Voltammetric measurement of copper(II)/organic interactions in estuarine waters

The voltammetry of copper in organic ligand/chloride media is dominated by the formation of CuCl^?₂ species and by induced adsorption of Cu(I) in organic coatings on the electrodes. These phenomena are utilised in a novel method for evaluating Cu(II)/organic ligand interactions, based on the principle of ligand exchange. The Cu(II)/organic species competes with glycine which forms copper glycinate. These two complexes can be distinguished voltammetrically: copper glycinate gives a higher surface excess of copper at a gelatin-coated hanging mercury drop electrode, partly because of the increased production of CuCl^?₂ from copper glycinate at the electrode surface. The method proved satisfactory for pure ligand/surfactant/chloride media and for estuarine waters. It is shown that there are two type of Cu(II)-binding ligand in estuarine waters: humic material (> 10^?6 mol l^?1, assuming 1:1 site binding) with polyelectrolyte-type binding, and discrete ligands (? 10^?6 M) with stability constants around 10⁹. The extent of Cu(II) binding by the humic material decreases down the estuary because of dilution and increased salinity.     

Electrochemical evaluation of a number of nickel complexes with P,N-heterocyclic ligands as catalysts for hydrogen oxidation/release

The efficiency of a series of nickel complexes of P,N-cyclic ligands (potential catalysts in hydrogen fuel cells) in the electrocatalytic reduction of H+ to hydrogen and the oxidation of H₂ in the coordination shell/cavity of the catalyst in DMF (acetonitrile with variable nickel: ligand ratio (1: 1, 1: 2) and different counterions (X=Cl⁻ and BF₄⁻)) was tested, and the most favorable conditions and structures were determined. The relation between the activity of the catalysts and the values of the electrochemical gap was found.     

On the redox reactions of radicals with AlIII(phthalocyaninate) pendants covalently bonded to poly(ethyleneamide). Mechanistic alterations when radicals are formed inside pockets of micelle‐like polymer aggregates

The mechanisms of the redox reactions between a polymer containing Al(III) sulfonated phthalocyanine pendants, (Al^III(^?NHS(O₂)trspc)^2?)₂, and radicals have been investigated in this work. Pulse radiolysis and photochemical methods were used for these studies. Oxidizing radicals, OH^?, HCO₃^?, (CH₃)₂COHCH₂^?, and N₃^?, as well as reducing radicals, e_aq^?, CO₂^??, and (CH₃)₂C^?OH, respectively accept or donate one electron forming pendent phthalocyanine radicals, Al^III(^?NHS(O₂)trspc ^?)^{? or 3?}. The kinetics of the redox processes is consistent with a mechanism where the pendants react with radicals formed inside aggregates of five to six polymer strands. Electron donating radicals, that is, CO₂^?? and (CH₃)₂C^?OH, produce one‐electron reduced phthalocyanine pendants that, even though they were stable under anaerobic conditions, donated charge to a Pt catalyst. While the polymer was regenerated in the Pt catalyzed processes, 2‐propanol and CO₂ were respectively reduced to propane and CO. The reaction of SO₃^?? radicals with the polymer stood in contrast with the reactions of the radicals mentioned above. A first step of the mechanism, the coordination of the SO₃^?? radical to the Al(III), was subsequently followed by the formation of a SO₃^?? ‐ phthalocyanine ligand adduct. The decay of the SO₃^?? ‐ phthalocyanine ligand adduct in a ～10² ms time domain regenerates the polymer, and it was attributed to the dimerization/disproportionation of SO₃^?? radicals escaping from the aggregates of polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Nickel complexes with cyclic ligands containing P and N atoms as coordination sites: novel biomimetic catalysts for hydrogen oxidation

Nickel complexes with new cyclic ligands containing phosphorus and nitrogen atoms as coordination sites are novel efficient catalysts for hydrogen oxidation. A systematic study of their electrochemical properties made it possible to classify the nickel systems in question into four groups according to the sequence of electron transfer processes in the reduction (M^II-M^I-M⁰) and to the nature of solvents and counterions. Regularities of catalytic transformations involving nickel complexes with P,N-cyclic ligands in the H₂ oxidation reaction in the coordination sphere of the catalyst and a correlation between the structure of the complex and its redox properties were established. The most efficient catalysts contain phenyl and 2-pyridyl substituents at the phosphorus atom and benzyl or 2-pyridyl substituents at the nitrogen atom.     

