Formation Of Mono Complexes Research Articles

Solution Equilibrium Studies on Salicylidene Aminoguanidine Schiff Base Metal Complexes: Impact of the Hybridization with L-Proline on Stability, Redox Activity and Cytotoxicity.

The proton dissociation processes of two tridentate salicylidene aminoguanidine Schiff bases (SISC, Pro-SISC-Me), the solution stability and electrochemical properties of their Cu(II), Fe(II) and Fe(III) complexes were characterized using pH-potentiometry, cyclic voltammetry and UV-visible, 1H NMR and electron paramagnetic resonance spectroscopic methods. The structure of the proline derivative (Pro-SISC-Me) was determined by X-ray crystallography. The conjugation of L-proline to the simplest salicylidene aminoguanidine Schiff base (SISC) increased the water solubility due to its zwitterionic structure in a wide pH range. The formation of mono complexes with both ligands was found in the case of Cu(II) and Fe(II), while bis complexes were also formed with Fe(III). In the complexes these tridentate ligands coordinate via the phenolato O, azomethine N and the amidine N, except the complex [Fe(III)L2]+ of Pro-SISC-Me in which the (O,N) donor atoms of the proline moiety are coordinated beside the phenolato O, confirmed by single crystal X-ray crystallographic analysis. This binding mode yielded a stronger Fe(III) preference for Pro-SISC-Me over Fe(II) in comparison to SISC. This finding is also reflected in the lower redox potential value of the iron-Pro-SISC-Me complexes. The ligands alone were not cytotoxic against human colon cancer cell lines, while complexation of SISC with Cu(II) resulted in moderate activity, unlike the case of its more hydrophilic counterpart.

Comparative equilibrium and structural studies of new pentamethylcyclopentadienyl rhodium complexes bearing (O,N) donor bidentate ligands

Complex formation processes of the (O,N) donor ligands 6-methylpicolinic acid (6-Mepic), quinoline-2-carboxylic acid (2-QA) and 3-isoquinolinecarboxylic acid (3-iQA) with the organometallic moiety (η5-pentamethylcyclopentadienyl)rhodium(III) (RhCp*) were studied in aqueous solution by the combined use of pH-potentiometry, 1H NMR spectroscopy and UV-Vis spectrophotometry. The solid phase structures of the [RhCp*(L)Cl] complexes bearing 6-Mepic and 2-QA were characterized by single-crystal X-ray diffraction analysis. Studies revealed the exclusive formation of mono complexes of the form [RhCp*(L)(H2O)]+ (L = deprotonated form of the ligands) and [RhCp*(L)(OH)]. The positively charged aqua species predominate at physiological pH even in the micromolar concentration range. The H2O/Cl− co-ligand exchange constants showed that all complexes preferably retain the chlorido ligand at the third coordination site at chloride ion concentrations present in the serum. In addition in vitro cytotoxicity of these [RhCp*(L)Cl] complexes was evaluated in three human cancer cell lines (A549, SW480 and CH1/PA-1) where they showed minor cytotoxic potency.

On the Initial Binding of Alginate by Calcium Ions. The Tilted Egg-Box Hypothesis

The initial binding of calcium ions by alginate chains was investigated in dilute solution. The use of viscometry, light scattering, circular dichroism, and fluorescence quenching performed on both Ca(2+) and Mg(2+) alginate systems allowed collecting new experimental data in addition to those already reported in the literature. This led us to propose an ion multicomplex binding modality and to disprove the Ca(2+)-alginate monocomplex formation. The first mode of bonding was proposed to be formed by four G residues from facing chains in a conformation which, albeit ordered, is different from the well-known "egg box" one. This was indicated as a locally tilted conformation (tilted egg-box). The addition of further bonding ions caused the well-known cooperative egg-box conformation (strong bonding) with notable variation in the physical-chemical properties of the dilute solution.

NMR study of cadmium(II)–triflate coordination

The coordination of cadmium(II) in triflic acid media is evaluated from the NMR chemical shift variation with concentration of Cd(tf) 2 in aqueous media. The cadmium triflate salt concentration dependence is explainable by the formation of a bis-triflate coordination compound having an overall formation constant of (4±0.5)×10 −3. The chemical shift for Cd(tf) 2 is found to be −180 ppm from that of the aqueous Cd(II) ion. The data analysis is consistent with either no mono complex formation or a chemical shift for the mono complex that is equal to that of the aqueous ion. Divergence of the experimental chemical shift from the predicted behavior for a simple bis complex equilibrium upon addition of a large excess of triflic acid to a dilute cadmium solution, indicates either the formation of higher complexes or increases in the formation constant for the bis species caused by decreases in the solvent dielectric constant.

