Synthesis,spectroscopic (IR,electronic, FAB-mass,and PXRD), magnetic,and antimicrobial studies of new iron(III) complexes containing Schiff bases and substituted benzoxazole ligands

Mixed ligand complexes of iron(III), [Fe(sb)₂(py)Cl]?·?2H₂O (1–9) [where sbH?=?Schiff bases (derived from condensation of 2-aminopyridine (sapH), 2-aminophenol (saphH), o-toluidine (o-smabH), aminobenzene (sabH), p-toluidine (p-smabH), 3-nitroaniline (snabH), and anthranilic acid (saaH) with salicylaldehyde and substituted (mercapto-)benzimidazole (mbzH), {2-(o-hydroxyphenyl)}benzoxazole, (pboxH)], have been synthesized by the interactions of iron(III) chloride with corresponding ligands in 1?:?2 molar ratio in refluxing pyridine. These complexes have been characterized by elemental analyses, melting points, spectral, and magnetic studies. Powder X-ray diffraction studies of some representative complexes are also reported herein. The antibacterial and antifungal activities of the free ligands and their iron(III) complexes were found in vitro. The complexes showed good antibacterial and antifungal effect to some bacteria and fungi. Two standard antibiotics (chloromphenicol and terbinafine) were used for comparison with these complexes.     

DNA binding and cleavage properties of certain ethylenediamine cobalt(III) complexes of modified 1,10-phenanthrolines

Two complexes of the type [Co(en)₂IP]³⁺ (IP = imidazo[4,5-f][1,10]-phenanthroline) and [Co(en)₂PIP]³⁺ (PIP = 2-phenylimidazo[4,5-f][1,10]-phenanthroline) have been synthesized and characterized by UV–VIS, IR and¹H NMR spectral methods. Absorption spectroscopy, emission spectroscopy, viscosity measurements and DNA melting techniques have been used to investigate the binding of these two complexes with calf thymus DNA and photocleavage studies have been used to investigate the binding of these complexes with plasmid DNA. The spectroscopic studies together with viscosity measurements and DNA melting studies support that complexes 1 and 2 bind to CT DNA(=calf thymus DNA) by an intercalation mode via IP or PIP into the base pairs of DNA. Complex 2 binds more avidly to CT DNA than 1, which is consistent with the extended planar ring π system of PIP. Noticeably, the two complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.     

Synthesis,structural characterization,and antibacterial activity of mononuclear cobalt(III) azido complexes of two pentadentate Schiff bases derived from 2-hydroxynaphthaldehyde

The structural, spectroscopic, and electrochemical properties of [Co{(naph)₂dien}(N₃)] and [Co{(naph)₂dpt}(N₃)], where (naph)₂dien?=?bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriaminedianion and (naph)₂dpt?=?bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriaminedianion have been investigated. These complexes are characterized by elemental analyses, IR, and UV–Vis spectroscopy. The crystal structures of these complexes have been determined by X-ray diffraction. The geometry around cobalt is distorted octahedral. The electrochemical behavior of these complexes in acetonitrile solution was also investigated. Both complexes show an irreversible Co^III–Co^II reduction at ca. ?0.8?V, accompanied by dissociation of the axial Co^II–N₃ bond. The in vitro antibacterial activities of these complexes were tested against Staphylococcus aureus and Bacillus licheniformis.     

Spectroscopic characterization and electrochemical studies of ruthenium(II) carbonyl complexes containing bidentate Schiff bases and triphenylphosphine or a nitrogen heterocycle

Reactions of ruthenium(II) carbonyl complexes of the type [RuHCl(CO)(PPh₃)₂(B)] [B?=?PPh₃, pyridine (py), piperidine (pip) or morpholine (mor)] with bidentate Schiff base ligands derived from the condensation of 2-hydroxy-1-naphthaldehyde with aniline, o-, m- or p-toluidine in a 1?:?1 mol ratio in benzene resulted in the formation of complexes formulated as [RuCl(CO)(L)(PPh₃)(B)] [L?=?bidentate Schiff base anion, B?=?PPh₃, py, pip, mor]. The complexes were characterized by analyses, IR, electronic and ¹H NMR spectroscopy, and cyclic voltammetric studies. In all cases, the Schiff bases replace one molecule of phosphine and a hydride ion from the starting complexes, indicating that Ru–N bonds in the complexes containing heterocyclic nitrogenous bases are stronger than the Ru–P bond to PPh₃. Octahedral geometry is proposed for the complexes.     

