On the behaviour of cysteine as ligand of cadmium(II)

The ability of cysteine to form complexes with cadmium(II) in aqueous solutions has been investigated at 25 degrees C and in constant ionic medium NaCl at two different concentrations, 1.00 and 3.00 mol l(-1). The presence of chloride ions was necessary to avoid the precipitation of cadmium(II). Two kinds of measurements were carried out. The electromotive force of galvanic cells containing glass and cadmium amalgam electrodes was measured as a function of cadmium and hydrogen ion concentrations in acid or moderately alkaline solutions in order to obtain the free concentration of cadmium(II) and hydrogen ions. The experimental data obtained in 1.00 mol l(-1) NaCl were explained by assuming the presence of CdHL and CdH(2)L(2), while those obtained in 3.00 mol l(-1) NaCl were accounted for with the formation of CdHL, CdH(2)L(2), CdH(3)L(3) and CdH(2)L(3). Moreover, polarographic measurements were carried out under the same experimental conditions but in alkaline solutions, and the formation of CdL(2) and CdL(3) was assumed from the shift of E(1/2) of cadmium(II) with an excess of cysteine. The stability constants of the assumed species were determined. Protonation constants of cysteine in 1.00 and 3.00 mol l(-1) NaCl have been also determined. A comparison with the behaviour of serine and alpha-aminopropanoate towards cadmium(II) is proposed.     

Extraction behaviour of copper(II) and silver(I) with a thiacrown ether carboxylic acid, 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid

The extraction behaviour of copper(II) and silver(I) with 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid (TTCTOHA) was investigated at 25+/-0.1 degrees C and ionic strength of 0.1. The value of the logarithmic distribution coefficient, logK(DR) of TTCTOHA between octan-1-ol and aqueous phases was determined to be 4.13. Copper(II) was extracted with TTCTOHA into octan-1-ol as CuL(2), where L represents the anionic species of TTCTOHA. The logarithmic extraction constant, logK(ex(10)), was determined at -7.42. Silver(I) was extracted with TTCTOHA into octan-1-ol as AgL and Ag(2)L(2). The logarithmic distribution constant, logK(DC), of AgL was estimated to be 0.49. On the other hand, silver(I) was extracted into 1,2-dichloroethane as AgL and the logarithmic extraction constant, logK(ex(10)), was determined to be -2.24.     

On the complex-formation between Cd(II) and EDTA

The complex-formation between cadmium and EDTA has been studied at 25 degrees in 1.0M sodium nitrate medium, by measuring with a glass electrode the hydrogen-ion concentrations of a series of solutions containing varying amounts of cadmium and EDTA, and the free concentration of cadmium with a cadmium-amalgam electrode. The experimental data, which were analysed by using the ETITR version of the general error-minimizing computer program LETAGROP, may be explained satisfactorily by assuming the formation of the species CdL, CdHL, CdH(2)L and Cd(2)L in the pH range 1.8-6.5. The equilibrium constants for the formation of these species are also reported.     

Molecular structures and stability constants of gossypol and its aza-derivative complexes with silver(I) cations studied by potentiometric, ESI MS, NMR, and AM1d semiempirical methods

Stability constants of complexes formed by gossypol and by ten of its Schiff bases with Ag (+) cations were determined by the potentiometric method. The potentiometric and ESI MS experiments indicate the formation of AgL (+) and Ag 2L (2+) complexes between the Schiff bases G1-G7 and Ag (+) cations as well as the formation of AgL (+), Ag 2L (2+), AgL 2 (+) and Ag 3L 2 (3+) complexes between the Schiff bases G8-G10 and Ag (+) cations. The highest stability constant was found for the AgL (+) complex of G8 Schiff base and the lowest one for the AgL (+) complex of G molecule. The (13)C NMR spectra of mixtures between G and AgClO 4 as well as G1-G10 and AgClO 4 indicate that the complexation of the Ag (+) cations is exclusively realized by the aldehyde-aldehyde tautomer of gossypol and by the enamine-enamine form of gossypol Schiff bases, respectively. We show that the main coordination sites for the Ag (+) metal cations are either the oxygen or the nitrogen atoms of the amine parts of the Schiff bases of gossypol. The energetically most favorable structures of the Ag (+) complexes with gossypol (G) or with the gossypol Schiff bases (G1-G10) were calculated and visualized by the AM1d method at an semiempirical level of theory.     

