Showing papers in "Transition Metal Chemistry in 2014"

M(II) Schiff base complexes (M = zinc, manganese, cadmium, cobalt, copper, nickel, iron, and palladium) supported on superparamagnetic Fe3O4@SiO2 nanoparticles: synthesis, characterization and catalytic activity for Sonogashira–Hagihara coupling reactions

Abstract: A series of magnetically separable catalysts consisting of Schiff base complexes of metal ions (Zn, Mn, Cd, Co, Cu, Ni, Fe and Pd) supported on superparamagnetic Fe3O4@SiO2 nanoparticles has been prepared. The structural features of the catalysts were characterized by XRD, FTIR, TEM, FE-SEM, DLS, VSM, UV–Vis, TGA, AFM and N2 adsorption–desorption. Some of the Fe3O4@SiO2/Schiff base complexes were found to be efficient catalysts for the Cu-free and the phosphine free Sonogashira–Hagihara coupling reaction of aryl halides and phenylacetylene. The catalysts are superparamagnetic, and thus could be easily separated by the utilization of an external magnetic field, and could be reused for six cycles without significant loss of activity.

Synthesis, characterization and crystal structure of a manganese(III) Schiff base complex and investigation of its catalytic activity in the oxidation of benzylic alcohols

Abstract: A new Mn(III) Schiff base complex was prepared by the reaction of 6,6′-diethoxy-2,2′-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenol with Mn(OAc)2·4H2O. The complex was characterized by physicochemical and spectroscopic methods. Also, its molecular structure was determined by single-crystal X-ray diffraction. The complex was used as a catalyst for the efficient oxidation of benzylic alcohols with tetrabutylammonium periodate. Various reaction parameters were optimized for the reaction of benzyl alcohol.

In situ prepared CuI nanoparticles on modified poly(styrene-co-maleic anhydride): an efficient and recyclable catalyst for the azide–alkyne click reaction in water

Abstract: A facile, high-yielding and straightforward methodology for the copper-catalyzed synthesis of 1,4-disubstituted 1,2,3-triazoles in water, using in situ prepared copper nanoparticles (NPs) on modified poly(styrene-co-maleic anhydride) [SMA] catalyst, is reported. The polymer support was easily prepared from the reaction of SMA with 4-aminopyridine and subsequently underwent reaction with CuI NPs. The catalyst was applied for the preparation of triazoles under air, followed by chromatographic separation of the products. The polymer-supported catalyst not only showed high catalytic activity but also showed high 1,4-regioselectivity for the [3 + 2] Huisgen cycloaddition in water as solvent. The products were obtained in good to excellent yields in all cases. The catalyst can be used without pre-activation and reloaded for at least five runs without significant decrease in its activity. The catalyst was characterized by SEM, energy dispersive spectroscopy analysis of X-rays, and inductively coupled plasma.

Selective catalytic oxidation of benzyl alcohol to benzaldehyde by a mononuclear oxovanadium(V) complex of a bis(phenolate) ligand containing bulky tert-butyl substituents

Abstract: A new mononuclear complex of vanadium(V), [V(O)(bp)(OCH3)] (1) has been synthesized, where H2bp is N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N′,N′-dimethylethylene-1,2-diamine. The complex was characterized by elemental analyses, spectroscopic methods and X-ray diffraction measurement. Single-crystal X-ray diffraction structure analysis of the complex revealed that the vanadium atom is octahedrally coordinated and that the bis(phenolate) ligand (bp2−) is N2O2-bonded to the vanadium(V) center in a tetradentate dinegative fashion.

