Polarographic study of mixed ligand complexes of Pb(II) with carboxylate ions and imidazole

Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart^2?), malonate (mal^2?) and citrate (citr^3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO₃) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β₁₁ = 4.19; with mal^2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)₂] and [Pb(mal)₂(im)]^2? with stability constants log β₁₁ = 4.3, log β₁₂ = 7.3 and log β₂₁ = 5.5 respectively are formed. With citr^3? and im a single mixed species, [Pb(citr)(im)]^? with stability constant log β₁₁ = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed.     

Differential Pulse Voltammetric Study of Complexes of Rare Earth Ion(Eu3+) with Glutarate and 1,2-Diminopropane

Abstract

The mixed complexes of Eu (III) with glutarate (Gluta) and 1,2-diaminopropane (DMPA) have been studied at 25°C, μ=0.12(NaClO₄) by differential pulse voltammetry(DPV). The reduction process in each case appears to be quasi-reversible and diffusion-controlled. The stability constants have been measured by Schaap and McMasters′ method. The stability constants of three mixed complexes formed are logβ₁₁=7. 414 for [Eu(Gluta) (DMPA)]⁺, logβ₂₁ = 8. 506 for [Eu(Gluta)₂ (DMPA)]^? and logβ₁₂ = 9. 984 for [Eu(Gluta) (DMPA)₂]⁺.     

Bacterial activity of cobalt(III) complexes. Part IV: Diethylenetriaminemonoacetatocobalt(III) complexes

Summary The activities of the diethylenetriaminemonoacetatocobalt(III) complexes, [Co(en)(DTMA)]I₂, [CoX₂(DTMA)] and [CoCO₃(DTMA)]·H₂O (DTMA=diethylenetriaminemonoacetato or formally 3-amino-3, 6-diazaoctanato; en=ethylenediamine, X=Cl^–, NO ₂ ^– , NCS^–) were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases. Activities decrease in the order: [Co(NCS)₂(DTMA)]> [Co(NO₂)₂(DTMA)]>[Co(en)(DTMA)]I₂>[CoCl₂(DTMA)] >[CoCO₃(DTMA)]·H₂O. The antagonistic activities of the complexes were also studied.     

Hydrolyse und Halogenidaustausch von Pentahalogenomonocarbonylosmaten(III)

Hydrolysis and Halide Exchange of Pentahalogenomonocarbonyl Osmates(III) The aquo complexes [OsX₄(CO)(H₂O)]^?, [OsX₃(CO)(H₂O)] and [OsX₂(CO)(H₂O)₃]⁺, X ? Cl, Br, I, produced by the stepwise hydrolysis of [OsX₅(CO)]^2?, are isolated as pure solutions by ionophoresis and characterized by their absorption spectra. Due to stability of the monaquo complexes and the different trans-effect of the halides it is possible to prepare the mixed complexes [OsX_4–nY_n(CO)(H₂O)]^?, X ≠ Y = Cl, Br, I, n = 1–3, and for n = 2 the pure stereoisomers are formed. A systematic shift is found in charge-transfer bands to the shorter wavelengths when the halides are replaced by H₂O, I by Br or Cl and Br by Cl.     

Study of Equilibria in the Aluminium(III)-Glycine and -Alanine Systems

The formation of various hydrolytic and mixed hydrolytic complexes of the aluminium(III) ion in the presence of glycine and L-alanine, has been studied in 0.5 mol dm^?3 (Na)NO₃ medium at 25deg;C, by emf method. The concentration ratios of amine acids to aluminium(III) were varied from 1 : 1 to 10 : 1. The least-squares treatment of the data obtained, in the absence of the amino acids, indicates the formation of the dimer, [Al₂(OH)₂]⁴⁺, and monomer, [AlOH]²⁺, with the stability constants log β₂₂ = ?7.03 ± 0.03 and log β₁₁ = ?5.65 ± 0.09, respectively. At pH values higher then ～4.0 formation of the trimer [Al₃(OH)₄]⁵⁺ (log β₃₄ = ?12.60 ± 0.08) becomes significant. In the presence of amino acids the evidence has been found for the formation of [Al₂(OH)₄]²⁺ (log β₂₄ = ?15.65 ± 0.09). Besides the formation of the pure hydrolytic complexes, equilibria in the title systems can be explained by assuming the main reaction products to have the compositions [Al(OH)₃Gly] (log β₁₃₁ = ?7.53 ± 0.04), [Al₂(OH)₂(Gly)₂] (log β₂₂₂ = 6.56 ± 0.09) and [Al(OH)₃Ala] (log β₁₃₁ = ?7.70 ± 0.03), [Al₂(OH)₂Ala₂] (log β₂₂₂ = 7.23 ± 0.07).     

