3. Results and discussion

#### 3.1. Structure description

From the charge balance in [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3], it can be suggested that the average oxidation state of Cu(2)/Se(2) is equal to 3, which would fit to 33.5% of Cu2+ and 58.2% of Se4+. This outcome was confirmed by performing a calculation of bond valence sums around the centers of the cation sites. The steps and expressions used in the calculation of the bond valence are published in [12]. More specifically, the bond valence (Sij) is expressed as Sij = exp [(R0 Rij)/B], where R0 and B are the experimentally determined parameters and Rij is the bond length of the cation-anion pair [12]. The sum of the bond valence (Σ<sup>j</sup> Sij) around an ion calculated must be equal to the formal valence (Vi) of this ion, based on the valence sum rule.

In this work, our calculation shows that, for the pyramidal sites (Se1 and Se3), the sum of bond valence is ~4, which is equal to selenium formal valence. Thus, the bond valence sums around the octahedral site of Cu(2) are typically consistent with the value +2.7, confirming the presence of selenium Se4+ and cuprite Cu2+ in the same site. It is also observed that the blue single crystal [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3] crystallizes in the orthorhombic system, space group Pbn21. Structurally, the crystal structure of [Cu0.332Se0.582(HSeO3)2CuCl3(H2O)3] represents a new type of structure for complexes of hydrogen selenites (Figure 1). The building blocks [Cu0.335Se0.582(HSeO3)2] and [CuCl3(H2O)3], hereunder drawn, are arranged to form layers in the structure parallel to the (001) plane between which the lone pairs E are located (Figure 2). Due to the stereochemical activity of the lone pairs E, Se has very asymmetric coordination polyhedral SeO3 pyramids.

Spatially, the high anisotropic distribution of anions observed around each cation is characteristically of a strong stereochemical activity of their electron lone pair E for the Se1 and Se3 atoms. The consequence for the coordination polyhedral is the description of a distorted SeO3 triangular pyramid, in which the SedO(7) and SedO(8) are marginally longer than the other SedO bonds (Table 2). Thereof, the lone pair E so directed to constitute the fourth vertex of an SeO3E tetrahedron (Figure 3).

The OdSedO with angles of values 98(2) and 102(2) formed from SedO chemical bonds are situated on one side of the Se atom, whereas the other side is hitherto a "dead" zone around

Figure 1. Perspective view of the [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3] unit cell content.

3. Results and discussion

From the charge balance in [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3], it can be suggested that the average oxidation state of Cu(2)/Se(2) is equal to 3, which would fit to 33.5% of Cu2+ and 58.2% of Se4+. This outcome was confirmed by performing a calculation of bond valence sums around the centers of the cation sites. The steps and expressions used in the calculation of the bond valence are published in [12]. More specifically, the bond valence (Sij) is expressed as Sij = exp [(R0 Rij)/B], where R0 and B are the experimentally determined parameters and Rij is the

Symmetry code: a: –x + 1/2, y + 1/2, z; b: –x + 3/2, y + 1/2, z; c: –x + 3/2, y 1/2, z; d: –x + 1/2, y 1/2, z; e: –x + 1, y + 2, z + 1/2.

O5dSe1dO7 = 102(2) O5dSe1dO4 = 102(2) O7dSe1dO4 = 98(2) O3dSe3dO6 = 98(3) O3dSe3dO8 = 101(3) O6dSe3dO8 = 100(2)

O4(b)dCu2/Se2dO6(a) = 91(2) O4(b)dCu2/Se2dO3 = 179(3) O6(a)dCu2/Se2dO3 = 90(2) O4(b)dCu2/Se2dO5 = 89(2) O6(a)dCu2/Se2dO5 = 180(4) O3dCu2/Se2dO5 = 90.1(2) Cl2dCu2/Se2dO6(a) = 89.52(8) O3dCu2/Se2dCl3(e) = 89.11(5) Cl2dCu2/Se2dO3 = 91.1(4) Cl2dCu2/Se2dO4(b) = 89.83(3) O5dCu2/Se2dCl2 = 94.18(7)

O1dCu1dO2 = 88.1(3) O1dCu1dCl3 = 176(2) O1dCu1dCl2 = 90.9(2) O2dCu1dCl2 = 176.1(5) O2dCu1dCl1 = 83(2) Cl3dCu1dCl2 = 92.2(3) Cl3dCu1dCl1 = 94.1(3)

calculated must be equal to the formal valence (Vi) of this ion, based on the valence sum rule. In this work, our calculation shows that, for the pyramidal sites (Se1 and Se3), the sum of bond valence is ~4, which is equal to selenium formal valence. Thus, the bond valence sums around

Sij) around an ion

bond length of the cation-anion pair [12]. The sum of the bond valence (Σ<sup>j</sup>

Table 2. Interatomic distances for [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3] samples (this study).

