-dihydrazothiazolone 9b showed excellent inhibition of A. fumigatus. Additionally, amongst the three synthesized metal complexes [M2L], only the zinc complex, [Zn2L] showed remarkable inhibition of both C. albicans and S. typhimurium and was even more potent than the free ligand, 9a itself.

Investigation of transition metal chelates with a ligand (3-cyano-6-thiophen-2-yl[4,4′]bipyridinyl-2-yloxy)-acetic acid hydrazide as corrosion inhibitors for copper in 1.0 M HCl solution

Mn(II), Fe(III),Co(II), Ni(II) and Cu(II) complexes of the ligand named (3-Cyano-6-thiophen-2-yl[4,4′]bipyridinyl-2-yloxy)-acetic acid hydrazide (abbreviated as HL) have been synthesized. Structure assignment of such chelates have been performed by means of analytical and spectral tools which joint assured the formulation of the chelates in 1 M: 1 L ratio with non-electrolytic character for all the complexes. Fe(III) complex is 1:3 electrolyte. The spectral IR toll proved the neutral tridentate ligand nature connecting to the metal ions by the azomethine nitrogen, carbonyl and ester oxygen atoms. Octahedral structure has been concluded for all the isolated chelates as deduced from the UV-Vis spectral analysis. The investigated complexes were tested to protect or restrain the corrosion of copper in 1.0 M HCl solution at 298 K using different techniques. The outcomes being acquired illuminated that the synthesized compounds were discovered to be efficient inhibitors and their % IEs were concluded to be dependent on both concentrations and structures. The order of the % IEs of the tested compounds was: HL-Mn> HL-Fe> HL-Co ≥ HL- Ni> HL-Cu> HL. The acquired high % IEs were ascribed to the powerful adsorption of the organic molecules on the surface of copper which was agreed with Langmuir adsorption isotherm. The kinetics of corrosion inhibition by the examined compounds appeared negative-first order process. PDP results indicated that the complex HL-Mn behaves as a mixed-kind inhibitor with slight anodic seniority. The employed techniques used for the complex HL-Mn were in a good consistence with each other.

Mixed Methyl/Chlorido Yttrium(III) Complexes Supported by a Neutral Tridentate N-Donor Ligand

Trimethylyttrium, supported by the neutral tridentate ligand Me3TACN (1,4,7-trimethyl-1,4,7-triazacyclononane), is readily synthesized from (Me3TACN)YCl3 (via salt metathesis with MeLi in THF) or [YMe3]n (via Me3TACN-donor addition in toluene). Such discrete complex (Me3TACN)YMe3 reacts with trimethylchlorosilane according to a silane elimination protocol, affording well-defined mixed methyl/chlorido complexes of the composition [(Me3TACN)YMe3–xClx] (x = 1, 2, 3). All complexes were characterized by X-ray diffraction, homo- and heteronuclear NMR (especially 89Y) and FTIR spectroscopies, and elemental analysis. The reaction of heteroleptic complex [(Me3TACN)YMe2Cl] with dibenzyl ketone was investigated.

Spectroscopic Characterization and Biological Activity of Hesperetin Schiff Bases and Their Cu(II) Complexes

The three Schiff base ligands, derivatives of hesperetin, HHSB (N-[2,3-dihydro-5,7-dihydroxy-2-(3-hydroxy-4-methoxyphenyl)chromen-4-ylidene]isonicotinohydrazide), HIN (N-[2,3-dihydro-5,7-dihydroxy-2-(3-hydroxy-4-methoxyphenyl)chromen-4-ylidene]benzhydrazide) and HTSC (N-[2,3-dihydro-5,7-dihydroxy-2-(3-hydroxy-4-methoxyphenyl)chromen-4-ylidene]thiosemicarbazide) and their copper complexes, CuHHSB, CuHIN, and CuHTSC were designed, synthesized and analyzed in terms of their spectral characterization and the genotoxic activity. Their structures were established using several methods: elemental analysis, FT-IR, UV-Vis, EPR, and ESI-MS. Spectral data showed that in the acetate complexes the tested Schiff bases act as neutral tridentate ligand coordinating to the copper ion through two oxygen (or oxygen and sulphur) donor atoms and a nitrogen donor atom. EPR measurements indicate that in solution the complexes keep their structures with the ligands remaining bound to copper(II) in a tridentate fashion with (O-, N, Oket) or (O-, N, S) donor set. The genotoxic activity of the compounds was tested against model tumour (HeLa and Caco-2) and normal (LLC-PK1) cell lines. In HeLa cells the genotoxicity for all tested compounds was noticed, for HHSB and CuHHSB was the highest, for HTSC and CuHTSC-the lowest. Generally, Cu complexes displayed lower genotoxicity to HeLa cells than ligands. In the case of Caco-2 cell line HHSB and HTSC induced the strongest breaks to DNA. On the other side, CuHHSB and CuHTSC induced the highest DNA damage against LLC-PK1.