Structure and Dynamics of Lanthanide Complexes of Triethylenetetramine‐N,N,N′,N″,N′′′,N′′′‐hexaacetic Acid (H6ttha) and of Diamides H4ttha(NHR) Derived from H6ttha as Studied by NMR,NMRD, and EPR

A multinuclear NMR study on [Ln(ttha)]^3? and [Ln{ttha(NHR)₂}]^? complexes (R=Et, CH₂(CHOH)₄CH₂OH) shows that coordinating groups of the organic ligands in these complexes are occupying all coordination sites of the metal ions, leaving no space for coordination of H₂O molecules (H₆ttha=triethylenetetramine‐N,N,N′,N″,N′′′,N′′′‐hexaacetic acid). The lanthanides of the first half of the series bind the ttha‐type ligands in a decadentate fashion, while the complexes formed with the smaller ions of the second half of the lanthanide series are nonadentate. One carboxylate group of the ligand remains unbound in the latter complexes. In principle, the ttha complexes can exist in six enantiomeric forms. Only one of the pair of diastereoisomers can interconvert without decoordination of the ligand. This pair of isomers seems to be predominant in solution. For the [Ln{ttha(NHR)₂}]^? complexes, the number of chiral centers is larger, resulting in 32 possible enantiomeric forms of the complexes. The NMR spectra of [Nd{ttha(NHEt)₂}]^? indicate that two dynamic processes occur between the isomers in solution. The NMRD curves of [Gd(ttha)]^3?, [Gd{ttha(NHEt)₂}]^?, and [Gd{ttha(NHgluca)₂}]^? (NHgluca=D ‐glucamine) show significant differences with the previously determined outer‐sphere contributions to the NMRD profiles of the corresponding [Gd{dtpa(NHR)₂}]^? complexes, which can be ascribed to differences in the parameters determining the electronic relaxation.     

Dependence of the mutual ligand arrangement in guanidinate complexes of lanthanoids on the ligand solid angles

Mutual ligand arrangement in binuclear lanthanoid complexes of the type [Gu₂Ln(μ-H)]₂, [Gu₂Ln(μ-Cl)]₂, and Gu₂Ln(μ-Cl)₂Li(THF)₂, where Gu is a substituted guanidinato ligand, is quantitatively analyzed based on the ligand solid angle approach. In complexes of Nd, Sm, and Gd the Gu ligands shield up to 87% of the metal and the bidentate ligands on opposite metal centers are in the eclipsed arrangement; in complexes of lanthanoids with smaller ionic radii Y, Yb, and Lu the Gu ligands shield over 88.3% of the metal surface and their staggered conformation is observed. The ligand solid angle approach is illustrated and its application to describing multidentate ligands is demonstrated.     

An SCF-MO study of the electronic structure of the [LiNH3] cation and related molecules

We examine the effect of the charge and degree of protonation of a ligand on its power as a donor. The following molecules are studied [LiNH₃]⁺, LiNH₂, Li₂NH, and Li₃N, which may to a good approximation be regarded as combinations of Li⁺ ions with the ligands NH₃, NH ₂ ^? , NH^?2, and N^?3.     

Theoretical study of aluminide clusters Al13X, Al13X−, and Al13X 2 − (X=H, Hal, OH, NH2, CH3, and C6H5)

