**1. Ionic state of indium in perchlorate solutions**

It is known that perchlorate ion does not form complex compounds even with extremely strong complexing metal ions [1]. The difficulty in preparing perchlorate metal complexes is the lack of suitable solvents. Water molecules and most non-aqueous donor media displace such a weak ligand as the ClO4 − ion from the inner sphere of the compound. The formation of a coordination bond between the perchlorate ion and the complexing cation is possible only in acceptor or very weakly donating solvents. The successful synthesis of perchloro-complexes in work [2] is associated with the use of anhydrous perchloric acid as a reaction medium.

These fairly well known provisions are fully confirmed for indium perchlorate, which is proved by various research methods [3–19]. The absence of coordination interaction of acid ions in the "In3 + - ClO4 − – H2O" system is indicated by the spectra of Raman scattering [5–11]. IR spectra [12] including near infrared [13–15] and spectroscopy of disturbed total internal reflection [13, 16], NMR signals [17, 18]. However, partial formation of ion pairs between them is allowed [8, 18].

In the Raman spectra of the perchlorate solution, only the lines of the ClO4 − anion and the aquocomplexes of the In3 + ion ⋅aq were found [6]. Raman and IR spectroscopic studies of indium hydration in perchlorate solutions revealed octahedral hexaaquocation [In(H2O)6] 3 +. According to the data of the Raman spectra, the aquocomplex is stable in acidic perchlorate solutions, and in the studied concentration range, neither inner sphere nor hydroxostructures are formed [9].

There is no evidence of the complexing effect of the highly concentrated electrolyte NaClO4 1.1÷9.1 M and by electrophoresis [19]. Spectrophotometrically in the ultraviolet region of the spectrum, there were no significant signs of direct interaction in aqueous solutions of In(ClO4)3 salts [20]. Also, no intrinsic complexation influencing the activity of In3+ was reliably detected up to a sodium perchlorate concentration of 16 mol/kg [19, 21] and with an In(ClO4)3 content of more than 4 M [6, 9].

Similar results, denying the likelihood of coordination interaction of In3+ with ClO4 − , were obtained when studying the solvation of cations by NMR on H1 and P31 nuclei in aqueous-organic mixtures [22].

The proton-magnetic resonance measurement of the coordination number of perchlorate water-organic systems testifies to the six fold coordination of water molecules around the indium cation and to the absence of strong evidence of contact ion pairing [23, 24]. It was not possible to detect the binding of indium to perchlorate ions ClO4 − by special experiments carried out in mixed water-nonaqueous mixtures and organic media [25].

The absence of complex compounds of indium with perchlorate ion is also indicated by the data of liquid extraction, in particular, three n-octylamine does not extract indium from a solution with an HClO4 concentration less than 2 M [4]. At the same time, from concentrated solutions of perchloric acid for cationic reagents - alkylphosphoric acids (for example, di-2-ethylhexylphosphoric acid; **Figure 1**) - a possible extractable form of indium compounds is the complex cation [InClO4]2+ [26]. It is also assumed that during the extraction of indium in aqueous solutions of hydrochloric acid at its various concentrations and constant ionic strength maintained by the addition of perchloric acid, indium is present in the organic phase in the form of ionic aggregates HClO4⋅HInCl4 [27]. The latter formation is possibly caused by the coextractability of perchloric acid due to its higher extraction affinity as compared to hydrochloric acid. In the aqueous phase, there are only chloride complexes, which are subjected to extraction with various oxygen-containing solvents.

The likelihood of the formation of perchlorate and mixed-ligand complexes also applies to extraction systems based on 4-methyl-2-pentanone and 4-methyl-2-pentanol, the extractable forms of which are compounds of the composition [In(ClO4)3], [InHal(ClO4)2], [InHal2(ClO4)], where bromine, iodide, or thiocyanate ion is present

**Figure 1.**

*Extraction of III subgroup metal ions with di (2-ethylhexyl) phosphoric acid depending on the concentration of perchloric acid: 1 - Ga (III), 2 - In (III), 3 - Tl (III) [26].*

**43**

*Features of the Ionic State of Indium in Perchlorate Solutions and the Physicochemical Properties…*

as the halide and pseudohalide of the ligand. The aqueous phase is characterized by a constant ionic strength of 4.0 due to the salt background of sodium perchlorate and salts of NaBr, NaJ or NaSCN of variable concentrations. The role of NaClO4 in liquid distribution is reduced not only to a change in the activity and composition of the solution, but also to the extraction of ion pairs of charged indium complexes, which

An example of the special effect of perchlorate ion on the extraction behavior of indium (III) is its interaction in a mixture of extractants 1-phenyl-3-methyl-4-acylpyrazol-5 (PhMAPr) with tri-n-phosphine oxide (TOPhO) in toluene [29] and PhMAPr with a base salt — Aliquat-336 [29]. If the reaction of interfluid distribu-

