Showing papers in "Transition Metal Chemistry in 2013"

Effect of organic bicarboxylates on the structures of cobalt(II) coordination polymers derived from a semi-rigid bis(benzimidazole) derivative

Abstract: Two new Co(II) coordination polymers, [Co(L)(glu)] (1) and [Co(L)(npht)]·H2O (2) (H2glu = glutaric acid, H2npht = 3-nitrophthalic acid, L = 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene), have been hydrothermally synthesized by self-assembly of cobalt chloride with a semi-rigid bis(benzimidazole) derivative and different organic bicarboxylic acids Single crystal X-ray diffraction analysis reveals that complex 1 is a one-dimensional tube-like coordination polymer containing one helical [Co-L] and two linear [Co-glu] chains In complex 2, two npht ligands connect two Co(II) atoms to form a binuclear [Co(npht)]2 subunit, which is further linked by L ligands with two kinds of conformations to form a 3-D CdSO4-like framework In addition, the electrochemical behaviors of the title complexes in bulk-modified carbon paste electrodes, and their thermal stabilities and fluorescent properties were investigated in this paper

Synthesis, crystal structure, DNA- and albumin-binding properties of a chromium(III) complex with 1,10-phenanthroline and a Schiff base derived from glycine

Abstract: A new Cr(III) complex, [CrCl(sal-gly)phen]·0.5H2O (sal-gly = Schiff base derived from salicylaldehyde and l-glycine), has been synthesized and characterized by physicochemical methods. There are two independent complex molecules and a water molecule in each asymmetric unit. Each Cr(III) atom is six-coordinated in a distorted octahedral coordination environment. In the crystal, a 3D network is formed via intermolecular hydrogen bonds. The interactions between the Cr(III) complex and calf thymus DNA (CT-DNA) and Bovine serum albumin (BSA) have been studied by spectroscopic methods. The results show that the complex binds to CT-DNA in an intercalative mode, and it can also bind to BSA and produce conformational changes in the protein.

Synthesis, crystal structures and catalytic properties of Ag(I) and Co(II) 1D coordination polymers constructed from bis(benzimidazolyl)butane

Abstract: Two metal–organic coordination polymers, {Co(bbbi)0.5(bm)(Hbtc)}n (1) and {Ag2(bbbi)2(ntp)(H2O)·4H2O}n (2), [bbbi = 1,1-(1,4-butanediyl)bis-1H-benzimidazole, bm = benzimidazole, H3btc = 1,2,4-trimellitic acid, and H2ntp = 2-nitroterephthalic acid], have been hydrothermally synthesized and characterized by physico-chemical and spectroscopic methods and single-crystal diffraction. 1 Features a 1D ladder-like chain and is further connected by O–H···O hydrogen bonding interactions to yield a 3D supramolecular architecture. 2 Possesses a 1D infinite zigzag chain connected by bbbi ligands in bis-monodentate mode, which is further extended into a 3D complicated supramolecular network by face-to-face π–π stacking interactions and O–H···O hydrogen bonds. Moreover, both compounds exhibit catalytic properties on degradation of methyl orange in Fenton-like process.

Two 2D cobalt(II) coordination frameworks with unusual binodal network topology: synthesis, structures, and catalytic properties

Abstract: Two coordination polymers, namely {[Co2(L1)2(btec)]∙4H2O}n (1) and [Co(L2)(btec)0.5(H2O)]n (2) [L1 = 1,3-bis(5,6-dimethylbenzimidazole)propane, btec = 1,2,4,5-benzenetetracarboxylate, L2 = 1,2-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene], have been synthesized and characterized by physicochemical and spectroscopic methods as well as single-crystal diffraction. The cobalt(II) atoms display different environments with a tetrahedral geometry in 1 and trigonal–bipyramidal geometry in 2. Both complexes show 2D layer structures with a rare binodal (3,4)-connected topology structure, named 3,4L13. Their catalytic activities were tested for the degradation of congo red azo dye in a Fenton-like process.

