Thermodynamic studies, complexation

A system is the region in space that is the subject of the thermodynamic study. It can be as large or small, or as simple or complex, as we want it to be, but it must be carefully and consistently defined. Sometimes the system has definite and precise physical boundaries, such as a gas enclosed in a cylinder so that it can be compressed or expanded by a piston. However, it may be also something as diffuse as the gaseous atmosphere surrounding the earth. 

Unsually short NMR T, relaxation values were observed for the metal-bonded H-ligands in HCo(dppe)2, [Co(H2)(dppe)]+ (dppe = l,2-bis(diphenylphosphino)ethane), and CoH(CO) (PPh3)3.176 A theoretical analysis incorporating proton-meta) dipole-dipole interactions was able to reproduce these 7) values if an rCo H distance of 1.5 A was present, a value consistent with X-ray crystallographic experiments. A detailed structural and thermodynamic study of the complexes [H2Co(dppe)2]+, HCo(dppe)2, [HCo(dppe)2(MeCN)]+, and [Co(dppe)2(MeCN)]2+ has been reported.177 Equilibrium and electrochemical measurements enabled a thorough thermodynamic description of the system. Disproportionation of divalent [HCo(dppe)2]+ to [Co(dppe)2]+ and [H2Co(dppe)2]+ was examined as well as the reaction of [Co(dppe)2]+ with H2. 

Thermodynamics of complex formation of silver with several ligands such amines,368 hindered pyridine bases,369 nitrogen donor solvents,370 and azoles371 have been carried out. Other studies include the secondary-ion mass spectra of nonvolatile silver complexes,372 the relationship between Lewis acid-base behavior in the gas phase and the aqueous solution,373 or the rates of hydride abstraction from amines via reactions with ground-state Ag+.374... 

There have been a very large number of other thermodynamic studies involving the interaction of crowns with a wide range of metal-ions (Izatt et al., 1985). In general, as for the examples already discussed, the complexes are found to be enthalpy-stabilized with the entropy term also contributing to the stability in a number of cases. 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

Among the questions that arise are the following, at least, is the metal present as a sorbed/hydrated species , were the conditions of metal incorporation such that precipitation of metal-containing species occurred , if a metal-organic compound was present, what is the chemical form of the sorbed complex Answers to such questions have been provided in part from thermodynamic studies (1-4,9) and from a variety of spectroscopic techniques (10-12 ). 

Compound [22] forms thermodynamically stable complexes with Ba2+ and K+. The binding of anions by free [22] is relatively weak the metal cation therefore cooperates in the anion complexation process. Electrochemical studies using CV and SWV have shown that [22] is capable of electrochemi-cally recognizing both cations and anions simultaneously and readers are urged to consult the original publication for a detailed explanation of this effect. 

Generally, there are two approaches to the investigation of mixed adsorbed films at an oil/water interface. One way is to study mixed adsorption of surfactants from the Scime bulk phase and the other is to study adsorption from both of the bulk phases. The former has been done by many workers from the physicochemical viewpoint to clarify the difference in molecular interaction between the adsorbed state and the bulk state. The latter has been made mostly from the practical point of view, e.g., solvent extraction and complex-forming reactions that take place at the interface, though little is known concerning the thermodynamic viewpoint D). The thermodynamic study is actually useful to elucidate the behavior of film molecules in the adsorbed state. 

In the thermodynamic study of duplex formation, a variety of complementary pairs of relatively simple, well-defined oligonucleotides are employed, " while the intercalation thermodynamics was examined with more complex or natural DNA duplexes. " Typical intercalating agents examined are acridine orange, acriflabine, actinomycin, daunomycin, ethidium bro-... 

These results indicate that studies of the donor-acceptor interactions on the model systems are quite justified. This study is the only possible approach to quantitative characterization of all the numerous complexes appearing in the epoxy-amine system. Today, we are making but initial efforts in the thermodynamic studies of the epoxyamine systems. For the time being, we have only managed to estimate the effective thermodynamic characteristics in such systems. The development of an algorithm for both the experimental and the theoretical approach to the study of similar systems still remains an important task. 

The process of complexation is believed to occur through the stepwise incorporation of the ligand, i.e. stepwise replacement of the existing solvation, or hydration, sheath. The process is likely to be entropy controlled and entropy increases have been noted in thermodynamic studies on these systems.33... 