Dinuclear silver(I)- N -heterocyclic carbene complexes of N-allyl substituted (benz)imidazol-2-ylidenes with pyridine spacers: synthesis, crystal structures, nuclease and antibacterial studies

Abstract: The synthesis, structures and antibacterial studies of silver complexes of N-heterocyclic carbene (NHC) ligands are reported. The NHC precursors, 2,6-bis(3-allylimidazol-1-ylmethyl) pyridine hexafluorophosphate (1) and 2,6-bis(3-allylbenzimidazol-1-ylmethyl)pyridine dibromide (2) were treated with Ag2O to yield 2,6-bis(3-allylimidazol-1-ylmethyl)pyridine disilver bis(hexafluorophosphate) (3) and 2,6-bis(3-allylbenzimidazolium-1-ylmethyl)pyridine disilver bis(hexafluorophosphate) (4). All four compounds were characterized by physico-chemical and spectroscopic techniques and by single-crystal X-ray diffraction. The compounds were screened for their antibacterial activities against Staphylococcus aureus (ATCC 12600) as a Gram-positive and Escherichia coli (ATCC 11303) as a Gram-negative bacteria. Compounds 1 and 2 showed no inhibition while 3 and 4 inhibited the growth of these bacteria. The nuclease activities of the compounds were evaluated by gel electrophoresis, and the results indicate that complexes 3 and 4 can degrade both DNA and RNA.

Synthesis, characterization and bio-activity of a bidentate NS Schiff base of S-allyldithiocarbazate and its divalent metal complexes: X-ray crystal structures of the free ligand and its nickel(II) complex

Abstract: Transition metal complexes ML2 (2–6) [where M = Ni(II), Cu(II), Zn(II), Cd(II), Pd(II) and HL = allyl-2-(4-benzyloxyphenylmethylene)hydrazine carbodithioate (1)] have been prepared by the reaction of the ligand with metal ions in 2:1 molar ratio and characterized by physicochemical techniques and spectroscopic methods. The crystal structures of the free ligand and its nickel(II) complex 2 have been determined by X-ray diffractometry. The ligand exists in its thione tautomeric form both in solution and in the solid state. In complex 2, square-planar coordination of nickel(II) was achieved by two chelating ligand moieties coordinating through the azomethine nitrogen and the deprotonated thione sulphur atom. Based on the crystal structures of analogous dithiocarbazate species, a square-planar geometry was assumed for the copper(II) and palladium(II) complexes, and a tetrahedral coordination sphere for the zinc(II) and cadmium(II) derivatives. The in vitro bactericidal activity suggests that the palladium(II) complex is strongly active against two bacteria. The cadmium(II) complex is moderately cytotoxic with an LC50 value of 409 μg/ml, but less active than gallic acid, LC50 = 78 μg/ml.

Synthesis, crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

Abstract: A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N2O2 type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H2L4 and its corresponding complex VOL4 were determined by X-ray crystallography.

Influence of copper(II) catalyst on the oxidation of l -histidine by platinum(IV) in alkaline medium: a kinetic and mechanistic study

Abstract: The kinetics of oxidation of l-histidine (His) by platinum(IV) in the absence and presence of copper(II) catalyst was studied using spectrophotometry in alkaline medium at a constant ionic strength of 0.1 mol dm−3 and at 25 °C. In both cases, the reactions exhibit a 1:1 stoichiometry ([His]:[PtIV]). The rate of the uncatalyzed reaction is dependent on the first power of each of the concentrations of oxidant, substrate and alkali. The catalyzed path shows a first-order dependence on both [PtIV] and [CuII], but the order with respect to both [His] and [OH−] is less than unity. The rate constants increase with increasing ionic strength and dielectric constant of the medium. The catalyzed reaction has been shown to proceed via formation of a copper(II)_histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. Platinum(IV) is reduced to platinum(II) by the substrate in a one-step two-electron transfer process. This is followed by other fast steps, giving rise to the oxidation products which were identified as 2-imidazole acetaldehyde, ammonia and carbon dioxide. A tentative reaction mechanism is suggested, and the associated rate laws are deduced. The activation parameters with respect to the slow step of the mechanism are reported and discussed.

