**2. Study of ion hydration by the method of electrical conductivity in the system**

"In(ClO4) 3 - HClO4– H2O" shows that the total number of water molecules oriented by the cation is nIn3+ = ~ 9, which includes water molecules that make up the near and far environment of the cation. The decrease in nIn3+ relative to the maximum value equal to 12 reflects the approach of the hydration and anionic environment of indium to what is characteristic of crystalline hydrates, and indium perchlorate crystallizes from an aqueous solution with eight water molecules. In the series of cations ΙΙΙ of the Al3+-In3+ subgroup, there is a tendency to a decrease in nMes+ with an increase in the crystal chemical radius. The reason for this is the decrease in the polarizing ability of the cations. Consequently, this leads to a weakening of the bonds of near and outer-sphere water molecules with a probable increase in the residence time of anions near the [Me(H2O)6] 3+ cation [35].

The solubility of indium perchlorate salt at 0° and 25°C is 3.23 and 3.53 mol/kg H2O, respectively. More accurately speaking about the macroscopic properties, about the possible composition of crystalline hydrates precipitating into the bottom phase, about the processes preceding crystal formation, allow the polytherms of solubility [36]. Their analysis shows that there is a qualitative similarity in the solubility polytherms of the aluminum subgroup perchlorates. The value of the molar fraction of water unbound to salt in the eutectic for perchlorates is constant (Nw = 0.94 ± 0.1). The freezing temperatures of eutectic compositions are close to −28 ÷ −31°С and all curves have an inflection - a maximum that corresponds to the existence of a chemical compound. In the case of indium perchlorate, this is a 28-aqueous crystalline hydrate. In addition, after reaching the concentration of 2.8 mol/kg H2O, the phenomenon of glass transition of this solution is observed. However, the position of the eutectic concentration on the solubility polytherm depends not so much on the nature of the cation as on the number of water molecules that are part of the

**45**

**Figure 3.**

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

crystalline hydrate. The reason for the existence of compounds enriched with water in the eutectic should be sought in the fact that the stable bridges formed as a result

Thus, providing the possibility of the formation of high-water crystalline hydrates at temperatures below 0°C. However, as the solution concentrates, structurally forced processes begin. Rearrangement of one dominant structure into another containing a smaller number of water molecules in the cybotactic group. These processes are

The structure of aqueous solutions of indium perchlorates and the state of water were studied by IR spectroscopy in the region of the first overtone of water (NIR spectra) using chemometric analysis to the concentration dependences of the spectra. It is noted that hydrolysis occurs in indium (III) perchlorate solutions, and due to the high enthalpy of hydration of In3 +, exclusively solvate-separated ion pairs are formed. In other words, the formation of complexes of the composition

ion: Тd → C3v → C2v with an increase in the concentration of indium in solu-

Perchlorate ion has the shape of a regular tetrahedron. Its hydration shell consists of eight water molecules. The distribution of these shells around the ClО<sup>4</sup>

Indium perchlorate salt is a hygroscopic substance readily soluble in water and it can be obtained by dissolving indium metal in perchloric acid at a moderate temperature. Its anhydrous modification crystallizes because of the interaction of silver perchlorate and indium chloride in a methanol solution. There are also several forms of indium hydroxopochlorates, which are precipitated in their solutions in the presence of sodium perchlorate [38]. At pH 4.82, a salt of the composition In4OH(ClO4)11 was isolated, at pH 3.77 - In2OH(ClO4)5, and in the pH range

Determination of the apparent ionic volumes of particles by measuring the density of indium (ΙΙΙ) perchloric acid solutions showed [39] that, depending on the degree of dilution, the formation of a compound of the composition

According to X-ray diffraction data, the structure of a hydrated indium ion (ΙΙΙ) in a 3 M aqueous solution of perchlorate is an aquo-complex, in which the first hydration shell contains six water molecules with a bond length of 2.15 ± 0.03 Å

entry of the perchlorate ion into the inner sphere of the indium aquion.

*Perchlorate solubility polytomes: (a) Al (ClO4)3, (b) Ga (ClO4)3, (c) In (ClO4)3 [36].*

occurs, where n = 1–2 with a decrease in the symmetry of the

2+. However, there are no convincing reasons to consider the possible

) are able to retain a large amount of water.

− ion

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

of local hydrolysis (cation ··· ОН<sup>−</sup> ··· Н3О<sup>+</sup>

accompanied by glass transition (**Figure 3**).

−

tions acidified with perchloric acid [14, 15].

is uniform. Presumably, it is low hydrating capacity [37].

In3+ (Н2О) n (ClO4)

2.56–3.14 - In4(OH)3(ClO4)9.

between In3+ and nearby H2O [40].

[In(H2O)5ClO4]

ClO4 −

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

crystalline hydrate. The reason for the existence of compounds enriched with water in the eutectic should be sought in the fact that the stable bridges formed as a result of local hydrolysis (cation ··· ОН<sup>−</sup> ··· Н3О<sup>+</sup> ) are able to retain a large amount of water. Thus, providing the possibility of the formation of high-water crystalline hydrates at temperatures below 0°C. However, as the solution concentrates, structurally forced processes begin. Rearrangement of one dominant structure into another containing a smaller number of water molecules in the cybotactic group. These processes are accompanied by glass transition (**Figure 3**).

The structure of aqueous solutions of indium perchlorates and the state of water were studied by IR spectroscopy in the region of the first overtone of water (NIR spectra) using chemometric analysis to the concentration dependences of the spectra. It is noted that hydrolysis occurs in indium (III) perchlorate solutions, and due to the high enthalpy of hydration of In3 +, exclusively solvate-separated ion pairs are formed. In other words, the formation of complexes of the composition In3+ (Н2О) n (ClO4) − occurs, where n = 1–2 with a decrease in the symmetry of the ClO4 − ion: Тd → C3v → C2v with an increase in the concentration of indium in solutions acidified with perchloric acid [14, 15].

