Showing papers in "Transition Metal Chemistry in 2015"

Synthesis, characterization and anticancer activity of 3-formylchromone benzoylhydrazone metal complexes

Abstract: A new Schiff base derived from 3-formylchromone and benzohydrazide (Hfcbh) and its Ni(II), Zn(II), Ru(II), Ru(III), Pd(II), Pt(II) and Ag(I) complexes were synthesized. These compounds were characterized on the basis of physicochemical and spectroscopic methods. Two modes of chelation for Hfcbh are reported: (1) neutral tridentate ligand through the chromone carbonyl oxygen, hydrazonic carbonyl oxygen and azomethine nitrogen atoms and (2) mononegative tridentate ligand via the chromone carbonyl oxygen, hydrazonic deprotonated hydroxy oxygen and azomethine nitrogen atoms. Free Hfcbh and its Ni(II), Zn(II), Ag(I), Pd(II) and Pt(II) complexes have been tested as anticancer agents against the human breast cancer (MDA-MB231) and human ovarian cancer (OVCAR-8) cell lines. The [Ag(fcbh)(PPh3)] complex shows the highest efficacy with a mean IC50 values of 1.0 (MDA-MB231) and 0.87 (OVCAR-8) µM, respectively.

Synthesis, crystal structures, electrochemical studies, and antioxidant activities of manganese(II) and copper(II) complexes of bis( N -allylbenzimidazol-2-ylmethyl)aniline

Abstract: Bis(N-allylbenzimidazol-2-ylmethyl)aniline (baba) and its transition metal complexes, [Mn(baba)(Cl)2] 1 and [Cu(baba)(Br)2]·DMF 2, have been synthesized and characterized by physico-chemical and spectroscopic methods. The structures of both complexes have been determined by X-ray single-crystal diffraction. The coordination environment of complex 1 can be described as distorted trigonal bipyramidal, while complex 2 has as a distorted square-pyramidal geometry. Cyclic voltammograms of complex 2 indicate an electrochemically irreversible Cu2+/Cu+ couple. In addition, the antioxidant activities of both baba and its complexes were investigated by hydroxyl and superoxide radical scavenging methods in vitro. Both of these complexes exhibit excellent radical scavenging activity.

A mixed-ligand ternary complex of nickel(II): synthesis, characterization and catalytic investigation for the synthesis of pyranopyrazoles

Abstract: A new mixed-ligand Ni(II) complex, [Ni(L)(mimi)], was prepared by the reaction of Ni(OAc)2·4H2O, 4-bromo-2-[(2-hydroxy-5-methylphenyl]iminomethyl]phenol [H2L] and 1-methylimidazole (mimi) in two forms of bulk and nanoparticle sizes using slow evaporation and ultrasonic irradiation, respectively. The complex was characterized by physicochemical and spectroscopic methods, and also by single crystal X-ray diffraction. The Ni(II) center is coordinated by the ONO donor ligand and the nitrogen of 1-methylimidazole. Scanning electron microscopy revealed that the particle size of the complex synthesized using ultrasonic irradiation was below 100 nm. Both the nano and bulk forms of [Ni(L)(mimi)] were found to be effective catalysts for four-component synthesis of dihydropyrano[2,3-c]pyrazoles from a stoichiometric mixture of ethyl acetoacetate, hydrazine hydrate, aldehyde and malononitrile in ethanol, and furthermore, the catalytic activity of the nano form of the complex is higher.

Sterically modulated silver(I) complexes of N-benzyl-substituted N-heterocyclic carbenes: synthesis, crystal structures and bioactivity

