Thermodynamics Of Complex Formation Research Articles

Co-ordination properties of dialkyltin(IV) in aqueous solution. Thermodynamics of complex formation with carboxylic acids

The complex formation of [SnMe2]2+ ion with acetate, malonate, and succinate ligands has been investigated by means of potentiometric measurements at 25 °C and I= 0.1 mol dm–3(KNO3). Values of ΔH⊖ and ΔS⊖ have been obtained by means of calorimetric titrations. On the basis of these values, bonding details have been inferred for the major species. The thermodynamic data are also discussed in view of the cis-trans disposition of the alkyl groups.

Thermodynamics of complex formation in chloroform + 1,4-dioxane

We have made new measurements of excess heat capacities and excess volumes of mixtures of chloroform and dioxane. In combination with published vapor pressures and excess enthalpies the results have been analyzed using the ideal associated solution model to yield K, ΔHθ, ΔCpθ, and ΔVθ for the formation of AB and A2B complexes. It is demonstrated that the ideal associated solution model is consistent with all of the available thermodynamic data for this system, indicating that chemical interactions of the two components can account for nearly all of the deviations from ideal solution behavior. The results of our thermodynamic analysis are discussed in relation to the results of similar analyses of other systems in which there are strong chemical interactions of chloroform with electron-donor molecules. Keywords: complex formation, hydrogen bonding, ideal associated solution model, chloroform, 1,4-dioxane.

ChemInform Abstract: Thermodynamics of the Complex Formation in Pyridine Between Gold(I) and Ligands Coordinating via N, P, As or Sb

Abstract The thermodynamics of complex formation between gold(I) and the ligands tricyclohexylphosphine, triphenylamine, -phosphine, -arsine, and -stibine has been determined in pyridine solution by potentiometric and calorimetric measurements. As expected, the very soft gold(I) displays a more marked stability (b)-sequence N ⪡ P > As > Sb than its lighter, and less soft, congener silver(I). Like all complexes of these ligands so far studied, the present ones are strongly enthalpy stabilized while the entropy changes are generally unfavourable. The stepwise entropy changes show quite peculiar differences between the various ligands, however. The thermodynamics of these complexes is in striking contrast to that of the gold(I) halido complexes in pyridine which are strongly entropy stabilized, while the enthalpy changes are small.

Thermodynamics of the complex formation in pyridine between gold(i) and ligands coordinating via N, P, As or Sb

The thermodynamics of complex formation between gold(I) and the ligands tricyclohexylphosphine, triphenylamine, -phosphine, -arsine, and -stibine has been determined in pyridine solution by potentiometric and calorimetric measurements. As expected, the very soft gold(I) displays a more marked stability (b)-sequence N ⪡ P > As > Sb than its lighter, and less soft, congener silver(I). Like all complexes of these ligands so far studied, the present ones are strongly enthalpy stabilized while the entropy changes are generally unfavourable. The stepwise entropy changes show quite peculiar differences between the various ligands, however. The thermodynamics of these complexes is in striking contrast to that of the gold(I) halido complexes in pyridine which are strongly entropy stabilized, while the enthalpy changes are small.

Structural changes during elongation of polymer solutions

During elongational flow experiments on polymer solutions certain anomalous examples of flow behaviour have been noted. These are, 1. (1) a non uniform velocity profile in the radial direction in strongly non-Newtonian fluids being elongated at high rates. 2. (2) the loss of tack in the filament as rate of elongation increased, 3. (3) the bouncing of the filament off a rotating drum at high elongation rates, and 4. (4) the development of sustained rubber-like lateral vibrations in the fluids elongated at high rate. In addition, droplet formation occurred on the surface of the solutions which were elongated rapidly then suddenly stopped. Photography showed that the filaments continued through these droplets. When captured and dried, it was observed that the filament contained the bulk of the solute. The droplets appeared to have only a low concentration of polymer. On the basis of the photographic evidence and the thermodynamics of complex formation between elongated polymer chains, it would appear that complexation of the chains is occurring at high elongation rates. This could partly account for the strain hardening encountered during elongation of many polymeric fluids. Where solubility parameter difference between polymer and solvent was large, the complex formed could come out of solution forming a gel and a solvent rich phase.