Silver(I) and Silver(II) Complexes with Some Tetraazamacrocyclic Ligands in Aqueous Solutions

The reactions of silver(I) with isocyclam, scorpiand,trans-Me₂[14]anN₄, cis-Me₆[14]anN₄,(N-Me)Me₂py[14]anN₄ and py[12]anN₄ were investigated.The stability constant of the Ag(I) complex with py[12]anN₄ was determined. The aqueous solutions of the silver(II) complexes with the 14-membered ligands were obtained, and characterized by means of UV-VIS and CVA measurements. The Ag²⁺ ion does not form a five-coordinate complex with scorpiand. The formal potentials of the Ag(II)/Ag(I) system in the presence of scorpiand, trans-Me₂[14]anN₄, cis-Me₆[14]anN₄ and(N-Me)Me₂py[14]anN₄ were determined. The mechanism is also proposedfor the electroreduction of the silver(II) complexes with these compounds on a platinum electrode in aqueous solution.     

Potentiometric study of complexation between taurine and metal ions

The protolytic and complexation properties of taurine are studied by a potentiometric method. The dissociation constants of 2-aminoethanesulfonic acid functional groups and the stability constants of taurine complexes with copper(II), cobalt(II), nickel(II), zinc(II), manganese(II), cadmium(II), silver(I), magnesium(II), calcium(II), strontium(II), and barium(II) ions are calculated.     

Conformational analysis of mixed oxathia crown ethers and their complexational ability towards Ag(I) and Pd(II)-an experimental solution NMR and theoretical molecular modelling study

Both the conformation and flexibility of four mixed oxathia crown ethers and their Ag(I) and Pd(II) complexes were studied by (1)H NMR (delta, J, NOE, T(1)), (13)C NMR, dynamic (1)H NMR spectroscopy and molecular modelling. The stoichiometry and stability constants of the complexes were determined from corresponding Job's plots in the case of Ag(I) complexes as the interchange between free and complexed states was fast on the NMR timescale; interchange for the Pd(II) complexes was sufficiently slow such that distinct sub-spectra were observable for the free and complexed states. In all cases where complexation was observed, 1 : 1 complexes were formed. Global minima structures determined from the modelling studies were analysed with respect to the barriers to ring interconversion, the flexibility of the species in solution and the preferred complexation of Ag(I) and Pd(II) to the sulfur atoms of the crown ethers.     

Polymeric silver(I) complexes with pyridyl dithioether ligands: experimental and theoretical investigations on the coordination properties of the ligands

The reactions of four flexible tetradentate ligands, 1,3-bis(2-pyridylthio)propane (L1), 1,4-bis(2-pyridylthio)butane (L2), 1,5-bis(2-pyridylthio)pentane (L3) and 1,6-bis(2-pyridylthio)hexane (L4) with AgX (X = BF4-, ClO4-, PF6-, or CF3SO3-) lead to the formation of seven new complexes: [AgL1(BF4)]2 (1), [[AgL2](ClO4)]infinity (2), [[AgL2(CH3CN)](PF6)]infinity (3), [[AgL3](BF4)(CHCl3)]2 (4), [[AgL3(CF3SO3)](CH3OH)(0.5)]infinity (5), [[Ag2L4(2)](BF4)2]infinity (6), and [[AgL4](PF6)]infinity (7), which have been characterized by elemental analyses, IR spectroscopy, and X-ray crystallography. Single-crystal X-ray analyses show that complexes 1 and 4 possess dinuclear macrometallacyclic structures, and complexes 2, 3 and 5-7 take chain structures. In all the complexes, the nitrogen atoms of ligands preferentially coordinate to silver atoms to form normal coordination bonds, while the sulfur atoms only show weak interactions with silver atoms and the intermolecular AgS weak contacts connect the low-dimensional complexes into high-dimensional supramolecular networks. Additional weak interactions, such as pi-pi stacking, F...F weak interactions, Ag...O contacts or C-H...O hydrogen bonds, also help to stabilize the crystal structures. It was found that the parity of the -(CH2)n- spacers (n = 3-6) affect the orientation of the two terminal pyridyl rings, thereby significantly influence the framework formations of these complexes. The coordination features of ligands and their conformation changes between free and coordination states have been investigated by DFT calculations.     