Perchlorate ion has the shape of a regular tetrahedron. Its hydration shell consists of eight water molecules. The distribution of these shells around the ClО<sup>4</sup> − ion is uniform. Presumably, it is low hydrating capacity [37].

Indium perchlorate salt is a hygroscopic substance readily soluble in water and it can be obtained by dissolving indium metal in perchloric acid at a moderate temperature. Its anhydrous modification crystallizes because of the interaction of silver perchlorate and indium chloride in a methanol solution. There are also several forms of indium hydroxopochlorates, which are precipitated in their solutions in the presence of sodium perchlorate [38]. At pH 4.82, a salt of the composition In4OH(ClO4)11 was isolated, at pH 3.77 - In2OH(ClO4)5, and in the pH range 2.56–3.14 - In4(OH)3(ClO4)9.

Determination of the apparent ionic volumes of particles by measuring the density of indium (ΙΙΙ) perchloric acid solutions showed [39] that, depending on the degree of dilution, the formation of a compound of the composition [In(H2O)5ClO4] 2+. However, there are no convincing reasons to consider the possible entry of the perchlorate ion into the inner sphere of the indium aquion.

According to X-ray diffraction data, the structure of a hydrated indium ion (ΙΙΙ) in a 3 M aqueous solution of perchlorate is an aquo-complex, in which the first hydration shell contains six water molecules with a bond length of 2.15 ± 0.03 Å between In3+ and nearby H2O [40].

**Figure 3.** *Perchlorate solubility polytomes: (a) Al (ClO4)3, (b) Ga (ClO4)3, (c) In (ClO4)3 [36].*

*Post-Transition Metals*

**system**

**Figure 2.**

**2. Study of ion hydration by the method of electrical conductivity in the** 

*Dependence of the distribution coefficients of indium in 0.1 M HClO4 (1.3) and 0.1 M HCl (2, 4) on the* 

"In(ClO4) 3 - HClO4– H2O" shows that the total number of water molecules oriented by the cation is nIn3+ = ~ 9, which includes water molecules that make up the near and far environment of the cation. The decrease in nIn3+ relative to the maximum value equal to 12 reflects the approach of the hydration and anionic environment of indium to what is characteristic of crystalline hydrates, and indium perchlorate crystallizes from an aqueous solution with eight water molecules. In the series of cations ΙΙΙ of the Al3+-In3+ subgroup, there is a tendency to a decrease in nMes+ with an increase in the crystal chemical radius. The reason for this is the decrease in the polarizing ability of the cations. Consequently, this leads to a weakening of the bonds of near and outer-sphere water molecules with a probable

The solubility of indium perchlorate salt at 0° and 25°C is 3.23 and 3.53 mol/kg H2O, respectively. More accurately speaking about the macroscopic properties, about the possible composition of crystalline hydrates precipitating into the bottom phase, about the processes preceding crystal formation, allow the polytherms of solubility [36]. Their analysis shows that there is a qualitative similarity in the solubility polytherms of the aluminum subgroup perchlorates. The value of the molar fraction of water unbound to salt in the eutectic for perchlorates is constant (Nw = 0.94 ± 0.1). The freezing temperatures of eutectic compositions are close to −28 ÷ −31°С and all curves have an inflection - a maximum that corresponds to the existence of a chemical compound. In the case of indium perchlorate, this is a 28-aqueous crystalline hydrate. In addition, after reaching the concentration of 2.8 mol/kg H2O, the phenomenon of glass transition of this solution is observed. However, the position of the eutectic concentration on the solubility polytherm depends not so much on the nature of the cation as on the number of water molecules that are part of the

3+ cation [35].

increase in the residence time of anions near the [Me(H2O)6]

*content of the organic solvent: 1 and 2 - methanol; 3 and 4 - acetone [31].*

**44**

To establish the structure of trivalent indium perchlorate, the crystalline salt was obtained by dissolving indium (III) oxide in an equimolar amount of perchloric acid on heating– [In(Н2О)6](ClO4)3. By isothermal evaporation at room temperature from an aqueous solution of In In(ClO4)3, crystals [In(Н2О)5](ClO4)3 unstable in air were isolated. X-ray structural analysis of two forms of indium perchlorate - [In(Н2О)6](ClO4)3 and single crystal [In(Н2О)6](ClO4)3⋅3H2O indicates that both these structures are formed by hexaaquocation [In(Н2О)6] 3+ and perchlorate ions. In this case, [In(Н2О)6](ClO4)3⋅3H2O contains crystallization water molecules. But the structure of [In(Н2О)6](ClO4)3 is cubic, and [In(Н2О)6](ClO4)3⋅3H2O is rhombic, each of them with the corresponding definite geometric parameters, in which the aquated indium complexes are close to the ideal octahedron. Special attention should be paid to the hydration state of indium perchlorates. In all likelihood, the hydration composition of its salt is not eight, but nine-water, consisting of six-coordinated water molecules and three crystallization ones. At the same time, the existence of a six-water modification unstable in air that does not contain molecules of crystallized water is possible. However, since the compound is highly hygroscopic, it is possible that partial dehydration occurs in the processes of prepreparation of samples for chemical analysis [In(Н2О)6](ClO4)3⋅3H2O [41].

The available X-ray diffraction measurements carried out for perchlorate solutions of indium (ΙΙΙ) at temperatures from 25 to 250° C under water vapor pressure indicate that the distance In3+ − oxygen (water) in the octahedral configuration of the aqua complex remains constant and equal to 2.14 ± 0.01 Å. In 1.0 M HClO4 solutions, the formation of the ion pair In3+ − perchlorate [InClO4(H2O)5] 2+ is observed, in which the distance In3+ − chlorine (perchlorate) changes from 3.14 to 3.12 Å with an increase in temperature to 250° С. At the same time, no noticeable destruction of the octahedral hydration shell of the aqua-ion of indium at temperatures up to 300° C was recorded [42].

