Formation of Complex Ions

Whenever a metal ion enters water, a complex ion forms, with water as the ligand. In many cases, when we treat this hydrated cation with a solution of another ligand, the bound water molecules exchange for the other ligand. For example, a hydrated M ion, M(H20)4, forms M(NH3)4 in aqueous NH3 M(H20)4 - (fl 7) -I- 4NH3(fl 7) M(NH3)4 (a 7) -b AHjOd) 

At equilibrium, this system is expressed by a ratio of concentration terms whose form follows that of any other equilibrium expression  

Once again, because the concentration of water is essentially constant in aqueous reactions, we incorporate it into and obtain the expression for a new equilibrium constant, the formation constant, K  

The sum of the equations gives the overall equation, so the product of the individual formation constants gives the overall formation constant  

In this case, the K for each step is much larger than 1 because ammonia is a stronger Lewis base than water. Therefore, if we add excess ammonia to the M(H20)4 solution, the H2O ligands are replaced and essentially all the M ion exists as M(NH3)4 .  

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The ability to form hydrogen bonds explains the formation of complex ions such as HFJ and HjFj when a fluoride salt, for example potassium fluoride, is dissolved in aqueous hydrofluoric acid ... 

Special techniques for experimentation with the actinide elements other than Th and U have been devised because of the potential health ha2ard to the experimenter and the small amounts available (15). In addition, iavestigations are frequently carried out with the substance present ia very low coaceatratioa as a radioactive tracer. Such procedures coatiaue to be used to some exteat with the heaviest actinide elements, where only a few score atoms may be available they were used ia the earHest work for all the transuranium elements. Tracer studies offer a method for obtaining knowledge of oxidation states, formation of complex ions, and the solubiHty of various compounds. These techniques are not appHcable to crystallography, metallurgy, and spectroscopic studies. 

The other halides of Zn and Cd are in general hygroscopic and very soluble in water ( 400g per lOOcm for ZnXa and 100g per lOOcm for CdXa). This is at least partly because of the formation of complex ions in solution, and the anhydous forms are best prepared by... 

The stability of tin over the middle pH range (approximately 3-5-9), its solubility in acids or alkalis (modified by the high hydrogen overpotential), and the formation of complex ions are the basis of its general corrosion behaviour. Other properties which have influenced the selection of tin for particular purposes are the non-toxicity of tin salts and the absence of catalytic promotion of oxidation processes that may cause changes in oils or other neutral media affecting their quality or producing corrosive acids. 

On the other hand, the presence of CN ions greatly increases the zone of corrosion, owing to the formation of complex ions. Silver, therefore, is thermodynamically stable in reducing acids, e.g. hydrochloric acid, acetic acid, phosphoric acid, provided oxidising substances are absent. 

All the six platinum-group metals are highly resistant to corrosion by most acids, alkalis, and other chemicals. Their high nobility is the main factor determining their chemical resistance, and the formation of. complex ions in solution is principally responsible for their dissolution under certain conditions. 

Electro-conductivity of molten salts is a kinetic property that depends on the nature of the mobile ions and ionic interactions. The interaction that leads to the formation of complex ions has a varying influence on the electroconductivity of the melts, depending on the nature of the initial components. When the initial components are purely ionic, forming of complexes leads to a decrease in conductivity, whereas associated initial compounds result in an increase in conductivity compared to the behavior of an ideal system. Since electro-conductivity is never an additive property, the calculation of the conductivity for an ideal system is performed using the well-known equation proposed by Markov and Shumina (Markov s Equation) [315]. 

Based on Equation (55), it was concluded/assumed that niobium-containing oxyfluoride melts are characterized by the formation of complex ions NbOF63. ... 

Volkov, Grischenko and Delimarsky [293] mentioned a similar tendency of the complexes to increase in strength with the increase in the polarity of ligands along the sequence F to I. This concept confirms the significance of the covalent share in the energetics of the formation of complex ions in molten media. 

In Section 16-6, we describe how metal cations in aqueous solution can form bonds to anions or neutral molecules that have lone pairs of electrons. This leads to formation of complex ions and to chemical equilibria involving complexation. The complexation equilibrium between Ag and NH3 is an example ... 

We can treat other types of equilibria in much the same way as the ones previously discussed. For example, there is an equilibrium constant associated with the formation of complex ions. This equilibrium constant is the formation constant, Kt. 