Two dinuclear copper(II) complexes based on 5,6-dimethylbenzimidazole ligands: synthesis, crystal structures, and catalytic properties

Abstract: Two new dinuclear copper(II) complexes, Cu2(L1)4(mal)2(H2O)2 (1) (L1 = 5,6-dimethylbenzimidazole, mal = malonate), Cu2(L2)2(pydca)2·4H2O (2) (L2 = 1,5-bis(5,6-dimethylbenzimidazole)pentane, pydca = pyridine-2,6-dicarboxylate) have been synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. The Cu(II) atoms in 1 and 2 both have square pyramidal coordination geometry. In 1, the two similar mononuclear structures are linked by π–π stacking as well as multiple hydrogen bonding interactions to generate a 2D supramolecular layer, while complex 2 is connected with two different patterns of π–π stacking and hydrogen bonding interactions into a 3D supramolecular network. The catalytic activities of 1 and 2 for the degradation of Congo red have been investigated.

Synthesis, characterization, and luminescent properties of a series of silver(I) complexes with organic carboxylic acid and 1,3-bis(4-pyridyl)propane ligands

Abstract: The reaction of AgNO3 with combinations of 1,3-bis(4-pyridyl)propane (bpp), pyridine-3,5-dicarboxylic acid (H2pdc), oxybis(benzoic acid) (H2oba), and 4,4′-oxidiphthalic acid (H4odpt) in aqueous alcohol/ammonia at room temperature produces crystals of [Ag2(bpp)2](pdc)·8H2O, [Ag2(bpp)2(H2O)](oba)·5H2O, and [Ag2(bpp)2(H2O)2](odpt)·2H2O. All three complexes consist of 1D infinite silver-bpp cationic chains, interspersed with organic carboxylate anions that provide charge compensation in the crystal structures. The lattice water molecules are situated among the framework of the crystal structure and show rich hydrogen-bonding interactions, which serve to orientate the organic carboxylate anions in the crystal packing, while the presence of Ag···N and Ag···Ag contacts strengthens the frameworks. The luminescent properties of the complexes have been investigated.

Control of molecular architecture by hydrogen bonding: mononuclear versus dinuclear copper(II) complexes with tridentate N2O donor Schiff base isomers

Abstract: Two isomeric Schiff bases, HL 1 = 1-[(2-dimethylamino-ethylimino)-methyl]-naphthalen-2-ol and HL 2 = 1-[(2-ethylamino-ethylimino)-methyl]-naphthalen-2-ol, have been used to prepare copper(II) complexes in presence of thiocyanate. HL 1 forms a mononuclear complex [Cu(L 1 )NCS] with terminal thiocyanate, whereas the isomeric Schiff base HL 2 , which is capable of hydrogen bonding, gives a dimeric complex, [Cu2 (L 2 ) 2(NCS)2], with double μ-1,1-NCS bridges. Both complexes are characterized by physico-chemical and spectroscopic methods as well as by single crystal X-ray diffraction studies.

Encapsulation of tetraazamacrocyclic complexes of cobalt(II), copper(II) and oxovanadium(IV) in zeolite-Y and their use as catalysts for the oxidation of styrene

Abstract: Encapsulation of tetraazamacrocyclic complexes of Co(II), Cu(II) and V(IV) into zeolite-Y has been accomplished, and the resulting materials were used as heterogeneous catalysts for aerobic oxidation of styrene. The materials were prepared by a ship-in-a-bottle method, in which the transition metal cations were first ion-exchanged into zeolite-Y and then reacted with ethylenediamine, followed by acetylacetone. The pure tetraazamacrocyclic complexes were characterized by FTIR, solid UV–Vis and elemental analysis. The structural integrity throughout the immobilization procedure, the successful immobilization of the macrocyclic complexes, and the loadings of metal ions and macrocyclic ligands were determined by characterization techniques such as FTIR, diffuse reflection UV–Vis, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, TG/DTA and powder X-ray diffraction. Compared with their homogeneous analogues, the catalytic properties of the encapsulated macrocyclic complexes in the oxidation of styrene with air were investigated. The immobilized complexes proved to be active catalysts and could be reused without significant loss in activity.