(o) 3(o) ex In + 3HPhMAPr In (PhMAPr) +3H with high l « = ogK 1.50, (1)

and from aqueous solutions of H(Na)Cl, ClO4 during extraction with a mixture PhMAPr and TOPhO have a synergistic effect and the process is described by the

+

where n = 0–3, then in the case of perchlorate salt Aliquat-336, this phenomenon

When studying the coordination properties of polyvalent metal ions, including indium, by titrimetric and ion-exchange methods, only weak signs of complexation

The cation-exchange behavior of indium (III) ions in the presence of perchloric acid and an organic solvent in the form of methyl alcohol and acetone also indicates the absence of fundamental changes in the ionic state of indium in such a sorption system. Both in the presence and in the absence of these solvents, the indium ion interfacial distribution indices in the perchloric acid medium are higher than in the hydrochloric acid medium (picture 2) [31]. Thus, if the coordination properties of such acid ligands as halides, sulfate, thiocyanate [32], and to some extent nitrite [33] in aqueous-organic mixtures can be activated, which leads to the formation of more acid-saturated complexes, then the perchlorate ion under these conditions in

relation to indium, as a complexing agent, remains very passive (**Figure 2**).

From other alternative points of view, attention is drawn to the study of the effect of the salting-out electrolyte on the distribution coefficient of indium during the extraction of its tenoyl-three-fluoroacetonate complex with benzene from aqueous perchlorate solutions, where the presence of complexation of indium with

The revealed relationship between the salting-out parameter and the stability of indium complexes with various anions formed in the aqueous phase indicates that the strength of the acidic complexes by the nature of the ligand changes in the series

A characteristic feature of indium perchlorate solutions, like other indium salts, is the extremely high viscosity of aqueous solutions of In(ClO4)3, due to the increased degree of hydration of the three-charged indium ion [6]. A simple substance with the composition In(ClO4)3 ~ 8H2O crystallizes from concentrated aqueous solutions of indium perchlorate [11], and in dilute perchloric acid, indium

3+.

o on 3 n

ClО<sup>4</sup> − -

, although when using in

(2)

[ ] ( ) ( ) ( )

the same system high-molecular-weight ammonium in chloride and nitrate forms,

InCln 3 – n HPhMAPr 2TOPhO InCl PhMAPr

+ +«

*DOI: http://dx.doi.org/10.5772/intechopen.94258*

equation (2):

3 n


in perchloric acid were noted [30].

the perchlorate ion was confirmed.

of salts: NaCl > > NaNO3 > NaClO4 [34].

is in the form of the cation [In(H2O)6]

greatly increases in the presence of perchlorate ions [28].

tion in a perchlorate medium proceeds according to the equation (1):

3+ +

o

the effect of synergism is not only preserved, but also increased.

× +

is not observed due to its finding in the form of R4N+

2TOPhO 3 – n H

*Features of the Ionic State of Indium in Perchlorate Solutions and the Physicochemical Properties… DOI: http://dx.doi.org/10.5772/intechopen.94258*

as the halide and pseudohalide of the ligand. The aqueous phase is characterized by a constant ionic strength of 4.0 due to the salt background of sodium perchlorate and salts of NaBr, NaJ or NaSCN of variable concentrations. The role of NaClO4 in liquid distribution is reduced not only to a change in the activity and composition of the solution, but also to the extraction of ion pairs of charged indium complexes, which greatly increases in the presence of perchlorate ions [28].

An example of the special effect of perchlorate ion on the extraction behavior of indium (III) is its interaction in a mixture of extractants 1-phenyl-3-methyl-4-acylpyrazol-5 (PhMAPr) with tri-n-phosphine oxide (TOPhO) in toluene [29] and PhMAPr with a base salt — Aliquat-336 [29]. If the reaction of interfluid distribution in a perchlorate medium proceeds according to the equation (1):

$$\text{In}^{3+} \text{ + 3HPhMAP}\_{\text{(o)}} \leftrightarrow \text{ In (PhMAPr)}\_{\text{3(o)}} \star \text{3H}^{\*} \text{ with high } \log \text{K}\_{\text{ex}} = \text{1.50, } \text{ (1)}$$

and from aqueous solutions of H(Na)Cl, ClO4 during extraction with a mixture PhMAPr and TOPhO have a synergistic effect and the process is described by the equation (2):

$$\begin{aligned} \left[\text{InCln}\right]^{3-\text{n}} + \left(\text{3-n}\right)\text{HPhMAPr}\_{\text{o}} + 2\text{TOPhO}\_{\text{o}} &\leftrightarrow \text{InCl}\_{\text{n}}\left(\text{PhMAPr}\right)\_{\text{3-n}}\\ \cdot \text{2TOPhO}\_{\text{o}} + \left(\text{3-n}\right)\text{H}^{+} \end{aligned} \tag{2}$$

where n = 0–3, then in the case of perchlorate salt Aliquat-336, this phenomenon is not observed due to its finding in the form of R4N+ ClО<sup>4</sup> − , although when using in the same system high-molecular-weight ammonium in chloride and nitrate forms, the effect of synergism is not only preserved, but also increased.