Abstract: The reaction of non-symmetrically substituted N-benzyl benzimidazolium salts (1–3) with Ag2O gives Ag(I)–NHC complexes (4–6) of the type [NHC–Ag–NHC]PF6, (NHC: benzimidazol-2-ylidene). Structures of these compounds were elucidated by physico-chemical and spectroscopic techniques. The mononuclear structures of complexes 4 and 5 in the solid state were further confirmed by single-crystal X-ray diffraction studies. The effect of substitutions on antibacterial activities of compounds 1–6 by successive N-alkylation has been investigated. The compounds were screened for their antibacterial efficacy against Staphylococcus aureus (ATCC 12600) as a Gram-positive bacterium and Escherichia coli (ATCC 25922) as a Gram-negative bacterium. All the Ag(I)–NHC complexes, in general, showed good antibacterial activities while their corresponding salts were inactive against both strains of bacteria. The results of this investigation showed that E. coli and S. aureus appeared markedly inhibited. It was observed that the derivatives of the Ag(I)–NHC complexes with longer alkyl chains were more bioactive. In order to gain preliminary insights into their actual mode of action(s), circular plasmid pTS414 DNA was exposed to gel electrophoresis and it was found that all the complexes were efficient in promoting the cleavage or degradation of DNA in the absence of an oxidant.

Syntheses, crystal structures and magnetism of azide-bridged five-coordinate binuclear nickel(II) and cobalt(II) complexes

Abstract: The bulky ligand 2,9-dimethyl-1,10-phenanthroline (dmphen) has been used to construct pentacoordinate transition metal complexes. Two such doubly end-on azido-bridged dinuclear complexes [M2(dmphen)2(μ1,1−N3)2Cl2] [M = Ni (1) or M = Co (2)] have been obtained and characterized by single-crystal X-ray diffraction analysis and magnetic studies. Both complexes consist of dimeric square pyramidal M(II) centers bridged by two end-on azide ligands. Magnetic studies suggest that both complexes display intramolecular intermetallic ferromagnetic coupling. The coupling constants for pentacoordinate azide-bridged dinuclear Ni(II) complexes are found to decrease with the increasing Ni–N–Ni bond angle.

Use of a molybdenum(VI) dioxide complex as a homogeneous and heterogeneous magnetically recoverable epoxidation catalyst

Abstract: A Mo(VI) complex, [MoO2HL(HOCH3)], HL = 2-[(2-hydroxy-benzylidene)-amino]-3-(4-hydroxy-phenyl)-propionic acid, was reacted with 3-(chloropropyl)-trimethoxysilane-functionalized silica that had been fused with magnetite to yield a magnetically separable catalyst in which the Mo complex was covalently linked to the silica matrix through a silane linkage. Both the free [MoO2HL(HOCH3)] and the immobilized complex function as efficient catalysts for the oxidation of olefins in the presence of tert-butylhydroperoxide as primary oxidant. The Fe3O4@SiO2/[MoO2L(HOCH3)] showed lower catalytic activity and turnover numbers compared to its homogeneous counterpart. However, the immobilized catalyst could be readily recovered from the reaction mixture by using a magnet and could be reused up to seven times without any loss of activity.

Synthesis of a ruthenium(II) tryptophan-associated complex and biological evaluation against Ehrlich murine breast carcinoma

Abstract: The synthesis, characterization and effects on cell cycle arrest and induced apoptosis of the ruthenium(II) complex [Ru(Trp)(dppb)(bipy)]PF6 (Trp = tryptophan; dppb = 1,4-bis(diphenylphosphine)butane bipy = 2,2′-bipyridine) are reported. The complex was characterized by elemental analysis, spectroscopic and electrochemical techniques. It showed higher cytotoxic potential against Ehrlich tumor cells than L-929 basal cells, causing a decrease in cell proliferation and inducing cell death by apoptosis.

Kinetics and mechanism of uncatalyzed and silver(I)-catalyzed oxidation of l -histidine by hexachloroplatinate(IV) in acid medium

Abstract: Kinetics of hexachloroplatinate(IV) (HCP) oxidation of l-histidine (His) in H2SO4 medium has been investigated in the absence and presence of silver(I) catalyst at constant ionic strength 2.0 mol dm−3 and temperature 25 °C. The progress of both uncatalyzed and silver(I)-catalyzed oxidation reactions has been monitored spectrophotometrically. Both uncatalyzed and catalyzed paths show first-order dependence on [HCP] and fractional-first-order dependence each on [His] and [acid]. The catalyzed path is first order in [AgI]. Increasing ionic strength and dielectric constant decreases the oxidation rates. The catalyzed reaction has been shown to proceed via formation of a silver(I)-histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. The final oxidation products of histidine were identified as the corresponding aldehyde (2-imidazole acetaldehyde), ammonium ion and carbon dioxide. The mechanisms of these reactions have been proposed and the appropriate rate laws are deduced.