Tetraphosphinitoresorcinarene complexes: cationic silver(I) and copper(I) halide complexes as mercurate(II) anion receptors

The reactions of mercury(II) halides with the tetraphosphinitoresorcinarene complexes [P4M5X5], where M=Cu or Ag, X=Cl, Br, or I, and P4=(PhCH2CH2CHC6H2)4(O2CR)4(OPPh2)4 with R=C6H11, 4-C6H4Me, C4H3S, OCH2CCH, or OCH2Ph, have been studied. The reactions of the complexes with HgX2 when M=Ag and X=Cl or Br occur with elimination of silver(I) halide and formation of [P4Ag2X(HgX3)], but when M=Ag and X=I, the complexes [P4Ag4I5(HgI)] are formed. When M=Cu and X=I, the products were the remarkable capsule complexes [(P4Cu2I)2(Hg2X6)]. When M=Ag and X=I, the reaction with both CuI and HgI2 gave the complexes [P4Cu2I(Hg2I5)]. Many of these complexes are structurally characterized as containing mercurate anions weakly bonded to cationic tetraphosphinitoresorcinarene complexes of copper(I) or silver(I) in an unusual form of host-guest interaction. In contrast, the complex [P4Ag4I5(HgI)] is considered to be derived from an anionic silver cluster with an iodomercury(II) cation. Fluxionality of the complexes in solution is interpreted in terms of easy, reversible making and breaking of secondary bonds between the copper(I) or silver(I) cations and the mercurate anions.     

Ternary complexes in the spectrophotometric determination of trace amounts of silver(I) and cadmium(II)

The reaction of silver(I) and cadmium(II) with 1,10-phenanthroline (PHEN) and Eosin (2,4,5,7-tetrabromofluorescein) gives coloured association complexes. The solution spectra of the mixed-ligand complexes are characterised by high intensity (∈ ≈ 10⁴) metal-to-ligand charge-transfer bands at 540–555nm. The optimum conditions for the spectrophotometric determination of Ag(I) or Cd(II) have been established. A simple, sensitive and selective method was proposed for the determination of traces of the metal ions either in aqueous or organic media. In the presence of EDTA only aluminium and cyanide interfere.     

Electronic Structures of Copper(I) and Silver(I) beta-Diketonate Complexes

The valence electronic structures of [Cu(hfac)L] (hfac = CF(3)C(O)CHC(O)CF(3); L = PMe(3), CNMe), [Ag(hfac)(PMe(3))], and [Ag(fod)(PEt(3))] (fod = t-BuC(O)CHC(O)C(3)F(7)) have been studied by recording their photoelectron spectra and by performing Xalpha-SW calculations on the model compounds [M(dfm)(PH(3))] (dfm = HC(O)CHC(O)H; M = Cu, Ag) and [Cu(dfm)(CNH)]. For the copper complexes, the spectra were recorded between 21 and 160 eV using He I, He II and synchrotron radiation; while, for the silver complexes, He I and He II, spectra were recorded. Assignments were made by comparison of experimental and calculated values of band energies, and, for the copper complexes, by similar comparison of experimental and theoretical branching ratios as a function of photon energy. For the silver complexes, a more limited comparison of band intensities in the He I and He II spectra was made. In analogous compounds, it is shown that the binding energies follow the sequence Ag 4d > Cu 3d, with an energy difference of almost 2 eV.     