A study of mixed ligand complexes using differential pulse polarography

Differential pulse polarography was used to study the mixed ligand complexes of trimethylenediamine (TMDA) and oxalate (OX) with Cd(II) at constant ionic strength (μ = 1, NaNO₃) at 25°C. It has been found that the reduction of complexes is reversible and diffusion-controlled. Three mixed complexes, [Cd(TMDA)(OX)], [Cd(TMDA)(OX)₂]^2? and [Cd(TMDA)₂(OX)], are formed. Their overall stability constants are: log β₁₁ = 6.78, log β₁₂ = 7.53 and log β₂₁ = 8.20, respectively.     

Iron(III)‐Complexes Engaged in the Biochemical Processes in Seawater. II. Voltammetry of Fe(III)‐Malate Complexes in Model Aqueous Solution

Characteristics of iron(III) complexes with malic acid in 0.55 mol L^?1 NaCl were investigated by voltammetric techniques. Three iron(III)‐malate redox processes were detected in the pH range from 4.5 to 11: first one at ?0.11 V, second at ?0.35 V and third at ?0.60 V. First process was reversible, so stability constants of iron(III) and iron(II) complexes were calculated: log K₁(Fe^III(mal))=12.66±0.33, log β₂(Fe^III(mal)₂)=15.21±0.25, log K₁(Fe^II(mal))=2.25±0.36, and log β₂(Fe^II(mal)₂)=3.18±0.32. In the case of second and third reduction process, conditional cumulative stability constants of the involved complexes were determined using the competition method: log β(Fe(mal)₂(OH)_x)=15.28±0.10 and log β(Fe(mal)₂(OH)_y)=27.20±0.09.     

Kinetics and mechanism for the aquation of bismalonatoethylenediaminecobaltate(III) ion in acid perchlorate media

Summary The title complex aquates in acid media, first to [Co(mal)-(H₂O)₂(en)]⁺ (1) (Step 1) and subsequently to [Co(H₂O)₄(en)]³⁺ (2) (Step 2). Complex species (1) has been separated and characterised in solution. While Step 1 involves only a second-order acid catalysed path, Step 2 involves both a first-order acid independent path and a second-order acid catalysed path. The rate constants and activation parameters evaluated for these reaction paths have been compared with those for similar carboxylato-cobalt(III) complexes. This, together with an observed isokinetic relation, indicates that the rate-determining step involves opening of the unprotonated (in the spontaneous acid independent path) or the protonated (for the acid catalysed path) chelate ring of the malonate ligand and insignificant solvation of the central metal ion.     

Synthesis and photoluminescence of the solid phases of the binary system of mixed-ligand Eu(III) and Tb(III) dithiophosphinate complexes

Solid phases of the [Eu(Phen)(i-Bu₂PS₂)₂(NO₃)]–[Tb(Phen)(i-Bu₂PS₂)₂(NO₃)] binary system are synthesized. The results of X-ray diffraction phase analysis and photoluminescence measurements allow the synthesized isostructural phases to be classed with substitutional solid solutions. The photoluminescence measurements revealed Tb(III)→Eu(III) energy transfer which induces Eu³⁺ luminescence.     

La(III) and Eu(III) 2-D coordination polymers of 5-nitroisophthalic acid (H2Nip) and 1,10-phenanthroline (phen), [M(phen)(HNip)(Nip)] n

Lanthanum(III) and europium(III) complexes of 1,10-phenanthroline (phen) with 5-nitroisophthalate, [La(phen)(HNip)(Nip)] _n (1) and [Eu(phen)(HNip)(Nip)] _n (2), have been synthesized and characterized by elemental analysis and IR spectroscopy and studied by X-ray crystallography. The single crystal X-ray analyses show that both lanthanum(III) and europium(III) are coordinated by two nitrogens of phen and six oxygens from “Nip^2?” and “HNip^?”, resulting in a distorted square antiprism.     