Three- and four-coordinate Ag(I) complexes of crotonate and bis(benzimidazole)-2-oxapropane ligands: syntheses, crystal structures, DNA-binding studies and antioxidant activities

Abstract: Two V-shaped ligands, namely 1,3-bis(1-ethylbenzimidazol-2-yl)-2-oxapropane (etobb) and 1,3-bis(1-benzylbenzimidazol-2-yl)-2-oxapropane (bobb), have been prepared. Reaction of these ligands with AgNO3 and sodium crotonate under in the dark afforded the complexes, [Ag(etobb)2](crotonate)·C2H5OH·2(CH3CN)·2(H2O) 1 and [Ag(crotonate)(bobb)] 2. Both complexes have been characterized by physicochemical and spectroscopic methods and also by X-ray single-crystal diffraction. The coordination environment of complex 1 can be described as distorted tetrahedral, while complex 2 has as a trigonal planar geometry. The DNA-binding properties of these complexes have been investigated by fluorescence, electronic absorption and viscosity measurements. The experimental results suggest that they bind to DNA by an intercalation mode. Complex 2 also exhibits excellent hydroxyl radical scavenging activity.

Three nickel(II) coordination polymers with flexible bis(benzimidazole) and tetrabromoterephthalate ligands

Abstract: By tuning the spacer length of flexible bis(5,6-dimethylbenzimidazole) ligands, three nickel(II) coordination polymers {[Ni(L1)(tbta)(H2O)2]·H2O} n (1), {[Ni(L2)(tbta)(H2O)2·H2O]} n (2) and {[Ni(L3)2(tbta)]·5H2O} n (3) (L1 = 1,4-bis(5,6-dimethylbenzimidazole)butane, L2 = 1,3-bis(5,6-dimethylbenzimidazole)propane and L3 = 1,1′-bis(5,6-dimethylbenzimidazole)methane, H2tbta = tetrabromoterephthalic acid) were synthesized under hydrothermal conditions. These complexes were characterized by physico-chemical and spectroscopic methods and by single-crystal diffraction. All the three complexes feature 2D {44·62} sql/Shubnikov tetragonal plane networks. Complex 1 is further extended into a 3D supramolecular framework via weak C–H···O hydrogen-bonding interactions. Complex 3 shows a 3D supramolecular network through π–π stacking interactions. The fluorescence properties and catalytic activities of these complexes for the degradation of Congo red azo dye in a Fenton-like process were investigated.

Kinetic study of the oxovanadium(IV)–salen-catalyzed H2O2 oxidation of phenols

Abstract: The oxovanadium(IV)–salen-catalyzed H2O2 oxidation of phenols gives o-catechol and hydroquinone as the reaction products. The reaction follows Michaelis–Menten-type kinetics, and the rate is accelerated by electron-donating substituents on both the substrate and the salen ligand. This peculiar substituent effect is accounted for in terms of bond formation between peroxo group of the oxidant and the benzene ring of the substrate in the transition state. A suitable mechanism for the reaction is proposed.

Antioxidant and DNA binding studies of Cu(II) complexes of N , N ′-(1,1′-dithio-bis(phenylene))-bis(salicylideneimine): synthesis and characterization

Abstract: Four Cu(II) complexes [Cu(HL–LH)Cl2].H2O (1), [Cu2(L–L)Cl2] n (2), [Cu(LH)2]0.5H2O (3) and [CuL] n (4) derived from a disulfide Schiff base ligand N,N′-(1,1′-dithio-bis(phenylene))-bis(salicylideneimine) (HL–LH) were synthesized under different reaction conditions in the absence and presence of N-donor ligands and characterized by spectral, elemental, magnetic and thermal studies. A single-crystal X-ray analysis of 4 revealed that the Cu atom is in a square planar geometry, coordinated to phenolic oxygen, azomethine nitrogen and two sulfur atoms with cleavage of the S–S bond in HL–LH. Complexes 1–4 were found to be better antioxidants than HL–LH. Complexes 1 and 3, possessing free OH groups, showed higher antioxidant potentials. The interactions of the Schiff base Cu(II) complexes with DNA were investigated by UV–visible and fluorescence spectroscopies and agarose gel electrophoresis. The binding constants were in the order 103–105 M−1 suggesting moderate binding affinity of the complexes toward CT-DNA, with complex 1 showing the maximum binding affinity. In competitive binding experiments with ethidium bromide, complex 1 displayed the highest quenching constant, consistent with the UV binding results. Complexes 1–4 were found to cleave DNA efficiently in its nicked or linear forms.