Dioxygen activation in photooxidation of diphenylmethane by a dioxomolybdenum(VI) complex anchored covalently onto mesoporous titania

Abstract: A dioxomolybdenum(VI) complex has been covalently anchored onto mesoporous titania by a silicon-assisted transesterification route. The grafting of the complex to the mesoporous structure was confirmed by diffuse reflectance infrared Fourier transform, Raman and UV–Vis spectroscopy and by nitrogen sorption experiments. The ability of the grafted complex to activate molecular oxygen (O2) has been evaluated in the photooxidation of diphenylmethane to produce benzophenone. The photooxidation of diphenylmethane was monitored continuously by in situ dispersive Raman spectroscopy. A scheme for the activation of molecular oxygen under very mild conditions is proposed. A comparison with the same complex anchored onto commercial titanium P-25 and silica gel revealed both the beneficial effect of the mesoporous structure and the existence of a synergistic effect between MoO/TiO2/O2/light entities, which promotes the photooxidation process under green chemistry conditions. Finally, the heterogeneous catalyst is sustainable; it can be recycled and reused without significant loss in activity or selectivity.

Deep oxidative desulfurization of fuels catalyzed by molybdovanadophosphoric acid on amino-functionalized SBA-15 using hydrogen peroxide as oxidant

Abstract: This study reports the usage of molybdovanadophosphoric acid catalyst on amino-functionalized SBA-15(PMoV2/SBA-15-NH2) for the removal of sulfur from model oil (dibenzothiophene dissolved in n-hexane). To increase the tendency for adsorption of heteropoly acids, mesoporous SBA-15 silica was functionalized with amino groups by postsynthesis grafting, using 3-aminopropyltrimethoxy silane as the coupling agent. Immobilization of molybdovanadophosphoric acid on pure SBA-15 (PMoV2/SBA-15) was also studied for comparison and the catalysts were characterized by physicochemical and spectroscopic methods. It was found that the catalysts exhibit high catalytic activities and PMoV2/SBA-15-NH2 is more durable than PMoV2 impregnated on unmodified mesoporous SBA-15 silica. The results may bring about improvement for oxidative desulfurization of transportation fuels.

Selective coupling of carbon dioxide and epoxystyrene via salicylaldimine-, thiophenaldimine-, and quinolinaldimine-iron(II), iron(III), chromium(III), and cobalt(III)/Lewis base catalysts

Abstract: A series of chromium(III)-, cobalt(III)-, and iron(III)-based complexes of the general formula [(N∩O)2MCl] (1–7) (N∩O: N-salicylidene(R)amine, R = 1-naphthyl or cyclohexyl) have been applied as catalysts for the coupling reaction of carbon dioxide and epoxystyrene (styrene oxide) in the presence of tetrabutylammonium bromide (Bu4NBr) as a cocatalyst. The reactions were carried out under relatively low pressure and solvent-free conditions. In addition, iron complexes (8–10) containing the ligands, N′-(thiophene-2-methylene)benzene-1,2-diamine, (8), N′-(quinoline-2-methylene)benzene-1,2-diamine (9), and sodium N-(4-sulfonato-salicylidene)-1,2-phenylenediamine (10) were also utilized for the catalytic reaction. The influence of metal center, ligand, temperature, and reaction time on the coupling reaction was investigated. The catalyst systems proved to be selective in the coupling reaction of CO2 and styrene oxide, resulting in cyclic styrene carbonate. In general, the iron(III)- and cobalt(III)-based catalysts bearing the aromatic 1-naphthyl terminal groups showed the highest catalytic activity under similar reaction conditions.

