**20.1. Copper compounds**

Copper exists in two ionic states, Cu(I) and Cu(II). The ionic radius of Cu(II) is 0.73 A.U. The electronic configuration of Cu(I) is [Ar] 3d10 and hence has no unpaired electron in its outermost orbit. Hence it exhibits diamagnetism. The electronic configuration of Cu(II) is [Ar]3d9 and has one unpaired electron which is responsible for its para magnetism. The main resources of copper are its minerals. Structural properties could be explored using electronic and EPR spectra which provides information on bonding between ligands and metal ion.

#### **20.2. Electronic spectra of copper compounds**

In optical spectroscopy, transitions proceed between the split orbital levels whereas in EPR spectroscopy they occur between spin sub- levels that arise due to the external magnetic field. Thus EPR spectroscopy is a natural sequel to optical spectroscopy.

## **20.3. Optical spectra**

In octahedral crystal field, the ground state electronic distribution of Cu2+ is t2g6eg3 which yields 2Eg term. The excited electronic state is t2g5eg4 which corresponds to 2T2g term. Thus only one single electron transition, i.e., 2Eg 2T2g, is expected in an octahedral crystal field. The difference is 10Dq. Octahedral coordination is distorted either by elongation or compression of octahedron leading to tetragonal symmetry.

Normally, the ground 2Eg state is split due to Jahn-Teller effect and hence lowering of symmetry is expected for Cu(II) ion. This state splits into 2B1g(dx2-y2) and 2A1g(dz2) states in tetragonal symmetry and the excited term 2T2g also splits into 2B2g(dxy) and 2Eg(dxz,dyz) levels. In rhombic field, 2Eg ground state is split into 2A1g(dx2-y2) and 2A2g(dz2) whereas 2T2g splits into 2B1g(dxy), 2B2g(dxz) and 2B3g(dyz) states. Thus, three bands are expected for tetragonal (C4v) symmetry and four bands are expected for rhombic (D2h) symmetry. Energy level diagram of d-orbitals in tetragonal elongated environment is shown in Fig. 5.

The transitions in the tetragonal field are described by the following equations:

38 Advanced Aspects of Spectroscopy

EPR signal at room temperature.

optical data by the following equation <sup>8</sup>

transition of the perfect octahedral site. λ is 324 cm-1 for free Ni2+ ion.

carbon dioxide forming hydroxy copper carbonate (Cu2(OH)2CO3 ).

in animals are the tissues, liver, muscle and bone.

**20.2. Electronic spectra of copper compounds** 

**20.1. Copper compounds** 

**20.3. Optical spectra** 

Ni2+(d8) has no unpaired electron (square planer) in its orbit. Therefore it does not exhibit

But in certain conditions, it shows EPR signal. The EPR data could be related with the

Copper is one of the earliest known elements to man. The average percentage of copper in the earth's crust is 0.005%. Pure copper is soft and malleable. An important physical property of copper is its color. Most people refer copper colour as reddish-brown tint. Copper-63 and copper-65 are two naturally occurring isotopes of copper. Nine radioactive isotopes of copper are also known. Among them two radioactive isotopes, copper-64 and copper-67 are used in medicine. Copper easily reacts with oxygen and in moist air, it combines with water and

Animals like crustaceans (shellfish like lobsters, shrimps, and crabs) do not have hemoglobin to carry oxygen through the blood but possess a compound called hemocyanin. This is similar to hemoglobin but contains copper instead of iron. Copper is an essential micronutrient for both plants and animals. A healthy human requires not more than about 2 mg of copper for every kg weight of the body. The main body parts where copper is found

Copper exists in two ionic states, Cu(I) and Cu(II). The ionic radius of Cu(II) is 0.73 A.U. The electronic configuration of Cu(I) is [Ar] 3d10 and hence has no unpaired electron in its outermost orbit. Hence it exhibits diamagnetism. The electronic configuration of Cu(II) is [Ar]3d9 and has one unpaired electron which is responsible for its para magnetism. The main resources of copper are its minerals. Structural properties could be explored using electronic and EPR spectra which provides information on bonding between ligands and metal ion.