Ni(II) and Co(III) complexes of 5-methyl-1,3,4-thiadiazole-2-thiol: syntheses,spectral, structural,thermal analysis,and DFT calculation

Two new complexes, [Ni(en)₂(mtt)₂] (1) and [Co(en)₂(mtt)₂](mtt) (2) (Hmtt = 5-methyl-1,3,4-thiadiazole-2-thiol and en = ethylenediamine), have been synthesized and characterized by various physicochemical techniques. Complexes 1 and 2 crystallize in monoclinic and orthorhombic system with space groups P 21/n and P 21 21 21, respectively. The molecular structures of 1 and 2 show that the metal ions are six-coordinate bonded through four equatorial nitrogens of two en and two axial nitrogens of mtt ligands. The crystal structures of the complexes reveal that mtt is present in thione form and bound to the metal ion through the thiadiazole nitrogen. The crystal structures of the complexes are stabilized by various intermolecular hydrogen bonding providing supramolecular architecture. Complex 2 is also stabilized by weak π···π interactions occurring between two thiadiazole rings. The bioefficacies of the ligand and complexes have been examined against the growth of bacteria to evaluate their antimicrobial potential. The biological results suggest that 2 is more active than the ligand and 1 against the tested bacteria. The geometries of the ligand and the complexes have been optimized by the DFT method and the results are compared with the X-ray diffraction data. The Co(III) complex exhibits an irreversible Co(III)/Co(II) process while the Ni(II) complex displays quasi-reversible Ni(II)/Ni(III) redox processes with large peak separation as compared to that expected for a one electron process which is thought to be coupled with some chemical reaction.     

Kinetic Analyis of TG Data XXXV. Spectroscopic and thermal studies of some cobalt(III) chelates with ethylenediamine

A number of 30 [Co(en)₃ ]Y₃ , [Co(en)₂ X₂ ]Y and [Co(en)₂ X(amine)]Y₂ type complexes (X =Cl, Br; Y =Cl, Br, I, NCO, NCS, NO₃ , ClO₄ , etc.; amine =aromatic and alkylamines) were obtained from trans-[Co(en)₂ Cl₂ ]Cl by double decomposition and by substitution reactions, respectively. The structure of the complexes was proved by means of far and middle FTIR spectra. The thermal decomposition was studied by TG, DTA and DSC measurements. Mass spectra were also recorded. In the case of [Co(en)₃ ]Y₃ complexes the nitrate, perchlorate and dimesoperiodates decompose suddenly, frequently explosion like. The halides and thiocyanates seem to substitute an ethylenediamine ligand, yielding a rather unstable intermediate. The pyrolysis of [Co(en)₂ X₂ ]Y type derivatives yields no relatively stable intermediates, but the decomposition temperatures may be correlated with the nature of Y and with the cis or trans configuration of the compound. With the [Co(en)₂ X(amine)]Y₂ type complexes one observes the formation of [Co(en)₂ XY]Y as intermediate product. From the TG curves kinetic parameters were derived for some dehydration and deamination processes, by using the nomogram method. The validity of a non-linear kinetic compensation law was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of Ni(II) complexes of O,N-donor Schiff bases derived from acyl pyrazolone analogues

Two bidentate Schiff bases, 5-methyl-2-p-tolyl-4-(1-p-tolylimino-propyl)-2H-pyrazol-3-ol (L1) and 2-(3-chloro-phenyl)-5-methyl-4-(1-p-tolylimino-propyl)-2H-pyrazol-3-ol (L2), were synthesized by condensation of 4-acyl pyrazolones with p-toluidine in ethanol. These ligands have been characterized by elemental analysis, infrared (IR), ¹H NMR, and mass spectra. A single crystal molecular structure of ligand L2 was also solved. Nickel(II) complexes of these ligands with general formula [ML₂?·?2H₂O] have been prepared by the interaction of aqueous solution of Ni-acetate with ethanolic solution of the appropriate ligand. The complexes were separated, analyzed, and their structures were elucidated on the basis of elemental analysis, Ni(II) determination, IR, UV-Vis, conductance, mass, and TGA-DTA data. Octahedral structure was proposed for the synthesized complexes.     