Reaction between [Ru(H2O)6]2+ and DMF: A Complete Volume Profile of a Monocomplex Formation Reaction on a d6 Low Spin Aquaion

The reaction between [Ru(H 2 O) 6 ] 2+ and dimethylformamide (DMF) was studied as a function of the temperature and the pressure at pH 1. When a slight excess of Ru aquaion is used, [Ru(H 2 O) 5 DMF] 2+ is the only product of the reaction observed in the NMR spectra and the DMF is bound through the oxygen atom. From variable temperature experiments, the rate constants, activation enthalpies and entropies for the formation and the dissociation of the monocomplex were determined. These are as follows: 10 4 x k f 298 =(8.2 ± 0.4) kg mol -1 s -1 ΔΗ ☨ f = 83.6 ± 3 k J mol -1 Δ S ☨ f = -23.7 ± 10 J K -1 mol -1 for the formation reaction, 10 3 x k d 298 = (1.10 ± 0.04) s -1 ΔΗ ☨ f = 90.2 ± 2 kJ mol -1 ΔS ☨ f , = +1.0 ± 7 J Κ -1 mol -1 for the dissociation reaction. The thermodynamic parameters (equilibrium constant at 298.15 K, reaction enthalpy and entropy) were also determined:K 298 eq = 0.74 ± 0.02 kg mol -1 , ΔH 0 = -6.6 ± 2 k j mol -1 , ΔS 0 =-24.7 ± 6 JK -1 . The k f value is similar to the previously reported rate constants for monocomplex formation reactions with other ligands and confirms that the entering ligand has no effect on the rate. From variable pressure experiments, the activation volumes for the formation and the dissociation reactions and the reaction volume were determined: ΔV f ☨ = +2.7 ± 0.6 cm3 mol -1 , ΔV d ☨ = 0.9 ± 0.7 cm 3 mol -1 , ΔV° = +3.6 ± 0 . 9 cm3 mol -1 respectively. These results show that the volume of the transition state is intermediate between the volume of the reactants and the volume of the products. It demonstrates that the mechanism is the same as for the water exchange on [Ru(H 2 O) 6 ] 2+ , i.e. an Id mechanism. Contraction of the bonds between Ru and the spectator ligands at the transition state may explain the abnormally small activation volumes. The need of theoretical calculations on these systems is emphasized.

Monocomplex formation and dissociation of some first row divalent transition metal ions with 2-chloro-1,10-phenanthroline by the high-pressure stopped-flow technique

The kinetics of the monocomplex formation and dissociation of [Co(Cl-phen)] 2+ and [Ni(Cl-phen)] 2+ (Cl-phen=2-chloro-1,10-phenanthroline) in aqueous solution have been studied as a function of temperature, pressure and excess metal ion. The dissociation of these complexes was followed by adding Cu 2+ to a solution of the complex [Co(Cl-phen)] 2+ or [Ni(Cl-phen)] 2+. The rate constants, activation enthalpies, entropies and volumes, and the corresponding thermodynamic parameters obtained for [Co(Cl-phen)] 2+ (and for [Ni(Cl-phen)] 2+) are as follows: k 298 f (M −1 s −1)=5.7x10 4 (1.3x10 3); k 298 r (s −1)=7.1 (0.025); Δ H ‡ f (kJ mol −1)=47.1 (53.5); Δ H ‡ f (kJ mol −1)=59.2 (80.7); Δ S ‡ f (J K −1 mol −1)=+4 (−6); Δ S ‡ f (J K −1 mol −1)=−30 (−5); Δ V ‡ f (cm 3 mol −1)=+6.6 (+6.0); Δ V ‡ r (cm 3 mol −1)=+0.2 (+2.1); log K 298 (M −1)=3.91 (4.71); Δ H o (kJ mol −1)=−12.1 (−27.2); Δ S o (J K −1 mol 1)=+34 (−1); Δ V o (cm 3 mol −1)=+6.4 (+3.9). It is concluded that the complex formation reactions on both metal ions take place via dissociative interchange I d mechanisms.

Kinetics and mechanisms of the reactions of chromium(III) and heptane-3,5-dione in aqueous solution

The equilibra and kinetics of mono-complex formation of chromium(III) with heptane-3,5-dione have been investigated spectrophotometrically in aqueous solution at 50 °C and 0.5 mol dm–3 NaClO4. The mechanism proposed to account for the kinetic data involves pathways in which both Cr3+ and Cr(OH)2+ react with the enol tautomer of the ligand with rate constants of 6.60 × 10–2 dm3 mol–1 s–1 and 1.42 dm3 mol–1 s–1, respectively. By comparing rate laws derived on the basis of the theory of coupled sets of first-order reactions with rate laws derived using the steady-state approximation, a useful confirmation of the validity of this mechanism has been provided. The assumptions made in the steady-state approach that the keto–enol equilibrium is maintained and that the protolytic reactions are rapid compared with complex formation are valid.