In optical spectroscopy, transitions proceed between the split orbital levels whereas in EPR spectroscopy they occur between spin sub- levels that arise due to the external magnetic

In octahedral crystal field, the ground state electronic distribution of Cu2+ is t2g6eg3 which yields 2Eg term. The excited electronic state is t2g5eg4 which corresponds to 2T2g term. Thus

field. Thus EPR spectroscopy is a natural sequel to optical spectroscopy.

*g* 2.0023

where ∆ is the energy of the

**19.3. EPR spectra** 

**20. Copper** 

$$\mathrm{P}^{2}\mathrm{B}\_{\mathrm{lg}} \rightarrow \mathrm{^{2}}A\_{\mathrm{lg}} : \left[6Dq - 2Ds - 6Dt - \left(6Dq + 2Ds - Dt\right)\right] = 4Ds + 5Dt \tag{37}$$

$$\mathrm{P}^{2}\mathrm{B}\_{1\_{\mathcal{S}}} \rightarrow \,^{2}\mathrm{B}\_{2\_{\mathcal{S}}} : \left[ -4\mathrm{D}q + 2\mathrm{D}\mathrm{s} - \mathrm{D}t - \left( 6\mathrm{D}q + 2\mathrm{D}\mathrm{s} - \mathrm{D}t \right) \right] = 10\mathrm{D}q \tag{38}$$

$$\mathrm{P}^{2}\mathrm{B}\_{\mathrm{lg}} \rightarrow \mathrm{^{2}}E\_{\mathrm{g}} : \left[ -4Dq - \mathrm{Ds} + 4\mathrm{Dt} - \left( 6Dq + 2\mathrm{Ds} - \mathrm{Dt} \right) \right] = 10\mathrm{D}q + 3\mathrm{Ds} - 5\mathrm{Dt} \tag{39}$$

In the above equations, Dq is octahedral, Ds and Dt are tetragonal crystalfield parameters. The same sign of Dq and Dt indicates an axial elongation [Fig. 5] and opposite sign indicates an axial compression .

**Figure 5.** (a) Energy level diagram of Jahn-Teller distortion in d-orbital in octahedral and tetragonal elongation

The Jahn-Teller distortion is either tetragonal elongation along the Z axis or contraction in the equatorial xy plane which may ultimately result in a square planar environment in extreme cases as in D4h.

The optical absorption bands observed for Cu(II) in octahedral coordination with rhombic (D2h) symmetry are: 2A1g(dx2-y2) → 2A2g(dz2), 2A1g(dx2-y2) → 2B1g(dxy), 2A1g(dx2-y2) → 2B2g(dxz), 2A1g(dx2-y2)→ 2B3g(dyz) states respectively. This is shown in Fig.6. In rhombic (D2h) field, i.e., C2V symmetry, the strong band 2A1g(dx2-y2) → 2B1g(dxy) gives 10Dq value which depends on the nature of the compound.

**Figure 6.** Energy level diagram of d-orbitals in rhombic distortion.

#### **20.4. EPR spectra of copper compounds**

When any Cu(II) compound in the form of powder is placed in a magnetic field, it gives a resonance signal. The signal is of three types. They are shown in Fig.-7:

