Crown ethers appended copper tetraazamacrocyclic complexes as receptors for cationic guests

Tetraazamacrocyclic copper(II) complexes linked by the system of conjugated double bonds with one or two benzo-15-crown-5 ether moieties (4Cu and 5Cu) as well as model compounds were synthesized and characterized. The CV of these complexes in acetonitrile (ACN) solution exhibited reversible Cu^II/I redox process. Complexation of Na⁺ and Mg²⁺ cations with 5Cu in the gas phase was confirmed by electrospray mass spectrometry. In solution complexation of Li⁺ and Na⁺ with 5Cu was weak. Complexation of Cl⁻ anion to coordinated copper in 5Cu resulted in an appreciable shift in the Cu^II/I redox potential after addition of studied cations. The addition of increasing amounts of Mg²⁺ cation to the solution of 5Cu resulted in a significant shift of the Cu^II/I reduction process accompanied by further reduction to Cu⁰ followed by replacement of copper by Mg²⁺ cation. Barium(II) cation interacted only with reduced (Cu⁺) form of 5Cu.     

Crown ether bridged homo- and heterodinuclear copper(II) and nickel(II) cyclidene complexes: Interaction with anions

Homodinuclear (3CuCu, 3NiNi) and heterdionuclear (3CuNi) cyclidene complexes linked by two 1,10-diaza-18-crown-6 ethers were synthesized and their properties characterized. For the 3CuCu in the negative potential range the mixed-valence state Cu^I-Cu^II was observed and the comproportionation constants were determined. The redox potentials of M^II/III showed a good correlation with DN of the solvent. In acetonitrile solution containing 0.1 mol dm⁻³ Bu₄NPF₆ reversible M^II/III redox processes were observed. However, in the presence of stronger ion pairing anions (e.g. BF₄⁻ and ClO₄⁻) the “potential inversion” occurred. Redox potentials of dinuclear complexes were compared with mononuclear cyclidene complexes. The influence of selected anions (Cl⁻ and NO₃⁻) on the redox process M^II/III was studied. The effect of Cl⁻ anion was different for 3CuCu and 3NiNi. In 3CuCu coordination of two chloride anions took place after oxidation of copper centers. In the 3NiNi complex two Cl⁻ anions were coordinated to one of the nickel(II) centers facilitating oxidation, at different potentials, of both nickel(II) cations. The behaviour of heteronuclear complex with Cl⁻ anions was similar to 3NiNi. All dinuclear complexes interacted with NO₃⁻ anions and the observed potential shifts were larger for nickel(II) than for copper(II) cations.     

A novel one-dimensional nickel(II) complex with a hydrogen-bond-link

A novel compound [Ni(L)(H₂O)₂]_0.5[Ni(L)(WO₄)₂]_0.5·4H₂O (1) (L=3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) has been structurally and magnetically characterized. The nickel(II) ions are shown to be in distorted octahedral environments with secondary amines of macrocycles in which two trans water molecules and two trans tungstate ions are assembled around each metal center. Two nickel(II) complexes are connected into a one-dimensional chain via hydrogen bonds. The magnetic susceptibility measurement for 1 indicates weak antiferromagnetic interaction (J=−1.01(2) cm⁻¹; H=−JΣS_i·S_i+1) between the S=1 nickel(II) paramagnetic centers.     

Novel nickel(II)-based catalysts for the polymerization of ethylene

A series of Ni(II)-based bidentate -diimine complexes bearing two alkyl (alkyl = methyl, ethyl and isopropyl) substituents on each imine aryl group were studied as precatalysts for the polymerization of ethylene. These new catalysts were observed to show high activity in combination with methyl aluminoxane (MAO) and produced high molecular weight polyethylenes. The effects of the steric bulk of ortho-aryl substituents of the ligand on the catalytic activity and the resulting polyethylene microstructure were investigated. Kinetics of polymerization was also studied by changing important parameters such as temperature and MAO concentration. The polymerization activity, polymer molecular weight and resulting polymer microstructure were drastically changed according to the catalyst structure modification and polymerization parameters.     

The interaction of alkaline earth cations with metal-oxygen cluster compounds and the implications for their use as heterogeneous catalysts

The magnesium, calcium, strontium and barium salts of 12-tungstophosphoric and 12-molybdophosphoric acids have been prepared. Evidence of the presence of the Keggin anion (primary structure) was obtained from infrared spectroscopic measurements but powder X-ray diffraction and differential thermal analysis measurements indicated that changes to the secondary structure had occurred. BET surface areas were small for all of the materials studied and no dependence on the cation radius was observed. A crystallographic investigation demonstrated that divalent cations were not incorporated into the lattice suggesting that materials believed to be divalent 12-heteropoly salts are mixtures of the parent acid and a divalent cation salt.     