Synthesis, crystal structures, spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

Abstract: New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H2L1), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H2L2); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H2L3), namely [CoIII(L1)(N-MeIm)3]PF6 (1), [CoIII(L1)(py)3]ClO4 (2), [Co(L1)(py)3][Co(L1)2] (3) and [CoIII(L2)(N-MeIm)3]PF6 (4) and [Co(L3)(N-MeIm)2]PF6 (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.

Nickel(II) complexes of polyhydroxybenzaldehyde N4-thiosemicarbazones: synthesis, structural characterization and antimicrobial activities

Abstract: Nickel(II) complexes with 2,3-dihydroxybenzaldehyde N4-substituted thiosemicarbazone ligands (H3L1–H3L4) have been synthesized and characterized with the aim of evaluating the effect of N4 substitution in the thiosemicarbazone moiety on their coordination behavior and biological activities. Two series of nickel(II) complexes with the general formulae [Ni(H3L)(H2L)]ClO4 and [Ni2(HL)2] were characterized by analytical and spectral techniques. The molecular structure of one of the complexes, namely, [Ni(H3L4)(H2L4)]ClO4 was established by single crystal X-ray diffraction studies. The crystal structure of this complex revealed that two H3L4 ligands are coordinated to nickel(II) in different modes; one as a neutral tridentate ONS ligand and the other is as a monoanionic tridentate (ONS−) ligand. The antimicrobial activities of the compounds were tested against 25 bacterial strains via the disc diffusion method, and their minimum inhibitory concentration (MIC) and minimum microbicidal concentration were evaluated using microdilution methods. With a few exceptions, most of the compounds exhibited low-to-moderate inhibitory activities against the tested bacterial strains. However, the complexes [Ni2(HL3)2] (7) and [Ni2(HL4)2] (8) indicated higher inhibitory activity against Salmonella enterica ATCC 9068 (MIC values 15.7 and 50 μg/ml). The toxicities of the compounds were tested on brine shrimp (Artemia salina), where no meaningful toxicity level was noted for both the free ligands and the complexes. The cytotoxicities of the compounds on cell viability were determined on MCF7, PC3, A375, and H413 cancer cells in terms of IC50; complexes [Ni(H3L3)(H2L3)]ClO4 (3), [Ni2(HL3)2] (7) and [Ni2(HL4)2] (8) exhibited significant cytotoxicity on the tested cell lines.

4-Vinylbenzyl-substituted silver(I) N -heterocyclic carbene complexes and ruthenium(II) N -heterocyclic carbene complexes: synthesis and transfer hydrogenation of ketones

Abstract: 4-Vinylbenzyl-substituted Ag(I) N-heterocyclic carbene (NHC) complexes and Ru(II) NHC complexes have been synthesized. The Ag(I) complexes were synthesized from the imidazolium salts and Ag2O in dichloromethane at room temperature. The Ru(II) complexes were prepared from Ag(I) NHC complexes by transmetallation. The six 4-Vinylbenzyl-substituted Ag(I) NHC complexes and six 4-Vinylbenzyl-substituted Ru(II) NHC complexes have been characterized by spectroscopic techniques and elemental analyses. The Ru(II) NHC complexes show catalytic activity for the transfer hydrogenation of ketones.

Mixed-ligand metal complexes containing an ONS Schiff base and imidazole/benzimidazole ligands: synthesis, characterization, crystallography and biological activity

Abstract: Salicylaldehyde-4-methylthiosemicarbazone (H2MTSali) has been prepared via the condensation reaction of 4-methyl-3-thiosemicarbazide and salicylaldehyde. Four new mixed-ligand copper(II) and nickel(II) complexes with a general formula [M(MTSali)L] (M = Cu2+ or Ni2+; L = co-ligand) were synthesized, where L is either imidazole (im) or benzimidazole (bzim). The Schiff base and its mixed-ligand complexes were characterized by IR and UV/Vis spectroscopy, and the complexes by molar conductivity and magnetic susceptibility measurements. The spectroscopic data indicated that the Schiff base behaves as a tridentate ONS donor ligand coordinating via the phenoxide-oxygen, azomethine-nitrogen, and thiolate-sulphur atoms. Magnetic data indicate a square planar environment for the nickel(II) complexes while molar conductance values indicate that the metal complexes are essentially non-electrolytes in DMSO solution. X-ray crystallography shows Cu(MTSali)bzim (1) and Ni(MTSali)bzim (3) to be isostructural, with the metal(II) ions being coordinated by a N2OS donor set that defines an approximate square planar geometry; in both cases, the benzimidazole is splayed with respect to the coordination plane. The copper(II) complexes were active against MDA-MB-231 and MCF-7 breast cancer cell lines, more so than H2MTSali, whereas the nickel(II) complexes were inactive.