Synthetic aspects, crystal structures and antibacterial activities of manganese(III) and cobalt(III) complexes containing a tetradentate Schiff base

Abstract: Three new Schiff base complexes, namely [Mn(L)Cl] · H2O (1), [Co(L)Cl]2 · 2CH3COCH3 (2) and [Co(L)NCS]2 (3), where H2L = 2,2′-[propane-1,2-diylbis(nitriloeth-1-yl-1-ylidene)]diphenol, have been prepared and characterized. The syntheses of 1 and 2 have been achieved by reacting equimolar amounts of the respective metal chloride and the tetradentate Schiff base ligand (H2L). While the mononuclear Mn(III) complex 1 was obtained with MnCl2 in acetone medium, the same synthetic system yielded the binuclear Co(III) complex 2 in the presence of CoCl2. Dissolution of 1 and 2 followed by crystallization with ammonium thiocyanate in methanol yielded two isostructural phenoxo-bridged binuclear complexes, namely [Mn(L)NCS]2 (previously reported by us) and a new complex [Co(L)NCS]2 (3), respectively. All the complexes 1–3 have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1 adopts a distorted tetragonal pyramidal geometry while 2 and 3 comprise dimeric Co(III) units with bridging phenolate oxygen atoms. All the complex units in 1–3 and the respective solvent molecules are held together by weak intermolecular H-bonding to constitute a supramolecular network in the solid state. The antibacterial activity of the complexes has been tested against some Gram(+) and Gram(−) bacteria.

DNA binding and nuclease activity of a water-soluble sulfonated manganese(III) corrole

Abstract: The interaction of a water-soluble sulfonated Mn(III) corrole Mn(tpfc)(SO3Na)2 [tpfc = 5,10,15-tris(pentafluorophenyl)corrole] with calf thymus DNA (ct-DNA) has been studied by spectroscopic methods, and the nuclease activity of this complex has also been examined by agarose gel electrophoresis. Mn(tpfc)(SO3Na)2 exhibits weak aggregation tendency in buffer solution and can bind to ct-DNA via an outside binding mode with a binding constant of 1.25 × 104 M−1. The observed increase in Stern–Volmer quenching constant with increasing temperature indicates that the competition of the manganese corrole and ethidium bromide with ct-DNA is a dynamic process. Moreover, the manganese corrole displays good chemical nuclease activity in the presence of hydrogen peroxide via oxidative cleavage of DNA.

Synthesis, structure and catalytic activity of an oxo-bridged dinuclear oxovanadium complex of an isonicotinohydrazide ligand

Abstract: A mononuclear dioxo vanadium(V) complex of a hydrazone ONO donor ligand, [VVO2(L1)] (1), was synthesized by the reaction of V2O5 and terephthalic acid with H2L1 in 1:1:1 mol ratio, while an oxo-bridged bis(vanadium(IV)oxo) complex, [μ 2–O–{VIVO(L2)}2] (2), was synthesized by the treatment of isonicotinic acid hydrazide, salicylaldehyde and CoSO4·7H2O with bis(acetylacetonato)oxovanadium(IV) (H2L1 = isonicotinic acid(2-hydroxy-benzylidene)-hydrazide, H2L2 = isonicotinic acid (1-methyl-3-oxo-butylidene)-hydrazide). The complexes were characterized by elemental analyses and spectroscopic methods. The crystal structure of complex 2 was determined by X-ray analysis. The complexes were tested as catalysts for the oxidation of cycloalkenes and benzyl alcohol using H2O2 as terminal oxidant. Excellent selectivity was achieved in the oxidation of cyclohexene.