Synthesis, Characterization, and Thermal Analysis of a New Acidicazo Ligand's Metal Complexes

The researchers wanted to make a new azo imidazole as a follow-up to their previous work. The ligand 4-[(2-Amino-4-phenylazo)-methyl]-cyclohexane carboxylic acid as a derivative of trans-4-(aminomethyl) cyclohexane carboxylic acid diazonium salt, and synthesis a series of its chelate complexes with metalions, characterized these compounds using a variety technique, including elemental analysis, FTIR, LC-Mass, 1H-NMRand UV-Vis spectral process as well TGA, conductivity and magnetic quantifications. Analytical data showed that the Co (II) complex out to 1:1 metal-ligand ratio with square planner and tetrahedral geometry, respectively while 1:2 metal-ligand ratio in the Cu(II), Cr(III), Mn(II), Zn(II), Ru(III)and Rh(III)complexes with octahedral geometry except Mn complex has tetrahedral geometry. The Ligand functions as a neutral tridentate ligand in all complex investigations, coordinating Cr(III), Zn(II), Ru(III), and Rh(III) ions via the N atom of amine and azo groups, as well as the O phenolic OH group. When coordinated with the Cu(II), Co(II), and Mn(II) ions via the two N atoms of the amine and azo groups, this Ligand functions as a neutral bidentate.

Can One Novel Series of Transition Metal Complexes of Oxy-dianiline Schiff Base Afford Advances in Both Biological Inorganic Chemistry and Materials Science?

ABSTRACT This paper provides a manifestation of a new tradition by which Comments on Inorganic Chemistry starts publishing original research content that, nonetheless, preserves the Journal’s identity as a niche for a critical discussion of contemporary literature in inorganic chemistry; for previous manifestations, see Comments Inorg. Chem. 2020, 40, 277-303 and references cited in the abstract thereof as Yaseen W. K.; Sanders S. F.; Almotawa R. M.; Otten B. M.; Bhat S.; Alamo D. C.; Marpu S. B.; Golden T. D.; Omary M. A. “Are Metal Complexes” Organic, Inorganic, Organometallic, or Metal-Organic Materials? A case Study for the Use of Trinuclear Coinage Metal Complexes as “Metal-Organic Coatings” for Corrosion Suppression on Aluminum Substrates Comments Inorg. Chem. 2019, 39, 1-26 and also, Mohapatra R. K.; Das P. K.; Pradhan M. K.; El-Ajaily M. M.; Das D.; Salem H. F.; Mahanta U.; Badhei G.; Parhi P. K.; Maihub A. A.; Kudrat -E-Zahan Md. “Recent Advances in Urea- and Thiourea-Based Metal Complexes: Biological, Sensor, Optical, and Corrosion Inhibition Studies” Comments Inorg. Chem. 2019, 39, 127-147). In this work, the Schiff base 1-(6-(1-((4-(4-aminophenoxy)phenyl)imino)ethyl)-pyridin-2-yl)ethan-1-one (L) and eight transition metal complexes were synthesized. The reaction of 4,4-oxy-dianiline with 2,6-diacetylpyridine in 1:1 molar ratio affords to the ligand which was employed in the synthesis of the corresponding metal complexes by reacting with the Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) chlorides in 1:1 molar ratio. All the compounds were characterized by using different analytical methods. Structures of complexes were found to be octahedral as deduced from the spectroscopic and magnetic moment measurements. The ligand behaves as a neutral tridentate ligand where it coordinated to metal ions through N-azomethine, N-pyridine, and O-carbonyl group. Besides, experimental investigations for their antibacterial activity against different bacteria species were studied, molecular docking studies were reported with receptors 4ME7, 4K3V, 3T88 and 4WJ3. Density functional theory (DFT) calculations for ligand were reported. Finally, the evaluation of corrosion inhibition efficiency was measured by using different techniques such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and electrochemical frequency modulation (EFM). Scanning electron microscope (SEM) and energy dispersive X-Ray analysis (EDX) were measured to affirm the presence of barrier film on the carbon steel surface by inspecting the surface morphologies and elemental composition of corrosion products.