The structural, electronic, energy, and vibrational characteristics of the Al₁₃X^? and Al₁₃X ₂ ^? clusters, with an aluminum-centered (Al_c) icosahedral cage Al₁₃ and with one or two outer-sphere ligands X=H, F, Cl, Br, OH, NH₂, CH₃, C₆H₅, have been calculated within the B3LYP approximation of the density functional theory using the 6-31G* and 6-311+G* basis sets. In all Al₁₃X^? radicals, the unpaired electron is localized at the cage atom Al* located opposite the Al-X bond. This Al* atom is the most favorable site for attaching the second X ligand of any nature (trans-addition rule). According to the previously suggested molecular model of the valence state of the [Al ₁₃ ^? ] “superatom,” the calculated energies D ₁(Al ₁₃ ^? -X) of addition of the first ligand to the Al ₁₃ ^? anion are about 1 eV lower than the corresponding energies of addition of the second ligand D ₂(XAl ₁₃ ^? -X). The structure of the Al₁₃ cage depends on the nature of the nature of the substituent X and can radically change in going from anions to their neutral congeners. In the lowest-lying Al₁₃X isomer with electronegative substituents X (Hal, OH, NH₂, CH₃, etc.), the aluminum cage has a marquee structure (1, symmetry C _s) with a hexagonal base and a pentagonal “roof.” For Al₁₃X analogues with electropositive ligands X (Al, Li, Na), a tridentate isomer (T, C _3v ) with the X substituent coordinated to a face of the Al₁₃ icosahedron is preferable. In the case of moderately electronegative X ligands (of the H type), the marquee (1) and icosahedral (T) isomers are close in energy. The stretching vibration frequencies of isomers 1 and T differ significantly in magnitude and intensity so that vibrational spectroscopy methods can be especially applicable to their experimental identification.     

Heavy-metal extraction capability of chalcogenoic aminophosphines derived from 1-amino-4-methylpiperazine

Aminophosphine of the type (Ph₂PNHR) derived from 1-amino-4-methylpiperazine and its chalcogen derivatives (Ph₂P(X)NHR X = S, Se) were used as ligands in solvent extraction of metal picrates such as Cu²⁺, Ni²⁺, and Pb²⁺ from the aqueous to the organic phase. Influence of parameters such as pH of the aqueous phase, ligand concentration in the organic phase, and concentration of the extractant extracted from the aqueous to the organic phase was investigated to determine the ligands’ ability to extract metal ions. Metal picrate extraction was investigated at 25°C using UV-VIS spectrophotometry in dichloromethane in the absence and in the presence of Ph₂PNHR and chalcogenides. The extraction results revealed that the extraction percentage of Cu²⁺, Ni²⁺, and Pb²⁺ metals was much higher at lower pH values, indicating an acidity dependent complexation equilibrium.     

Four iron(II) carbonyl complexes containing both pyridyl and halide ligands: Their synthesis,characterization, stability,and anticancer activity

Four iron(II) carbonyl complexes, fac‐[Fe (CO)₃X₂(py)] (X = I^?, 1 and Br^?, 3 ), fac‐[{Fe (CO)₃X₂}₂(bipy)] (X = I^?, 2 and Br^?, 4 ), were facilely synthesized by reacting cis‐[Fe (CO)₄X₂] (X = I^?, Br^?) with pyridine (py) and 4,4′‐dipyridine (bipy) ligands, respectively, in good yields (70%~85%). These complexes were fully characterized, and the structures of Complexes 2 and 3 were crystallographically analyzed. In dimethyl sulfoxide, they decomposed rapidly to release carbon monoxide (CO), and in methanol, they showed better stability which allowed kinetically analyzing their decomposing behaviors. The self‐decomposing in methanol fitted first‐order kinetics with a half‐time ranging from several minutes to 1 h. Our results suggested that the ligand with great conjugation (bipy) and strong electron‐donating capability (iodide) could stabilize the iron(II) carbonyl complexes. The decomposition of the iodo complexes ( 1 and 2 ) involved the production of iodine radicals. MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide) assessments revealed that the efficacy against human bladder carcinoma cell line (RT112) is in the following trend: 1 > 2 > 3 > 4 . The relatively strong efficacy of Complexes 1 and 2 is mainly contributed to the in situ generated iodine radicals. The combination of the cytotoxicity of the in situ generated radicals with the anticancer activity of CO as reported in literatures may lead to developing novel anticancer drugs with enhanced efficacy.     

Hydration structure of -NH 2 + and -COO− of L-proline zwitterion from data of 1D-RISM integral equation method

The hydration structure of hydrophilic groups of L-proline zwitterion is studied by means of the 1D-RISM integral equation method. The structural parameters of hydration and features of hydrogen bonding between water and -NH ₂ ⁺ and -COO^? groups are discussed.     