**Figure 7.** Different forms EPR spectra of Cu(II)

Fig.7(i) is due to high concentration of copper; if the copper content in the compound is high, it gives a broad resonance line. Therefore the hyperfine line from either 63Cu or 65Cu cannot be resolved. The g value for this resonance is around 2.2. (ii) Compression in the equatorial plane results in the elongation of Z axis .Elongation in the equatorial plane results in the compression of Z-axis. Thus there are two types of possibilities in the EPR spectrum. Hence an EPR spectrum similar to Fig. 7(ii) & (iii) is obtained. If g11 > g , the ground state is 2B1g, [Fig. 7(a)] whereas if g >g11 or g11 = 2.00, the ground state is 2A1g [fig.7(ii).]. The highest-energy of the half occupied orbital is dx \_2 y2 as it has the largest repulsive interaction with the ligands in the equatorial plane. Here g11(corresponding to the magnetic field oriented along the z axis of the complex) > g > 2.00. This is a characteristic feature of dx2-y2 ground state. Additionally, copper has a nuclear spin of (I)) 3/2 which couples with the electron spin to produce a four line hyperfine splitting of the EPR spectrum. This is shown in Fig-7(ii) and 7(v). Tetragonal cupric complexes generally have large A11 value than those of complexes with D4h symmetry. If g11 > g , the ground state is 2B1g whereas if g >g11 or g11 = 2.00, the ground state is 2A1g. EPR results give rise to a new parameter, G which is defined as

40 Advanced Aspects of Spectroscopy

**Figure 6.** Energy level diagram of d-orbitals in rhombic distortion.

resonance signal. The signal is of three types. They are shown in Fig.-7:

When any Cu(II) compound in the form of powder is placed in a magnetic field, it gives a

Fig.7(i) is due to high concentration of copper; if the copper content in the compound is high, it gives a broad resonance line. Therefore the hyperfine line from either 63Cu or 65Cu cannot be resolved. The g value for this resonance is around 2.2. (ii) Compression in the equatorial plane results in the elongation of Z axis .Elongation in the equatorial plane results in the compression of Z-axis. Thus there are two types of possibilities in the EPR spectrum. Hence an EPR spectrum similar to Fig. 7(ii) & (iii) is obtained. If g11 > g , the ground state is 2B1g, [Fig. 7(a)] whereas if g >g11 or g11 = 2.00, the ground state is 2A1g [fig.7(ii).]. The highest-energy of the half occupied orbital is dx \_2 y2 as it has the largest repulsive interaction with the ligands in the equatorial plane. Here g11(corresponding to the magnetic field oriented along the z axis of the

**20.4. EPR spectra of copper compounds** 

**Figure 7.** Different forms EPR spectra of Cu(II)

$$G = \frac{\left(\mathbf{g}\_{11} - \mathbf{g}\_{\epsilon}\right)}{\left(\mathbf{g}\_{\perp} - \mathbf{g}\_{\epsilon}\right)}\tag{40}$$

If G value falls in between 3 and 5, the unit cell contains magnetically equivalent ions. If G value is less than 3, the exchange coupling among the magnetically non- equivalent Cu(II) ions in the unit cell is not very strong. If G is greater than 5, a strong exchange coupling takes place among the magnetically non -equivalent Cu(II) ions in the unit cell. Truly compressed structures are relatively rare when compared to elongated structures. In other words, g > g11, is an unusual observation and this implies two possibilities:


$$H\_p = 2.3g\_o \beta \rho \sqrt{s(s+1)}\tag{41}$$

where β is the Bohr magneton, s = spin, gO = average value of g factor, ρ = density (2.22 x 1021 spins/cc).

The calculated g values provide valuable information on the electronic ground state of the ion. If g1> g2 > g3, the quantity R value is given by (g2 –g3) / (g1-g2) which is greater than unity and the ground state is 2A2g(dz2); if it is less than unity, the ground state is 2A1g(dx2-y2). A large value of g1 is indicative of more ionic bonding between metal and ligand. Further the structure of the compound is an elongated rhombus. From the spin –Hamiltonian parameters, the dipolar term (P) and the Fermi contact term (k) are calculated using the following expressions:

$$P = 2\gamma\_{Cu} \beta\_O \beta\_N \left( r^{-3} \right) \tag{42}$$

$$k = \left(\begin{array}{c} A\_{\odot} \\ \searrow \mathcal{P} \end{array}\right) + \Lambda \mathsf{g}\_{\circ} \tag{43}$$

Here γCu is the magnetic moment of copper, βo is the Bohr magneton, βN is the nuclear magneton and r is the distance from the central nucleus to the electron, Ao is the average A value and ∆go = go – ge where go is the average g value and ge is the free electron g-value (2.0023). The Fermi contact term, k, is a measure of the polarization produced by the uneven distribution of d-electron density on the inner core s-electron and P is the dipolar term. By assuming either the value of P or k, the other is calculated. Using these values, the hyperfine constant is calculated. This is the average value of g1, g2 and g3.