Potential inhibitors of DNA topoisomerase II: ruthenium(II) poly-pyridyl and pyridyl-azine complexes

In search of new DNA probes a series of new mono and binuclear cationic complexes [RuH(CO)(PPh₃)₂(L)]⁺ and [RuH(CO)(PPh₃)₂(-μ-L)RuH(CO)(PPh₃)₂]²⁺ [L=pyridine-2-carbaldehyde azine (paa), p-phenylene-bis(picoline)aldimine (pbp) and p-biphenylene-bis(picoline)aldimine (bbp)] have been synthesized. The reaction products were characterized by microanalyses, spectral (IR, UV-Vis, NMR and ESMS and FAB-MS) and electrochemical studies. Structure of the representative mononuclear complex [RuH(CO)(PPh₃)₂(paa)]BF₄ was crystallographically determined. The crystal packing in the complex [RuH(CO)(PPh₃)₂(paa)]BF₄ is stabilized by intermolecular π-π stacking resulting into a spiral network. Topoisomerase II inhibitory activity of the complexes and a few other related complexes [RuH(CO)(PPh₃)₂(L)]⁺ {L=2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and 2,3-bis(2-pyridyl)-pyrazine (bppz)} have been examined against filarial parasite Setaria cervi. Absorption titration experiments provided good support for DNA interaction and binding constants have also been calculated which were found in the range 1.2 × 10³-4.01 × 10⁴ M⁻¹.     

Interaction Between the Low Molecular Mass Components of Blood Serum and the Vanadium(III)–2,2′-Bipyridine System

The complex species formed between vanadium(III)?C2,2??-bipyridine (Bipy) and the small blood serum bioligands lactic (HLac), oxalic (H₂Ox), citric (H₃Cit) and phosphoric (H₃PO₄) acids were studied in aqueous solution by means of electromotive forces measurements emf(H) at 25?°C and 3.0?mol?dm^?3 KCl as the ionic medium. The data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic products of vanadium(III) and the binary complexes formed. Formation of the complexes [V(Bipy)(Lac)]²⁺, [V(Bipy)(Lac)₂]⁺, [V(OH)₂(Bipy)(Lac)] and [V₂O(Bipy)₂(Lac)₂]^? were observed in the vanadium(III)?CBipy?CHLac system. Also, the species [V(Bipy)(HOx)]²⁺, [V(Bipy)(Ox)]⁺, [V(OH)(Bipy)(Ox)], [V(OH)₂(Bipy)(Ox)]^? and [V(OH)₃(Bipy)(Ox)]^2? were found in the vanadium(III)?CBipy?CH₂Ox system, the complexes [V(Bipy)(HCit)]⁺, [V(Bipy)(Cit)], [V(OH)(Bipy)(Cit)]^? and [V(OH)₂(Bipy)(Cit)]^2? were found in the vanadium(III)?CBipy?CH₃Cit system, and the species [V(Bipy)(H₂PO₄)]²⁺ and [V(Bipy)(HPO₄)]⁺ were detected in the vanadium(III)?CBipy?CH₃PO₄ system. The stability constants of these complexes were determined.     

Base hydrolysis ofcis-dichlorobis(1,2-diaminoethane),cis-α-dichloro(1,8-diamino-3,6-diazaoctane) andcis-α-chlorohydroxo-(1,8-diamino-3,6-diazaoctane) ruthenium(III) complexes

The kinetics of base hydrolysis ofcis-[RuCl₂(en)₂]⁺ (en=1,2-diaminoethane),cis-α-[RuCl₂(trien)]⁺ andcis-α-[RuCl(OH)(trien)]²⁺ (trien=1,8-diamino-3,6-diazaoctane) have been studied. All the reactions are fast and obey the second-order rate law,-d[complex]/dt=k[OH⁻][complex], with complete retention of configuration. A conjugate base mechanism involving a squarepyramidal intermediate is suggested. The Arrhenius parameters and rate constants found are respectively: ΔH^≠ 14.2±0.5, 7.2±0.1, 10.9±0.1 M cal mol⁻¹; ΔS^≠ 1.3, 29, 22 cal deg⁻¹ mol; log A 13.5, 6.9, 8.6 k_OH 533 (27.2°C) 14.5 (24.4° C) 1.65 (25°C) M⁻¹s⁻¹.     