Nano-sized some transition metal complexes of Schiff base ligand based on 1-aminoquinolin-2(1H)-one

The novel Schiff base ligand that is based on the condensation of 1-aminoquinolin-2(1H)-one and 2-hydroxybenzaldehyde and its metal complexes with Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions have been synthesized. Furthermore, the structure, electronic properties, and chemical reactivity of Schiff base and its metal complexes have been examined via Elemental analysis, Mass, (1H, 13C and 15N) NMR, FT-IR, CV, ESR spectra, Thermal analysis, and theoretically using the density functional theory. Initially, the ligand behaved as a neutral tridentate (NOO) ligand and all complexes displayed octahedral geometry, except Hg(II), which showed tetrahedral geometry. The values of molar conductance in DMSO suggested the non-electrolytic nature for all complexes. The coordinated and crystalline water molecules have been investigated by (TG/DTG) studies. The kinetic and thermodynamic parameters were computed using Horowitz–Metzger and Coats–Redfern methods. Moreover, the data obtained from XRD, SEM, TEM, EDX and AFM images unequivocally asserted the nano-sized metal chelates. In molecular modelling the geometries of Schiff base and its nano-sized Cu(II), Co(II) and Zn(II) hybrids were fully optimized with respect to the energy generated due to using the DFT method from DMOL3 calculations. The anticancer activity of the parent Schiff base and its nano-sized metal hybrids were screened, in addition to the interaction of the complexes with calf thymus CT–DNA, which was investigated via the UV–visible absorption method. Additionally, the mode of CT‒DNA binding to the HL ligand and its nano-sized hybrids has been explored. Therefore the DNA cleavage activity by the HL ligand and its nano-sized hybrids was performed allowing the measurement of the solid-state dc electrical conductivity of the HL ligand and its nano-sized Co(II), Cu(II) and Zn(II) hybrids over 303–423 K, which were then found to be of semiconducting nature.

Synthesis, characterization of Schiff base metal complexes and their biological investigation

A new Schiff base ligand named (E)‐2‐(((3‐aminophenyl)imino)methyl)phenol (HL) was prepared through condensation reaction of m‐phenylenediamine and 2‐hydroxybenzaldehyde in 1:1 molar ratio. The new ligand was characterized by elemental analysis and spectral techniques. The coordination behavior of a series of transition metal ions named Cr (III), Mn (II), Fe (III), Co (II), Ni (II), Cu (II), Zn (II) and Cd (II) with the newly prepared Schiff base ligand (HL) is reported. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, IR, UV–Vis, 1H NMR, mass, electronic spectra, magnetic susceptibility and conductivity measurements and further their thermal stability was confirmed by thermogravimetric analysis (TG). From IR spectra, it was observed that the ligand is a neutral tridentate ligand coordinates to the metal ions through protonated phenolic oxygen, azomethine nitrogen and nitrogen atom of NH2 group. The existence, the number and the position of the water molecules was studied by thermal analysis. The molecular structures of the Schiff base ligand (HL) and its metal complexes were optimized theoretically and the quantum chemical parameters were calculated. The synthesized ligand and its complexes were screened for antimicrobial activities against bacterial species (Staphylococcus aureus and Bacillis subtilis, (gram positive bacteria)), (Salmonella SP., Escherichia coli and Pseudomonas aeruginosa, (gram negative bacteria)) and fungi (Aspergillus fumigatus and Candida albicans). The complexes were found to possess high biological activities against different organisms. Molecular docking was used to predict the efficiency of binding between Schiff base ligand (HL) and both receptors of Escherichia coli (3 T88) and Staphylococcus aureus (3Q8U). The receptor of Escherichia coli (3 T88) showed best interaction with Schiff base ligand (HL) compared to receptor of Staphylococcus aureu (3Q8U).