Thermodynamics of Complex Formation between Neodymium(III) and Carboxymethylthiosuccinic Acid and Equilibrium Study of Mixed Complexes with Simple and Substituted Dicarboxylic Acids

Thermodynamics of Complex Formation between Neodymium(III) and Carboxymethylthiosuccinic Acid and Equilibrium Study of Mixed Complexes with Simple and Substituted Dicarboxylic Acids

Kinetics and thermodynamics of complex formation between aluminium(III) and citric acid in aqueous solution

By stopped-flow and pressure-jump relaxation measurements, equilibrium and rate constants for the formation of aluminium citrate complexes have been determined at 293.7 K. For the monodentate complex, AlH2Cit2+, the bidentate complex, AlHCit+, and the tridentate complex, AlCit, the stability constants are (8.2 ± 1.5)× 102, (3.6 ± 1.6)× 106 and (5.3 ± 2.3)× 1010 dm3 mol–1, respectively. The rate constants for the formation of the monodentate and the bidentate complexes are (5.4 ± 0.5)× 103 and 80 ± 10 dm3 mol–1 s–1, respectively.

Contribution to thermodynamics of complex-formation and ion association in extraction system with two immiscible liquid phases

Contribution to thermodynamics of complex-formation and ion association in extraction system with two immiscible liquid phases

PYRIDINE DERIVATIVES AS COMPLEXING AGENTS XII. Thermodynamics of Complex Formation with 2-Pyridylmethyl-iminodiacetic Acid and its 6-Methyl Substituted Derivative

Abstract The equilibrium constants and the involved thermodynamic data for the formation of the complexes between two pyridyl-methyl-iminodiacetic acids and the following cations: Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+, Hg2+ and Ag+ have been obtained by potentiometric and direct calorimetric measurements. The data are discussed in relation with the results for other similar ligands.

Lipophilic enterobactin analogs. Terminally N-alkylated spermine/spermidine catecholcarboxamides

The selective, reductive alkylation of the terminal nitrogen atoms of spermidine (1) and spermine (2) has been accomplished by using excess ketone/aldehyde in aqueous or alcoholic medium at room temperature under hydrogen (less than or equal to 3 atm, catalyzed by 5% Pd/C). Where aldehydes were used, a prereduction period of at least 15 h was allowed for Schiff base formation to avoid reduction of the aldehyde itself. Isolated yields ranging from 14% to 80% were obtained of the crystalline hydrochloride salts which were conveniently recrystallized from alcoholic media. Characterization of the dialkyl derivatives was readily achieved by /sup 1/H NMR. Regardless of the individual terminal N-alkyl group, synthesis of the representative (catecholcarboxamide LICAM) compounds was routinely accomplished by using previously reported procedures. Their 2,3-dimethoxybenzoyl precursors exhibited no IR absorbance near 3400 cm/sup -1/ (CONH; normally quite intense in the unsubstituted compounds). Removal of the methyl protecting groups of the catechol oxygens with excess BBr/sub 3/ produced, in good yields LICAM ligands of increased lipophilicity. An examination of CPK molecular models indicates there should be no deleterious steric effects of the N-alkyl groups on Pu/sup 4 +//Fe/sup 3 +/ complex formation; the measurement of the effect of these bulky groupsmore » on the kinetics and thermodynamics of complex formation, and in vivo organ distribution and toxicity continue to be actively studied.« less

Thermodynamics of complex formation in ternary liquid mixtures containing acetonitrile

Vapor—liquid and liquid—liquid equilibria and excess enthalpies for ternary mixtures formed from acetonitrile, benzene, n-heptane, toluene, and carbon tetrachloride are successfully correlated with a modified version of the associated solution theory proposed by Lorimer and Jones in 1977, which assumes two types of self-association for acetonitrile and binary complexes between acetonitrile and unsaturated hydrocarbons and does not include any ternary parameters.