Colloidal Stability of TiO2 Nanoparticles: The Roles of Phosphonate Ligand Length and Solution Temperature

Surface ligands are essential tools for the stabilization of colloidal nanoparticles (NPs) in solvents. However, knowledge regarding the effects of the ligand shell, especially the ligand length, is insufficient and controversial. Here we demonstrate solution-based experiments on n-alkylphosphonate-capped TiO₂ NPs to investigate the effects of ligand length and solution temperature on colloidal stability. A robust ligand-exchange process is achieved that draws free ligands and impurities away from the colloidal solution. In the case of 8 nm anatase NPs in toluene, the dodecylphosphonate ligand provided better colloidal stability than all the other n-alkylphosphonate ligands. In addition, relaxation studies suggested there is kinetic hysteresis in the dispersion/agglomeration transition. The proposed method is applicable to a wide range of surface ligands designed to maximize the colloidal stability of NPs.     

Preparation and structural studies on the Bu2Sn(IV) complexes with aromatic mono- and dicarboxylic acids containing hetero {N} donor atom

Nine complexes of ^tBu₂Sn(IV)²⁺ were obtained in the solid state with ligands containing -COOH group(s) and aromatic {N} donor atom. The binding sites of the ligands were identified by FT-IR spectroscopic measurements. It was found that in most cases the -COO⁻ groups are co-ordinated in monodentate manner. Nevertheless, in some of our complexes, the -COO⁻ group forms bridges between two central {Sn} atoms resulting in the formation of an oligomeric structure, a motif that is characteristic only to the nicotinate compound. These pieces of information and the rationalisation of the experimental ¹¹⁹Sn Mössbauer nuclear quadrupole splittings, Δ, - according to the point charge model formalism - support the formation of octahedral (O_h) or trigonal bipyramidal (TBP) molecular structures. The X-ray diffraction analysis of one complex obtained as single crystal revealed the distortion of the TBP geometry towards square pyramidal (SP) one. This was rationalised by PM3 molecular modelling of the ^tBu₂Sn(pdc) complex. In the asymmetric unit, the two chemically similar but symmetry independent molecules form pseudo-dimers, in which the Sn?Sn separation amounts to ca. 6.4 Å. The crystal lattice is stabilised by C-H?O hydrogen bonding between individual molecules.     

Study of the temperature effect on IR spectra of crystalline amino acids,dipeptides, and polyamino acids. IV. L-cysteine and DL-cysteine

A study of the IR spectra of L- and DL-cysteine is carried out in a range of frequencies from 4000 cm^?1 to 600 cm^?1 and temperatures from 333 K to 83 K. Changes in the spectra of L- and DL-cysteine (NH ₃ ⁺ CH(CH₂SH)-COO^?) on cooling are analyzed in comparison with the spectra of L- and DL-serine (NH ₃ ⁺ CH(CH₂OH)-COO^?) and three polymorphs of glycine (NH ₃ ⁺ CH₂-COO^?) previously studied under temperature variation. Changes in the IR spectra at variable temperatures are correlated with previously obtained diffraction data on anisotropic compression of the structure and changes in the geometric parameters of hydrogen bonds. Special attention is paid to temperature regions in which anomalies were detected by vibrational spectroscopy, X-ray diffraction, and calorimetry.     

Synthesis of multidentate ligands with amido or amino donor groups for the preparation of rhenium and technetium radiopharmaceuticals

A new method to prepare novel semi-rigid multidentate ligands containing nitrogen atom, to coordinate with rhenium and technetium, was established. The method was based on formylation of substituted anilines, followed by Mannich reaction with glycine and paraformaldehyde. The method was very promising to design ligands of various molecular structures (L₁–L₅) to coordinate with rhenium metal ions. The complexes were prepared through ligand exchange with the complex ReOCl₃(PPh₃)₂, giving new complex of the structure ReOCl₃L_(1–5). The prepared ligands and complexes were identified by the use of UV–vis, and infrared absorption spectrometric techniques, elemental analysis, molecular weight determination by depression of freezing point. These ligands were labeled with ^99mTc pertechnetate, and the labeling efficiency of the complexes was measured using a well type scintillation gamma counter equipment and obtained a good yield.     