Ion-pair formation between Cd(II), Na(I), and Ag(I) complex ions with 18-crown-6 ether derivatives and various pairing anions in water: an understanding of the ion-pair formation based on the HSAB principle

The ion-pair formation constants (K(MLX)(0)/mol(-1) dm(3)) of CdL(2+) with Br(-) or NaL(+) with N,N-diethyldithiocarbamate ion (DDTC(-)) in water were determined potentiometrically at 25°C; ionic strength (I)→0: L denotes 18-crown-6 ether (18C6) and its mono-benzo derivative for the CdBr(2)-L system and 15-crown-5 ether and 18C6 for the NaDDTC-L one. The formation constant corresponding to the simple salt, NaDDTC, in water was also determined at I→0. Using the log K(CdLX)(0) values of CdLCl(+), CdLBr(+), CdLPic(+), and CdLSO(4), then CdL(2+) and picrate ion (Pic(-)) in water have been classified with the hard and soft acids and bases principle, where the values were available in the literature, except for CdLBr(+). The same classification was examined in NaX-L systems with X(-) = DDTC(-), trifluoroacetate ion, MnO(4)(-), ReO(4)(-), Pic(-), and BPh(4)(-) and the AgPic-L one. Consequently, CdL(2+), NaL(+), and AgL(+) were classified as the hard acids, while Pic(-) and BPh(4)(-) as the hard bases. These results reflected the reactivities of the complex ions in ion-pair formation with X(-) and SO(4)(2-) in water.     

Syntheses and Crystal Structures of Two Silver(I) Complexes Isolated by the Reaction of [Ag(PPh3)2(MeCN)](SbF6) with a N6 Ligand

1 INTRODUCTION The polyaza macrocyclic and macrobicyclic mo-lecules have been extensively studied due to theirinclusion ability for neutral molecules, coordinationability for metal cations and versatile roles in thefields of recognition, transformation…     

Real and Hypothetical Intermediate-Valence Ag(II)/Ag(III) and Ag(II)/Ag(I) Fluoride Systems as Potential Superconductors

With the aim of gauging their potential as conducting or superconducting materials, we examine the crystal structures and magnetic properties of the roughly one hundred binary, ternary, and quaternary Ag(II) and Ag(III) fluorides in the solid state reported up to date. The Ag(II) cation appears in these species usually in a distorted octahedral environment, either in an [AgF](+) infinite chain or as [AgF(2)] sheets. Sometimes one finds discrete square-planar [AgF(4)](2-) ions. The Ag(III) cation occurs usually in the form of isolated square-planar [AgF(4)](-) ions. Systems containing Ag(III) (d(8)) centers are typically diamagnetic. On the other hand, the rich spectrum of Ag(II) (d(9)) environments in binary and ternary fluorides leads to most diverse magnetic properties, ranging from paramagnetism, through temperature-independent paramagnetism (characteristic for half-filled band and metallic behavior) and antiferromagnetism, to weak ferromagnetism. Ag(II) and Ag(III) have the same d-electron count as Cu(II) (d(9)) and Cu(III) (d(8)), respectively. F(-) and O(2-) ions are isoelectronic, closed-shell (s(2)p(6)) species; both are weak-field ligands. Led by these similarities, and by some experimental evidence, we examine analogies between the superconducting cuprates (Cu(II)/Cu(III)-O(2-) and Cu(II)/Cu(I)-O(2-) systems) and the formally mixed-valence Ag(II)/Ag(III)-F(-) and Ag(II)/Ag(I)-F(-) phases. For this purpose we perform electronic-structure computations for a number of structurally characterized binary and ternary Ag(I), Ag(II), and Ag(III) fluorides and compare the results with similar calculations for oxocuprate superconductors. Electronic levels in the vicinity of the Fermi level (x(2)-y(2) or z(2)) have usually strongly mixed Ag(d)/F(p) character and are Ag-F antibonding, thus providing the potential of efficient vibronic coupling (typical for d(9) systems with substantially covalent bonds). According to our computations this is the result not only of a coincidence in orbital energies; surprisingly the Ag-F bonding is substantially covalent in Ag(II) and Ag(III) fluorides. The electron density of state at the Fermi level (DOS(F)) for silver fluoride materials and frequencies of the metal-ligand stretching modes have values close to those for copper oxides. The above features suggest that properly hole- or electron-doped Ag(II) fluorides might be good BCS-type superconductors. We analyze a comproportionation/disproportionation equilibrium in the hole-doped Ag(II) fluorides, and the possible appearance of holes in the F(p) band. It seems that there is a chance of generating an Ag(III)-F(-)/Ag(II)-F(0) "ionic/covalent" curve crossing in the hole-doped Ag(II)-F(-) fluorides, significantly increasing vibronic coupling.     