Two palladium(II) complexes based on Schiff base ligands: synthesis, characterization, luminescence, and catalytic activity

Abstract: Two Pd(II) complexes involving Schiff base ligands, namely, [Pd(L1)2] (1), [Pd2(L2)Cl2] (2) [HL1 = 2-((2,6-diisopropylphenylimino)methyl)-4,6-dibromophenol, L2 = N-(4-isopropylbenzylidene)-2,6-diisopropylbenzenamine] have been synthesized using solvothermal methods and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV–vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a mononuclear cyclometalated Pd(II) complex, whereas complex 2 is a μ-chloro-bridged dinuclear. Both 1 and 2 display photoluminescence in the solid state at 298 K and possess fluorescence lifetimes (τ 1 = 86.40 ns, τ 2 = 196.21 ns, τ 3 = 1,923.31 ns at 768 nm for 1, τ 1 = 69.92 ns, τ 2 = 136.40 ns, τ 3 = 1,714.26 ns at 570 nm for 2). The Suzuki reactions of 4-bromotoluene with phenylboronic acid by complexes 1–2 have also been studied.

Two cobalt(II) complexes based on a flexible bis(5,6-dimethylbenzimidazole) and rigid organic dicarboxylate ligands

Abstract: Two new bis(5,6-dimethybenzimidazole)-based CoII complexes, Co(pydca)(L)2·2H2O (1) and [Co(bdc)(L)] n (2) (L = 1,3-bis(5,6-dimethylbenzimidazol-1-yl)-2-propanol, H2pydca = pyridine-2,6-dicarboxylic acid, H2bdc = 1,4-benzenedicarboxylic acid) were synthesized and characterized by physicochemical, spectroscopic methods and single-crystal diffraction. The cobalt(II) centers display different environments with distorted square-pyramidal geometry in 1 and a perfect tetrahedral geometry in 2. Complex 1 is a mononuclear structure, which is further assembled into a 3D supramolecular network via strong hydrogen bonding as well as π–π interactions; while complex 2 possesses a 2D corrugated (4,4) network that is further formed into a (3,4,4)-connected network with (62.84)(63)2(64.82)2-3,4,4T25 topology due to classical hydrogen bonds. The fluorescence and catalytic performances of the two complexes for the degradation of methyl orange by sodium persulfate have been investigated.

Synthesis, structure, and luminescent properties of three silver(I) complexes with organic carboxylic acid and 4,4′-bipyridine-like ligands

Abstract: The reactions of AgNO3 with combinations of 1,2-bis(4-pyridyl)ethane(bpa)/4,4′-bipyridine (bpy), 4,4′-stilbenedicarboxylic acid (H2sda)/2,2′-diphenylaminedicarboxylic acid (H2dpadc)/2,6-naphthalenedicarboxylic acid (H2ndc) in aqueous alcohol/ammonia at room temperature produce block-like crystals of [Ag2(bpa)1.5(sda)0.5](sda)0.5·7H2O, [Ag2(bpa)2(H2O)3](dpadc), [Ag2(bpy)2](ndc)·4H2O. All three complexes consist of 1D infinite silver–ligand cationic chains, interspersed with organic carboxylate anions that provide charge compensation in the crystal structures. The lattice water molecules are situated among the framework of the crystal structure and show rich hydrogen-bonding interactions, which help to orientate the organic carboxylate anions in the crystal packing, and the presence of Ag···N and Ag···Ag contacts contributes to strengthen the frameworks. The luminescent properties and thermogravimetric analyses of the three complexes are also presented.

Encapsulation of a binuclear manganese(II) complex with an amino acid-based ligand in zeolite Y and its catalytic epoxidation of cyclohexene

Abstract: A Schiff base ligand was synthesized by the condensation of salicylaldehyde with l-tyrosine. Interaction of this ligand with Mn(II)-exchanged zeolite Y leads to encapsulation of the ligand within the zeolite and complexation of the metal. The encapsulated complex has been characterized by spectroscopic studies and chemical analyses. This material serves as a catalyst for the oxidation of cyclohexene to cyclohexene epoxide and 2-cyclohexene-1-ol using H2O2 as oxidant. The reaction conditions have been optimized for solvent, temperature and amount of oxidant and catalyst. The catalyst shows high activity and selectivity toward production of cyclohexene epoxide in acetonitrile at 60 °C with [H2O2]/[C6H10] = 2.5 molar ratio. Comparison of the encapsulated catalyst with the corresponding homogeneous catalyst showed that the heterogeneous catalyst had higher activity and selectivity than the homogeneous catalyst.