Using the data of EPR and dipolar term P, the covalency parameter (α2) is calculated .

$$\alpha^2 = \frac{7}{6} \left| \left( \frac{A\_3 - A\_1}{P} \right) - \left( \mathbf{g}\_\varepsilon - \mathbf{g}\_1 \right) + \frac{11}{14} (\mathbf{g}\_\varepsilon - \mathbf{g}\_3) - \frac{6}{14} (\mathbf{g}\_\varepsilon - \mathbf{g}\_2) \right| \tag{44}$$

Thus the important bonding information is obtained. The bonding parameter, α2, would be closer to unity for ionic bonding and it decreases with increasing covalency. Further the term, *k,* is calculated using the EPR data,

$$A\_{\rm n1} = k\alpha^2 + P\left[ -\frac{4}{7}\alpha^2 + \Delta \mathbf{g}\_{\rm i1} + \frac{3}{7}\Delta \mathbf{g}\_{\perp} \right] \tag{45}$$

$$A\_{\perp} = k\alpha^2 + P\left[\frac{2}{7}\alpha^2 + \frac{11}{14}\Delta\mathbf{g}\_{\perp}\right] \tag{46}$$

#### **20.5. Relation between EPR and optical absorption spectra**

The optical absorption and EPR data are related as follows. In tetragonal symmetry, EPR studies are correlated with optical data to obtain the orbital reduction parameter in rhombic compression.

$$\mathbf{g}\_1 = \mathbf{g}\_\epsilon + \frac{8a^2 k\_1^2 \mathcal{A}}{\Delta E\_{\text{xy}}} \tag{47}$$

$$\mathbf{g}\_1 = \mathbf{g}\_\epsilon + \frac{2k\_z^2 \mathcal{A} \left(a + \sqrt{3}b\right)^2}{\Delta E\_{zz}} \tag{48}$$

$$\mathcal{g}\_1 = \mathcal{g}\_\epsilon + \frac{2k\_3^2 \mathcal{A} \left(a + \sqrt{3}b\right)^2}{\Delta E\_{yz}} \tag{49}$$

Similarly for rhombic elongation,

$$\mathbf{g}\_1 = \mathbf{g}\_\varepsilon - \frac{8a^2 k\_1^2 \mathcal{A}}{\Delta E\_{\text{yy}}} \tag{50}$$

Electronic (Absorption) Spectra of 3d Transition Metal Complexes 43

$$\mathcal{g}\_1 = \mathcal{g}\_\epsilon - \frac{2k\_2^2 \mathcal{A} \left(a + \sqrt{3}b\right)^2}{\Delta E\_{xx}} \tag{51}$$

$$\mathbf{g}\_1 = \mathbf{g}\_\epsilon - \frac{2k\_\mathbf{j}^2 \lambda \left(a + 3b\right)^2}{\Delta E\_{yz}}\tag{52}$$

where cos *a* and sin *b* which are coefficients for the mixing of the z2 and x2-y2 orbitals. a2 +b2 = 1 and k1, k2, k3 are the orbital reduction parameters. λ is the spin- orbit coupling constant for free Cu(II) ion = -830 cm-1.