Group 11 complexes with the bis(3,5-dimethylpyrazol-1-yl)methane ligand. How secondary bonds can influence the coordination environment of Ag(I): the role of coordinated water in [Ag2(mu-L)2(OH2)2](OTf)2

The complexation properties of the ligand bis(3,5-dimethylpyrazol-1-yl)methane (L) towards group 11 metals have been studied. The reaction in a 1 : 1 molar ratio with [Cu(NCMe)4]PF6 or Ag(OTf) complexes gives the mononuclear [CuL(NCMe)]PF6 (1), with crystallographic mirror symmetry, or dinuclear [Ag2(mu-L)2](OTf)2 (2) (OTf = trifluoromethanesulfonate) in which the ligand bridges both silver centres, an unprecedented mode of coordination for this type of ligands. Compound 2 crystallizes with two water molecules and forms a supramolecular structure through classical hydrogen bonding. The reaction in a 2 : 1 ratio affords in both cases the four-coordinated derivatives [ML2]X (M = Cu, X = PF6 (3); Ag, X = OTf 4). The treatment of [Ag(OTf)(PPh3)] with the ligand L gives [AgL(PPh3)]OTf (5). The gold(I) derivative [Au2(C6F5)2(mu-L)] (6) has also been obtained by reaction of L with two equivalents of [Au(C6F5)(tht)]. These complexes present a luminescent behaviour at low temperature; the emissions being mainly intraligand but enhanced after coordination of the metal. Compounds 1-4 have been characterized by X-ray crystallography. DFT studies showed that, in the silver complex 2, coordination of H2O to Ag in the binuclear complex is favoured by formation of a hydrogen-bonding network, involving the triflato anion, and releasing enough energy to allow distortion of the Ag2 framework.     

Mono and binuclear Ag(I), Cu(II), Zn(II) and Hg(II) complexes of a new azo-azomethine as ligand: synthesis, potentiometric, spectral and thermal studies

New azo-azomethine dyes were prepared by reaction of p-aminobenzoic acid, o-anisidine, o-nitroaniline, and p-bromoaniline with salicylaldehyde respectively to form azo compounds and then condensation by urea to form 4-(R-arylazo 2-salicylaldene)-urea azo-azomethine derivatives (I(a-d)). The complexes of these ligands with Ag(I), Cu(II), Zn(II) and Hg(II) metal ions were prepared. The structure of the free ligands and their complexes were characterized by using elemental analysis (C, H, N), (1)H NMR, IR and UV-Vis-spectra. The proton dissociation constants of the ligands and the stability constant of their complexes have been determined potentiometrically in 40% (v/v) alcohol-water medium as well as the stoichiometry of complexes were determined conductometrically. The data reveal that the stoichiometries for all complexes were prepared in molar ratios (1:1) and (1:2) (M:L). The electrolytic and nonelectrolytic natures of the complexes were assigned based on molar conductance measurements. The thermogravimetric (TG), and differential thermal analyses (DTA) were studied in nitrogen atmosphere with heating rate 10°C/min. The kinetic and thermodynamic parameters for thermal decomposition of complexes have been calculated by graphical method using Coats-Redfern (CR) method.     

Different nuclearity silver(I) complexes with novel tetracyano pendant-armed hexaazamacrocyclic ligands

A new series of different nuclearity silver(I) complexes with a variety of tetracyano pendant-armed hexaazamacrocyclic ligands containing pyridine rings (Ln) has been prepared starting from the nitrate and perchlorate Ag(I) salts in acetonitrile solutions. The ligands and complexes were characterized by microanalysis, conductivity measurements, IR, Raman, electronic absorption and emission spectroscopy, and L-SIMS spectrometry. (1)H NMR titrations were employed to investigate silver complexation by ligands L3 and L.(4) The compounds [Ag2L2(NO3)2] (2), ([Ag2L2](ClO4)2.2CH3CN)(infinity) (4), [AgL3](ClO(4)).CH3CN (5), and [Ag4(L4)2(NO3)2](NO3)2.4CH3CN.2H2O (7) were also characterized by single-crystal X-ray diffraction. The complexes have different nuclearities. Complex 2 is dinuclear with an {AgN3O2} core and a significant intermetallic interaction, whereas complex 4 has a polymeric structure formed by dinuclear distorted {AgN4} units joined by nitrile pendant arms. Compound 5 is mononuclear with a distorted {AgN2} linear geometry, and complex 7 consists of discrete units of a tetranuclear array of silver atoms with {AgN3O} and {AgN4} cores in distorted square planar environments. Complexes 2 and 4 were found to be fluorescent in the solid state at room temperature because of the Ag-Ag interactions.     