1,1′-bis(diphenylphosphino)ferrocene as an intramolecular or intermolecular bridging ligand related to the phenyl-functionalized diiron propanedithiolate complex: synthesis and catalysis of the reduction of protons

Abstract: Reaction of the diiron propanedithiolate complex [μ-(SCH2)2CHC6H5]Fe2(CO)6 (A) with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in refluxing xylene yielded an intramolecular bridged complex [(μ-SCH2)2CHC6H5]Fe2(CO)4(μ-dppf) (1), while in MeCN in the presence of Me3NO·2H2O gave an intermolecular bridged complex [(μ-SCH2)2CHC6H5Fe2(CO)5]2(μ,κ1,κ1-dppf) (2). The structures of both complexes were fully characterized by spectroscopic methods and X-ray crystallography. In the solid state, the diphosphine spans the iron–iron vector, adopting cis basal–basal arrangement as expected in intramolecular bridged complex 1, while the diphosphine connects the two [2Fe2S] clusters by coordinating one of the two Fe atoms of each [2Fe2S] cluster in intermolecular bridged complex 2. The Fe–Fe bond length of 2.63 A in 1 is longer than that in 2, among the longest of Fe–Fe bonds in the synthetic active sites of Fe–Fe hydrogenases. Electrochemical investigation showed that complex 1 catalyzed the reduction of protons to give dihydrogen in the presence of HBF4, but did not catalyze the oxidation of dihydrogen in the presence of pyridine.

Mixed ligand palladium(II) complexes of N -hydroxy-methylsaccharin (Sac-CH 2 OH): synthesis, characterization and biological studies

Abstract: Reaction of Na2PdCl4 with two equivalents of N-hydroxymethylsaccharin (Sac-CH2OH) in the presence of NEt3 afforded trans-[Pd(κ2-Sac-CH2O)2]. Further reaction of [Pd(κ2-Sac-CH2O)2] with one equivalent of diphosphine (L2), Ph2P(CH2) n PPh2, (n = 1, dppm; 2, dppe and 3, dppp), Ph2P(S)(CH2)P(S)Ph2 (dppmS2) or Ph2P(O)(CH2)2P(O)Ph2 (dppeO2) afforded mixed ligand complexes [Pd(κ1-Sac-CH2O)2(L2)], while reaction with two equivalents of Ph3P, Ph3PO or Ph3PS (L) gave trans-[Pd(κ1-Sac-CH2O)2(L)2]. The N-hydroxymethylsaccharinate anion acts as a monodentate ligand, coordinating to the palladium center through the hydroxymethyl oxygen atom. The complexes were characterized by physico-chemical and spectroscopic methods. In addition, the free ligand N-hydroxymethylsaccharin and some of the complexes were screened in vitro for antibacterial activity.

Four coordination polymers based on flexible carboxylic acid and bis(pyridyl) mixed ligands: synthesis, structures, fluorescent and magnetic properties

Abstract: Hydrothermal reactions of Zn(II), Cd(II), Co(II) or Cu(II) acetates with 2,4-DH and BPP as flexible ligands (2,4-DH = 2,4-dichlorophenoxyacetic acid, BPP = 1,3-bis(4-pyridyl)propane) afforded four new coordination polymers, [Zn(2,4-D)2(BPP)]n (1), [Cd4(2,4-D)8(BPP)4(H2O)2]n (2), [Co2(2,4-D)4(BPP)2(H2O)]n (3) and [Cu4(2,4-D)6(BPP)2(OH)2]n (4). In these complexes, the BPP ligands bridge different secondary building units, forming diverse networks based on different metal centers. Complex 1 displays a 1D chain structure with four-coordinated Zn(II) atoms connected by BPP ligands, and the resulting 1D chains are further assembled into 2D networks through aromatic π–π stacking interactions. In complexes 2 and 3, the binuclear Cd(II) or Co(II) units are bridged by the BPP ligands to generate 2D networks. Complex 4 shows a 1D double-chain structure with the tetranuclear Cu(II) units linked by BPP bridges. The fluorescence and magnetic properties of these complexes have been investigated.