Spectrophotometric Study of the Formation and Protolytic Equilibria for Iron(II) Complexes of Di-2-pyridylmethanone 2-Pyridyl-hydrazone and Di-2-pyridylmethanone 2-Quinolylhydrazone

The stoichiometrics, stability constants and deprotonation constants of the complexes formed between iron(II) and either of two heterocyclic hydrazones, di-2-pyridylmethanone 2-pyridylhydrazone (DPPH) or di-2-pyridylmethanone 2-quinolylhydrazone (DPQH), have been determined spectrophotometrically at 25° C and μ=0.2. Iron(II) reacts with DPPH and DPQH in acidic media to form a dipositively charged bis complex, Fe(HL)22+, which undergoes successive deprotonation to monocationic (Fe(HL)L*) and neutral bis (FeL2) complexes, along with a decrease in the solution acidity. The acid-strengthening effect of coordinated metal on the imino group of the ligand is briefly discussed. There was no evidence for the formation of mono complexes. The logarithmic stability constants of the neutral complexes, FeL2, were 36.8 and 33.0 for the DPPH and DPQH complexes, respectively.

Interfacial Phenomena in Ion-Association Extraction Kinetics of Iron(II) with 1,10-Phenanthrolines

Abstract The role of the interface in ion-association extraction kinetics of iron(II) with 1,10-phenanthroline(phen), 4,7-dimethyl-1,10-phenanthroline(DMP) or 4,7-diphenyl-1,10-phenanthroline(DPP) from sodium salt solutions was investigated by means of a high-speed stirring technique and a stopped-flow method. The initial extraction rates of the ion pairs were proportional to the first order of both iron(II) and the ligand concentrations in all cases studied; it was therefore suggested that the rate-controlling step is the formation of mono-complexes. From analyses using the adsorption constants and the distribution constants of the ligands and the formation-rate constants of the mono-complexes in the aqueous phase it was concluded that the location where the rate-controlling reaction takes place depends on the ligands: a bulk aqueous phase in phen, an interface in DPP, and both of a bulk aqueous phase and an interface in the case of DMP. The extraction rates were apparently reduced by an interfacial adsorption of the ion pairs, which was governed by the hydrophobicity of the ligands and the hydrophilicity of the counter anions.

Variable-pressure kinetic and equilibrium study of monocomplex formation of copper(II) and zinc(II) with 2-chloro-1,10-phenanthroline in aqueous solution

The kinetics of formation and dissociation of Cu(Cl-phen) 2+ and of dissociation of Zn(Cl-phen) 2+ (Cl-phen=2-chloro-1,10-phenanthroline) have been studied in aqueous solution as a function of excess metal ion, temperature, and pressure

Use of aqueous DMSO in resolving ‘proton ambiguity’ in the formation of monocomplexes of iron(III)

The formation of FeL2+ (L−=N 3 − , SCN−) in H2O-dimethylsulphoxide (DMSO) mixtures was studied by equilibrium, stopped flow and temperature jump observations. The acid dissociation constants associated with LH and Fe(H2O) 6 3+ and the formation constants associated with FeL2+ were determined at various solvent compositions. In kinetic studies, the solvent composition dependence of the overall equilibration rate was explained in terms of equations predicted by a reaction scheme which includes DMSO coordinated species. Analysis of results on the basis of these equations identified Fe·OH2+·HN3 and Fe3+·SCN− as the dominant transition states contributing to pH-independent paths of formation of FeL2+ in the cases of N 3 − and SCN− respectively. Thus, the results which support the Eigen-Tamm-Wilkins mechanism have resolved the mechanistic ambiguity in the pH-independent paths of formation of FeL2+. It is also shown that we cannot neglect species such as FeOH·HN 3 2+ , Fe·OH·N 3 + and Fe·HN 3 3+ while accounting for the kinetic behaviour.