In addition to the crystalline hydrate of the composition In(ClO4)3⋅8H2O, isolated from an aqueous solution, the corresponding dimethylforamide solvate In(ClO4)3⋅6(CH3)2NCHO was isolated by the preparative method of double recrystallization due to the solvation effect caused by the peculiarities of the chemical interaction of indium ions with molecules of an organic solvent [43].

The anhydrous salt of indium (III) perchlorate is obtained in the course of the exchange reaction between InCl3 or InJ3 with AgClO4 in methanol solution [44].

Sequential thermal dehydration of indium perchlorate heptahydrate leads to the decomposition of the salt, the final product of which is indium trioxide [45].

When studying the effect of the composition and concentration of the watersalt system on the EMF of the cell Hg(liquid)//Hg2Cl2(solid.)/NaCl(saturated.)/Na*Ani*// Ме(ClO4)n, In(ClO4)3/In(solid.), где Ме*n*<sup>+</sup> = Li, Na, Mg; Na*Ani* = 5416 M NaCl, 4,0 M NaNO3, 3,72 M and 6,72 M NaClO4 it was shown that the nature of the salts that form the salt bridge and their amount have a definite effect on the EMF of the cell. The greatest difference in the EMF values was noted when comparing the units of 4.0 M NaNO3 and 6.72 M NaClO4, and in the case of 3.72 M NaClO4, the values are very close. The chemical composition and concentration of the salt background have the greatest effect on the emf and the activity coefficient of the In3 + cation (γ ±): the γ ± values rapidly increase (by 5–6 orders of magnitude) with a change in the magnesium salt content from 0.5 to 4 M and up to 13 M sodium salts. Depending on the nature of the salt background, γ ± is ranked in the order Mg(ClO4)2 > LiClO4 > NaClO4 [21].

IR spectroscopy of the synthesized series of compounds of the cationic type [In(*Lig*)n](ClO4)3, when n = 6, 4, 3, and 2, and the ligands are urea, dimethyl sulfoxide, *Ph*3P, *Ph*3PO4, 2,2′-*Dipy*, *En*, 2,2,2′-three-pyridyl and others, indicates that the perchlorate ion is a part of the anionic part of the complex structure [46]. By means

**47**

hydrolysis.

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

of an exchange reaction in acetone solutions, hexa aqua salt [In(H2O)6] (ClO4)3 under the action of dimethyl sulfoxide or dimethylformamide is easily converted into solvates [In(DMSO)6](ClO4)3 and [In(DMFA)6](ClO4)3 [47]. Subsequently, X-ray structural studies established the structure of the crystal complex of indium

Thus, there are clearly no compelling reasons to consider the existence of complexes of indium with perchlorate ion, especially its anionic forms, as possible, and as a consequence, the indium ion in such a medium is a simple hydrated cation. Apparently, under certain conditions, it is possible to admit the formation of ion pairs, where the perchlorate ligand is localized in the outer sphere with respect to

Therefore, in the practice of studying the complexing properties of indium, as well as most other metal ions, salt perchlorate and perchloric acid are traditionally used to create a given ionic strength of a solution and as a source of acid anions that do not form complexes. And also in those cases when it is necessary to assess the interaction of cations, for example, with water, not complicated by the formation of

The macro-properties of aqueous solutions of electrolytes of the gallium subgroup are significantly influenced by the peculiarities of the interaction of metal cations with water. The regularities of changes in such characteristics as the bulk properties of perchlorate solutions, isobaric expandability, adiabatic compressibility and heat capacity (isobaric and isochoristic) [49, 50] were analyzed from the point of view of the specificity of reactions of metal cations with dipoles of water molecules, depending on their electronic structure p- and d-metals of the third

It is quite natural that the studied macroproperties change nonmonotonically in the gallium subgroup. In this case, the type of non-monotony corresponds to the unequal sensitivity of each property to one or another result of interaction with water. It can be seen from **Figure 4** that when passing from the dependences ∆Fк to the dependences ∆V, ∆FE and ∆Ср, the direction of the break in the Ga – In – Tl line gradually changes to the opposite. It follows from this that the ratio of the factors of water binding and its polarization is different for different properties. The factor of water binding predominates in the influence of the ∆Fк compressibility, which leads to the appearance of a rather sharp maximum on the "∆Fк - NGa-In-Tl" contour at the point of the least vigorously hydrated indium ion. In the case of the characteristics of the specific volume ∆V, the effect of compression of the bound water is partly compensated by the formation of openwork outer-sphere associates, as a result of

The course of the dependence "∆FE - NGa-In-Tl" is antibate to the curve "∆Fк - NGa-In-Tl", which may, firstly, be a consequence of the unequal degree of compaction of water molecules during hydration, and the greater the degree of compaction, the more ∆FE, and, secondly, is due to different degrees of water polarization and localized hydrolysis of cations. Finally, the dependence "∆Ср - NGa-In-Tl" demonstrates the absolute predominance of the effects of water polarization and localized hydrolysis over the influence of differences in the degree of water binding by cations, since the last of these factors should have caused the reverse course of the curve. Such a significant positive effect of water polarization and localized hydrolysis on heat capacity is apparently caused by corresponding changes in the set of frequencies of intra- and intermolecular vibrations of the aqua complex as a result of polarization, as well as redistribution of "O – H" bonds and hydrogen bonds due to local

The comparisons made refer to the region of relatively dilute solutions. With an increase in concentration, the pattern of changes in properties from subgroup

hexa (dimethylsulfoxide) perchlorate (ΙΙΙ) [In(*ДМСО*)6](ClO4)3 [48].