Inner-sphere oxidation of ternary iminodiacetatochromium(III) complexes involving DL-valine and L-arginine as secondary ligands. Isokinetic relationship for the oxidation of ternary iminodiacetato-chromium(III) complexes by periodate

Background  

In this paper, the kinetics of oxidation of [Cr^III(HIDA)(Val)(H₂O)₂]⁺ and [Cr^III(HIDA)(Arg)(H₂O)₂]⁺ (HIDA = iminodiacetic acid, Val = DL-valine and Arg = L-arginine) were studied. The choice of ternary complexes was attributed to two considerations. Firstly, in order to study the effect of the secondary ligands DL-valine and L-arginine on the stability of binary complex [Cr^III(HIDA)(IDA)(H₂O)] towards oxidation. Secondly, transition metal ternary complexes have received particular focus and have been employed in mapping protein surfaces as probes for biological redox centers and in protein capture for both purification and study.     

Mixed fluoroamine complexes of chromium(III)

Summary Mixed difluoro(diamine)(diamme)chromium(III) complexes have been synthesized with ethylenediamine (en), 1,3 propanediamine(tn) and 1,2-cyclohexanediamine(chxn):trans-[CrF₂(aa)(bb)]Br (aa=en, bb=tn; aa=tn, bb= chxn) andcis-[CrF₂(aa)(bb)]Br (aa=en, bb=chxn). The corresponding fluoroaqua(diamine) (diamine)chromium(III) complexes have been prepared by acid hydrolysis as perchlorate or iodide salts. All have been characterized by chemical analysis, electronic and i.r. spectra and conductivity measurements.     

Studies on the bacterial activity of cobalt(III) complexes. Part II. Cobalt(III) aminoacidato-complexes

Summary Cobalt(III) complexes of the typetrans-[Co(AA)₂(ox)] (where AA = aminoacidato, gly = glycinato, sar = sarcosinato, DL-ala = DL-alaninato, L-ala = L-alaninato; ox = oxalate); [Co(L-val)₂CO₃] and DL-[Co(en)₂sar]I₂ where L-val = L-valinato, en = ethylenediamine) have been investigated for their bacterial activity againstEscherichia coli B using well-cultured techniques on EMB agar and in minimal glucose media. The activities decrease in the order:trans-(N)(+)K[Co(sar)₂(ox)] >trans-(N)(+)K[Co(L-ala)₂(ox)] >trans-(N)(–)K[Co (gly)₂(ox)] >trans-(N)(+)K[Co(DL-ala)₂(ox)] >trans-(N)(+)K[Co(gly)₂(ox)] >trans(+)K[Co(DL-ala)₂(ox)] >trans-K[Co(L-val)₂CO₃].     

The Eu(III) Ion as Luminescent Probe: Investigation of the Metal-Ion Sites in a Dicyclohexyl-18-crown-6 Complex

The metal ion sites of the 3:2 complex between europium nitrate and the A -isomer of dicyclohexyl-18-crown-6, [Eu(NO₃)₂(DC18C6)]₂[Eu(NO₃)₅], have been probed by high-resolution excitation and emission spectra at 296 and 77 K. The [Eu(NO₃)₅]^2? anion gives rise to a luminescent spectrum dominated by the ⁵D₀→⁷F₂ transition. The crystal-field splitting of the ⁷F_j levels is close to that observed for (Phe₄As)₂[Eu(NO₃)₅], pointing to a structurally similar pentakis(nitrato) species. The ⁵D₀←⁷F₀ excitation spectrum of the two crystallographically independent complex cations displays five maxima. A detailed analysis of the corresponding and selectively excited emission spectra leads to the following conclusions. Well differentiated spectra are assigned to different conformations of the complex cation, in which half of the ligand atoms, including O-atoms, Present large thermal motions. The other spectra are very similar and arise from slightly unequivalent [Eu(NO₃)₂(DC18C6)]⁺ moieties differing in the conformation of their ethylene bridges. This dimonstrates the sensitivity of the Eu(III) ion as conformational probe in the solid state.     