Synthesis, toxicities and cell proliferation inhibition of CO-releasing molecules containing cobalt

Abstract: A series of carbon monoxide-releasing molecules (CO-RMs) based on µ2-alkyne dicobalt(0)hexacarbonyl complex esters, Co2(CO)6HCC–CH2OCOR (R = 2-acetyloxybenzoic acid 1; R = 2-hydroxy-benzoic acid 2; R = 3-phenyl-2-propenoic acid 3; R = ibuprofen 4; R = naproxen 5; R = glycyrrhetinic acid 6; R = glycyrrhizic acid 7), were synthesized and characterized by spectroscopic methods In addition, the crystal structures of complexes 2 and 6 were determined by X-ray diffraction Cytotoxic effects of all the complexes were assayed by MTT analysis, and their IC50 values were determined as 36–125 µM Toxicity tests on mice by the oral acute toxic class method gave LD50 values for complexes 1 and 5 in the range of 2500–5000 mg kg−1 and for complex 6 over 5000 mg kg−1 The alkyne substituents significantly affect the rate of CO release and cytotoxicity The apoptotic effects on HeLa cells were consistent with their cytotoxicities The cell apoptosis rates were dependent on complex doses, and cell apoptosis mainly occurred by “late apoptosis” In addition, the complexes also blocked the cell cycle at the G2/M phase and led to the loss of the mitochondrial membrane potential

Synthesis and molecular studies of half-sandwich arene ruthenium and Cp*Rh/Cp*Ir complexes containing (3-picolyl)thiourea derivatives as N,S-bidentate donor ligands

Abstract: Series of mononuclear complexes of arene Ru and Cp*Rh/Cp*Ir complexes containing (3-picolyl)thiourea derivative ligands, of general formulae [(η6-arene)Ru(L)Cl]Cl and [Cp*M(L)Cl]Cl {L = benzoyl(3-picoylyl)thiourea, arene = benzene (1); p-cymene (2) and M = Rh (3); Ir (4); L = 1,3-bis(3-picolyl)thiourea, arene = benzene (5); p-cymene (6) and M = Rh (7); Ir (8)}, have been synthesized and characterized by spectroscopic methods. X-ray crystallographic studies of complexes (2)–(5), (7), and (8) reveal a typical piano-stool geometry around the metal center with a six-membered metallacycle, in which L acts as an N,S-chelating ligand. Intramolecular N–H···S, S···O, and N–H···N interactions are found to play a significant role in the molecular structures.

Synthesis, characterization and antioxidant evaluation of metal complexes derived from a dianil ligand with a flexible linkage: anomalous magnetic behavior of the nickel complex

Abstract: The synthesis and characterization of N,N′-bis (1-naphthaldimine)-p-oxydianiline, H2L, and its Zn(II), Cu(II), Ni(II) and Co(II) complexes are reported. Single crystal X-ray structural analysis showed that H2L consists of two tautomers where the central diphenylether unit is flanked by either two ketoamino forms or by one ketoamino and one enolimino form. Physico-chemical data revealed the formation of non-electrolytic [M2L2(2H2O) n ]·mH2O (n and m = 0–2) complexes with variable geometries. The nickel complex exhibited anomalous magnetic behavior compared to literature analogues. This result is attributed to molecular association and suggests the existence of both planar and octahedral forms in a conformational equilibrium. These complexes exhibit thermal stability up to 700 °C, except for the Ni(II) complex which degraded to its oxide. Antimicrobial screening data showed that H2L had no efficacy against a panel of pathogenic microorganisms, whereas the Ni(II) complex exhibited potency both as an antibacterial and antifungal agent. The properties of the complexes with respect to DPPH radical scavenging, acetyl cholinesterase inhibition and antihemolytic activity were evaluated.