3.1. Structure description

a: SeO3 polyhedron Se1dO4 = 1.70(5) Se1dO5 = 1.70(5) Se1dO7 = 1.71(5) Se3dO3 = 1.67(4) Se3dO6 = 1.66(6) Se3dO8 = 1.77(5)

32 Chalcogen Chemistry

b: Cu(Se)O4Cl2 Cu2/Se2dO3 = 1.98(4) Cu2(c)/Se2(c)dO4(b) = 1.91(4) Cu2/Se2dO5 = 1.94(4) Cu2(d)/Se2(d)dO6(a) = 2.01(5) Cu2/Se2dCl2 = 2.77(2) Cu2/Se2dCl3(e) = 2.80(2)

c: CuCl3(H2O) octahedron Cu1dCl1 = 2.66 (8) Cu1dCl2 = 2.30 (2) Cu1dCl3 = 2.30(2) Cu1dO1 = 1.99(7) Cu1dO2 = 2.02(6) Cu1dO9 = 2.21(3)

the lone pair E of the Se atom. As such, the SeO3 polyhedral has strong dipole moments, due to such a sharp asymmetry of the atomic arrangement of the first coordination spheres, which provide considerable dipole-dipole contribution to the inter-anion potentials. Taking a closer look at the structure in Figure 4, one can easily see that each Cu(1) atom is surrounded by three oxygen (O) atoms and three chlorine (Cl) atoms. This basically forms a slightly distorted octahedron with distances ranging from 1.99(7) to 2.21(3) Å for CudO and 2.30 (2) Å for

The Characterization of a Newly Layered Bimetallic Hydrogen Selenite Copper-Selenium: Synthesis and Structure

A remarkable deviation from full occupancy was exhibited in the occupancy of the Cu(2) site during refinement. This is an indication of a substitution with Se, resulting in final occupancies constrained in sum to 1.0, and refined to 0.335(4) and 0.582(2), respectively. It should be noted that the deviation from 1.0 is due to the mixed valence between Cu and Se, for Cu(2) and Se(2), respectively. As shown in Figure 5, the Cu(2)/Se(2) atoms are surrounded by four oxygen

From the earlier arguments, the structure depicted in Figure 2 can be ascribed to being formed by Cu(1), Se(2)/Cu(2) polyhedral that structurally shares chlorine (Cl) corners in infinite chains along the direction [001]. Therein, the sequential metal atoms in the chain trend schematically

polyhedral generated by the symmetry operation: 1 – x, 2 – y, �0.5 + z, in the [010] direction. As a result, the three-dimensional network is thus formed. It can be argued that the lattice cohesion may be strengthened by the hydrogen bonds within the layer (O(8)dH(7)dO(4))

dSe(2)/Cu(2)dCu(1), whereby the prime refers to the

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atoms and two chlorine atoms to form an irregular octahedron.

following Cu(1)dSe(2)/Cu(2)dCu(1)<sup>0</sup>

and (O(7)dH(8)dO(3)) or outside the layer.

Figure 4. Structural environment of copper cations Cu(1).

CudCl.

Figure 2. A projected along a-axis view of the [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3] unit cell content.

Figure 3. Environment of selenium Se(1), Se(3) cations.

the lone pair E of the Se atom. As such, the SeO3 polyhedral has strong dipole moments, due to such a sharp asymmetry of the atomic arrangement of the first coordination spheres, which provide considerable dipole-dipole contribution to the inter-anion potentials. Taking a closer look at the structure in Figure 4, one can easily see that each Cu(1) atom is surrounded by three oxygen (O) atoms and three chlorine (Cl) atoms. This basically forms a slightly distorted octahedron with distances ranging from 1.99(7) to 2.21(3) Å for CudO and 2.30 (2) Å for CudCl.