Deep oxidative desulfurization of dibenzothiophene with molybdovanadophosphoric heteropolyacid-based catalysts

Abstract: Three hydrophobic Keggin-type heteropolyacid catalysts, [C3H3N2(CH3)(C2H4)]5PMo10V2O40 ([C2mim]PMoV), [C3H3N2(CH3)(C4H8)]5PMo10V2O40 ([C4mim]PMoV) and [C3H3N2(CH3)(C6H12)]5PMo10V2O40 ([C6mim]PMoV), were synthesized by reacting molybdovanadophosphoric acid with imidazolium bromides, and characterized by spectroscopic methods. Their use as catalysts in the extractive catalytic oxidative desulfurization process using hydrogen peroxide as the oxidant and acetonitrile as phase transfer agent was studied. The catalytic properties decreased in the order: [C6mim]PMoV > [C4mim]PMoV > [C2mim]PMoV. The main factors influencing the rate of removal of dibenzothiophene (DBT) were investigated, including reaction temperature, the amounts of catalyst, H2O2 and acetonitrile. Nearly 100 % sulfur removal rate was achieved under optimal conditions. The catalyst could be recycled six times with only a slight decrease in activity. A reaction mechanism for DBT oxidation is proposed, in which the Keggin anions first obtain active oxygen from H2O2, then the DBT is oxidized to dibenzothiophene sulfones.

Kinetic and mechanistic investigations on the oxidation of N’-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium

Abstract: Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-N’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO4−]0 and [Azn-F]0, but with a fractional first-order dependence on [OH−]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.

Two copper(II) complexes of curcumin derivatives: synthesis, crystal structure and in vitro antitumor activity

Abstract: Two Cu(II) complexes of curcumin derivatives, formulated as CuL 2 a (1) and CuL 2 b (2) [HLa = 1,7-bis(4-ethyloxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione and HLb = 1,7-bis(4-butyloxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione], have been synthesized and characterized by single-crystal X-ray diffraction, along with physicochemical and spectroscopic methods In both complexes, each Cu(II) center is surrounded by four oxygen atoms from two β-diketone ligands in a square planar geometry Complex 1 forms a 2D layer structure through intermolecular π–π stacking interactions, as well as weak coordination interactions between the Cu and O atoms of the solvent 1,4-dioxane molecules Complex 2 displays a 1D column structure stabilized by intermolecular π–π stacking interactions MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays were used to evaluate the cytotoxicities of these complexes against three human cancer cell lines The results show that the Cu(II) complexes exhibit more potent inhibition tumor growth in comparison with the free ligands

Synthesis, structures, and Helicobacter Pylori urease inhibition of hydroxamate-coordinated oxovanadium complexes with benzohydrazone ligands

Abstract: A new acetohydroxamate-coordinated oxovanadium(V) complex, [VOL(AE)] (1), and a new benzohydroxamate-coordinated oxovanadium(V) complex, [VOL(BE)] (2), where L is the dianionic form of N′-(2-hydroxy-5-methylbenzylidene)-2-methoxybenzohydrazide, have been synthesized and characterized by physicochemical methods and single-crystal X-ray diffraction. The V atom in each complex adopts octahedral coordination. Thermal stabilities and urease inhibitory activities of the complexes were studied. The percent inhibition of complexes 1 and 2 at the concentration of 100 μmol L−1 on Helicobacter pylori urease is 81.2 and 46.7 %, respectively. Complex 1 has an IC50 value of 27.0 μmol L−1. A molecular docking study of the complexes with the H. pylori urease was performed.