Encapsulation of a copper(II) tetradentate Schiff base complex in zeolite NaY: an efficient heterogeneous catalyst for the synthesis of benzimidazoles

Abstract: A copper(II) complex of 2,2′-(((methylenebis(oxy))bis(2,1-phenylene))-bis(azanylylidene))bis(methanylylidene)) diphenol (H2L) was encapsulated in the supercages of zeolite NaY by the flexible ligand method. The resulting product was characterized by physicochemical and spectroscopic methods. The encapsulated complex and its corresponding free complex were used as catalysts for the synthesis of benzimidazoles. The results showed that the catalytic activity and stability of the complex were both increased by encapsulation. The effects of amount of catalyst, solvent, leaching and reusability of the heterogeneous catalyst were investigated.

A cis -dioxomolybdenum Schiff base complex: synthesis, crystal structure and catalytic activity in oxidation of olefins using hydrogen peroxide

Abstract: A cis-dioxomolybdenum(VI) Schiff base complex [MoO2L] has been synthesized and structurally characterized. Homogeneous oxidation of olefins using the complex as a catalyst with hydrogen peroxide as oxidant in ethanol solution showed high catalytic activity for this complex. Under reflux conditions, the oxidation of cyclooctene, styrene, α-methyl styrene, 4-methyl styrene and 1-methyl cyclohexene with hydrogen peroxide gave the corresponding epoxides as the sole products.

Construction of 0D, 1D and 2D cobalt(II) complexes containing flexible bis(benzimidazole) and dicarboxylic acid ligands

Abstract: Three complexes {[Co0.5(HL1)(H2O)2]·(tbta)} n (1), [Co0.5(L2)(ndc)0.5] n (2) and [Co(L3)(tp)] n (3) (L1 = 1,3-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, H2tbta = tetrabromoterephthalic acid, L2 = 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, H2ndc = 2,6-naphthalenedicarboxylic acid, L3 = 1,3-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H2tp = 1,4-benzenedicarboxylic acid) based on flexible bis(benzimidazole) derivatives have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis. The analysis reveals that complex 1 features a mononuclear structure, which is further assembled into a 2D supermolecular framework via O–H···O hydrogen bond interactions. Complex 2 shows a 1D zigzag chain connected by ndc2− ligands, while 3 exhibits a 2D 4-connected layer and ultimately is extended into a 3D supramolecular network through two kinds of π···π stacking interactions. Moreover, the fluorescence and catalytic properties of the complexes for the degradation of the Congo red azo dye in a Fenton-like process are discussed.

Reduction of ormaplatin by a dithiol model compound for the active site of thioredoxin: stopped-flow kinetic analysis

Abstract: Ormaplatin ([Pt(dach)Cl4]) is a prototypical of Pt(IV) anticancer prodrug; its reduction by 3,6-dioxa-1,8-octanedithiol (DODT, a model compound for the active site of thioredoxin), has been characterized at 25.0 °C and in a wide pH range by rapid scan spectral and kinetic analysis. The reduction follows overall second-order kinetics, being first-order each in [Pt(IV)] and in [DODT]; the observed second-order constant k′ versus pH profile has been established. A 1:1 reaction stoichiometry is obtained, indicating that DODT is oxidized to its intramolecular disulfide; these characteristics are consistent with the redox properties of thioredoxin. A reaction mechanism has been proposed which involves the three protolytic species of DODT attacking [Pt(dach)Cl4] in parallel as rate-determining steps. The rate equation is derived from the reaction mechanism and rate constants of the rate-determining steps have been evaluated. The thiol–thiolate and dithiolate forms of DODT are 105–106 times more reactive than the dithiol form. Comparisons of the rate constants highlight that the electron density of the sulfur atom plays a key role in determining the reactivity of DODT toward ormaplatin and similar Pt(IV) compounds. It is concluded that the reduced thioredoxin is a strong competitor to other thiol-containing compounds in the reduction processes of Pt(IV) anticancer prodrugs.