A remarkable deviation from full occupancy was exhibited in the occupancy of the Cu(2) site during refinement. This is an indication of a substitution with Se, resulting in final occupancies constrained in sum to 1.0, and refined to 0.335(4) and 0.582(2), respectively. It should be noted that the deviation from 1.0 is due to the mixed valence between Cu and Se, for Cu(2) and Se(2), respectively. As shown in Figure 5, the Cu(2)/Se(2) atoms are surrounded by four oxygen atoms and two chlorine atoms to form an irregular octahedron.

From the earlier arguments, the structure depicted in Figure 2 can be ascribed to being formed by Cu(1), Se(2)/Cu(2) polyhedral that structurally shares chlorine (Cl) corners in infinite chains along the direction [001]. Therein, the sequential metal atoms in the chain trend schematically following Cu(1)dSe(2)/Cu(2)dCu(1)<sup>0</sup> dSe(2)/Cu(2)dCu(1), whereby the prime refers to the polyhedral generated by the symmetry operation: 1 – x, 2 – y, �0.5 + z, in the [010] direction. As a result, the three-dimensional network is thus formed. It can be argued that the lattice cohesion may be strengthened by the hydrogen bonds within the layer (O(8)dH(7)dO(4)) and (O(7)dH(8)dO(3)) or outside the layer.

Figure 4. Structural environment of copper cations Cu(1).

Figure 2. A projected along a-axis view of the [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3] unit cell content.

Figure 3. Environment of selenium Se(1), Se(3) cations.

34 Chalcogen Chemistry

In this chapter, the band corresponding to the symmetric stretching vibrations of SeO2 groups

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broad band is observed in the infrared (IR) spectrum for this mode. These findings are in agreement with those reported by Cody and al. and Micka et al. for vibrational analysis on a series of alkali hydrogen selenites. From the work of these authors, the symmetric stretching

the 686–740 cm<sup>1</sup> region, a corresponding IR spectrum with an intense (broad) frequency absorption is present. In the literature [16, 17], these modes have been observed at a very much

Another observation is that copper (selenium) atoms are located at the center of CuO4Cl2 coordination octahedra. The axial CudCl bonds are longer than the others, and they are coordinated to water molecules. It can be stated that the high spin d-configuration of Cu leads to Jahn-Teller distortions by Jahn and Teller [18] hitherto producing planar CudO bonds in the 1.91–1.98 Å range and an axial CudCl distance of 2.77–2.80 Å. It can be ascertained that the planar oxygen (O) atoms are shared by Cu and Se atoms which can lead to the observed

cally appear in the 600–650 cm<sup>l</sup> region [16, 17], are also appearing at lower wave numbers

). In the IR spectrum, this mode is observed as an intense broad band at 532 cm<sup>1</sup>

From Figure 7, a band of very weak intensity is observed at 710 cm<sup>1</sup>

Figure 6. Infrared spectrum of [Cu0.332Se0.582(HSeO3)2CuCl3(H2O)3] at room temperature.

lower wave numbers than those in alkali hydrogen selenites.

reduction in the stretching frequencies of the SeO2 groups.

Typically, the stretching vibrations of the HSeO3

in the Raman spectrum (Figure 7). Similarly, a strong intense

ion (νSedOH), which often characteristi-

, which is ascribed to asymmetric stretching vibrations of SeO2 groups. In

, accompanied by a

.

was observed at around 825 cm<sup>l</sup>

shoulder at 738 cm<sup>1</sup>

(~627 cm<sup>1</sup>

vibrations are around 850 cm<sup>1</sup> [13–15].

Figure 5. Environment of copper/selenium cations Cu(2)/Se(2).

#### 3.2. Spectroscopic studies

In order to confirm the crystallographic results of the following compound: [Cu0.335Se0.582 (HSeO3)2CuCl3(H2O)3], IR, and Raman spectroscopy were used. Figure 6 shows that the IR spectrum is restricted to the mid-infrared frequency range: 400–4000 cm<sup>1</sup> .