N-heterocyclic carbene adducts of cyclopalladated ferrocenylpyridine containing chloride or iodide anions: synthesis, crystal structures and application in the coupling of terminal alkynes with arylboronic acids

Abstract: Two air-stable N-heterocyclic carbene (NHC) adducts of cyclopalladated ferrocenylpyridine containing chloride or iodide anions 2–3 have been easily prepared from the bridge-splitting reaction of the palladacyclic dimer 1 and anion exchange reaction, respectively. They were characterized by elemental analysis, IR, 1H, and 13C NMR. Additionally, the structures of these complexes were determined by single-crystal X-ray analysis. These adducts have been successfully applied to the coupling of terminal alkynes with arylboronic acids under atmospheric conditions.

Dinuclear 3D metal complexes based on a carbacylamidophosphate ligand: redetermination of the ligand crystal structure

Abstract: Dinuclear Ni(II), Co(II) and Zn(II) complexes of general formula $$ \left[ {{\text{M}}_{ 2}^{\text{II}} {\text{Cl}}_{ 4} \left( {\text{HL}} \right)_{ 4} \left( {\text{i-PrOH}} \right)_{ 2} \cdot 2\left( {\text{i-PrOH}} \right)} \right] $$ with a carbacylamidophosphate ligand, namely 2,2,2-trichloro-N-(dipiperidine-1-yl-phosphoryl)acetamide (CCl3C(O)N(H)P(O)[N(CH2)5]2), were synthesized and characterized by physicochemical and spectroscopic methods. Electronic absorption spectra of the nickel and cobalt complexes were measured at room temperature in toluene and in the solid state. The crystal structures of HL and [Ni2Cl4(HL)4(i-PrOH)2·2(i-PrOH)] have been determined by single-crystal XRD studies. Earlier, the structure of a monoclinic C2/c modification of HL was reported. In this paper, redetermination of the structure of HL with triclinic crystal system, P $$ \overline{1} $$ , was made. The nickel complex is a chloro-bridged dimer, in which the Ni(II) centers are in a distorted octahedral geometry and the neutral HL is coordinated via its phosphoryl oxygen atom. This coordination mode was determined for the first time for 3D metal carbacylamidophosphate complexes.

Crystal structure of an unsymmetrical Schiff base, immobilization of its cobalt and manganese complexes on a silica support, and catalytic studies

Abstract: An unsymmetrical tetradentate Schiff base (H2L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H2L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 °C. The catalysts can be reused several times without significant loss of performance.

Preparation and crystal structure of a triple parallel interpenetrated copper coordination polymer based on a flexible bis(imidazole) ligand

Abstract: A Cu(II) coordination polymer, [Cu(L)(bdc)] n (L = 1,4-bis(imidazole)butane, bdc = 1,3-benzenedicarboxylate) has been hydrothermally synthesized and characterized by elemental analysis, IR spectrum, thermogravimetric analysis, and single-crystal X-ray diffraction. The complex is a rare example of a threefold parallel interpenetrated coordination bonding network based on undulant [Cu4(μ 2-L)2(μ 2-bdc)2] parallelograms with 44-sql layer. The heterogeneous catalytic activity of the complex was tested for the degradation of Congo red azo dye in a Fenton-like process in which the degradation efficiency reached 94 % after 100 min. Kinetic analysis indicates that the degradation rate of the dye can be approximated by pseudo-first-order kinetics.