An iron Schiff base complex loaded mesoporous silica nanoreactor as a catalyst for the synthesis of pyrazine-based heterocycles

Abstract: An iron Schiff base complex was encapsulated in SBA-15 mesoporous silica to afford a Fe(III)-Schiff base/SBA-15 heterogeneous nanocatalyst for the synthesis of pyridopyrazine and quinoxaline heterocycles. These reactions proceeded in water with excellent yields. The catalyst was characterized by physico-chemical and spectroscopic methods and found to retain the characteristic channel structures of the SBA-15, allowing good accessibility of the encapsulated metal complex.

Synthesis and electrochemistry of phenyl-functionalized diiron propanedithiolate complexes with bidentate phosphine ligands

Abstract: Carbonyl substitution reactions of [μ-(SCH2)2CHC6H5]Fe2(CO)6 with bidentate phosphine ligands, cis-1,2-bis(diphenylphosphine)ethylene (cis-dppv) and N,N-bis(diphenylphosphine)propylamine [(Ph2P)2N-Pr-n], yielded an asymmetrically substituted chelated complex [(μ-SCH2)2CHC6H5]Fe2(CO)4(k 2-dppv) and a symmetrically substituted bridging complex [(μ-SCH2)2CHC6H5]Fe2(CO)4[μ-(PPh2)2N-Pr-n] under different reaction conditions. Both complexes were fully characterized by spectroscopic methods and by X-ray crystallography. Their electrochemical behaviors were observed by cyclic voltammetry, and the catalytic electrochemical reduction of protons from acetic or trifluoroacetic acid to give dihydrogen mediated by complex [(μ-SCH2)2CHC6H5]Fe2(CO)4(k 2-dppv) was investigated.

Synthesis, crystal structures, luminescence and catalytic properties of three silver(I) coordination polymers with bis(imidazole) and benzenedicarboxylic acid ligands

Abstract: Three new silver coordination compounds with empirical formula [Ag2(L1)2·(ntp)·(H2O)3.25]n (1), [Ag1.5(L1)1.5·(H0.5bdc)·(H2O)4]n (2) and [Ag(L2)(Hmip)]n (3) (L1 = 1,4-bis(imidazol-1-ylmethyl)benzene, L2 = 1,1′-(1,4-butanediyl)bis-1H-benzimidazole, H2ntp = 2-nitroterephthalic acid, H2bdc = 1,3-benzenedicarboxylic acid, H2mip = 5-methylisophthalic acid) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction and physico-chemical spectroscopic methods. The silver centers display different environments with a linear geometry in 1 and 2 and distorted T-shaped geometry in 3. In 1–3, the bidentate N-donor ligands (L1 and L2) bridge neighboring silver centers to form 1D infinite chain structures. Complexes 2 and 3 are extended into 2D layers, and 1 is packed into a 3D 3,4,4,6-connected supermolecular network via classical O–H···O hydrogen bonds, while 3 is further extended into 3D framework through π–π interactions. The luminescence properties of complexes 1, 2 and 3 were investigated in the solid state. These coordination polymers possess a remarkable activity for degradation of methyl orange by persulfate in a Fenton-like process.

Synthesis, crystal structures, antioxidant activities and DNA-binding studies of two manganese(II) complexes with 1,3-bis(1-ethylbenzimidazol-2-yl)-2-oxopropane ligands

Abstract: Two manganese(II) complexes, [Mn(Etobb)2](pic)2·2DMF (pic = picrate) 1 and Mn(Etobb)Cl2 2, where Etobb is 1,3-bis(1-ethylbenzimidazol-2-yl)-2-oxopropane, were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of both complexes have been determined by X-ray single crystal diffraction. The coordination environment of the Mn(II) atom in complex 1 can be described as distorted, while complex 2 has as a distorted square-pyramidal geometry. For both complexes, π–π stacking interactions link the structures into 1D infinite networks. The interactions of free Etobb and its complexes with calf thymus DNA were investigated by using electronic absorption titration, ethidium bromide-DNA displacement experiments and viscosity measurements. Furthermore, the antioxidant activities of the complexes were determined by superoxide and hydroxyl radical scavenging methods in vitro; both complexes are able to suppress O 2 −· and HO·, and complex 1 is more effective than complex 2.