As in the hydrolysis of polyphosphates (Sections IV,B, and IV,E,1), hydrolysis of the trimetaphosphate anion is eatalytically accelerated by added cations. Their effect is attributed, as in the ease of the polyphosphates, to the formation of complex ions of the type CafPsOs)- or Ba(P309)- and Na PsOs)3 (130, I44, 146). 

At first sight there appears to be nothing systematic about the formation of complex ions. Some are formed by reaction with oxygen ions, as for example... 

The discharging of the colour by oxalates, tartrates, etc., appears to be caused by the formation of complex ions with the ferric ions of the ionised ferric thiocyanate, which causes further dissociation of the red non-ionised salt and consequent loss of colour. 

If anion X- precipitates metal M+, it is often observed that a high concentration of X causes solid MX to redissolve. The increased solubility arises from the formation of complex ions, such as MX2, which consist of two or more simple ions bonded to each other. 

Equilibria in the formation of complex ions with metals are treated exactly as is the binding of small molecules and ions to macromolecules.87-89 Stepwise constants are defined for the formation of complexes containing one, two, or more ligands L bound to a central metal ion M. The binding constants K/s are usually referred to as P s as in Eq. 6-84. 

ZnCl2 vapour pressures, activities and partial molar energies have been determined for the fused salt system shown in equation (7). Deviations from ideality at high ZnQ2 concentrations are attributed to partial covalent bonding in ZnCl2, while deviations at low ZnCl2 concentrations are attributed to formation of complex ions.958,959... 

The element is difficult to maintain in aqueous solution in the form of simple salts. Solubility data seem to indicate that such amounts as can be dissolved probably do so entirely by formation of complex ions. Fluoride ion strongly complexes protactinium, and it is due to this that protactinium compounds are in general soluble in hydrofluoric acid. 

Using the same general formula that we used for K, we can examine constants for the formation of complex ions and determine what woulcfbe the best substance to use as a film fixer in other words, what substance can remove a large number of silver ions from the unexposed portion of the film. We use the symbol Kf for the formation constant of a complex ion. We know that thiosulfate ions are combined with silver ions to form the Ag(S203) 23- complex ... 

Ion-transfer reactions Such reaction result in formation of complex ions (e.g., NH4+, H30+, NH2-,... 

The deviations from ideal behavior can be calculated for all thermodynamic and transport functions of mixtures of molten salts, and these reflect the phenomena which take place at mixing ion associations, formation of complex ions, etc. 

The formation of complex ions is an important problem for the study of the structure and properties of molten salts. Several physicochemical measurements give evidence of the presence of complex ions in melts. The most direct methods are the spectroscopic methods which obtain absorption, vibration and nuclear magnetic resonance spectra. Also, the formation of complex ions can be demonstrated, without establishing the quantitative formula of the complexes, by the variation of various physicochemical properties with the composition. These properties are electrical conductivity, viscosity, molecular refraction, diffusion and thermodynamic properties like molar volume, compressibility, heat of mixing, thermodynamic activity, surface tension. 

Bredig [21] presumed that in a mixture of molten salts the variation of the interaction parameter X [see Eq. (8)] makes evident the formation of complex ions. Thus, in the KCl-CdCl2 and RbCl-MgCl2 systems it is observed variations of the X parameter and with the composition of the melt, and the minimum points of those variations correspond to the composition of complex ions. However, the most convincing data on the formation of complex ions can be obtained from measurements of the enthalpy of mixing [22],... 

Three factors, other than temperature, that affect solubility are the common-ion effect, pH, and the formation of complex ions. 

Note that milk contains considerably more cations than anions Jenness and Patton (1959) have suggested that this can be explained by assuming the formation of complex ions of calcium and magnesium with the weak acids. In the case of citrate (symbol ) the following equilibria exist ... 

Kossel in his fundamental publications on ionic bonding has already answered the question how the formation of complex ions must be explained. 

Based on Equation (55), it was concluded/assumed that niobium-containing oxyfluoride melts are characterized by the formation of complex ions NbOF63 Systematic investigations of the electro-conductivity of niobium-containing fluoride and oxyfluoride melts were not performed. Some measurements were performed on the molten mixtures KC1 - K2NbF7, KC1 - KF - K2NbF7 by... 

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