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

the central atom, i.e. attached to all aquo-ion.

which the maximum on the ∆V curve disappears.

their acidic complexes.

group [51].

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

of an exchange reaction in acetone solutions, hexa aqua salt [In(H2O)6] (ClO4)3 under the action of dimethyl sulfoxide or dimethylformamide is easily converted into solvates [In(DMSO)6](ClO4)3 and [In(DMFA)6](ClO4)3 [47]. Subsequently, X-ray structural studies established the structure of the crystal complex of indium hexa (dimethylsulfoxide) perchlorate (ΙΙΙ) [In(*ДМСО*)6](ClO4)3 [48].

Thus, there are clearly no compelling reasons to consider the existence of complexes of indium with perchlorate ion, especially its anionic forms, as possible, and as a consequence, the indium ion in such a medium is a simple hydrated cation. Apparently, under certain conditions, it is possible to admit the formation of ion pairs, where the perchlorate ligand is localized in the outer sphere with respect to the central atom, i.e. attached to all aquo-ion.

Therefore, in the practice of studying the complexing properties of indium, as well as most other metal ions, salt perchlorate and perchloric acid are traditionally used to create a given ionic strength of a solution and as a source of acid anions that do not form complexes. And also in those cases when it is necessary to assess the interaction of cations, for example, with water, not complicated by the formation of their acidic complexes.

The macro-properties of aqueous solutions of electrolytes of the gallium subgroup are significantly influenced by the peculiarities of the interaction of metal cations with water. The regularities of changes in such characteristics as the bulk properties of perchlorate solutions, isobaric expandability, adiabatic compressibility and heat capacity (isobaric and isochoristic) [49, 50] were analyzed from the point of view of the specificity of reactions of metal cations with dipoles of water molecules, depending on their electronic structure p- and d-metals of the third group [51].

It is quite natural that the studied macroproperties change nonmonotonically in the gallium subgroup. In this case, the type of non-monotony corresponds to the unequal sensitivity of each property to one or another result of interaction with water. It can be seen from **Figure 4** that when passing from the dependences ∆Fк to the dependences ∆V, ∆FE and ∆Ср, the direction of the break in the Ga – In – Tl line gradually changes to the opposite. It follows from this that the ratio of the factors of water binding and its polarization is different for different properties. The factor of water binding predominates in the influence of the ∆Fк compressibility, which leads to the appearance of a rather sharp maximum on the "∆Fк - NGa-In-Tl" contour at the point of the least vigorously hydrated indium ion. In the case of the characteristics of the specific volume ∆V, the effect of compression of the bound water is partly compensated by the formation of openwork outer-sphere associates, as a result of which the maximum on the ∆V curve disappears.

The course of the dependence "∆FE - NGa-In-Tl" is antibate to the curve "∆Fк - NGa-In-Tl", which may, firstly, be a consequence of the unequal degree of compaction of water molecules during hydration, and the greater the degree of compaction, the more ∆FE, and, secondly, is due to different degrees of water polarization and localized hydrolysis of cations. Finally, the dependence "∆Ср - NGa-In-Tl" demonstrates the absolute predominance of the effects of water polarization and localized hydrolysis over the influence of differences in the degree of water binding by cations, since the last of these factors should have caused the reverse course of the curve. Such a significant positive effect of water polarization and localized hydrolysis on heat capacity is apparently caused by corresponding changes in the set of frequencies of intra- and intermolecular vibrations of the aqua complex as a result of polarization, as well as redistribution of "O – H" bonds and hydrogen bonds due to local hydrolysis.

The comparisons made refer to the region of relatively dilute solutions. With an increase in concentration, the pattern of changes in properties from subgroup

*Post-Transition Metals*

C was recorded [42].

Ме(ClO4)n, In(ClO4)3/In(solid.), где Ме*n*<sup>+</sup>

the order Mg(ClO4)2 > LiClO4 > NaClO4 [21].

To establish the structure of trivalent indium perchlorate, the crystalline salt was obtained by dissolving indium (III) oxide in an equimolar amount of perchloric acid on heating– [In(Н2О)6](ClO4)3. By isothermal evaporation at room temperature from an aqueous solution of In In(ClO4)3, crystals [In(Н2О)5](ClO4)3 unstable in air were isolated. X-ray structural analysis of two forms of indium perchlorate - [In(Н2О)6](ClO4)3 and single crystal [In(Н2О)6](ClO4)3⋅3H2O indicates that both

In this case, [In(Н2О)6](ClO4)3⋅3H2O contains crystallization water molecules. But the structure of [In(Н2О)6](ClO4)3 is cubic, and [In(Н2О)6](ClO4)3⋅3H2O is rhombic, each of them with the corresponding definite geometric parameters, in which the aquated indium complexes are close to the ideal octahedron. Special attention should be paid to the hydration state of indium perchlorates. In all likelihood, the hydration composition of its salt is not eight, but nine-water, consisting of six-coordinated water molecules and three crystallization ones. At the same time, the existence of a six-water modification unstable in air that does not contain molecules of crystallized water is possible. However, since the compound is highly hygroscopic, it is possible that partial dehydration occurs in the processes of prepreparation of samples for chemical analysis [In(Н2О)6](ClO4)3⋅3H2O [41].