Reactions of metal ions with triketones. Part 2. Kinetics and mechanisms of the reactions of nickel(II) and cobalt(II) with heptane-2,4,6-trione in methanol-water (70: 30 v/v)

The kinetics and mechanisms of the reactions of nickel(II) and cobalt(II) with heptane-2,4,6-trione (H2hpto) to form the 1 : 1 and 2: 2 complexes have been studied in methanol–water (70:30 v/v) at 25 °C and an ionic strength of 0.5 mol dm–3(NaClO4). The rate constants of the mono complex formation with H2hpto (kHL) and with Hhpto–(kL) have been determined. For Ni2+, kHL= 180, kL= 4.88 × 104 dm3 mol–1 s–1, while for Co2+kHL= 476, and kL= 1.36 × 106 dm3 mol–1 s–1. The conversion of the 1 : 1 to the 2:2 complex takes place via a two-stage mechanism. The rate constants for Ni2+ are 6.1 and 0.21 s–1 while for Co2+ they are 24.6 and 0.026 s–1.

Kinetics and mechanism of iron(II), cobalt(II), and nickel(II) mono complex formation with acetohydroxamic acid

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics and mechanism of iron(II), cobalt(II), and nickel(II) mono complex formation with acetohydroxamic acidLawrence A. Dominey and Kenneth KustinCite this: Inorg. Chem. 1984, 23, 1, 103–108Publication Date (Print):January 1, 1984Publication History Published online1 May 2002Published inissue 1 January 1984https://doi.org/10.1021/ic00169a022RIGHTS & PERMISSIONSArticle Views129Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (656 KB) Get e-Alerts Get e-Alerts

Mono-complex Formation Kinetics of 2-Thenoyltrifluoroacetone with Nickel(II) and Copper(II) Ions in Aqueous Solution

Abstract The mono-complex formation of 2-thenoyltrifluoroacetone (HTTA) with nickel(II) and copper(II) ions was studied in aqueous solution at 25.0 °C and an ionic strength of 0.20 mol dm−3 by means of a stopped-flow method. The rate-[H+] profiles for the formation of these mono-complexes revealed that the rate-determining step of the complex formation interchanges depending upon hydrogen-ion concentration, as in the case of the Ni(II)–bpy complex. The rate constants of the mono-complex formation with TTA−, kf, and that with HTTA, kfh, were determined from the rate-[H+] profile in the region of the high hydrogen-ion concentration, where the pseudo-equilibrium of acid dissociation of the ligand was maintained during the complex formation; kf=(9.2±3.0)×102, kfh=(1.3±0.3)×10−1 mol−1 dm3 s−1 for the Ni(II)–TTA complex and kf=(2.0±1.2)×103, kfh=(5.0±0.9)×10−1 mol−1 dm3 s−1 for the Cu(II)–TTA complex. The deprotonation-rate constants of HTTA could be evaluated from the apparent rate constants of the complex formation in low hydrogen-ion concentration. The values thus obtained agreed well with that determined independently by a pH jump method.

Effect of Protolytic Behavior of Ligands on Formation Rates of Mono-complexes of Nickel(II) Ion with 2,2′-Bipyridine and 1,10-Phenanthroline in Aqueous Solution

Abstract The mono-complex formation of nickel(II) ion with 2,2′-bipyridine(bpy) and 1,10-phenanthroline (phen) was studied in aqueous solution by means of a stopped-flow method. The apparent complex formation rates of the Ni(II)–bpy and Ni(II)–phen complexes depended on the pH of the solution. The rate constants of the mono-complex formation with the ligand in the free base form, kf, and that with the monoprotonated ligand, kfh, were evaluated from the rate-[H+] profiles in the region of high hydrogen ion concentration where the pseudo-equilibrium of acid dissociation of the ligands was attained during the complex formation. The rate constants determined for the Ni(II)–phen were kf=(2.6±0.3)×103 mol−1 dm3 s−1 and kfh=2.4±0.3 mol−1 dm3 s−1, which are practically the same as those reported elsewhere. On the other hand, the rate constants for the Ni(II)–bpy were kf=(5.3±1.2)×103 mol−1 dm3 s−1 and kfh=5.0±2.6 mol−1 dm3 s−1, which are quite different from the values reported by other researchers. The validity of the present data was discussed in terms of slow proton-transfer reactions of the ligands.

Multi-step kinetics of aquo aluminum(III)-ferron (8-hydroxy-7-iodo-5-quinoline) complexation reactions

The interaction of excess hydrolyzed aluminum(III) cation in mildly acid aqueous media with ferron (7-iodo-8-hydroxyquinoline-5-sulfonic acid) has been studied unsing stopped-flow. Three distict transients are observed. The shortest-lived, which is largest in amplitude, has been assigned to mono-complex formation. The other two transients, which are much smaller in amplitude, are interpreted as reactions of dimeric and other polymeric aluminum(III) species. The hydrogen ion dependences of the observed rate constants for mono-complex formation indicate participation of Al(OH) + 2 in the dominant pathway. Analysis of these results, using the Eigen model of complexation, leads to a water exchange rate constant of(4.0 ± 0.4) × 10 7 sec −1 for Al(OH) − 2. The slower transients could not be adequately explained by formation of bis and tris-complexes. Assignment of these transients to reactions of μ-hydroxy-bridged aluminum dimer with ferron, coupled to mono-complex formation leads to an adequate data fit. The polyphasic nature of the aluminum-ferron interaction over the pH range 2–5 can be understood as showing different groups of reactions, rahter than differently reacting metal-containing species.