Electrocatalytic addition reaction of bromide compounds and activated olefins on nickel(II) tetraazamacrocyclic complex-modified graphite felt electrode

Electrocatalytic addition reaction of bromide compounds and activated olefins was studied using a nickel(II) tetraazamacrocyclic complex-modified graphite felt (GF) electrode. The modified GF electrode was observed a catalytic current in the presence of bromide compound by cyclic voltammetry. A preparative electrocatalytic addition reaction of bromide compounds and activated olefins was successfully achieved on the modified GF electrode with an adequate yield (24-82%) and turnover number of the nickel catalyst (983-1533).     

Electrocatalytic oxidation of chlorophenols by electropolymerised nickel(II) tetrakis benzylmercapto and dodecylmercapto metallophthalocyanines complexes on gold electrodes

This work reports on the use of nickel(II) tetrakis benzylmercapto (NiTBMPc) and dodecylmercapto (NiTDMPc) metallophthalocyanine complexes films on gold electrodes for the electrochemical oxidation of 4-chlorophenol (4-CP) and 2,4,5-trichlorophenol (TCP). Both NiTBMPc and NiTDMPc complexes were successfully deposited on gold electrodes by electropolymerisation. The films were electro-transformed in aqueous 0.1 M NaOH solution to the ‘O-Ni-O oxo’ bridged form. For both complexes, films with different thickness were prepared and characterised by electrochemical impedance and UV-vis (on indium tin oxide) spectroscopies and the results showed typical behaviour for modified electrodes with increasing charge transfer resistance values (R_p) with polymer thickness. The poly-Ni(OH)NiPcs showed better catalytic activity than their poly-NiPcs counterparts.     

Dinitrogen bonding modes to molecular nickel(II) halides: a matrix isolation IR and DFT study

A combination of matrix isolation IR and DFT studies has shown that when monomeric nickel dihalides (NiX₂, X=Cl, Br) are condensed in solid nitrogen matrices the initial species formed are NiX₂(N₂)_n with a physisorbed type of interaction between the nitrogen and the nickel centre. These can be converted by photolysis into pseudo-tetrahedral NiX₂(η¹-N₂)₂ moieties with end-on bonded dinitrogen ligands in a chemisorbed type of interaction, but only if the matrix is deposited at less than 10 K. On warming to ca. 20 K the chemisorbed species revert to the physisorbed state. For CoBr₂ only very very weak new bands were observed after photolysis in a nitrogen matrix, and no new bands were observed after photolysis for NiF₂, FeBr₂ or ZnBr₂ in nitrogen matrices.     

Metal chelates with some cellulose derivatives. Part III. Synthesis and structural chemistry of nickel (II) and copper (II) complexes with carboxymethyl cellulose

Cu(II) and Ni(II) complexes with three grades of carboxymethyl cellulose (CMC) with different degrees of substitution have been synthesized and characterized. Probable structures of the metal complexes are inferred from the electronic and IR spectra, elemental analysis data and magnetic moment measurements. CMC coordinates with cu(II) and Ni(II) via the carboxymethyl and hydroxyl groups. The effect of the degree of substition of the CMC on the mode of chelation is discussed. Ni(II) complexes show an octahedral geometry around the metal ion and exhibit the formula [NiL · 4H₂O]Cl. Cu(II) complexes exist in the square planar form and have the formula Cu(L)₂, where L is uninegatively charged bidentate CMC ligand. The ligand field parameters of Ni(II) complexes are also evaluated.     

Removal of nickel(II) from aqueous solutions using iminodiacetic acid functionalized polyglycidyl methacrylate grafted-carbon fibers☆

Iminodiacetic acid functionalized polyglycidyl methacrylate grafted-carbon fibers (PGMA-IDA/CFs) were prepared for Ni(II) removal from aqueous solutions. The effects of solution pH value, temperature and adsorption time were investigated. The maximum adsorption capacity of Ni(II) on PGMA-IDA/CFs is 0.923 mmol·L?1 · g?1 at pH 5.2 and 50 °C. Kinetic data indicate that the adsorption process matches the pseudo-second-order model and Elovich kinetic model. Thermodynamic data suggest that the adsorption process is endothermic spontaneous reaction.     