Synthesis, characterization, and catalytic activity for thioanisole oxidation of homogeneous and heterogeneous binuclear manganese(II) complexes with amino acid-based ligands

Abstract: A binuclear Mn(II) complex [Mn2(HL)2(H2O)4], HL = 2-[(2-Hydroxy-benzylidene)-amino]-3-(4-hydroxy-phenyl)-propionic acid, has been prepared and characterized by physico-chemical and spectroscopic methods. The results suggest that the amino acid Shiff base ligand is coordinated as a bivalent anion with a tridentate NO2 donor set involving the phenolic and carboxylic acid oxygens and azomethine nitrogen. A heterogenized binuclear manganese catalyst was synthesized by the covalent anchoring of [Mn2(HL)2(H2O)4] onto a modified silica gel surface, through the reactive (3-chloropropyl)-trimethoxysilane group. The surface properties of the functionalized catalyst were analyzed by physico-chemical and spectroscopic methods. The silica-supported metal complex, ([Mn2L(HL)(H2O)4]/SiO2), catalyzes the oxidation of thioanisole with H2O2, to give the sulfoxide and sulfone. [Mn2L(HL) (H2O)4]/SiO2 shows lower catalytic activity and turnover number compared to the homogeneous catalyst [Mn 2 II –(HL)2(H2O)4]. However, the activity of the immobilized catalyst remains nearly unchanged after five cycles, indicating that it is truly heterogeneous.

Multi-wall carbon nanotube supported manganese(III) porphyrin: an efficient and reusable catalyst for oxidation of 2-imidazolines with sodium periodate

Abstract: The oxidation of 2-substituted imidazolines with sodium periodate catalyzed by tetrakis(p-aminophenyl)-porphyrinatomanganese(III) chloride, [Mn(TNH2PP)Cl], supported on functionalized multi-wall carbon nanotubes is reported. A wide variety of 2-imidazolines were efficiently converted to their corresponding imidazoles by this catalytic system. When the same reaction was subjected to ultrasonic irradiation, the reaction times were reduced significantly and the product yields were increased. This catalyst could be reused several times without significant loss of activity. The effects of reaction parameters such catalyst amount, choice of solvent, and the effects of ultrasonic irradiation on the catalytic activity have been investigated.

A general method for the preparation of N-heterocyclic carbene–silver(I) complexes in water

Abstract: A new synthetic method leading to N-heterocyclic carbene–silver(I) complexes [(R2-NHC)2Ag]+ [AgX2]− is developed by using benzimidazolium compounds, NaOH (as a base), silver salts and water (as the reaction medium). Single-crystal X-ray structure revealed that compound 1 comprises a linear [Ag-(Et2-Bimy)2]+ cation and a linear [AgBr2]− anion. These two ions are linked through an AgI–AgI association and staggered at an angle of 90.3°.

Synthesis, spectral characterization, and structural investigation of mononuclear salen-type Cu(II) and Zn(II) complexes of a potentially octadentate N2O6 Schiff base ligand derived from binaphthol

Abstract: A new potentially octadentate N2O6 Schiff base ligand, H2L derived from the condensation of 2,2′-(1,1′-binaphthyl-2,2′-diylbis(oxy))dianiline and o-vanillin, along with its copper(II) and zinc(II) complexes, is synthesized and has been characterized by elemental analyses, IR, UV–vis, 1H and 13C NMR spectra, as well as conductivity measurements H2L forms mononuclear complexes of 1:1 (metal:ligand) stoichiometry with Cu(II) and Zn(II), and conductivity data confirm the non-electrolyte nature of these complexes The [ZnL] and [CuL] complexes display very different solid-state structures, as determined by X-ray crystallography While the [ZnL] complex has a distorted octahedral geometry about the metal, the [CuL] complex displays a distorted square planar geometry about the copper, with long Cu–O(ether) distances of 2667 A

Nickel(II) complexes with Schiff bases derived from 2-acetylpyrazine and tryptophan: synthesis, crystal structures and DNA interactions

Abstract: A pair of stereoisomers of nickel Schiff base complexes, namely [Ni(C17H15N4O2)2·2CH3OH]n (1) (C17H15N4O2 = 2-acetylpyrazine-l-tryptophan) and [Ni(C17H15N4O2)2·2CH3OH]n (2) (C17H15N4O2 = 2-acetylpyrazine-d-tryptophan), were synthesized and characterized by physico-chemical and spectroscopic methods. The X-ray diffraction single-crystal analyses indicate that the structure of 2 is essentially 0D monomeric, while a 2D layer structure is formed through N–H…O intermolecular hydrogen bonds for 1. The interactions between complex 1 and calf thymus DNA were investigated by spectroscopic and viscometric methods. The results indicate that complex 1 interacts with DNA very strongly (K b = 1.01 × 107 mol−1 L and K sq = 1.11). The nature of the binding seems to be mainly an electrostatic interaction between DNA and the complex. However, other binding modes, such as hydrogen bonding, may also be present in this system.