Electrochemistry of nickel(II) and copper(II) N,N'-ethylenebis(acetylacetoniminato) complexes and their electrocatalytic activity for reduction of carbon dioxide and carboxylic acid protons

Abstract: The effect of the metal center of [ML] complexes [M = Ni(II), Cu(II); L = N,N′-ethylenebis(acetylacetoniminato)] on their electrochemistry and electrocatalytic activity for the reduction of CO2 and protons has been studied using cyclic voltammetry and bulk electrolysis. The two complexes exhibit different electrochemistries, which are not significantly dependent on the nature of the solvent. The electrocatalytic activity of [NiL] is significantly higher than that of [CuL] for CO2 reduction, due to the higher stability of the electrochemically generated [Ni(I)L] complex, relative to the Cu(I) analog. The diffusion coefficient of [NiL] calculated from the steady-state diffusion limiting current is 3.0 × 10−6 cm2 s−1. The catalytic efficiency of [NiL] in non-aqueous solvents in terms of i p(CO2)/i p(N2) per nickel center is smaller than that of [Ni(cyclam)]2+, but greater than those of sterically hindered mononuclear [Ni(1,3,6,8,10, 13,15-heptaazatricyclo(11.3.1.1) octadecane)]2+ or multinuclear [Ni3 (X)]6+ where X = 8,8′,8″-{2,2′,2″(-nitrilotriethyl)-tris(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1) octadecane}. Both [NiL] and [CuL] are also electrocatalysts for the reduction of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN.

Synthesis, characterization, DNA binding and cleavage properties of a ternary copper(II) Schiff base complex

Abstract: A ternary coordination complex 2Cu(C14H8NO3Cl)(C12H8N2)·3CH3OH of a Schiff base (C14H8NO3Cl: 4-chloroanthranilic acid–salicylaldehyde) was synthesized from 4-chloroanthranilic acid, salicylaldehyde, copper acetate and 1,10-phenanthroline and characterized by physicochemical and spectroscopic methods. X-ray crystallography shows that the copper atom is five coordinated by the imine nitrogen, two nitrogen atoms from 1,10-phenanthroline, the hydroxyl oxygen and the carboxylate oxygen atom. The interaction of the complex with calf-thymus DNA was investigated by UV absorption spectroscopy, fluorescence emission spectroscopy and viscosity. In addition, the cleavage reaction with pBR322 supercoiled plasmid DNA was investigated. The complex binds to DNA and also exhibits significant DNA cleavage activity.

Synthesis and characterization of mixed-ligand copper(II) saccharinate complexes containing tridentate NNS Schiff bases. X-ray crystallographic analysis of the free ligands and one complex

Abstract: Four new Schiff bases containing N and S heteroatoms (HL1–HL4) have been prepared and characterized, including determination of the X-ray crystal structures of HL1 and HL3. Spectroscopic evidence indicates that these Schiff bases behave as uninegatively charged tridentate NNS ligands in complexes of general formula [Cu(Ln)sac] (Ln is the anionic form of NNS, and sac represents saccharinate anion). Crystals of both HL1 and [Cu(L4)sac)(H2O)]·Hsac crystallized in triclinic system with P $$ \bar{1} $$ space group, while HL3 crystallized in monoclinic system with P 21/c space group. [Cu(L4)sac)(H2O)]·Hsac has a distorted square-pyramidal structure with a non-bonded saccharin molecule present in the outer coordination sphere. The tridentate NNS ligands are coordinated to Cu through pyridine nitrogen, azomethine nitrogen and thiolate sulfur atoms, while the fourth and fifth coordination positions are occupied by the N-bonded saccharinate anion and a water ligand, respectively.