Stereospecific interactions through π -conjugated systems of sulfur-bridged dinuclear Co(III)-Pd(II) and Co(III)-Pt(II) complexes of optically active penicillaminates

The reaction of trans(N)-[Co(D-pen)₂]^? (pen = penicillaminate) or trans(N)-[Co(L-pen)₂]^? with [MCl₂(L)] (M = Pd or Pt, L = 2,2′-bipyridine (bpy) or 4,4′-dimethyl-2,2′-bipyridine (dmbpy)) stereoselectively gave an optically active S-bridged dinuclear complex, [M(L){Co(D-pen)₂}]Cl · 3H₂O or [M(L){Co(L-pen)₂}]Cl · 3H₂O. The mixture of equimolar amounts of these two enantiomers in H₂O crystallizes as [M(L){Co(D-pen)₂}]_0.5[M(L){Co(L- pen)₂}]_0.5Cl · nH₂O (1cCl · 7H₂O: M = Pd, L = bpy, n = 7; 2cCl · 7H₂O: M = Pd, L = dmbpy, n = 7; 3cCl · 6H₂O: M = Pt, L = dmbpy, n = 6), in which the enantiomeric complex cations are included in the ratio of 1 : 1. In the crystals of 1cCl · 7H₂O, [Pd(bpy){Co(D-pen)₂}]⁺ (1a) and [Pd(bpy){Co(L-pen)₂}]⁺ (1b) are arranged alternately while overlapping the bpy planes along the a axis, and the π electronic systems of bpy moieties interact with each other. This is quite a contrast to the optically active 1aCl · 3H₂O or 1bCl · 3H₂O, which exist as monomers without intermolecular interactions. In crystals of 2cCl · 7H₂O and 3cCl · 6H₂O, similarly, the two enantiomeric complex cations interact with each other through the dmbpy frameworks. However, the interplane distances between the stacked π systems in these dmbpy complexes are considerably longer than in the bpy complexes. Such structural characteristics significantly reflect their diffuse reflectance spectra.     

Synthesis,characterization, photocleavage,antimicrobial activity and DNA binding of [Co(bpy)2MHPIP]3+, [Co(dmb)2MHPIP]3+, and [Co(phen)2MHPIP]3+ complexes

4-Methyl-2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline) (MHPIP) and its complexes [Co(bpy)₂MHPIP]³⁺ (1) (bpy = 2,2′-bipyridine), [Co(dmb)₂MHPIP]³⁺ (2) (dmb = 4,4′-dimethyl-2,2′-bipyridine), and [Co(phen)₂MHPIP]³⁺ (3) (phen = 1,10-phenanthroline) have been synthesized and characterized by UV/VIS, IR, EA, ¹H, ¹³C-NMR, and mass spectra. The binding of the three complexes with calf-thymus-DNA (CT-DNA) has been investigated by absorption and emission spectroscopy, DNA-melting techniques, viscosity measurements, and DNA cleavage assay. The spectroscopic data and viscosity results indicate that these complexes bind to CT-DNA via an intercalative mode. The complexes also promote photocleavage of plasmid pBR322 DNA and were screened for antimicrobial activity.     

Ruthenium(III) chalconate complexes containing PPh3/AsPh3 and their use as catalysts

Ruthenium(III) complexes of the type [RuX(EPh₃)(L)₂] (X?=?Cl or Br; E?=?P or As; L?=?2-hydroxychalcone) have been prepared by reacting [RuX₃(EPh₃)₃] with 2-hydroxychalcones in benzene under reflux. The new complexes have been characterized by analytical and spectroscopic (infrared, electronic, electron paramagnetic resonance, and mass) methods. Redox potential studies of the complexes have been carried out to elucidate the electronic structure, geometry, and electrochemical features. On the basis of data obtained, an octahedral structure has been assigned for all the complexes. The new complexes exhibit catalytic activity for the oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N-methylmorpholine-N-oxide as co-oxidant and they were also found to be efficient catalyst for the transfer hydrogenation of ketones.     

Kinetic and Thermodynamic Studies of Facial and Meridional uns-cis-[Co(eddp)gly] Complexes

Thermal properties of facial and meridional uns-cis-[Co(eddp)gly]0.5H₂O complexes were investigated by means of DSC and TG techniques. It wasshown that the processes of thermal decomposition of these complexes are multi-stepdegradation processes, which can also be well separated into individual steps, depending onthe molecular symmetry. Thus, the process of thermal degradation of the meridional isomerof the above complex consists of 4 well-separated steps in the temperature interval from 100to 500°C. The corresponding kinetic and thermodynamic parameters of this process weredetermined, and a possible mechanism is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and spectral characterization of some complexes of platinum(II) containing η-methyleugenol

Several complexes of the formula trans-[Pt(Meug)(Am)Cl₂], Meug: methyleugenol (4-allyl-1,2-dimethoxybenzene), a η²-coordinated olefin, and Am: ammine, methylamine, diethylamine, o-toluidine, m-toluidine, p-toluidine, o-anisidine, m-anisidine and p-anisidine have been prepared. UV, IR, Raman, ¹H NMR, ¹³C NMR and 2D NMR spectra of the complexes were recorded and analyzed.     