Synthesis and characterization of new bis(crown ether)s of Schiff base type containing recognition sites for sodium and nickel guest cations

New bis(crown ether) ligands of Schiff base type ( 2 – 4 ) containing recognition sites for sodium and nickel guest cations have been synthesized by the condensation of two equivalents of 4′-formyl-5′-hydroxy(benzo-15-crown-5) ( 1 ) with diamines, H₂N–(CH₂)_n–NH₂(n = 2–4). Homonuclear ditopic crystalline 2 : 1 (Na⁺ : ligand) complexes ( 2a – 4a , 2b – 4b ) of the ligands with NaSCN and NaClO₄ have been prepared. The NaClO₄ complexes of 3 and 4 ( 3b and 4b ) form heteronuclear tritopic crystalline complexes with Ni²⁺ cations of stoichiometry 2 : 1 : 1 (Na⁺ : Ni²⁺ : ligand). A homonuclear monotopic Ni²⁺ complex has also been prepared by the reaction with Ni(CH₃COO)₂ · 6H_2O. The UV-VIS spectra of 2 – 4 and their NaClO₄ complexes ( 2b – 4b ) are studied in different solvents including acidic and basic media. In polar solvents, tautomeric equilibria (phenol–imine, O–H…︁N and ketoamine, O…︁H–N forms) are present, as supported by the UV-VIS data.     

Nickel(II) complexes of whole set of the simple ethylenediaminetetracarboxylate ligands: DFT study of complexes invoking molecular orbital and configurational analysis

The whole set of the nickel(II) complexes with no derivatized edta-type hexadentate ligands has been investigated from their structural and electronic properties. Two more complexes have been prepared in order to complete the whole set: trans(O₅)-Mg[Ni(ed3ap)]·8H₂O and trans(O₅O₆)-Ba[Ni(eda3p)]·4H₂O complexes. trans(O₅) geometry has been verified crystallographicaly and trans(O₅O₆) geometry of the second complex has been predicted by the DFT theory and spectral analysis. Mutual dependance has been established between: the number of the five-membered carboxylate rings, octahedral/tetrahedral deviation of metal-ligand/nitrogen-neighbour-atom angles, charge-transfer energies (CTE) calculated by the Morokuma’s energetic decomposition analysis and energy of the absorption bands and HOMO–LUMO gap.     

Cesium uptake by pentacyanoferrate(II) complexes with O-containing derivatives of chitosan

Here we report on synthesis of new organic-inorganic materials based on products of interaction between sodium aminoprusside and polymer ligands. Fourier transform infrared (FT-IR) and UV-visible spectroscopy and thermogravimetry were used to investigate the structure and stability of the complexes. It was found that ion and ligand exchange were the main reactions of the interaction of sodium aminoprusside with water-soluble polymer salts. All other composites in the Co(II) form were characterized in terms of sorption capacities and distribution coefficients (K_d) for cesium ions. The highest values of distribution coefficients were obtained for polyampholyte chitosan derivatives.     

Polymerization of methyl methacrylate catalyzed by mono-/bis-salicylaldiminato nickel(II) complexes and methylaluminoxane

Two types of salicylaldiminato-based nickel complexes, mono-ligated Ni(II) complexes ([O-C₆H₄-o- C(H)=N-Ar]Ni(PPh₃)(Ph) (5), [O-(3,5-Br₂)C₆H₂-o-C(H)=N-Ar]Ni(PPh₃)(Ph) (6), [O-(3-t-Bu)C₆H₃-o-C(H)=N-Ar]Ni(PPh₃)(Ph) (7)) and bis-ligated Ni(II) complexes ([O-(3,5-Br₂)C₆H₂-o-C(H)=N-Ar]₂Ni (8), [O-(3,5-Br₂)C₆H₂-o-C(H)=N-2-C₆H₄(PhO)]₂Ni (9), Ar=2,6-C₆H₃(i-Pr)₂) were synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), mass spectrography (MS) and elemental analysis (EA). In the presence of methylaluminoxane (MAO) as cocatalyst, all the nickel complexes exhibited high activities for the polymerization of methyl methacrylate (MMA) and syndiotactic-rich poly(methyl methacrylate) (PMMA) was obtained. The complexes with less bulky substituents on salicylaldiminato framework possessed higher activities, while with the same salicylaldiminato, the mono-ligated nickel complexes showed higher catalytic activity than bis-ligated ones.     