The available X-ray diffraction measurements carried out for perchlorate solutions of indium (ΙΙΙ) at temperatures from 25 to 250° C under water vapor pressure indicate that the distance In3+ − oxygen (water) in the octahedral configuration of the aqua complex remains constant and equal to 2.14 ± 0.01 Å. In 1.0 M HClO4 solu-

in which the distance In3+ − chlorine (perchlorate) changes from 3.14 to 3.12 Å with an increase in temperature to 250° С. At the same time, no noticeable destruction of the octahedral hydration shell of the aqua-ion of indium at temperatures up to 300°

In addition to the crystalline hydrate of the composition In(ClO4)3⋅8H2O, isolated from an aqueous solution, the corresponding dimethylforamide solvate In(ClO4)3⋅6(CH3)2NCHO was isolated by the preparative method of double recrystallization due to the solvation effect caused by the peculiarities of the chemical

The anhydrous salt of indium (III) perchlorate is obtained in the course of the exchange reaction between InCl3 or InJ3 with AgClO4 in methanol solution [44]. Sequential thermal dehydration of indium perchlorate heptahydrate leads to the

When studying the effect of the composition and concentration of the watersalt system on the EMF of the cell Hg(liquid)//Hg2Cl2(solid.)/NaCl(saturated.)/Na*Ani*//

= Li, Na, Mg; Na*Ani* = 5416 M NaCl,

decomposition of the salt, the final product of which is indium trioxide [45].

4,0 M NaNO3, 3,72 M and 6,72 M NaClO4 it was shown that the nature of the salts that form the salt bridge and their amount have a definite effect on the EMF of the cell. The greatest difference in the EMF values was noted when comparing the units of 4.0 M NaNO3 and 6.72 M NaClO4, and in the case of 3.72 M NaClO4, the values are very close. The chemical composition and concentration of the salt background have the greatest effect on the emf and the activity coefficient of the In3 + cation (γ ±): the γ ± values rapidly increase (by 5–6 orders of magnitude) with a change in the magnesium salt content from 0.5 to 4 M and up to 13 M sodium salts. Depending on the nature of the salt background, γ ± is ranked in

IR spectroscopy of the synthesized series of compounds of the cationic type [In(*Lig*)n](ClO4)3, when n = 6, 4, 3, and 2, and the ligands are urea, dimethyl sulfoxide, *Ph*3P, *Ph*3PO4, 2,2′-*Dipy*, *En*, 2,2,2′-three-pyridyl and others, indicates that the perchlorate ion is a part of the anionic part of the complex structure [46]. By means

tions, the formation of the ion pair In3+ − perchlorate [InClO4(H2O)5]

interaction of indium ions with molecules of an organic solvent [43].

3+ and perchlorate ions.

2+ is observed,

these structures are formed by hexaaquocation [In(Н2О)6]

**46**

#### **Figure 4.**

*Dependence of changes in macro properties during the formation of perchlorate solutions on the hydration characteristics of group III cations: 1 -* Δ*(Ср - Сv) (1.0 M solutions) (Cp and Cv isobaric and isochoric heat capacities); 2 -* Δ*V (specific volume); 3 -* Δ*FE (expandability); 4 -* Δ*FC (compressibility); 5 -* Δ*Cr (0.5 M); 6 - log* β*1 (*β*1 is the constant of the 1st stage of cation hydrolysis); 7 -* Δ*Нr (enthalpy of hydration of the cation); 8 -* Δ*Sr (entropy of cation hydration) [51].*

to subgroup, as well as within the subgroup, changes. For example, in **Figure 5** dependences "∆V - NIII" for the subgroup of gallium and scandium change places with increasing salt concentration. This is probably because at low concentrations the ∆V values reflect largely the change in the volume of the outer-sphere water, and at high concentrations, the water in the inner coordination sphere of cations.

Comparison of the tendencies of changes in the bulk properties of solutions from concentration **Figure 5**, apparently, show that the relative compression of the

**49**

likely [51].

**Figure 5.**

*mol/dm3*

larger its radius [52].

are arranged in a row ClO4

perchlorate [16].

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

outer-sphere water is greater for d-metal ions and the compression of water in the

*Dependence of changes in specific volume during the formation of solutions perchlorates with concentration,* 

In concentrated solutions, the regularities of changes in properties in both groups depend mainly on the state of water in the inner sphere: in the subgroup of d-elements - on the degree of its compression, and in the subgroup of p-elements on the degree of attraction and polarization. In dilute solutions, an important role is played by the state of the outer-sphere water, namely the degree of its destruction or, conversely, structuring. However, if, in the p-subgroup, the structuring of the outer-sphere water is more typical, and for the d-subgroup, destructuring is most

The viscosity and density of perchlorate solutions are significantly influenced by the ability of cations to hydrate. The increased relative kinematic viscosity and the relative activation energy of the aqueous flow of solutions of aluminum, gallium and indium perchlorates is obviously a consequence of the formation of a hydration shell with a branched network of very strong hydrogen bonds by the cation. Within the gallium subgroup, the positive hydration of the ion is expressed the weaker, the

In this case, although the anion is not an indifferent component, its nature does not play a particularly important role in the nature of changes in the macroproperties of solutions, since the perchlorate ion has an approximately equal effect on the destruction of the primary structure of water in all systems. The only exceptions are Tl(ClO4)3 solutions, where the formation of outer-sphere ionic associates

From the analysis of the compensation spectra of the multiply disturbed total internal reflection, it follows that according to their destructive effect, the anions

all. The formation of a covalent bond "water cation" leads to the strengthening of H-bonds in water, and in the case of solutions of triple-charged cations, additional stabilization of the water structure takes place, which complicates the process of destruction of hydrogen bonds even with such a strongly destructive anion as

The interrelation between the formation of outer-sphere water associates and the phenomenon of hydrolysis is especially evident from the comparison of the heat capacities of perchlorates in the series of triply charged cations of metals of

, and for sulfocation it is not found at

inner sphere is, on average, greater for p-metal ions.

*: 1–0.1; 2–0.5; 3–1.0; 4–3.0 by nature trivalent cations [51].*

with hydrated thallium (ΙΙΙ) cations is evident [51].