The Characterization of a Newly Layered Bimetallic Hydrogen Selenite Copper-Selenium: Synthesis and Structure http://dx.doi.org/10.5772/intechopen.76310 37

Figure 6. Infrared spectrum of [Cu0.332Se0.582(HSeO3)2CuCl3(H2O)3] at room temperature.

3.2. Spectroscopic studies

36 Chalcogen Chemistry

Figure 5. Environment of copper/selenium cations Cu(2)/Se(2).

In order to confirm the crystallographic results of the following compound: [Cu0.335Se0.582 (HSeO3)2CuCl3(H2O)3], IR, and Raman spectroscopy were used. Figure 6 shows that the IR

.

spectrum is restricted to the mid-infrared frequency range: 400–4000 cm<sup>1</sup>

In this chapter, the band corresponding to the symmetric stretching vibrations of SeO2 groups was observed at around 825 cm<sup>l</sup> in the Raman spectrum (Figure 7). Similarly, a strong intense broad band is observed in the infrared (IR) spectrum for this mode. These findings are in agreement with those reported by Cody and al. and Micka et al. for vibrational analysis on a series of alkali hydrogen selenites. From the work of these authors, the symmetric stretching vibrations are around 850 cm<sup>1</sup> [13–15].

From Figure 7, a band of very weak intensity is observed at 710 cm<sup>1</sup> , accompanied by a shoulder at 738 cm<sup>1</sup> , which is ascribed to asymmetric stretching vibrations of SeO2 groups. In the 686–740 cm<sup>1</sup> region, a corresponding IR spectrum with an intense (broad) frequency absorption is present. In the literature [16, 17], these modes have been observed at a very much lower wave numbers than those in alkali hydrogen selenites.

Another observation is that copper (selenium) atoms are located at the center of CuO4Cl2 coordination octahedra. The axial CudCl bonds are longer than the others, and they are coordinated to water molecules. It can be stated that the high spin d-configuration of Cu leads to Jahn-Teller distortions by Jahn and Teller [18] hitherto producing planar CudO bonds in the 1.91–1.98 Å range and an axial CudCl distance of 2.77–2.80 Å. It can be ascertained that the planar oxygen (O) atoms are shared by Cu and Se atoms which can lead to the observed reduction in the stretching frequencies of the SeO2 groups.

Typically, the stretching vibrations of the HSeO3 ion (νSedOH), which often characteristically appear in the 600–650 cm<sup>l</sup> region [16, 17], are also appearing at lower wave numbers (~627 cm<sup>1</sup> ). In the IR spectrum, this mode is observed as an intense broad band at 532 cm<sup>1</sup> .

Figure 7. Raman spectrum of the compound at room temperature.

The OdO distance involving the SedOH system with one of the equatorial oxygen atoms of the neighboring Cu(2)/Se(2)O4Cl2 group is 2.662 Å. The observed lowering of the SedO(H) vibrations from the free-state values is a confirmation of the corresponding strong hydrogen bonds determined in the X-ray diffraction data. As presented in Table 3, it is seen that symmetric deformation vibrations of the HSeO3 ion have given only weak bands of the Raman spectrum, while a medium intense broad band is obtained in the IR. In the corresponding asymmetric bending vibration, Raman spectrum shows medium intense bands with a weak band in the IR. A reduction in the symmetry of the HSeO3 ion may be causing the changes in the activity of these modes. From the observed strong hydrogen bonding and the distortion of Cu(Se)O4Cl2 octahedra, we can deduce that the Jahn-Teller distortion affects the HSeO3 vibrations.

Fundamentally, the hydrogen-bonded OH groups may lead to three vibrations, namely: ν(OH) stretching, the in-plane (OH), and the out-of-plane (OH) deformation vibrations. In fact, the stretching bands of strongly H-bonded systems are intense and usually built up of a number of unresolved components owing to strong interaction between the proton vibration and the ν(O…O) vibrations [19, 20]. It is also clearly elucidated from the literature [21, 22] that the broad ν(OH) band in Fermi resonance with the overtones of the ν(OH) modes splits into three bands A, B, and C. The A mode is typically observed as a strong broad band at 2850 cm<sup>1</sup> in the IR spectrum, while the B mode is obtained as a medium intense band at 2360 cm<sup>1</sup> . A medium intense broad band at 1900 cm<sup>1</sup> and a weak one at 1730 cm<sup>1</sup> are generally being assigned to C bands. From a practical viewpoint, the appearance of these bands confirms the existence of strong hydrogen bonds in the crystal. The in-plane bending ν(OH) vibrations are

less sensitive to the hydrogen bond strength than the ν(OH) mode [15]. A medium band observed at 1280 cm<sup>l</sup> in the IR spectrum is attributed to the in-plane ν(OH) bending mode

Relative intensities: sh, shoulder; m, medium; w, weak; vw; very weak; mbr, medium broad; s, strong; vs., very strong.