Synthesis and electron transfer kinetics of a surfactant–cobalt(III) complex: effects of micelles, β-cyclodextrin, and ionic liquids

Abstract: A surfactant–cobalt(III) complex, cis-[Co(en)2(4AMP)(DA)](ClO4)3, (en = ethylenediamine, 4AMP = 4-aminopyridine, DA = dodecylamine), was synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) value of this surfactant–cobalt(III) complex in aqueous solution was obtained from conductance measurements. Conductivity data were used for evaluation of the temperature-dependent CMC and the thermodynamics of micellization (\( \Updelta {\text{G}}_{\text{m}}^{ 0} \), \( \Updelta {\text{H}}_{\text{m}}^{0} \), and \( \Updelta {\text{S}}_{\text{m}}^{0} \)). The kinetics of reduction of this surfactant–cobalt(III) complex by ion(II) in micelles, β-cyclodextrin (β-CD), and ionic liquid (IL) were studied. The reaction was found to be second order, and the electron transfer is postulated as outer sphere. The second-order rate constant for the electron transfer reaction was found to increase with increasing concentration of IL, but inclusion of the long aliphatic chain of the surfactant complex into β-CD decreases the rate of the reaction. The results have been interpreted in terms of the amphiphilicity of the surfactant complex.

Synthesis and electrocatalytic properties of a dinuclear palladium(I) 1-[(2-bromo)benzene]-3-[(2-carboxymethyl)benzene]triazenide complex

Abstract: The reaction of 1-[(2-bromo)benzene]-3-[(2-carboxymethyl)benzene]triazene and [Pd(CH3CN)4]Cl2 gave a new dinuclear triazenido complex [Pd2L2] 1, which has been characterized by NMR spectra and X-ray crystallography. Electrochemical studies showed that complex 1 is capable of generating hydrogen from acetic acid in CH2Cl2.

Two cobalt(II) coordination polymers constructed from tetrafluoroterephthalate and hexamethylenetetramine ligands

Abstract: Two cobalt(II) coordination polymers, {[Co(Hmt)2(tfbdc)(H2O)2]·(H2tfbdc)·(EtOH)2}n (1) and {[Co(Hmt)(tfbdc)(H2O)2]·(H2O)2}n (2) (H2tfbdc = 2,3,5,6-tetrafluoroterephthalic acid; Hmt = hexamethylenetetramine) have been synthesized and characterized by physicochemical and spectroscopic methods, thermogravimetric analysis, and single-crystal X-ray diffraction. In both complexes, the coordination environment around cobalt is distorted octahedral. In 1, each Co(II) atom is linked by tfbdc2− anionic ligands to form a 1D zigzag chain, which is further connected into a 3D network via hydrogen bond interactions. In 2, each Co(II) atom is bridged by anionic tfbdc2− and Hmt ligands along two directions, respectively, forming an infinite 2D structure with a parallelogram-type grid; the 2D networks are further assembled to a 3D framework via intermolecular hydrogen bond interactions. Both complexes show blue fluorescence in the solid state at room temperature. Two new coordination polymers, {[Co(Hmt)2(tfbdc)(H2O)2]·(H2tfbdc)·(EtOH)2}n (1) and {[Co(Hmt)(tfbdc)(H2O)2]·(H2O)2}n (2) have been obtained via the reactions of H2tfbdc, Hmt, and cobalt chloride hexahydrate in different molar ratios and solvents.