− > NO3 − > > Cl−

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

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

#### **Figure 5.**

*Post-Transition Metals*

**48**

**Figure 4.**

*8 -* Δ*Sr (entropy of cation hydration) [51].*

to subgroup, as well as within the subgroup, changes. For example, in **Figure 5** dependences "∆V - NIII" for the subgroup of gallium and scandium change places with increasing salt concentration. This is probably because at low concentrations the ∆V values reflect largely the change in the volume of the outer-sphere water, and at high concentrations, the water in the inner coordination sphere of cations. Comparison of the tendencies of changes in the bulk properties of solutions from concentration **Figure 5**, apparently, show that the relative compression of the

*Dependence of changes in macro properties during the formation of perchlorate solutions on the hydration characteristics of group III cations: 1 -* Δ*(Ср - Сv) (1.0 M solutions) (Cp and Cv isobaric and isochoric heat capacities); 2 -* Δ*V (specific volume); 3 -* Δ*FE (expandability); 4 -* Δ*FC (compressibility); 5 -* Δ*Cr (0.5 M); 6 - log* β*1 (*β*1 is the constant of the 1st stage of cation hydrolysis); 7 -* Δ*Нr (enthalpy of hydration of the cation);* 

*Dependence of changes in specific volume during the formation of solutions perchlorates with concentration, mol/dm3 : 1–0.1; 2–0.5; 3–1.0; 4–3.0 by nature trivalent cations [51].*

outer-sphere water is greater for d-metal ions and the compression of water in the inner sphere is, on average, greater for p-metal ions.

In concentrated solutions, the regularities of changes in properties in both groups depend mainly on the state of water in the inner sphere: in the subgroup of d-elements - on the degree of its compression, and in the subgroup of p-elements on the degree of attraction and polarization. In dilute solutions, an important role is played by the state of the outer-sphere water, namely the degree of its destruction or, conversely, structuring. However, if, in the p-subgroup, the structuring of the outer-sphere water is more typical, and for the d-subgroup, destructuring is most likely [51].

The viscosity and density of perchlorate solutions are significantly influenced by the ability of cations to hydrate. The increased relative kinematic viscosity and the relative activation energy of the aqueous flow of solutions of aluminum, gallium and indium perchlorates is obviously a consequence of the formation of a hydration shell with a branched network of very strong hydrogen bonds by the cation. Within the gallium subgroup, the positive hydration of the ion is expressed the weaker, the larger its radius [52].

In this case, although the anion is not an indifferent component, its nature does not play a particularly important role in the nature of changes in the macroproperties of solutions, since the perchlorate ion has an approximately equal effect on the destruction of the primary structure of water in all systems. The only exceptions are Tl(ClO4)3 solutions, where the formation of outer-sphere ionic associates with hydrated thallium (ΙΙΙ) cations is evident [51].

From the analysis of the compensation spectra of the multiply disturbed total internal reflection, it follows that according to their destructive effect, the anions are arranged in a row ClO4 − > NO3 − > > Cl− , and for sulfocation it is not found at all. The formation of a covalent bond "water cation" leads to the strengthening of H-bonds in water, and in the case of solutions of triple-charged cations, additional stabilization of the water structure takes place, which complicates the process of destruction of hydrogen bonds even with such a strongly destructive anion as perchlorate [16].

The interrelation between the formation of outer-sphere water associates and the phenomenon of hydrolysis is especially evident from the comparison of the heat capacities of perchlorates in the series of triply charged cations of metals of

the gallium subgroup with the values: 6 - lg β1 (β1 is the constant of the 1st stage of hydrolysis of the cation); 7 - ΔНr (enthalpy of hydration of the cation); 8 - ΔSr (entropy of cation hydration) [51, 53, 54] where the polarizing effect of cations on water makes the greatest contribution to the heat capacity even in dilute solutions. All this, moreover, agrees with the results of studying the vibrational spectra of solutions of gallium and indium perchlorates, showing that the water molecules surrounding these ions are polarized not only in the first, but also in the second coordination layer, thus the fraction of polarized water molecules in these solutions is unusual. But high, their contribution to the heat capacity of the solution is also significant [55]. Thallium (III) perchlorate solutions have the highest heat capacity, but here it should be noted that the reason for this in this case may be not only water polarization and local hydrolysis, but also the tendency of Tl3+ ions to form perchlorate complexes [56].

The form of the dependences of the apparent molar heat capacity of the PS P2 of group III metal perchlorates on the salt concentration deviates from the rectilinear, especially for La(ClO4)3 and Tl(ClO4)3 **Figure 6a**. The regularities of changes in PS P2 are also explained in the light of ideas about the energy of interaction of ions with water, the state of water in hydration shells, and the effect of ions on the structure of water. In the gallium subgroup, the role of another factor, the hydrolysis of aquocations, increases significantly. Probably, the point for Ga(ClO4)3 owes its higher position to hydrolysis as compared with indium in **Figure 6b** [49].

Of the entire sum of contributions to the total change in the heat capacity of dissolution of perchlorates, the greatest effect of the specific nature of cations on the heat capacity of solutions occurs through the outer-sphere interactions (Δ*С*V). As you can see (**Figure 6b**). for the considered types of electrolytes in a significant range of concentrations ΔС are negative, which may be due not only to the outersphere hydration of ions, but also to their destructive effect on a certain part of the outer-sphere water. It is not yet possible to separate these two effects. However, at high concentrations, the sign of ΔCV hanges to the opposite, indicating, apparently, an increase in the role of the effect of outer-sphere aqueous, as well as ion-ion associates ([50], p. 266).