Formation and Characterization of Zr4+ Stabilized by Neutral Tridentate Ligands in the Gas Phase.

Ligated tetrapositive metal ions are rare gas-phase species which tend to form complexes with lower charges due to the high 4th ionization energies of metals. We report the observation of tetrapositive Zr(TMPDA)34+ and Zr(TMOGA)34+ complexes in the gas phase by electrospray ionization of Zr(ClO4)4/TMPDA and Zr(ClO4)4/TMOGA mixtures. The Zr4+ center in both complexes is coordinated by nine atoms from three neutral diamide ligands forming nine-coordinate twisted tricapped trigonal prismatic geometry on the basis of DFT calculations. Collision-induced dissociation of both complexes resulted in the loss of protonated ligands to form tripositive Zr(TMPDA)(TMPDA-H)3+ and Zr(TMOGA)(TMOGA-H)3+ products which retain the IV oxidation state of zirconium at the cost of charge reduction from 4+ to 3+ of the whole complexes. The very high 4th ionization energy of zirconium (34.34eV) makes tetrapositive zirconium complex the most challenging tetracation to be stabilized against charge reduction in the gas phase to date. Graphical abstract ᅟ.

Zinc–diethanolamine complex: synthesis, characterization, and formation mechanism of zinc oxide via thermal decomposition

Zn(OAc)2(H2DEA) was synthesized by the reaction of zinc acetate dihydrate (Zn(OAc)2•2H2O) with diethanolamine (H2DEA), and was characterized using single-crystal X-ray structural analysis, nuclear magnetic resonance spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and elemental analysis. Zn(OAc)2(H2DEA) had a trigonal bipyramidal geometry comprised of one zinc atom, two acetate groups, and one H2DEA as a neutral tridentate ligand to form two five-membered rings. The states of Zn(OAc)2(H2DEA) heated at various temperatures were determined by FT-IR spectroscopy. At 270 °C, the H2DEA ligand dissociated and was removed. The absorption bands assigned to Zn–O stretching vibration of Zn4O core such as the zinc-oxo cluster appeared. When heated at 500 °C, the absorption bands of μ4-oxozincate and the acetate group disappeared completely and hexagonal wurtzite structural ZnO was formed at 550 °C. A possible thermal decomposition pathway from Zn(OAc)2(H2DEA) to ZnO was proposed. The ZnO film was highly transparent and formed by the deposition of ZnO nanoparticles with size ~40 nm.

SYNTHESIS, CHARACTERIZATION AND FUNGICIDAL POTENTIALITIES OF SOME TRANSITION METAL COMPLEXES OF BENZIMIDAZOLEDITHIOCARBAMATE BASED LIGAND

New substituted benzimidazole dithiocarbamate ligand (HL) and a set of its transition metal complexes were synthesized and characterized based on the elemental analyses, IR, MS, solid reflectance, magnetic moment, molar conductance and thermal analyses (TGA and DrTG). From the obtained IR data, HL is a neutral tridentate ligand and its complexes were proposed to have the general formulae [MCl(HL)(H2O)2]Cl2.2H2O (M = Cr(III) and Fe(III)] and [MCl(HL)(H2O)2]ClyH2O (for y = 2: M = Mn(II), Co(II) and Cu(II) and for y = 1: M = Ni(II), Zn(II) and Cd(II)). The molar conductance data revealed that all the metal chelates were electrolytes. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of the synthesized complexes is octahedral. The thermal behaviour of these chelates showed that the hydrated complexes loss water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. Fungicidal activity of the new ligand and its related complexes was evaluated against three soil-borne fungi that cause many destructive diseases as damping off, root and stem rots of many plants. The tested fungi are Fusarium solani, Rhizoctonia solani and Sclerotium rolfesii. Data obtained showed that introducing an electron-withdrawing nitro group in position (5) of benzimidazole ring enhanced the biological potentialities of the parent ligand and some of its transition metal chelates to show better activity than the standard fungicide Pencycuron.