The diketonates of indium(III) are thermodynamically stable complexes in non-aqueous solution,9 and are sufficiently robust to allow studies of polarographic reduction, which has demonstrated one-electron reduction to the formally indium(II) and indium(I) compounds (see Section 25.2.3.3).30... 

Thermodynamic systems are parts of the real world isolated for thermodynamic study. The parts of the real world which are to be isolated here are either natural water systems or certain regions within these systems, depending upon the physical and chemical complexity of the actual situation. The primary objects of classical thermodynamics are two particular kinds of isolated systems adiabatic systems, which cannot exchange either matter or thermal energy with their environment, and closed systems, which cannot exchange matter with their environment. (The closed system may, of course, consist of internal phases which are each open with respect to the transport of matter inside the closed system.) Of these, the closed system, under isothermal and iso-baric conditions, is the one particularly applicable for constructing equilibrium models of actual natural water systems. 

Miguirditchian, M., Guillaneux, D., Guiflaumont, D. et ah 2005. Thermodynamic study of the complexation of trivalent actinide and lanthanide cations by ADPTZ, a tridentate N-donor ligand. Inorg. Chem. 44 (5) 1404—1412. 

This section is largely devoted to the results of thermodynamic studies of equilibria in aqueous solution involving hydrated cations M"+(aq), ligands and the complexes formed by these. Some of the thermodynamic properties of M +(aq) ions have already been discussed... 

The liquid metal mercury-solution interface presents the advantage that it approaches closest to an ideal polarizable interface and, therefore, it adopts the potential difference applied between it and a non-polarizable interface. For this reason, the mercury-solution interface has been extensively selected to carry out measurements of the surface tension dependence on the applied potential. In the case of other metal-solution interfaces, the thermodynamic study is much more complex since the changes in the interfacial area are determined by the increase of the number of surface atoms (plastic deformation) or by the increase of the interatomic lattice spacing (elastic deformation) [2, 4]. 

P. Martinez, J. Zuluaga, and S. Sieiro, Kinetic-thermodynamic study of the complexation of ascorbic acid with cupric ions, An. Quim. A., 80 (1984) 179-182. 

The common problems with those metallomicelles may be summarized as follows (1) Most of these complexes were prepared in situ and often were not isolated. Hence, the intended structures of the metallomicelles in solution or in the solid state were not verified. (2) The metal complexes in solution were not identified or characterized in rigorous thermodynamic senses by potentiometric pH titration, etc. The complexation constants and possible species distribution at various pH s were totally unknown. (3) Possible catalytically active species L-Mn+—OH were not identified by means of the thermodynamic pvalues. Those described were all obtained merely in kinetics. (4) The product (phosphate anion) inhibition was not determined. Accordingly, it often was not clear whether it was catalytic or not. (5) Often, the substrates studied were limited. (6) The kinetics was complex, probably as a result of the existence of various species in solution. Thus, in most of the cases only pseudo-first-order rates (e.g., with excess metal complexes) were given. No solid kinetic studies combined with thermodynamic studies have been presented. It is thus impossible to compare the catalytic efficiency of these metallomicelles with that of the natural system. Besides, different... 

In many solutions strong interactions may occur between like molecules to form polymeric species, or between unlike molecules to form new compounds or complexes. Such new species are formed in solution or are present in the pure substance and usually cannot be separated from the solution. Basically, thermodynamics is not concerned with detailed knowledge of the species present in a system indeed, it is sufficient as well as necessary to define the state of a system in terms of the mole numbers of the components and the two other required variables. We can make use of the expressions for the chemical potentials in terms of the components. In so doing all deviations from ideal behavior, whether the deviations are caused by the formation of new species or by the intermolecular forces operating between the molecules, are included in the excess chemical potentials. However, additional information concerning the formation of new species and the equilibrium constants involved may be obtained on the basis of certain assumptions when the experimental data are treated in terms of species. The fact that the data may be explained thermodynamically in terms of species is no proof of their existence. Extra-thermodynamic studies are required for the proof. 

Most kinetic studies (e.g., 29) and a thermodynamic study (30) of nuclear waste host dissolution focus on heterogeneous reactions with major concern for temperature, pH, and complexation. We believe that strongly reducing conditions are necessary to inhibit the undesirable U(IV)-U(VI) oxidation in nuclear waste matrices. Therefore, nuclear waste matrices should incorporate reductants or oxidation-reduction Eh buffers to maintain very low oxygen partial pressure, and leach studies should be conducted under oxidation-reduction conditions that nearly match repository conditions. 

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