Two prominent broad bands were observed in the stretching region of the typical water in the Raman spectra of the main (title) compound. Similarly, in the IR spectrum, a corresponding strong broad band with two distinct peaks exhibited at 3553 and 3170 cm<sup>l</sup> are noticeable for this mode. The bending mode of H2O that appears at around 1606 cm<sup>1</sup> in the IR is noteworthy. The considerable shifting of stretching and bending frequencies from those of a free water

and a medium intense broad band in the 870–940 cm<sup>1</sup> region to the ν(OH) mode.

Raman IR Assignments 3553 mbr 3170 wbr

2360 mbr νOH(B)

1606 mbr ν2H2O 1222 m δOH 1043–920 γOH

532 s νSedOH

2920 w 2850 w 2694 wbr

1900 vwbr 1730 vw

896 m 825 vs 825 s νsSeO2

> 740 s 686 s

425 vw 442 w δSeO2

380 vw δasOdSedOH

288 w CudO stretching

225 vw stretching modes of CudCl

738 wsh 710wbr 627 m

515 m 501 sh

350 sh 337 m

201 mbr 143wbr 129 m 120w 83 m

Table 3. Assignment and frequencies (cm<sup>1</sup>

2CuCl3(H2O)3] at room temperature.

ν1H2O

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The Characterization of a Newly Layered Bimetallic Hydrogen Selenite Copper-Selenium: Synthesis and Structure

νOH(A)

νOH(C)

δsOdSedOH

External modes

) observed for IR and Raman spectra of [Cu0.335Se0.582(HSeO3)

The Characterization of a Newly Layered Bimetallic Hydrogen Selenite Copper-Selenium: Synthesis and Structure http://dx.doi.org/10.5772/intechopen.76310 39


Relative intensities: sh, shoulder; m, medium; w, weak; vw; very weak; mbr, medium broad; s, strong; vs., very strong.

Table 3. Assignment and frequencies (cm<sup>1</sup> ) observed for IR and Raman spectra of [Cu0.335Se0.582(HSeO3) 2CuCl3(H2O)3] at room temperature.

The OdO distance involving the SedOH system with one of the equatorial oxygen atoms of the neighboring Cu(2)/Se(2)O4Cl2 group is 2.662 Å. The observed lowering of the SedO(H) vibrations from the free-state values is a confirmation of the corresponding strong hydrogen bonds determined in the X-ray diffraction data. As presented in Table 3, it is seen that

Raman spectrum, while a medium intense broad band is obtained in the IR. In the corresponding asymmetric bending vibration, Raman spectrum shows medium intense bands with a weak band in the IR. A reduction in the symmetry of the HSeO3 ion may be causing the changes in the activity of these modes. From the observed strong hydrogen bonding and the distortion of Cu(Se)O4Cl2 octahedra, we can deduce that the Jahn-Teller distortion affects the

Fundamentally, the hydrogen-bonded OH groups may lead to three vibrations, namely: ν(OH) stretching, the in-plane (OH), and the out-of-plane (OH) deformation vibrations. In fact, the stretching bands of strongly H-bonded systems are intense and usually built up of a number of unresolved components owing to strong interaction between the proton vibration and the ν(O…O) vibrations [19, 20]. It is also clearly elucidated from the literature [21, 22] that the broad ν(OH) band in Fermi resonance with the overtones of the ν(OH) modes splits into three bands A, B, and C. The A mode is typically observed as a strong broad band at 2850 cm<sup>1</sup> in the IR spectrum, while the B mode is obtained as a medium intense band at 2360 cm<sup>1</sup>

medium intense broad band at 1900 cm<sup>1</sup> and a weak one at 1730 cm<sup>1</sup> are generally being assigned to C bands. From a practical viewpoint, the appearance of these bands confirms the existence of strong hydrogen bonds in the crystal. The in-plane bending ν(OH) vibrations are

ion have given only weak bands of the

. A

symmetric deformation vibrations of the HSeO3

Figure 7. Raman spectrum of the compound at room temperature.