Synthesis, structural characterization, DFT studies and biological activity of Cu(II) and Ni(II) complexes of novel hydrazone

Novel hydrazone 2-(2-((1E,2E)-2-(2-phenylhydrazineylidene)propylidene)hydrazineyl)pyridine and its nickel(II) and copper(II) complexes have been synthesized and characterized. The ligand (H2PGl) was prepared by the condensation reaction of 1-(2-phenylhydrazineylidene)propan-2-one and 2-hydrazinopyridine. The crystal structure of Ni(II) complex was determined. In both Ni(II) and Cu(II) complexes, H2PGl act as a neutral tridentate ligand forming two fused five-membered chelation rings through NNN set of donor atoms. Octahedral geometry is proposed for both chelates as illustrated in both magnetic and spectroscopic data. ESR spectroscopy was performed for Cu(II) complex which exhibited a considerable Cu–Cu interaction and harmonize directly with measured magnetic moment. The molecular modeling structures were optimized and showed the bond length, bond angle, reactivity, MEP and atomic charges for all the title frameworks. Hypothetical infrared intensities and 1H NMR of H2PGl was estimated on the basis of DFT scheme. A comparison of the experimental and theoretical data was very useful in creating correct assignments and understanding the basic chemical shift. Biological activity of the synthesized compounds were investigated versus some Gram positive, Gram negative bacteria and some fungal strains. Also, the antitumor activity was investigated.

Anti‐neurotoxic evaluation of synthetic and characterized metal complexes of thiosemicarbazone derivatives

Quinoline‐2‐caboxyaldehyde thiosemicarbazone (HL1) and quinoline ‐2‐caboxyaldehyde N‐dimethyl thiosemicarbazone (HL2) metal complexes were prepared and characterized using analytical and spectroscopic techniques. The measurements showed that ligands behave as monovalent or neutral tridentate ligands bonding via azomethine, quinoline ring nitrogen atoms and sulfur atoms in thiol or thion forms. The anti‐neurotoxic effect of ligands and their complexes showed that, exposure to aluminum increase oxidative stress in the brain, an effect that could be offset by concomitant thiosemicarbazone complexes. Complexes could be having an effect on absorption or excretion of aluminum, due to their chelating activity. These findings may shed light on the potential clinical importance of thiosemicarbazone complexes in Alzheimer's disease.

Rare Earth Nitrate Complexes with an ONO Schiff Base Ligand: Spectral, Thermal, Luminescence and Biological Studies

Five rare earth complexeslanthanum(III),praseodymium(III),neodymium(III), samarium(III) and europium(III) have been synthesized from Schiff base ligand (N,N-bis (2-hydroxy-1-naphthylidene) acetylhydrazone). The complexes were characterized based on elemental analysis, molar conductance, ultraviolet, infrared, mass, thermogravimetric and powder X-ray diffraction studies. Infrared spectra suggest ligand act as a neutral tridentate ligand. The Schiff base ligand coordinating through the naphtholic oxygen without proton displacement, azomethine nitrogen atom and hydrazone carbonyl oxygen atoms of the ligand to the lanthanide ion. The conductivity and thermal decomposition studies indicate the presence of two coordinated nitrate ion acts as bidentate fashion. Powder X-ray diffraction studies reveal the neodymium complex has an orthorhombic system with different unit cell parameters. Europium, samarium, neodymium and praseodymium complexes exhibit the characteristic luminescence. Further, the in vitro antimicrobial activities of the metal complexes exhibited greater activity as compared with the ligand.

Synthesis, X-ray crystal structure and DFT studies of two octahedral cobalt(II) complexes with N,N,N-tridentate triazine-type ligand