Exploring the conformational space of cobalt(III)–salen catalyst for CO2/epoxide copolymerization: Effect of quaternary ammonium salts on preference of alternative isomers

Model catalysts for CO₂/epoxide copolymerization based on Co(III) complexes were studied, with focus on the preference of their alternative isomers, cisβ vs. trans. The systems range from model structures without the co‐catalyst, as derived from crystallographic data, to complex models with two  (CH₂)₄N⁺R₃ co‐catalyst chains (R = Me, Bu) grafted onto a Co(III)–salcy core. To explore the conformational space of the latter complexes, a computational protocol was developed, combining a systematic model‐building approach with static and molecular dynamics calculations, and multilevel energy assessment (PM7 and DFT). Results demonstrate an influence of the co‐catalyst on the relative stability of the isomers. The cisβ isomer is preferred for complexes without N⁺‐chains and the cisβ ↔ trans isomerization is feasible. Five‐coordinate species and open‐shell electronic configurations are energetically disfavored. The cisβ preference decreases with the introduction and enlargement of  (CH₂)₄N⁺R₃: both isomers can be populated for R = Me, while the trans isomer is visibly preferred for R = Bu. © 2018 Wiley Periodicals, Inc.     

Synthesis, spectral and structural studies of 1-ethoxycarbonyl-piperazine-4-carbodithioate and its Co(III), Zn(II) and Cd(II) complexes

The new complexes [Co(ecpzdtc)₃] (2) [Zn(ecpzdtc)₂(py)] (3) and [Cd(ecpzdtc)₂(py)]·H₂O (4) have been synthesized from sodium 1-ethoxycarbonyl-piperazine-4-carbodithioate [(Na⁺(ecpzdtc)⁻]. The ligand and the complexes have been characterized by elemental analyses, IR, magnetic susceptibility and single crystal X-ray data. The [Zn(ecpzdtc)₂(py)] and [Cd(ecpzdtc)₂(py)]·H₂O complexes contain pyridine as the co-ligand. [Co(ecpzdtc)₃] (2) crystallizes in the monoclinic system, whereas [Zn(ecpzdtc)₂(py)] (3) and [Cd(ecpzdtc)₂(py)]·H₂O (4) crystallize in the triclinic system. The sulfur donor sites of the bidentate ligand chelate the metal center, forming a four-membered CS₂M ring. The cobalt complex has a distorted octahedral geometry, the zinc complex is almost between trigonal bipyramidal and square pyramidal, whereas the cadmium complex is square pyramidal. The crystal structures of all the complexes are stabilized by various types of inter and intramolecular hydrogen bonding.     

Syntheses,crystal structures,and antibacterial activities of two cobalt(III) complexes

Syntheses, structures, and antimicrobial activities of cobalt(III) complexes with two tetradentate Schiff-base ligands, (BA)₂en?=?bis(benzoylacetone)ethylenediimine dianion and (acac)₂en?=?bis(acetylacetone)ethylenediimine dianion, and two axial pyridines (py) have been investigated. These complexes were characterized by FT-IR, ¹H-NMR, UV-Vis spectroscopy, and elemental analysis. The crystal structures of the complexes were determined by X-ray crystallography. Single-crystal X-ray diffraction analyses revealed that both complexes have distorted octahedral environments, Schiff-base ligand coordinates cobalt in four equatorial positions, and the two axial positions are occupied by pyridines. The pyridines and Schiff-base ligands are involved in N–H···O hydrogen bonds with perchlorate. Biological activities of the ligands and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, and Bacillus subtilis by the well diffusion method. The activity data show the metal complexes to be more potent than the parent ligand against two bacterial species.     

Mononuclear gallium(III) complexes based on salicylaldoximes: Synthesis,structure and spectroscopic characterization

The reactions of Ga(acac)₃ with salicylaldoxime (saoH₂) and methyl-salicylaldoxime (Me-saoH₂) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)₂] (1) and [Ga(acac)₃][Ga(acac)(MesaoH)₂] (2), respectively, in high yields. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH⁻ and one bidentate chelate acac⁻ ligands. A [Ga(acac)₃] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. ¹H and ¹³C NMR data in CDCl₃ indicate that the salicylaldoximato complexes isomerize in solution.     