HSeO3 vibrations.

38 Chalcogen Chemistry

less sensitive to the hydrogen bond strength than the ν(OH) mode [15]. A medium band observed at 1280 cm<sup>l</sup> in the IR spectrum is attributed to the in-plane ν(OH) bending mode and a medium intense broad band in the 870–940 cm<sup>1</sup> region to the ν(OH) mode.

Two prominent broad bands were observed in the stretching region of the typical water in the Raman spectra of the main (title) compound. Similarly, in the IR spectrum, a corresponding strong broad band with two distinct peaks exhibited at 3553 and 3170 cm<sup>l</sup> are noticeable for this mode. The bending mode of H2O that appears at around 1606 cm<sup>1</sup> in the IR is noteworthy. The considerable shifting of stretching and bending frequencies from those of a free water molecule (H2O) [23] may be an indication of the presence of strong hydrogen bonding in the new crystal. The external modes of the HSeO3 ion, lattice modes of water, and metal-oxygen stretching modes appear approximately below 200 cm�<sup>l</sup> [1].

4. Conclusion

Acknowledgements

Author details

Mohamed Loukil

Tunisia

References

1985;39:809

in order to confirm the nature of this transformation.

Address all correspondence to: m.loukil@yahoo.fr

[4] Boldt K. Thesis, Universita Siegen; 1994

[5] Valkonen J. Journal of Solid State Chemistry. 1986;65:363

The author gratefully acknowledges the support of the University of Sfax.

Sfax Faculty of Sciences - Sfax University, Laboratory Material Sciences and Environment,

[1] Koskenlinna M, Valkonen J. Acta Crystallographica Section C. 1995;51:1637

[2] Micka Z, Cermak M, Niznansky D. Chemical Communications. 1990;55:2441

[7] Trombe JC, Lafront AM, Bonvoisin J. Inorganica Chimica Acta. 1997;23:847

[3] Unterderweide K, Engelen B, Boldt K. Journal of Molecular Structure. 1994;322:233

[6] Hiltunen L, Leskela M, Niinisto L, Tammenmaa M. Acta Chemica Scandinavica. Series A.

In conclusion, the author ascertains that a novel substituted hydrogen selenites [Cu0.335Se0.582 (HSeO3)2CuCl3(H2O)3], have been successfully prepared via slow evaporation method. The crystal structure of the novel compound is characterized by the presence of structural blocs with structures as such [Cu0.335Se0.582(HSeO3)2] and [CuCl3(H2O)3]. The principal compound is arranged to form layers in the structure parallel to the (001) plane between which the lone pairs E are located. So, the main feature of the structure of this compound is based on different coordination polyhedral, SeO3 pyramids, and [CuCl3(H2O)3] groups. The presence of hydrogen selenites (SedOdH) was confirmed by IR and Raman spectra. The particularity of [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3] is that it undergoes a phase transition on heating at 383 K. High temperature structure investigation of the new compound is in our future plans

The Characterization of a Newly Layered Bimetallic Hydrogen Selenite Copper-Selenium: Synthesis and Structure

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#### 3.3. Dielectric studies

Figure 8 shows an illustration of the temperature dependence of the dielectric constant (ε<sup>0</sup> ) in the frequency range [1–10] KHz, and in the temperature region of 300–500 K obtained for [Cu0.335Se0.582(HSeO3)2CuCl3(H2O)3]. These curves (Figure 8) exhibit the following characteristics:

(1) There is one anomaly in the dielectric constant ε<sup>0</sup> observed at about 383 K, (2) there is a maxima in the permittivity curves, displaced to higher temperatures with increasing frequency, and (3) apparently, this is a transition which can be attributed to the "order-disorder" phase transition, probably characterizing the motion of H+ diffusion related to the motion of HSeO3 groups, as reported in the literature [16, 17].

Figure 8. Temperature dependence of ε' as a function of frequency.