catena‐Poly[[bis[5‐(4‐pyridyl‐κN)‐2‐(2‐pyridylmethylsulfanyl)‐1,3,4‐oxadiazole]cadmium(II)]‐di‐μ‐thiocyanato‐κ2N:S;κ2S:N]

The title compound, [Cd(NCS)₂(C₁₃H₁₀N₄OS)₂]_n, contains SCN⁻ anions acting as end‐to‐end bridging ligands which utilize both S and N atoms to link cadmium(II) centers into one‐dimensional double chains. The multidentate 5‐(4‐pyridyl)‐2‐(2‐pyridylmethylsulfanyl)‐1,3,4‐oxadiazole ligands behave as monodentate terminal ligands, binding metal centers only through the N atoms of the 4‐pyridyl groups. Two types of eight‐membered rings are formed by two SCN⁻ anions bridging Cd^II centers, viz. planar and chair conformation, which are alternately disposed along the same chain. Finally, chains define a two‐dimensional array through two different interchain π–π stacking interactions.     

Synthesis and characterization of manganese and rhenium tricarbonyl complexes with (O,O,O)-donor ligands

Complexes of the type [(C₅H₅)Co{P(O)R₂}₃]^?, R = OCH₃, OC₂H₅, react as tridentate oxygen ligands L^? with [MBr(CO)₅], M = Mn, Re, in hexane or tetrahydrofuran to give the tricarbonyl derivatives [LM(CO)₃]. The slightly volatile yellow crystalline compounds have been characterized by elemental analysis, ¹H NMR, IR and mass spectra. The low CO stretching frequencies indicate that the ligands L^? are good π-donor ligands.     

To Sandwich Technetium: Highly Functionalized Bis‐Arene Complexes [99mTc(η6‐arene)2]+ Directly from Water and [99mTcO4]−

The labeling of (bio)molecules with metallic radionuclides such as ^99mTc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis‐arene sandwich complexes are generally prepared by the Fischer–Hafner reaction. In extension of this, we show that [^99mTc(η⁶‐C₆R₆)₂]⁺‐type complexes are directly accessible from water and [^99mTcO₄]^?, even using arenes incompatible with Fischer–Hafner conditions. To unambiguously confirm the nature of these unprecedented ^99mTc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η⁶‐C₁₀H₈)₂]⁺ with the corresponding phenyl groups. The ease with which highly stable [^99mTc(η⁶‐C₆R₆)₂]⁺ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures.     

A novel three‐dimensional heterometallic coordination polymer: poly[[hexaaquabis[μ3‐3,5‐dicarboxylatopyrazolato‐κ5O3,N2:N1,O5:O5′](μ2‐oxalato‐κ4O1,O2:O1′,O2′)copper(II)dierbium(III)] trihydrate]

The title novel heterometallic 3d–4f coordination polymer, {[CuEr₂(C₅HN₂O₄)₂(C₂O₄)(H₂O)₆]·3H₂O}_n, has a three‐dimensional metal–organic framework composed of two types of metal atoms (one Cu^II and two Er^III) and two types of bridging anionic ligands [3,5‐dicarboxylatopyrazolate(3−) (ptc³⁻) and oxalate]. The Cu^II atom is four‐coordinated in a square geometry. The Er^III atoms are both eight‐coordinated, but the geometries at the two atoms appear different, viz. triangular dodecahedral and bicapped trigonal prismatic. One of the oxalate anions is located on a twofold axis and the other lies about an inversion centre. Both oxalate anions act as bis‐bidentate ligands bridging the latter type of Er atoms in parallel zigzag chains. The pdc³⁻ anions act as quinquedentate ligands not only chelating the Cu^II and the triangular dodecahedral Er^III centres in a bis‐bidentate bridging mode, but also connecting to Er^III centres of both types in a monodentate bridging mode. Thus, a three‐dimensional metal–organic framework is generated, and hydrogen bonds link the metal–organic framework with the uncoordinated water molecules. This study describes the first example of a three‐dimensional 3d–4f coordination polymer based on pyrazole‐3,5‐dicarboxylate and oxalate, and therefore demonstrates further the usefulness of pyrazoledicarboxylate as a versatile multidentate ligand for constructing heterometallic 3d–4f coordination polymers with interesting architectures.