Structural diversity of transition-metal coordination polymers derived from isophthalic acid and bent bis(imidazole) ligands

Abstract: Four coordination polymers associated with bent bis(imidazole) 1,3-bis(imidazol-l-yl-methyl)benzene (mbix) and isophthalic acid (H2ip) or 5-methylisophthalic acid (H2mip) ligands, formulated as {[Cd(mbix)(mip)]·H2O} n (1), {[Co(mbix)(mip)]·0.4H2O} n (2) [Ni(mbix)(mip)H2O] n (3) and [Ni(mbix)(ip)] n (4), were synthesized under hydrothermal conditions and characterized by physico-chemical and spectroscopic methods. Complexes 1 and 2 are isomorphous and exhibit a 1D loop-like chain. Complex 3 features a 2D (4,4) layer, which further extends into an unusual 2D (3,5)-connected 3,5L2 double-layered supramolecular network via classical O–H···O hydrogen bonding interactions. Complex 4 is a 3D network, which shows a rare binodal (3,5)-connected 3,5T1 framework. Moreover, the luminescence and catalytic properties of the complexes for the degradation of methyl orange by sodium persulfate in a Fenton-like process are reported.

Cytotoxicity, antioxidant and glutathione S -transferase inhibitory activity of palladium(II) chloride complexes bearing nucleobase ligands

Abstract: Palladium(II) chloride complexes bearing the nucleobases, adenine, cytosine and guanine, have been synthesized and characterized by UV–vis spectrophotometric methods, magnetic susceptibility, molar conductivity, elemental analysis, FTIR and 1H-NMR. The complexes were found to have the general composition PdCl2(NH3L) (where L = adenine, cytosine or guanine). Square-planar geometry is proposed for these Pd(II) complexes based on magnetic evidence and electronic spectra. The complexes as well as the free nucleobase ligands show varying degrees of cytotoxicity on human promyelocytic leukemia (HL60) and human histiocytic leukemia (U937) cell lines, with cis-[PdCl2(NH3)(Gua)] showing IC50 values of 48.03 ± 9.67 and 11.12 ± 3.42 µM against HL60 and U937, respectively. The complexes as well as the ligands did not show anti-proliferative activity against a normal human cell line (NB1RGB). The complexes also show significant antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl radical as well as glutathione S-transferase inhibitory activity.

Cobalt(II) and silver(I) coordination polymers constructed from flexible bis(5,6-dimethylbenzimidazole) and substituted isophthalate co-ligands

Abstract: Two coordination polymers, [Co(L1)(IPA] n (1) and {[Ag(L2)(HMIPA)]·H2O} n (2) (H2IPA = isophthalic acid, L1 = 1,2-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, H2MIPA = 5-methylisophthalic acid, L2 = 1,6-bis(5,6-dimethylbenzimidazol-1-yl)hexane, have been synthesized and characterized by physicochemical and spectroscopic methods, as well as single-crystal X-ray diffraction. In 1, six-coordinated cobalt centers are bridged by L1 and IPA2− ligands to generate a (4,4) two-dimensional layer. However, complex 2 features a 1D chain structure, which is further extended by O–H···O hydrogen bonding interactions into a 2D supramolecular layer with (63) topology. The fluorescence and thermal gravimetric analysis of both complexes were also explored. Furthermore, the complexes 1 and 2 exhibit remarkable catalytic properties for the degradation of methyl orange dyes in a Fenton-like process.

