Search results for "complex"
showing 10 items of 5889 documents
Iron(II) Complexes with Scorpiand-Like Macrocyclic Polyamines: Kinetico-Mechanistic Aspects of Complex Formation and Oxidative Dehydrogenation of Coo…
2017
The Fe(II) coordination chemistry of a pyridinophane tren-derived scorpiand type ligand containing a pyridine ring in the pendant arm is explored by potentiometry, X-ray, NMR, and kinetics methods. Equilibrium studies in water show the formation of a stable [FeL]2+ complex that converts to monoprotonated and monohydroxylated species when the pH is changed. A [Fe(H–2L)]2+ complex containing an hexacoordinated dehydrogenated ligand has been isolated, and its crystal structure shows the formation of an imine bond involving the aliphatic nitrogen of the pendant arm. This complex is low spin Fe(II) both in the solid state and in solution, as revealed by the Fe–N bond lengths and by the NMR spect…
Hydrolysis of (CH3)Hg+ in Different Ionic Media: Salt Effects and Complex Formation
1998
The hydrolysis of monomethylmercury(II) was studied potentiometrically, in NaNO3, Na2SO4, and NaCl aqueous solution, in a wide range of ionic strengths (NaNO3, 0 ≤ I ≤ 3.25; Na2SO4, 0 ≤ I ≤ 1; NaCl, 0 ≤ I ≤ 3 mol dm-3) and at t = 25 °C. For the reaction (CH3)Hg+ = (CH3)Hg(OH)° + H+, we found log K1 = −4.528 (I = 0 mol dm-3). The species [(CH3)Hg]2(OH)+ was also found, with log β2 = −2.15. Monomethylmercury(II) forms quite strong complexes with Cl- (log K = 5.45, I = 0 mol dm-3) and SO42- (log K = 2.64, I = 0 mol dm-3). The dependence on ionic strength of formation constants was considered by using a Debye−Huckel type equation. Hydrolysis and complex formation constants (at different ionic s…
Coordination chemistry of N,N′-bis(coordinating group substituted)oxamides: a rational design of nuclearity tailored polynuclear complexes
1999
Abstract The coordinating properties of N , N ′-bis(coordinating group substituted)oxamides have been thoroughly investigated both in aqueous solution and in the solid state. The easy cis – trans isomerization equilibria that they exhibit together with the great variety of N , N ′-substituents which can be used to play on the overall charge, complexing ability and polarity, make them very suitable ligands in designing homo- and heterometallic species. The knowledge of their complex formation in aqueous solution by potentiometry and using the hydrogen ion concentration as a probe, allowed us to settle the basis of a rational design of oxamidate-containing polynuclear species whose nuclearity…
Azacoronands and Azacyclophanes
2012
Azacycloalkanes and azacyclophanes are among the first macrocyclic ligands developed in the field of supramolecular chemistry. Since they are polyamines, they show dual nature in the coordination of both metal cations, when they are in the free-base form, and anionic species, when they are protonated. As a matter of fact, they played a key role in the birth of macrocyclic chemistry of transition metal complexes and anion coordination chemistry. Furthermore, azacyclophanes fostered also the birth of apolar complexation in aqueous solution, since their aromatic units act as binding sites for apolar substrates. Keywords: azacycloalkanes; azacyclophanes; metal complexes; anion complexes; apolar…
Sequestering Ability of Aminopolycarboxylic (APCs) and Aminopolyphosphonic (APPs) Ligands Toward Palladium(II) in Aqueous Solution
2014
The binding capacity of three aminopolycarboxylates [nitrilotriacetic acid (NTA), ethylene-glycol-bis(2-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA), and diethylenetriamine-N,N,N,NN-pentaacetic acid (DTPA)] and two aminopolyphosphonates {(1-hydroxyethane-1,1-diyl)bis(phosphonic acid) (HEDP) and [[(phosphonomethyl)imino]bis[2,1-ethanediylnitrilobis(methylene)]] tetrakis-phosphonic acid (DTPP)} toward palladium(II) ion was studied by potentiometric and spectrophotometric titrations at different temperatures (283.15 ≤ T/K ≤ 318.15) and ionic strengths (0.1 ≤ I/mol·dm -3 ≤ 1.0) in NaClO4. The hydrolysis of Pd2+ and the protonation of ligands were always taken into account in the speciation…