In equations (48) to (50), when a = 0, tetragonal compression is obtained [ground state is 2A1g(dz2)].

$$\mathbf{g}\_{11} = \text{ 2.0023} \\ \mathbf{= g}\_{\iota} \tag{53}$$

$$\mathcal{g}\_{\perp} = \mathcal{g}\_{\epsilon} - \frac{6\mathcal{X}}{\Delta E\_{\perp(\text{ay},\text{yz})} \left( \,^2 \mathcal{B}\_1 \to \,^2 E \right) = \Delta\_{\perp}} \tag{54}$$

Also in equations (51) to (53), when b is equal to zero, tetragonal elongation is obtained [ground state is 2B1g(dx2-y2)].

$$\mathbf{g}\_{11} = \mathbf{g}\_s - \frac{8\lambda}{\Delta E\_{11(\text{xy})} \left( \,^2 \mathbf{B}\_1 \to \,^2 \mathbf{B}\_2 \right) = \boldsymbol{\Lambda}\_{11}} \tag{55}$$

$$\mathbf{g}\_{\perp} = \mathbf{g}\_{\epsilon} - \frac{2\lambda}{\Delta E\_{\perp \text{(xy,yz)}} \left( ^2 \mathcal{B}\_1 \to \,^2 E \right) = \Delta\_{\perp}} \tag{56}$$

Further, if A11, g11 and *g*⊥ values are known, α2 can be estimated using the equation [53]

$$\alpha^2 = -\left[ \left( \frac{A\_{11}}{0.036} \right) - \left( \mathbf{g}\_{11} - \mathbf{g}\_{\epsilon 1} \right) + \frac{3}{7} \left( \mathbf{g}\_{\perp} - \mathbf{g}\_{\epsilon} \right) + 0.04 \right] \tag{57}$$

#### **20.6. Typical examples**

42 Advanced Aspects of Spectroscopy

Here γCu is the magnetic moment of copper, βo is the Bohr magneton, βN is the nuclear magneton and r is the distance from the central nucleus to the electron, Ao is the average A value and ∆go = go – ge where go is the average g value and ge is the free electron g-value (2.0023). The Fermi contact term, k, is a measure of the polarization produced by the uneven distribution of d-electron density on the inner core s-electron and P is the dipolar term. By assuming either the value of P or k, the other is calculated. Using these values, the hyperfine

Using the data of EPR and dipolar term P, the covalency parameter (α2) is calculated .

7 11 6 6 14 14 *eee*

11 11

1

*e*

*e*

1

*g g <sup>E</sup>*

*g g <sup>E</sup>*

1

1

**20.5. Relation between EPR and optical absorption spectra** 

7 7 *Ak P g g*

 

2 2 2 11 7 14 *Ak P g*

 

The optical absorption and EPR data are related as follows. In tetragonal symmetry, EPR studies are correlated with optical data to obtain the orbital reduction parameter in rhombic

> 2 2 1

*xy a k*

 <sup>2</sup> <sup>2</sup>

*xz*

 <sup>2</sup> <sup>2</sup>

*yz*

2 2 1

*xy a k*

8 *e*

*g g <sup>E</sup>*

8 *e*

*g g <sup>E</sup>*

2

3

2 3

2 3

*ka b*

*ka b*

<sup>2</sup> 3 1

Thus the important bonding information is obtained. The bonding parameter, α2, would be closer to unity for ionic bonding and it decreases with increasing covalency. Further the

*<sup>g</sup> g gg gg <sup>P</sup>*

4 3

 

132

(44)

(45)

(46)

(47)

(48)

(49)

(50)

constant is calculated. This is the average value of g1, g2 and g3.

*A A*

term, *k,* is calculated using the EPR data,

compression.

Similarly for rhombic elongation,

2 2

EPR and optical absorption spectral data of selected samples are discussed. The data are chosen from the literature for each typical sample. However, it is to be noticed that the crystal field parameters, EPR parameters often depend on chemical composition, nature of ligands and temperature of the compound. The data should be considered as representative only. For more complete information on specific example, the original references are to be consulted. The X-band spectra and optical absorption spectra of powdered samples are mostly recorded at room temperature (RT).

1. The EPR spectrum of covellite is shown in Fig-9. It is similar to the Fig 8(i). It consists of a broad line with a small sextet. The g value for the broad line is 2.24 which is due to the presence of Cu(II) in the sample. The hyperfine line from either 63Cu or 65Cu could not be resolved since the copper content (Cu = 66 wt%) in the mineral is very high. Several copper compounds exhibit this type of EPR spectra.