Thermodynamics of complexes formation between UO 2staggered2+ and thiocicarboxyxlic acids and equilibrium study of the mixed complexes with quinolinic acid

Thermodynamics of complexes formation between UO 2staggered2+ and thiocicarboxyxlic acids and equilibrium study of the mixed complexes with quinolinic acid

Thermodynamics of complex formation with multidentate ligands

Thermodynamics of complex formation with multidentate ligands

Thermodynamics of complex formation with multi-dentate ligands

Complex formation in solution is generally described by a reaction of type I This formulation does not correspond to what actually takes place, namely ▪ process II, because of the omission of the solvent as ▪ reacting partner. Indeed the entropy of complex formation is generally positive and large, depending strongly on the dentateness of the ligand, and not negative as it would be expected for reaction I, because of the decrease of the number of species in solution. The influence of the solvent seems also to be reflected in the value of the enthalpy of complex formation: for complexes with multidentate charged O-ligands it is generally not very different from zero. This is because the endothermic effect for the dehydration of the reacting species is almost compensated by the exothermic effect of the ligand coordination. On the contrary, for neutral ligands, the enthalpy is remarkably negative as a result of ( 1) the lower hydration of the ligand, ( 2) the covalency of the bonding, and ( 3) no charge neutralisation occurs. In multidentate ligands the donor atoms connected together by chains which, on complex formation, give rise to chelate rings. These are considered responsible for the higher stability of complexes with multidentate ligands with respect those of monodentate ligands, if in the complexes the same number of donor atoms are involved. The interpretation of this effect, the Chelate Effect, has been the years and it is still a matter of opinion. In this connection, one should consider not only for five-, six- and seven-membered chelate rings a positive Chelate Effect, is observed. If there are more than six atoms between the donor atoms or chelating units, their neutral influence decreases and eventually reduces to that of a statistical effect. The values of the enthalpy and of the entropy for complex formation with the same ligand and a series of related metal ions, such as the alkaline earth, the 3d divalent metal or the 4f trivalent lanthanide ions can be correlated with stereochemical and electronic effects at the central ion such as the dentateness of the ligand, the coordination number of the metal ion and ligand field effects. The formation of mixed (ternary) complexes will be also considered in some detail. These have recently received more attention, especially because of their increased stability with respect to that expected by statistical consideration and in relation of their importance in biological systems.

Thermodynamics of complex formation: DL-isoserine with nickel(II) and copper(II)

Researches in this laboratory have shown how in aqueous solution, the aminoacids, DL-4-amino-3-hydroxy-butanoic and DL-3-amino-2-hydorxypropanoic acid (isoserine) form complexes with divalent metals. The complexes contain the pentatomic chelate ring ▪ where the alcoholic group appears to be ionized even in acidic solution [1, 2]. On the other hand the corresponding isomers, threonine and serines bind the metal via the α-aminoacid moiety and only in alkaline solution the hydroxyl group dissociates and is involved in chelation to the metal [3]. In order to explain the different roles of aminoethanolate and aminocarboxylate moieties in complex formation, we have now undertaken the calorimetric determination of enthalpy changes in the reactions of DL-isoserine with Ni(II) and Cu(II) in aqueous solution at 25 °C and I = 0.1 mol dm −3 (KCl). The calorimetric measurements have been carried out by a modified LKB 8700-2 calorimeter. The values of the thermistor resistence in the reaction vessel were obtained by measuring the output voltage of the unbalanced Wheatstone bridge by a digital microvoltmeter HP 3455A. The e.m.f. values were printed at regular time intervals by a strip-printer HP 5150A with timer and converted to resistence values by an empirical relation. The ΔH 0 values obtained for the protonation reaction of isoserine, H 2NCH 2CH(OH)COOH, H 2L, are: ▪ The enthalpy changes of Ni(II) complexes are: ▪ The data for Cu(II) complexes are: ▪The corresponding entropy changes are rather high, particularly in the copper complexes. This stands for a remarkable entropy contribution to the stability of the complexes, coming from redistribution of water molecules involved in the process. Some hypotheses on the structure of the complexes can be put forward. They will be tested by extending the calorimetric studies to other ligands containing the aminoethanol moiety.