Constantes de formation des complexes de l'argent(I) avec differents ligands: Formation constants of silver(I) complexes with various ligands

Formation constants of silver(I) complexes with various ligandsThe various complexes AgL, AgL₂ and Ag₂L and the associated protonated or hydroxo complexes, formed between silver(I) ions and aminopolycarboxylic acids (DTPA, DCTA, EGTA, HEDTA, NTA), glutamic acid, α-alanine, diethylenetriamine and triethylenetetramine are described. Formation constants were calculated from potentiometric measurements with glass and silver electrodes at ionic strength 0.1 and 25°C.     

Investigations on equilibria between Ag(I) and tetraazacyclic amines in dimethylsulfoxide

Summary The formation constants of complexes of Ag(I) with 1,4,8,11-tetraazacyclotetradecane (TACT), 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMTACT), and 1,4,8,12-tetraaza-cyclopentadecane (TACP) as well as equilibrium constants of the disproportionation of Ag(TACT)⁺ and Ag(TACP)⁺ in dimethylsulfoxide have been determined by spectrophotometry and potentiometry. Ag(II) complexes of the same amines have also been characterized by spectrophotometry. The mechanism of the electrode processes of the complexes under investigations has been elucidated by voltammetric and coulometric methods; formal potentials of the redox systems have been determined.

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Untersuchungen der Gleichgewichte zwischen Ag(I) und tetraazacyclischen Aminen in Dimethylsulfoxid

Zusammenfassung Die Bildungskonstanten von Komplexen zwischen Ag(I) und 1,4,8,11-Tetraazacyclotetradecan (TACT), 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecan (TMTACT) und 1,4,8,12-Tetraazacyclopentadecan (TACP) sowie die Gleichgewichtskonstanten der Disproportionierungsreaktion von Ag(TACT)⁺ und Ag(TACP)⁺ wurden in Dimethylsulfoxid spektrophotometrisch und potentiometrisch ermittelt. Ag(II)-Komplexe derselben Amine wurden ebenfalls spektrophotometrisch charakterisiert. Der Mechanismus der Elektrodenprozesse der untersuchten Komplexe wurde mittels voltammetrischer und coulometrischer Methoden aufgeklärt; die formalen Potentiale der Redoxsysteme wurden bestimmt.

     

Aqueous complexation studies of lead(II) and cadmium(II) with 1,3-bis(tris(hydroxymethyl)methylamino)propane pH buffer

Hydrogen buffers are important in biological studies, as a steady hydrogen concentration is of great importance in most scientific studies. One of these buffers is 1,3-bis(tris(hydroxymethyl)methylamino)propane (BTP), which, considering its structure, has complexing capabilities, as previously shown for other metals. In order to know the stability constants for Cd(II) or Pb(II) with BTP, glass electrode potentiometry and direct current polarography studies were carried out. Our results show that both metals form metal complexes, with Pb(II) forming stronger complexes with BTP as evidenced by its higher stability constants. In the Pb-BTP system, five species were described; PbHL, PbL, PbL₂, PbL₂(OH), and PbL₂(OH)₂, and their stability constants were determined to be 11.4 ± 0.3, 4.7 ± 0.3, 8.8 ± 0.2, 14.4 ± 0.3, and 18.4 ± 0.3, respectively. For the Cd-BTP system, four complexes were detected; CdHL, CdL, CdL(OH), and CdL(OH)₂, and their stability constants were also determined as 10.9 ± 0.4, 4.10 ± 0.07, 8.2 ± 0.2, and 10.9 ± 0.2, respectively. These complexes decrease considerably the amount of free metal in solution within the buffering pH range. This fact should be considered when planning experiments were BTP and Pb(II) and/or Cd(II) ions are present.