Synthesis,characterization, molecular modeling,and thermal analyses of bioactive Co(II) and Cu(II) complexes with diacetylmonoxime and different amines

Condensation of diacetylmonoxime with 2-amino-5-mercapto-1,3,4-thiadiazole, 2-amino-1,3,4-thiadiazole or 3-amino-5-methylisoxazole in the presence of Co(II) and Cu(II) salts with different anions produced nine complexes. The synthesized complexes have been characterized by elemental analyses, molar conductivities, thermal analyses, magnetic moments, IR, electron spin resonance, and UV-Vis spectral studies. The spectral data show that sulfur, oxygen, and nitrogen participate in chelation with the metal ions. The complexes are tetrahedral, octahedral, or square planar based on the amine used and the nature of anion. Molar conductance measurements of the complexes in DMF indicate non-electrolytes. CS Chem 3-D Ultra Molecular Modeling and Analysis Program has been used for optimization of the molecular structures of some complexes. In vitro cytotoxicities of the complexes were tested against different carcinoma cell lines. Antimicrobial activities of the complexes were screened against Gram-positive (Staphylococcus aureus), Gram negative bacteria (Escherichia coli), and fungal species (Aspergillus flavus, Candida albicans, and Microsporum canis).     

Tetradentate asymmetric Schiff bases and their Ni(II) and Fe(III) complexes

Three asymmetric Schiff-base tetradentate diimines H₂L¹, H₂L², and H₂L³ [(2-OH)C₆H₄N=CHC₆H₄2-N=CHC₆H₃(2-OH)(5-X), X?=?H, CH₃, Cl respectively] have been synthesized by a two step process. The reaction of 2-hydroxy aniline with 2-nitro-benzaldehyde in EtOH gave the starting Schiff base, 2-hydroxy-N-(2-nitrobenzylidene)aniline (SB-NO₂), which was reduced into the amino derivative (SB-NH₂) in solution. Reacting SB-NH₂ with 2-hydroxybenzaldehyde, 2-hydroxy-5-methylbenzaldehyde and 2-hydroxy-5-chlorobenzaldehyde gave the three new ligands H₂L¹, H₂L², and H₂L³ respectively. Their dimeric, binuclear metal complexes with Ni(II) and Fe(III) have also been synthesized. The ligands and their complexes were characterized by elemental analyses, LC–MS, IR, electronic, ¹H and ¹³C-NMR spectra, TGA, conductivity and magnetic measurements. All of the spectroscopic, analytical and other data indicate octahedral geometry M₂L₂(H₂O)X₂ (M: Ni,Co;X: Cl or H₂O), except for NiL² which is monomeric. Antimicrobial activities of the ligands and the complexes were evaluated against five bacteria. While the ligands and the Ni complexes are inactive towards Pseudomonas aeruginosa and Staphylococcus aureus, Fe complexes are active; only Fe complexes are inactive against Escherichia coli. All of the compounds have antimicrobial activities against Bacillus subtilis, and Yersinia enterecolitica.     

Iminoimidazole‐based Co(II) and Fe(II) complexes: Syntheses,characterization, and catalytic behaviors for isoprene polymerization

A stereoselectivity switchable polymerization of isoprene has been developed, which is catalyzed by iminoimidazole‐Co(II) and ‐Fe(II) complexes. The influence of substituents ranging from electron donating to the electron withdrawing on the iminoimidazole‐Co(II) and ‐Fe(II) catalysts is investigated for isoprene polymerization. Two sets of iminoimidazole‐Co(II) and ‐Fe(II) complexes have been prepared and fully characterized. X‐ray crystallography analysis reveals that the complexes Co1 and Fe1 adopt distorted tetrahedral geometries. In the presence of AlEt₂Cl as co‐catalyst, all the Co(II) complexes are active and the catalytic activity is highly dependent on the molar ratio of Al/Co. All the Co(II) complexes exhibit higher activities at low Al/Co ratio. Compared with the Co(II) complexes, the Fe(II) complexes are essentially inactive under the identical condition. However, on activation with combination of AlEtCl₂ and [Ph₃C][B(C₆F₅)₄], both Co(II) and Fe(II) complexes display high activities with good conversions of isoprene (up to >99%). Additionally, low molecular weight and high trans‐1,4‐unit (>96%) selectivity are characteristics of the resultant polyisoprene. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 767–775