Thermodynamic and kinetic studies on the Cu2+ coordination chemistry of a novel binucleating pyridinophane ligandElectronic supplementary information…
2003
The synthesis and coordination chemistry of the novel pyridine-functionalized ligand 2,6,9,12,16-pentaaza[17]-(2,6)pyridinophane (L1) is described. The compound behaves as a hexaprotic base in aqueous solution. NMR studies indicate a protonation pattern in which the sp2 pyridine nitrogen (N(py)) does not undergo a net protonation although it is involved in formation of hydrogen bonds. L1 forms mono and binuclear hydroxylated complexes. The crystal structure of [CuL1](ClO4)2 shows a square planar coordination for Cu2+ with the pyridine and the three central nitrogens of the chain forming the vertices of the square. The benzylic nitrogens could be occupying the axial positions of a strongly a…
Stability−Charge and Stability−Structure Relationships in the Binding of Dicarboxylic Ligands by Open-Chain Polyammonium Cations
2000
The stability of complexes formed by 5 dicarboxylic ligands with 11 open-chain polyammonium cations (40 systems) was studied potentiometrically, in aqueous solution, at 25 °C. In all the systems ALHr species (A = amine, L = dicarboxylic ligand, r = 1 ... n; diamines n = 3, triamines n = 4, tetraamines n = 4 or 5) were found. Formation constants for the various complexes studied in this work, together with data for the analogous systems previously studied (20 systems), were examined as a function of charges involved in the formation reaction and of the structure of both the dicarboxylic ligand and the polyammonium cation. Structure generally has little effect on stability, while charges play…
Cysteamine and its homoleptic complexes with group 12 metal ions. Differences in the coordination chemistry of ZnII, CdII, and HgII with a small N,S-…
2005
2-Ammoniumethanethiolate, (-)SCH(2)CH(2)NH(3)(+), the first structurally characterized zwitterionic ammoniumthiolate, is the stable form of cysteamine (HL) in the solid state and in aqueous solution. Reactions of ZnCl(2), Cd(Oac)(2), and HgCl(2) with cysteamine and NaOH in a 1:2:2 ratio, respectively, lead to the homoleptic complexes ML(2). Their single-crystal X-ray structures demonstrate basic differences in the coordination chemistry of Zn(II), Cd(II), and Hg(II). While chelating N,S-coordination modes are found for all metal ions, Zn(II) forms a mononuclear complex with a distorted tetrahedral Zn(N(2)S(2)) coordination mode, whereas Hg(II) displays a dimer with Hg(N(2)S(2)) coordinated …
Palladium(II) sequestration by phytate in aqueous solution. Speciation analysis and ionic medium effects.
2010
Environmental context.In the last 20 years, the demand for palladium and other platinum-group elements has intensified, causing a significant increase in their concentration in the environment, with particular accumulation in urban areas. Knowledge about Pd2+ speciation in aqueous media is fundamental for the understanding of its biological and environmental activity in contaminated areas. Phytic acid appears to be a good sequestering agent towards Pd2+ under various conditions, indicating its potential use in the remediation of contaminated sites. Abstract. Palladium(II) speciation in the presence of phytate (Phy12–) was studied by H+ ion selective electrode (ISE) potentiometry at 25°C in…
Speciation of tin(II) in aqueous solution: thermodynamic and spectroscopic study of simple and mixed hydroxocarboxylate complexes
2013
This contribution reports the results of potentiometric and Mossbauer investigations on the formation, stability, and structure of binary and ternary mono- and binuclear complexes of Sn2+ with three hydroxocarboxylic ligands (namely L = tartrate, malate, and citrate) and chloride at T = 298.15 K in different ionic media and ionic strengths (0.15 and 1.00 mol dm−3 in NaCl(aq) and 1.00 mol dm−3 in NaNO3(aq)). The stability constants of various simple Sn i H j L (2+−) and mixed Sn i H j L k Cl (2+−−) species obtained in the different experimental conditions are reported, and various speciation diagrams of the simple and mixed systems are shown in different conditions. The sequestering ability …