Synthesis, characterization and the electrocatalytic behaviour of nickel (II) tetraamino-phthalocyanine chemically linked to single walled carbon nanotubes

In this work we report on the synthesis, characterization and the electrochemical behavior of amide linked nickel (II) tetraamino-phthalocyanine (NiTAPc)-single walled carbon nanotube (SWCNT) nanomaterials (NiTAPc-SWCNT (linked)). UV-vis, XRD, IR and Raman spectroscopies were used in characterization whilst cyclic voltammetry was used to study the electrochemical behavior of NiTAPc-SWCNT (linked)-GCE. Relative to the bare glassy carbon electrode (bare-GCE), SWCNT-GCE, NiTAPc-GCE, and NiTAPc/SWCNT (mixed)-GCE, the NiTAPc-SWCNT (linked)-GCE gave the best current responses for the oxidation of 2-mercaptoethanol (2-ME). The catalytic rate constant is of the magnitude of 10³ M⁻¹ s⁻¹ while the detection limit (LOD) is 0.15 μM using the 3δ notation, with a sensitivity of 2.53 μA μM⁻¹ cm⁻².     

Vinyl polymerization of norbornene with bis(imino)pyridyl nickel(II) complexes

A series of different steric hindrance nickel(II) complexes 1 – 6 bearing 2,6‐bis(imino)pyridine ligands have been synthesized and characterized. The molecular structures of the complexes 3 – 5 were determined by X‐ray diffraction analysis. The coordination geometry around the nickel center of the complexes is either square pyramid for complexes 3 and 4 or trigonal bipyramid for complex 5 . All of the nickel complexes exhibit high catalytic activity for norbornene polymerization in the presence of MAO, although low activity for ethylene oligomerization and polymerization. The effects of the Al/Ni ratio, halogen, monomer concentration, temperature, and reaction time on activity of catalyst for norbornene polymerization and polymer microstructure were investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of macrocyclic nickel(II) complexes with α-methylbenzyl groups as chiral pendants

Novel nickel(II) hexaaza macrocyclic complexes, [Ni(L^R,R)](ClO₄)₂ (1) and [Ni(L^S,S)](ClO₄)₂ (2), containing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized (L^R,R/S,S = 1,8-di((R/S)-α-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane). The crystal structures of 1 and 2 were determined by single-crystal X-ray analysis. Each complex has a square-planar coordination environment for the nickel(II) ion, and is either an R or an S enantiomorph depending on the pendant groups. The circular dichroism spectrum of 1 showed a negative, positive and negative peak at 345, 440, and 492 nm, respectively, and that of 2 exhibited an enantiomeric pattern.     

Reduction of nitroaromatics with poly(vinylpyridine) complexes of palladium(II) and platinum(II)

Palladium(II) and platinum(II) anchored to 2- and 4-vinylpyridine polymers of different molecular weights were used for the dihydrogen reduction of various nitroaromatics and benzaldehyde in ethanol at 50°C. Palladium(II) complexes were far more effective than their platinum(II) analogues and the activity decreased with increasing molecular weights of the polymers. The nitroaromatics were selectively and almost completely reduced to the corresponding anilines. During reduction, the orange palladium(II) complexes changed to voluminous green precipitates, which could be used repeatedly and preserved for a long time without any loss of activity. A rate equation of the type: rate = K[Cat] [H₂] has been derived and a reduction mechanism has been proposed on the basis of experimental results and kinetic data.     

Gasification of woody biomass char with CO2: The catalytic effects of K and Ca species on char gasification reactivity

The effects of alkali and alkaline earth metals such as potassium (K) and calcium (Ca) on CO₂ gasification reactivity of Japanese cypress (hinoki) char under various temperatures (1123-1223 K) and CO₂ concentration (20-80 vol.%) were studied using thermal gravimetric analysis. The presence of K and Ca compounds in char improved the reactivity of hinoki char for CO₂ gasification catalytically. It was also confirmed that K and Ca compounds can be supported on char to exhibit an enhanced catalytic effect during CO₂ gasification of K-char and Ca-char. The char gasification rate increased with the increase of CO₂ concentration at higher temperatures (1173-1223 K), however at lower temperature (1123 K) the gasification rate decreased at 80% CO₂. The retardation of char gasification rate at higher CO₂ concentration is caused by the inhibition effect of CO: CO is disproportionated on alkali metal catalysts to CO₂ and carbon, and affected the CO₂ gasification rate. The dependence of char gasification rate on reaction temperature yielded a straight line in an Arrhenius-type plot which indicated that there was no significant change in the gasification mechanism in the temperature range of 1123-1223 K.