Kinetics of Ni(II) and Co(II) monocomplex formation with O-phospho- dl-serine

The complexation reactions of O-phospho-DL-serine with Ni(II) or Co(II) were studied at 25°C and ionic strength 0.2 M (KNO 3) by temperature-jump. The observed rate constants for formation of the Ni 2+ and Co +2 monocomplexes were (1.32 ± 0.09) × 10 5 and (1.73 ± 0.33) × 10 7 M −1 sec −1, respectively. Complexation is postulated to involve formation of a monocoordinated steady state intermediate followed by rate-determining chelate ring closure.

ChemInform Abstract: RATES AND ACTIVATION PARAMETERS FOR THE STEPWISE FORMATION OF MONO COMPLEXES OF THE HEXAKIS(DIMETHYL SULFOXIDE)ALUMINUM(III) ION WITH UNI‐, BI‐, AND TER‐DENTATE NITROGEN‐DONOR LIGANDS IN NITROMETHANE SOLUTION

Chemischer InformationsdienstVolume 10, Issue 9 Organoelement Compounds ChemInform Abstract: RATES AND ACTIVATION PARAMETERS FOR THE STEPWISE FORMATION OF MONO COMPLEXES OF THE HEXAKIS(DIMETHYL SULFOXIDE)ALUMINUM(III) ION WITH UNI-, BI-, AND TER-DENTATE NITROGEN-DONOR LIGANDS IN NITROMETHANE SOLUTION A. J. BROWN, A. J. BROWNSearch for more papers by this authorO. W. HOWARTH, O. W. HOWARTHSearch for more papers by this authorP. MOORE, P. MOORESearch for more papers by this authorW. J. E. PARR, W. J. E. PARRSearch for more papers by this author A. J. BROWN, A. J. BROWNSearch for more papers by this authorO. W. HOWARTH, O. W. HOWARTHSearch for more papers by this authorP. MOORE, P. MOORESearch for more papers by this authorW. J. E. PARR, W. J. E. PARRSearch for more papers by this author First published: February 27, 1979 https://doi.org/10.1002/chin.197909263Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue9February 27, 1979 RelatedInformation

Rates and activation parameters for the stepwise formation of mono complexes of the hexakis(dimethyl sulphoxide)aluminium(III) ion with uni-, bi-, and ter-dentate nitrogen-donor ligands in nitromethane solution

Rates and activation parameters for the formation of mono complexes of the [Al(dmso)6]3+ ion (dmso = dimethyi suiphoxide) with pyridine, 2,2′-bipyridine (bipy), 2.2′ : 6′,2″-terpyridine (terpy). 1, 10-phenanthroiine (phen), and t-butyiamine have been determined in nitromethane solution by following the release of the co-ordinated dmso molecules using stopped-flow Fourier-transform 1H n.m.r. spectroscopy. Activation parameters for the soivent-exchange process (using [2H6]dmso) are also reported from data covering a wide temperature range (263–338 K). The reactions with bipy and terpy proceed in two and three distinct steps respectively, and activation parameters are reported for the first bond formations and for the subsequent slower cheiate-ring closures. The reaction with pyridine is significantly retarded by the addition of a ten-fold excess of the non-ligating substrate 2,6-dibromo-pyridine, the rate constant decreasing from 167 to 55.6 dm3 mol–1 s–1 This rate retardation is in line with the observation of unusually large outer-sphere associations (K0 in the range 2 × 102–75 × 102 dm3 mol–1) during the first bond formations, the large values of K0 accounting for the unexpectedly rapid rates of these reactions.

ChemInform Abstract: RATES OF FORMATION OF NICKEL(II) CHELATE COMPLEXES WITH BIDENTATE SUBSTITUTED‐PYRIDINE LIGANDS IN DIMETHYL SULPHOXIDE SOLUTION

AbstractDie Geschwindigkeitsdaten und Aktivierungsparameter der Bildung von mono‐ Komplexen des Nickel(II) mit den zweizähnigen Liganden (I) werden mitgeteilt.