The recorded changes in the bulk properties of perchlorates of the aluminum subgroup from their concentration are also associated with the individual nature

#### **Figure 6.**

*Dependence of the apparent molar heat capacity of metal perchlorates (Ps) (a, b) [49] and the heat capacity due to outer-sphere interactions of ions (*Δ*C) (c) ([53], p. 266), on the concentration: 1 - Al(ClO4)3, 2 - In(ClO4)3, 3 - Sc(ClO4)3, 4 - Ga(ClO4)3, 5 - La(ClO4)3, 6 - Y(ClO4)3, 7 - Tl(ClO4)3, 8 and 9 МеIII(ClO4)3–0.1 m, 10–0.5 m, 11–3.0 m.*

**51**

**Figure 7.**

the cation [13].

at a concentration of 300 g/dm3

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

As follows from **Figure 7** the values of FV and compressibility FК monotonically increase with an increase in the electrolyte concentration, but the FV for Al(ClO4)3 decrease, and in the case of Ga(ClO4)3 and In(ClO4)3, in all likelihood, pass through a maximum. The dependences of FV on m½ are straightforward, and FK are curvilinear and for different cations they differ from each other both in their position and in the angle of inclination. The profile of the expansibility curves of PU differs greatly from the characteristics of volumes (FV) and compressibility (FK), including

The influence of the coordination number on the compressibility of cations is, of course, due to the fact that the coordination water in the first layer practically loses its compressibility. The fact of compressibility manifests itself rather through external-sphere water than through coordination water. This is probably why the hydration numbers of cations, calculated from the compressibility data, turn out to be higher than their c.n. The data are reflected in the **Table 1**, which also shows the

The correlation between the polarizing forces of the cation (P) and the eutectic concentration of aqueous solutions of perchlorates (**Figure 8**) indicates that the higher the value of the polarizing force, the stronger the cation interacts with water molecules. Therefore, due to the greater polarizing force of the cations of the gallium subgroup, which characterizes the state of the "cation - water" bond, there is a significant destruction of the intrinsic structure of water and an increase in the number of water molecules drawn from the solution into the sphere of influence of

In addition to indium perchlorate salts, for elements of the aluminum subgroup, their iodates МеΙΙΙ(JO3)3⋅*n*H2O, are also known, including indium iodate with the composition In(JO3)3⋅2H2O [57, 58]. In contrast to perchlorate, indium iodate is characterized by a low degree of solubility, which in water at a temperature of 25° C is ~0,05% by weight (logSP = 2.5), and slightly more passes into solution under the action of nitric acid, showing the maximum value of solubility equal to 16.9 g/dm3

Indium (III) is quantitatively precipitated from the solution in the pH range 1.9–7 with sodium (potassium) periodate with the formation of a precipitate

*Dependence of: a – apparent molar volumes (FV), b – compressibility (FК) and c – expandability (FЕ). From* 

*m perchlorates: 1 - Al(ClO4)3, 2 - Ga(ClO4)3 3– In (ClO4)3 [49].*

of the interaction of ions with water and among themselves. The densities of Al(ClO4)3, Ga(ClO4)3 In(ClO4)3 solutions at temperatures of 24, 25, and 27° C, the speed of sound, specific adiabatic compressibility and isobaric expandability in the concentration range from 0.1 m to saturation, and the shape dependences of appar-

ent molar volumes (FV), compressibility (FК) and expandability (FЕ).

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

the sequence of arrangement of metal ions [49, 50].

change in the isochoric heat capacity of similar electrolytes [53].

HNO3.

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

of the interaction of ions with water and among themselves. The densities of Al(ClO4)3, Ga(ClO4)3 In(ClO4)3 solutions at temperatures of 24, 25, and 27° C, the speed of sound, specific adiabatic compressibility and isobaric expandability in the concentration range from 0.1 m to saturation, and the shape dependences of apparent molar volumes (FV), compressibility (FК) and expandability (FЕ).

As follows from **Figure 7** the values of FV and compressibility FК monotonically increase with an increase in the electrolyte concentration, but the FV for Al(ClO4)3 decrease, and in the case of Ga(ClO4)3 and In(ClO4)3, in all likelihood, pass through a maximum. The dependences of FV on m½ are straightforward, and FK are curvilinear and for different cations they differ from each other both in their position and in the angle of inclination. The profile of the expansibility curves of PU differs greatly from the characteristics of volumes (FV) and compressibility (FK), including the sequence of arrangement of metal ions [49, 50].

The influence of the coordination number on the compressibility of cations is, of course, due to the fact that the coordination water in the first layer practically loses its compressibility. The fact of compressibility manifests itself rather through external-sphere water than through coordination water. This is probably why the hydration numbers of cations, calculated from the compressibility data, turn out to be higher than their c.n. The data are reflected in the **Table 1**, which also shows the change in the isochoric heat capacity of similar electrolytes [53].

The correlation between the polarizing forces of the cation (P) and the eutectic concentration of aqueous solutions of perchlorates (**Figure 8**) indicates that the higher the value of the polarizing force, the stronger the cation interacts with water molecules. Therefore, due to the greater polarizing force of the cations of the gallium subgroup, which characterizes the state of the "cation - water" bond, there is a significant destruction of the intrinsic structure of water and an increase in the number of water molecules drawn from the solution into the sphere of influence of the cation [13].

In addition to indium perchlorate salts, for elements of the aluminum subgroup, their iodates МеΙΙΙ(JO3)3⋅*n*H2O, are also known, including indium iodate with the composition In(JO3)3⋅2H2O [57, 58]. In contrast to perchlorate, indium iodate is characterized by a low degree of solubility, which in water at a temperature of 25° C is ~0,05% by weight (logSP = 2.5), and slightly more passes into solution under the action of nitric acid, showing the maximum value of solubility equal to 16.9 g/dm3 at a concentration of 300 g/dm3 HNO3.