Theoretical studies on the structure and protonation of Cu(II) complexes of a series of tripodal aliphatic tetraamines: Good correlations with the experimental data

DFT(B3LYP) studies on first protonation step of a series of Cu(II) complexes of some tripodal tetraamines with general formula N[(CH₂)_nNH₂][(CH₂)_mNH₂][(CH₂)_pNH₂] (n = m = p = 2, tren; n = 3, m = p = 2, pee; n = m = 3, p = 2, ppe; n = m = 3, tpt; n = 2, m = 3, p = 4, epb; and n = m = 3, p = 4; ppb) are reported. First, the gas‐phase proton macroaffinity of all latter complexes was calculated with considering following simple reaction: [Cu(L)]²⁺(g) + H⁺(g) → [Cu(HL)]³⁺(g). The results showed that there is a good correlation between the calculated proton macroaffinities of all complexes with their stability constants in solution. Then, we tried to determine the possible reliable structures for microspecies involved in protonation process of above complexes. The results showed that, similar to the solid state, the [Cu(L)(H₂O)]²⁺ and [Cu(HL)(H₂O)₂]³⁺ are most stable species for latter complexes and their protonated form, respectively, at gas phase. We found that there are acceptable correlations between the formation constants of above complexes with both the ? and ? of following reaction: [Cu(L)(H₂O)]²⁺(g) + H⁺(g) + H₂O(g) → [Cu(HL)(H₂O)₂]³⁺(g). The ? of the latter reaction can be defined as a theoretically solvent–proton macroaffinity of reactant complexes because they have gained one proton and one molecule of the solvent. The unknown formation constant of [Cu(epb)]²⁺ complex was also predicted from the observed correlations. In addition, the first proton affinity of all complexes was studied in solution using DPCM and CPCM methods. It was shown that there is an acceptable correlation between the solvent–proton affinities of [Cu(L)(H₂O)]²⁺ complexes with formation constants of [Cu(HL)(H₂O)₂]³⁺ complexes in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Axial Ligand and Spin‐State Influence on the Formation and Reactivity of Hydroperoxo–Iron(III) Porphyrin Complexes

The present study focuses on the formation and reactivity of hydroperoxo–iron(III) porphyrin complexes formed in the [Fe^III(tpfpp)X]/H₂O₂/HOO^? system (TPFPP=5,10,15,20‐tetrakis(pentafluorophenyl)‐21H,23H‐porphyrin; X=Cl^? or CF₃SO₃^?) in acetonitrile under basic conditions at ?15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high‐spin [Fe^III(tpfpp)(OOH)] and low‐spin [Fe^III(tpfpp)(OH)(OOH)] could be observed with the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O? O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo‐ to heterolytic O? O bond cleavage is observed for high‐ [Fe^III(tpfpp)(OOH)] and low‐spin [Fe^III(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron‐rich porphyrin ligands, electron‐deficient [Fe^III(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe^III(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)–oxo porphyrin π‐cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.     

Complex Formation of PdII Ion with the Tripodal Ligand Tris[2-(dimethylamino)ethyl]amine

The complex formation of Pd^II with tris[2-(dimethylamino)ethyl]amine (N(CH₂CH₂N(CH₃)₂)₃, Me₆tren) was investigated at 25° and ionic strength I = 1, using UV/VIS, potentiometric, and NMR measurements. Chloride, bromide, and thiocyanate were used as auxiliary ligands. The stability constant of [Pd(Me₆tren)]²⁺ in various ionic media was obtained: log β([Pd(Me₆tren)] = 30.5 (I = 1(NaCl)) and 30.8 (I = 1(NaBr)), as well as the formation constants of the mixed complexes [Pd(HMe₆tren)X]²⁺ from [Pd(HMe₆tren)(H₂O)]³⁺:log K = 3.50 = Cl^?) and 3.64 (X^? = Br^?) and [Pd(Me₆tren)X]⁺ from [Pd(Me₆tren)(H₂O)]²⁺: log K = 2.6 (X^? = Cl^?), 2.8(Br^?) and 5.57 (SCN^?) at I = 1 (NaClO₃). The above data, as well as the NMR measurements do not provide any evidence for the penta-coordination of Pd^II, proposed in some papers.