Effect of substituents and encapsulation on the catalytic activity of copper(II) complexes of two tridentate Schiff base ligands based on thiophene: benzyl alcohol and phenol oxidation reactions

Abstract: Encapsulation of Cu(II) complexes of methyl-2-(2-hydroxybenzylideneamino)-4,5,6,7-tetrahydrobenzo[b]-thiophene-3-carboxylate (HL1) and 2-ethyl-4-methyl 5-(2-hydroxybenzylideneamino)-3-methylthiophene-2,4-dicarboxylate (HL2) in the supercages of zeolite NaY was performed by the flexible ligand method. The neat and encapsulated complexes were characterized by physicochemical and spectroscopic methods and employed as catalysts for oxidation of benzyl alcohol and phenol. The encapsulated complexes were both more reactive and stable as catalysts than the corresponding free complexes. The encapsulated complexes could be reused several times. Complexes of HL2 were more reactive than those of HL1, probably due to the electron-withdrawing effect of the CO2Et group.

Self-assembly of two 2D cobalt(II) coordination polymers constructed from 5-tert-butyl isophthalic acid and flexible bis(benzimidazole)-based ligands

Abstract: Two cobalt(II) coordination polymers, [Co(L1)(tbi)(H2O)] n (1) and [Co(L2)(tbi)] n (2) (L1 = 1,4-bis(benzimidazole)butane, L2 = 1,4-bis(2-methylbenzimidazole)butane, H2tbi = 5-tert-butyl isophthalic acid) have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as by single-crystal X-ray diffraction analysis. Both complexes exhibit similar 2D (4,4) layer structures, constructed from tbi2− and bis(benzimidazole)-based bridging ligands. The cobalt centers display different coordination environments, with an octahedral geometry in 1 and a distorted square-pyramidal configuration in 2. The thermal stabilities, fluorescence and catalytic properties of both complexes have been investigated.

Nickel(II) complexes of thiosemicarbazones: synthesis, characterization, X-ray crystallographic studies and in vitro antitubercular and antimicrobial studies

Abstract: Three nickel(II) thiosemicarbazone complexes have been synthesized and characterized by spectroscopic and physicochemical techniques. The molecular structures of two of the complexes have been determined by single-crystal X-ray diffraction studies. In both of these complexes, the nickel center is coordinated by two tridentate ligands in a meridional fashion using C=S, C=N and neutral hydroxyl OH donors. The ligand is bound to nickel in its thione form in all three complexes. The synthesized compounds were tested for antimicrobial activity against Gram-positive and Gram-negative bacteria and fungi. Additionally, all the compounds were screened for antituberculosis activity. Several complex/organism combinations returned an MIC value of 0.8 μg/mL or better, which is almost 8 times more active than the standard (streptomycin, 6.25 μg/mL).

Understanding the electronic and π-conjugation roles of quinoline on ligand substitution reactions of platinum(II) complexes

Abstract: A kinetic and mechanistic study of chloride substitution by thiourea nucleophiles, namely thiourea, N-methylthiourea, N,N-dimethylthiourea and N,N,N′,N′-tetramethylthiourea in the complexes chlorobis-(2-pyridylmethyl)amineplatinum(II) (Pt1), chloro N-(2-pyridinylmethyl)-8-quinolinamineplatinum(II) (Pt2), chloro N-(2-pyridinylmethylene)-8-quinolinamineplatinum(II) (Pt3) and chlorobis(8-quinolinyl)amineplatinum(II) (Pt4) was undertaken under pseudo-first-order conditions using UV–visible spectrophotometry The study showed that lability of the chloro leaving group is dependent on the strength of π-interactions between the filled dπ-orbitals of the metal and the empty π*-orbitals of the chelating ligand in the following manner: Pt1 > Pt3 > Pt2 > Pt4 Introduction of the quinoline moiety within the non-labile chelated framework of the Pt(II) complexes results in a more electron-rich metal centre which retards the approach of the nucleophile through repulsion Moreover, the net σ-effect of the ligand moiety plays a significant role in controlling the reactivity of the complexes The experimental results are interpreted with the aid of computational data obtained by density functional theory (B3LYP(CPCM)/LANL2DZp//B3LYP/-LANL2DZp) calculations The mode of substitution remains associative as supported by negative entropies and the dependence of the second-order rate constants on the concentration of entering nucleophiles