When studying the coordination properties of polyvalent metal ions, including indium, by titrimetric and ion-exchange methods, only weak signs of complexation in perchloric acid were noted [30].

The cation-exchange behavior of indium (III) ions in the presence of perchloric acid and an organic solvent in the form of methyl alcohol and acetone also indicates the absence of fundamental changes in the ionic state of indium in such a sorption system. Both in the presence and in the absence of these solvents, the indium ion interfacial distribution indices in the perchloric acid medium are higher than in the hydrochloric acid medium (picture 2) [31]. Thus, if the coordination properties of such acid ligands as halides, sulfate, thiocyanate [32], and to some extent nitrite [33] in aqueous-organic mixtures can be activated, which leads to the formation of more acid-saturated complexes, then the perchlorate ion under these conditions in relation to indium, as a complexing agent, remains very passive (**Figure 2**).

From other alternative points of view, attention is drawn to the study of the effect of the salting-out electrolyte on the distribution coefficient of indium during the extraction of its tenoyl-three-fluoroacetonate complex with benzene from aqueous perchlorate solutions, where the presence of complexation of indium with the perchlorate ion was confirmed.

The revealed relationship between the salting-out parameter and the stability of indium complexes with various anions formed in the aqueous phase indicates that the strength of the acidic complexes by the nature of the ligand changes in the series of salts: NaCl > > NaNO3 > NaClO4 [34].

A characteristic feature of indium perchlorate solutions, like other indium salts, is the extremely high viscosity of aqueous solutions of In(ClO4)3, due to the increased degree of hydration of the three-charged indium ion [6]. A simple substance with the composition In(ClO4)3 ~ 8H2O crystallizes from concentrated aqueous solutions of indium perchlorate [11], and in dilute perchloric acid, indium is in the form of the cation [In(H2O)6] 3+.

*Post-Transition Metals*

perchlorate ions ClO4

nuclei in aqueous-organic mixtures [22].

−

aqueous mixtures and organic media [25].

with various oxygen-containing solvents.

*perchloric acid: 1 - Ga (III), 2 - In (III), 3 - Tl (III) [26].*

ClO4 −

aquocomplex is stable in acidic perchlorate solutions, and in the studied concentra-

There is no evidence of the complexing effect of the highly concentrated electrolyte NaClO4 1.1÷9.1 M and by electrophoresis [19]. Spectrophotometrically in the ultraviolet region of the spectrum, there were no significant signs of direct interaction in aqueous solutions of In(ClO4)3 salts [20]. Also, no intrinsic complexation influencing the activity of In3+ was reliably detected up to a sodium perchlorate concentration

Similar results, denying the likelihood of coordination interaction of In3+ with

The proton-magnetic resonance measurement of the coordination number of perchlorate water-organic systems testifies to the six fold coordination of water molecules around the indium cation and to the absence of strong evidence of contact ion pairing [23, 24]. It was not possible to detect the binding of indium to

The absence of complex compounds of indium with perchlorate ion is also indicated by the data of liquid extraction, in particular, three n-octylamine does not extract indium from a solution with an HClO4 concentration less than 2 M [4]. At the same time, from concentrated solutions of perchloric acid for cationic reagents - alkylphosphoric acids (for example, di-2-ethylhexylphosphoric acid; **Figure 1**) - a possible extractable form of indium compounds is the complex cation [InClO4]2+ [26]. It is also assumed that during the extraction of indium in aqueous solutions of hydrochloric acid at its various concentrations and constant ionic strength maintained by the addition of perchloric acid, indium is present in the organic phase in the form of ionic aggregates HClO4⋅HInCl4 [27]. The latter formation is possibly caused by the coextractability of perchloric acid due to its higher extraction affinity as compared to hydrochloric acid. In the aqueous phase, there are only chloride complexes, which are subjected to extraction

The likelihood of the formation of perchlorate and mixed-ligand complexes also applies to extraction systems based on 4-methyl-2-pentanone and 4-methyl-2-pentanol, the extractable forms of which are compounds of the composition [In(ClO4)3], [InHal(ClO4)2], [InHal2(ClO4)], where bromine, iodide, or thiocyanate ion is present

*Extraction of III subgroup metal ions with di (2-ethylhexyl) phosphoric acid depending on the concentration of* 

by special experiments carried out in mixed water-non-

and P31

, were obtained when studying the solvation of cations by NMR on H1

tion range, neither inner sphere nor hydroxostructures are formed [9].

of 16 mol/kg [19, 21] and with an In(ClO4)3 content of more than 4 M [6, 9].

**42**

**Figure 1.**

#### **Figure 2.**

*Dependence of the distribution coefficients of indium in 0.1 M HClO4 (1.3) and 0.1 M HCl (2, 4) on the content of the organic solvent: 1 and 2 - methanol; 3 and 4 - acetone [31].*