Two new Co(II) complexes, [CoL2]X2∙2H2O, with N,N,N-tridentate triazine type ligand (L) and X = Cl− (1) or NO3− (2) are synthesized and characterized using elemental analysis, FTIR spectra, and single-crystal X-ray diffraction. Complexes 1 and 2 are crystallized in the centrosymmetric space groups P-1 and C2/c, respectively. The Co atoms are surrounded by two neutral tridentate ligands coordinated via nitrogen atoms, thus forming a distorted octahedral coordination sphere. Hirshfeld topology analyses of the molecular packing revealed that the polar Cl⋯H, O⋯H and N⋯H contacts are the most important intermolecular interactions while the nonpolar C⋯H and C⋯C (π–π stacking) contacts are weak and insignificant, respectively. DFT calculations indicated that the high-spin state is energetically more favored than the low-spin case. The Co(II) center transfers its spin density to the ligand donor atoms via the spin delocalization mechanism. Based on the atoms in molecules (AIM) results, all Co–N interactions have a predominant covalent character. The strength of the Co–N interactions decreases in the order Co–N(hydrazone) > Co–N(triazine) > Co–N(amine). The metal anti-bonding natural orbitals involved in the Co–N interactions have high and s-orbital characters. Both complexes showed good thermal stability up to 276°C and 250°C for complexes 1 and 2, respectively.

Synthesis, structural studies, and antibacterial activity of zinc, copper, and silver complexes derived from N′-(1-(pyrazin-2-yl)ethylidene)isonicotinohydrazide

The multidentate Schiff-base ligand N′-(1-(pyrazin-2-yl)ethylidene)isonicotinohydrazide (HL) has been prepared. Reaction with zinc, copper, and silver nitrate afford three complexes, [Zn(HL′)2](NO3)2·3H2O (1), {[Cu2(L)2(NO3)(H2O)2]·NO3}n (2) and {[Ag2(L)2]·3H2O}n (3). These complexes have been characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. In 1, HL is a neutral tridentate ligand, whereas in 2 and 3, HL is a deprotonated tetradentate ligand. The hydrogen bonding interactions between NO3− and the host framework result in various supramolecular polymeric structures: a 2-D layer for 1 and 3-D network for 2 and 3. The antibacterial activities of these complexes have been investigated and the results indicate that 3 showed good antibacterial activities.

Spectral characterization and DNA binding properties of lanthanide(III) complexes with 2-acetylpyridine isonicotinoylhydrazone (APINH)

The lanthanide(III) complexes of general formula of [Ln(APINH) 2 (NO 3 ](NO 3 ) 2 .nH 2 O (where, Ln = La, Ce, Pr, Nd, Sm; APINH = 2-acetylpyridine isonicotinoyl hydrazone, n = 0, 2 and 5 for La/Ce/Pr, Sm and Nd complexes, respectively) were synthesized under mild reaction conditions with excellent yields. The complexes were characterized based on elemental analysis, molar conductivity, and infrared spectroscopy. Molar conductivity data suggest that the complexes are 1:2 electrolytes. IR spectral data suggest that APINH acts as neutral tridentate ligand. Spectral data of complexes suggest that the ligand binds metal ion through pyridine- nitrogen, azomethine-nitrogen and amido-oxygen donor atoms. Electrochemical behaviour of metal complexes was investigated by using cyclic voltammetry. The complexes undergo quasi-reversible one electron reduction. The binding interaction of complexes with CT-DNA was investigated using absorption spectrophotometry. Based on spectral changes, groove binding of complexes to DNA is suggested. KEY WORDS : Lanthanide(III) complexes, 2-Acetylpyridine isonicotinoylhydrazone, Spectral characterization, DNA binding Bull. Chem. Soc. Ethiop. 2016 , 30(2), 221-230. DOI: http://dx.doi.org/10.4314/bcse.v30i2.6

Synthesis and Characterization of a Cobalt(II) Complex with(E)-Ń-(2-Hydroxy-3-Methoxybenzylidene)Isonicotinohydrazide and (E)-Ń-(2-Hydroxy-3-Methoxybenzylidene)Isonicotinohydrazidanium Nitrate as a By-Product

A Schiff base ligand was synthesized from the reaction of isonicotinic acid hydrazide with 3-methoxysalicylaldehyde. The reaction of LH with Co(NO3)2 .6H2O in methanol gave dark red crystals of [Co(HL)2](NO3)2.3H2O and colorless crystals of the protonated ligand (HLH)+ with nitrate as the counter ion, (HLH)(NO3). In coordination to metal, Schiff base ligand was protonated via hetrocyclic nitrogen atom of the pyridine ring and deprotonated on the phenolic OH group, two ligands behave as neutral tridentate ligands. The extensive O–H···O and N–H···O hydrogen bonding interactions in the solid state contribute to the formation of an infinite one-dimensional chain in the complex.