Synthesis and characterization of three cobalt(II) coordination polymers with tetrabromoterephthalic acid and flexible bis(benzimidazole) ligands

Abstract: Three cobalt(II) coordination polymers, namely {[Co(tbta)(pbdmbm)]·0.5H2O} n (1), [Co(tbta)(bbdmbm) (H2O)2] n (2), and [Co(tbta)(bbbm)] n (3), have been hydrothermally synthesized by self-assembly of cobalt(II) nitrate with tetrabromoterephthalic acid (H2tbta) and three flexible bis(benzimidazole) ligands, respectively, 1,1′-(1,4-butanediyl)bis-1H-benzimidazole (bbbm), 1,1′-(1,3-propanediyl)bis(5,6-dimethylbenzimidazole) (pbdmbm), and 1,1′-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole) (bbdmbm). Single-crystal X-ray diffraction analysis reveals that complex 1 has a 1D ladder-like chain structure, while both complexes 2 and 3 feature a uninodal 2D (4, 4) layer structure with a {44.62}-sql topology. Additionally, the fluorescence properties and catalytic activities of the complexes for degradation of congo red by a Fenton-like process were investigated.

A platinum(IV)-based metallointercalator: synthesis, cytotoxicity, and redox reactions with thiol-containing compounds

Abstract: A Pt(IV)-based metallointercalator, trans-dichloro(1,10-phenanthroline)(ethylenediamine)platinum(IV) trans-[PtCl2(phen)(en)]Cl2, was synthesized and characterized by 1H NMR, ESI–MS, and elemental analysis. Three human carcinoma cell lines Hela, MCF-7, and A549 were employed for in vitro cytotoxicity evaluations using the standard MTT assay. Based on the measured IC50 values, the cytotoxicity of this metallointercalator is very similar to that of cisplatin. Reduction of trans-[PtCl2(phen)(en)]2+ by l-glutathione and 3,6-dioxa-1,8-octanedithiol was studied by 1H NMR and ESI–MS; the Pt(IV) complex was reduced to its Pt(II) counterpart. The oxidation products of l-glutathione and 3,6-dioxa-1,8-octanedithiol were identified as the glutathione disulfide and the cyclic intramolecular disulfide, respectively. Mechanisms for these reductions are proposed.

Syntheses, crystal structures, antitumor and antioxidant activities of two hydrazide–hydrazone-based transition metal complexes

Abstract: Two isostructural hydrazide–hydrazone-based complexes, namely [Zn(L)(HL)(ClO4)]·H2O and [Ni(L)(HL)(ClO4)]·H2O (HL = 2-acetylpyridine isonicotinohydrazone), have been obtained and characterized by physicochemical and spectroscopic methods. In each complex, the first ligand is in the neutral keto form, while the second is in the deprotonated monoanionic enolate form. Both complexes have excellent antitumor activity toward A549 human lung cancer, and BGC823 and SGC7901 human gastric cancer cell lines. Furthermore, both complexes are active scavengers for O 2 −· and OH·, exerting superior activities compared to the free ligand.

Three silver complexes constructed from organic carboxylic acid and 1,2-bis(4-pyridyl)ethane ligands: syntheses, crystal structures, and luminescent properties

Abstract: Three silver-based complexes, namely [Ag2(bpa)2](Brtp)·6H2O (1), [Ag3(bpa)3](Hdcdcpb)·9H2O (2), and [Ag2(bpa)2(oa)]·2H2O (3), were synthesized via the reactions of AgNO3, 1,2-bis(4-pyridyl)ethane (bpa), and 2-bromoterephthalic acid (H2Brtp), 2,3-dicarboxyl-(2′,3′-dicarboxylazophenyl)benzene (H4dcdcpb) or 4,4′-oxybisbenzoic acid (H2oa) in aqueous alcohol/ammonia solution at room temperature. Complexes 1 and 2 consist of 1D infinite cationic [Ag(bpa)] + chains, interspersed with non-coordinated and completely deprotonated Brtp2− or partly deprotonated Hdcdcpb3− anions acting as discrete counter-ions to balance the charge. The lattice water molecules are situated among the framework of the crystal structure and show rich hydrogen-bonding interactions, while the presence of Ag…N and Ag…Ag contacts strengthens the frameworks. Complex 3 consists of 2D neutral [Ag2(bpa)2(oa)] in which the completely deprotonated oa2− units both act as bidentate ligands and as counter-ions. All three complexes exhibit luminescent properties, which can be assigned to ligand-to-metal charge transfer and Ag…Ag interactions.