Thermodynamics of complex formation in dimethyl sulfoxide with ligands coordinating via N, P, As, Sb, OR Bi : III. A comparison between aromatic and aliphatic amines and phosphines

The stabilities of the complexes formed by silver(I), cadmium(II) and zinc(II) with tri-n-butylamine and tri-n-butylphosphine have been determined in dimethyl sulfoxide (DMSO). For the two latter metal ions, it has also been found that complexes are not formed in appreciable amounts with the triphenyl compounds Ph 3X, X = N, P and, in the case of cadmium(II), also As. From these and earlier measurements referring to DMSO as well as aqueous solutions, it was found that the stepwise stability constants increase by roughly one power of ten for each aromatic ring replaced by an aliphatic group, evidently as a consequence of the improved donor properties of the coordinating atoms. Further, for ligands of the same type, the stabilities are always markedly lower in DMSO than in aqueous solution. This is certainly due to the fact that the solvent molecules compete more strongly for the coordination sites in DMSO than in water, as reflected by the larger heats of solvation found in the former solvent for the metal ions concerned.

Thermodynamics of Complex Formation between Cadmium(II), Thiosemicarbazide and 4-Methylthiosemicarbazide.

Thermodynamics of Complex Formation between Cadmium(II), Thiosemicarbazide and 4-Methylthiosemicarbazide.

The linear free-energy relation in the thermodynamics of complex formation. Part 2. Analysis of the formation constants of complexes of the large metal ions silver(I), mercury(II), and cadmium(II) with ligands having ‘soft’ and nitrogen-donor atoms

A potentiometric and calorimetric study has been made of the complex formation of AgI, HgII, and CdII with ligands containing ‘soft’ and N-donor atoms. It has been found that linear enthalpy relations exist, and that they mirror quite closely the division of the free-energy data into separate groups for the ‘soft’ and N-donor atom ligands, for the pair of metal ions AgI–HgII and for AgI–CdII. It seems that a linear entropy relation also exists, to within experimental error, for the pair AgI–HgII which has a gradient and intercept that can be rationalised in terms of the Powell–Latimer–Cobble semi-empirical theory of ionic entropy. The entropy contributions are small compared with those of the enthalpy in these predominantly enthalpy-stabilised complexes. The significance of the relatively simple behaviour of the free energies compared with their enthalpy and entropy components is discussed.

Thermodynamics of Complex Formation in Dimethyl Sulfoxide with Ligands Coordinating via N, P, As, Sb or Bi. II. Copper(I) and Mercury(II) Complexes.

Thermodynamics of Complex Formation in Dimethyl Sulfoxide with Ligands Coordinating via N, P, As, Sb or Bi. II. Copper(I) and Mercury(II) Complexes.

Thermodynamics of complex formation in binary liquid mixtures: application to systems containing acetonitrile

Equations for enthalpies and volumes of mixing are derived from thermodynamic association theory for complex binary liquid mixtures containing self-associating species and binary complexes. The various species can interact through general non-specific interactions of the simple mixture type.The equations, along with equations for the excess Gibbs energy, are applied to experimental data on excess Gibbs energies, heats, and volumes of mixing for the three binary systems formed from acetonitrile, carbon tetrachloride, and chloroform. The data require a theoretical model that involves two types of self-association of acetonitrile, one type of self-association of chloroform and formation of a binary complex CH3CN•2CHCl3. Thermodynamic parameters for the various types of association and interaction are derived by constrained least-squares methods, and provide a unified picture of the thermodynamic properties of these mixtures.