Indium (III) is quantitatively precipitated from the solution in the pH range 1.9–7 with sodium (potassium) periodate with the formation of a precipitate

#### **Figure 7.**

*Dependence of: a – apparent molar volumes (FV), b – compressibility (FК) and c – expandability (FЕ). From m perchlorates: 1 - Al(ClO4)3, 2 - Ga(ClO4)3 3– In (ClO4)3 [49].*

*Post-Transition Metals*

rate complexes [56].

associates ([50], p. 266).

the gallium subgroup with the values: 6 - lg β1 (β1 is the constant of the 1st stage of hydrolysis of the cation); 7 - ΔНr (enthalpy of hydration of the cation); 8 - ΔSr (entropy of cation hydration) [51, 53, 54] where the polarizing effect of cations on water makes the greatest contribution to the heat capacity even in dilute solutions. All this, moreover, agrees with the results of studying the vibrational spectra of solutions of gallium and indium perchlorates, showing that the water molecules surrounding these ions are polarized not only in the first, but also in the second coordination layer, thus the fraction of polarized water molecules in these solutions is unusual. But high, their contribution to the heat capacity of the solution is also significant [55]. Thallium (III) perchlorate solutions have the highest heat capacity, but here it should be noted that the reason for this in this case may be not only water polarization and local hydrolysis, but also the tendency of Tl3+ ions to form perchlo-

The form of the dependences of the apparent molar heat capacity of the PS P2 of group III metal perchlorates on the salt concentration deviates from the rectilinear, especially for La(ClO4)3 and Tl(ClO4)3 **Figure 6a**. The regularities of changes in PS P2 are also explained in the light of ideas about the energy of interaction of ions with water, the state of water in hydration shells, and the effect of ions on the structure of water. In the gallium subgroup, the role of another factor, the hydrolysis of aquocations, increases significantly. Probably, the point for Ga(ClO4)3 owes its higher

Of the entire sum of contributions to the total change in the heat capacity of dissolution of perchlorates, the greatest effect of the specific nature of cations on the heat capacity of solutions occurs through the outer-sphere interactions (Δ*С*V). As you can see (**Figure 6b**). for the considered types of electrolytes in a significant range of concentrations ΔС are negative, which may be due not only to the outersphere hydration of ions, but also to their destructive effect on a certain part of the outer-sphere water. It is not yet possible to separate these two effects. However, at high concentrations, the sign of ΔCV hanges to the opposite, indicating, apparently, an increase in the role of the effect of outer-sphere aqueous, as well as ion-ion

The recorded changes in the bulk properties of perchlorates of the aluminum subgroup from their concentration are also associated with the individual nature

*Dependence of the apparent molar heat capacity of metal perchlorates (Ps) (a, b) [49] and the heat capacity due to outer-sphere interactions of ions (*Δ*C) (c) ([53], p. 266), on the concentration: 1 - Al(ClO4)3, 2 - In(ClO4)3, 3 - Sc(ClO4)3, 4 - Ga(ClO4)3, 5 - La(ClO4)3, 6 - Y(ClO4)3, 7 - Tl(ClO4)3, 8 and 9* 

position to hydrolysis as compared with indium in **Figure 6b** [49].

**50**

**Figure 6.**

*МеIII(ClO4)3–0.1 m, 10–0.5 m, 11–3.0 m.*


#### **Table 1.**

*Change in isochoric heat capacity.*

#### **Figure 8.**

*Correlation of the polarizing forces of cations (P) and the eutectic concentration (meut) of aqueous solutions of group III perchlorates MeIII(ClO4)3 ([50], pp. 124–126).*

corresponding to formula In5(JO6)3, the composition of which is constant at a temperature of 120–270° C. The crystalline compound of indium paraperiodate is slightly soluble in water, and respectively, in 1%, 0.3% and 0.5–1% carbonate, nitrate and ammonium acetate, but it is readily soluble in dilute mineral acids. The solubility of indium paraperiodate in water at 20° C is 6,4⋅10−4 g-mol/dm3 or 7,9⋅10−3 g/dm3 . The gravimetric and titrimetric methods for the determination of indium using the periodate ion are based on these analytical characteristics [59].

Answering the question whether the ClO4 − ion is included in the inner coordination sphere of indium, it can be considered proven that indium acidic complexes are not formed in aqueous solutions, and in this case we are only talking about the possibility of the outer-sphere interaction of ClO4 − ions with aquocation. However, in a number of organic systems, apparently, their participation in complex formation is possible, but such states, being weaker than contact interactions, are rather difficult to fix. Perchlorate ion and perchloric acid in indium compounds perform primarily the function of a dehydrating agent; therefore, their presence leads to a change in the characteristics of the interaction of ions with water, which is reflected in the physicochemical properties of indium perchlorates.

Apparently, in relatively dilute solutions, the role of ClO4 − is reduced to destructuring water, which contributes to the stabilization of hydration shells around hydrophilic indium cations. In concentrated solutions, ClO4 − anions enter into some competition with cations for water, as a result of which, in particular, an increase in the asymmetry of coordination water molecules and its additional polarization is possible. Indium (III) cations attach a larger number of layers of water and, to varying degrees, affect its state, and through it, the action spreads further to the

**53**

**Author details**

Boris Radionov Konstantinovich and Ilya Svirsky Anatolievich\*

\*Address all correspondence to: sviskill.171993@gmail.com

provided the original work is properly cited.

Ural Federal University Named After B.N. Yeltsin, Yekaterinburg, Russia

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

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

ability, in solutions of group III perchlorates forms exclusively solvate-separated ion pairs due to the high enthalpy of hydration of the corresponding metal cations.

−

ion, being structure-forming and exhibiting a protoacceptor

ions in concentrated

property and the boundary medium. Thus, this causes either the destructuring

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

−

solutions.

Thus, the ClO4

effect or a change in the state of chemical bonds of ClO4

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

property and the boundary medium. Thus, this causes either the destructuring effect or a change in the state of chemical bonds of ClO4 − ions in concentrated solutions.

Thus, the ClO4 − ion, being structure-forming and exhibiting a protoacceptor ability, in solutions of group III perchlorates forms exclusively solvate-separated ion pairs due to the high enthalpy of hydration of the corresponding metal cations.