Three coordination polymers constructed from bis(imidazol-l-yl-methyl)benzene: syntheses, structures, and third-order nonlinear optical properties

Abstract: Three coordination polymers, {[Ni(H2O)2(bib)2]-(H2BTA)·2H2O} n (1), {[Co2(bib)2(BTA)]·H2O} n (2), and {[Co2(bib)2(CA)2]·H2O} n (3), (H4BTA = biphenyl-3,3′,4,4′-tetracarboxylic acid; bib = 1, 2-bis(imidazol-l-yl-methyl)benzene; H2CA = camphanic acid), have been synthesized under hydrothermal conditions. In complex 1, bib serves a bridging ligand to link two Ni(II) atoms into an infinite joint-like chain. In 2, binuclear units are connected by BTA and bib ligands to form 2-D sheets. In 3, each Ni(II) atom is coordinated with two bib ligands to give a 22-membered ring, which is further linked by CA ligands to form a ladder-like chain. The third-order nonlinear optical (NLO) properties of the complexes were determined by Z-scan technique in DMSO solution. All three complexes exhibit strong third-order NLO absorption with absorptive coefficients β(MKS) 1.44 × 10−10 m W−1 for 1, 1.68 × 10−10 m W−1 for 2, and −6.31 × 10−10 m W−1 for 3, respectively, of which compound 3 shows saturable absorption. The third-order NLO susceptibilities |χ (3)| were calculated as 0.32 × 10−10 for 1, 0.37 × 10−10 for 2, and 1.39 × 10−10 esu for 3, while the hyperpolarizabilities γ′ are 9.95 × 10−29 for 1, 5.85 × 10−29 for 2 and 4.64 × 10−28 esu for 3, respectively.

Synthesis, crystal structures and photocatalytic properties of Zn(II), Ni(II), Co(II) complexes with a symmetric open-chain N2O4-donor bis-Schiff base ligand

Abstract: Three complexes, Zn(C40H36N4O8)·3CH3OH (1), Ni(C40H36N4O8)·3CH3OH (2) and Co(C40H36N4O8)·3CH3OH (3), with a sexidentate (N2O4) symmetric bis-Schiff base ligand (C40H36N4O8 = 1,2-bis(2-methoxy-6-formylphenoxy)ethane-l-tryptophan) have been synthesized and characterized by physicochemical and spectroscopic methods. The X-ray crystal structures show that the metal atoms of three complexes are all six-coordinated by two nitrogens from C=N groups, two oxygens from ether groups and two carboxylic oxygens in the mono-ligand, forming a distorted octahedral geometry. The complexes were screened as photocatalysts for the degradation of methylene blue, rhodamine B and methyl violet. All three complexes proved to be good candidates for the photocatalytic degradation of methylene blue and complexes 2–3 are also good photocatalysts for the degradation of rhodamine B. The mechanism of these photocatalytic degradations is discussed. The main characterization and photocatalytic experiment of three complexes.

A palladium–phosphine catalytic system as an active and recycable precatalyst for Suzuki coupling in water

Abstract: The Suzuki–Miyaura reaction of various aryl halides with aryl boronic acids using {[Ph2PCH2PPh2CH=C(O)(C10H7)]PdCl2} as a catalyst has been investigated. The X-ray crystal structure of the catalyst reveals a five-membered chelate ring formed by coordination of the ligand through the phosphine group and the ylidic carbon atom to the metal center. This palladacycle exhibited excellent activities and reusability in the aqueous phase for the Suzuki cross-coupling reactions of arylboronic acids with aryl halides. The proposed protocol featured mild reaction conditions and notable simplicity and efficiency using Cs2CO3 as a base in water. The catalytic system could be reused four times without significant loss of activity.

Two fluorescent cyclopalladated arylpyrazine complexes: synthesis, crystal structures and application in the double Suzuki coupling of N-heteroaryl halides with 1,4-benzenediboronic acid

Abstract: Two 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (Sphos) adducts of cyclopalladated arylpyrazine complexes have been synthesized and characterized. Additionally, the structures of both complexes were determined by single-crystal X-ray analysis. These palladacycles are fluorescent in CH2Cl2 at room temperature. They have been applied to the double Suzuki coupling of N-heteroaryl halides with 1,4-benzenediboronic acid, giving the desired products in good yields.