**Figure 8.** EPR spectrum of covellite at RT

**Figure 9.** EPR spectrum of beaverite at RT

2. *Beaverite* [Pb(Fe3+,Cu,Al)3(SO4)2(OH)6]: X-band EPR spectrum of powdered sample recorded at RT is shown in Fig-9. This is similar to Fig-7(ii). The g values are: *g*11 = 2.42 and *g*⊥ = 2.097. In addition to the above, a *g* value of 2.017 is observed which is due to Fe(III) impurity. Fig.9 indicates expanded form of EPR spectrum of Cu(II) and is not resolved because of high copper percentage. Tetragonal cupric complexes with D4h symmetry, possessing axial elongation have ground state 2B1g (d*x*2−*<sup>y</sup>*2).The EPR results are in the order of *g*11 > *g*⊥ > ge and hence the ground state is 2B1g. Though the optical absorption spectrum shows two sites for Cu(II) with same ground state, the same is not noticed in the EPR spectrum because the percentage of copper is high in the sample.

A typical EPR spectrum of *enargite* is shown in Fig.10. The spectrum is symmetric with *g*11 = 2.289 and *g*⊥ = 2.048 which are due to Cu(II). Since *g*11 > *g*⊥ > ge, the ground state for Cu(II) is 2B1g (d*x*2−*<sup>y</sup>*2). Using EPR and optical absorption results, the orbital reduction parameters are evaluated, i.e., K11 = 1.03 cm-1 and *K* = 1.93 cm-1. Also G seems to be 5.0 which indicates that the unit cell of the compound contains magnetically equivalent ions.

**Figure 10.** EPR spectrum of enargite at RT

44 Advanced Aspects of Spectroscopy

**Figure 8.** EPR spectrum of covellite at RT

**Figure 9.** EPR spectrum of beaverite at RT

1. The EPR spectrum of covellite is shown in Fig-9. It is similar to the Fig 8(i). It consists of a broad line with a small sextet. The g value for the broad line is 2.24 which is due to the presence of Cu(II) in the sample. The hyperfine line from either 63Cu or 65Cu could not be resolved since the copper content (Cu = 66 wt%) in the mineral is very high. Several

copper compounds exhibit this type of EPR spectra.

**Figure 11.** EPR spectrum of CuO-ZnO nano composite.

*CuO-ZnO nano composite:* EPR spectrum of CuO-ZnO nano composite recorded at room temperature is shown in Fig-11. The calculated g values are 1.76, 2.31 and 2.05. The g value of 1.76 is assigned to free radical of O2-. Further gII value of 2.31, g┴value of 2.05 are due to Cu(II) in tetragonal distortion. Also it has A11 =13.3 mT. These results show that the ground state of Cu(II) as dx2- y2. Further, the covalency parameter, α2 (0.74) suggests that the composite has some covalent character.

3. *Atacamite* [Cu2(OH)3Cl]: The EPR spectrum is shown in Fig.12. The g values corresponding to three sets of the resolved four lines in low, mid and high fields are g1 = 2.191, g2 =2.010 and g3 = 1.92. The corresponding hyperfine structure constants are A1 = 11.0 mT, A2 = 3,0 mT and A3 = 5.0 mT respectively. Since g1 > g2 > g3, the quantity R = (g2 –g3)/(g1-g2) = 0.50 which is less than unity. This indicates 2A1g(dx2-y2) is the ground state for Cu(II) which is in an elongated rhombic field. The optical absorption spectrum of the compound at RT shown in Fig-13 shows bands at 15380, 11083, 10296 and 8049 cm-1. Using the EPR results, the energy states are ordered as 2A1g(dx2-y2) < 2A2g(dz2) < 2B1g(dxy) < 2B2g(dxz) < 2B2g(dyz). Thus we have four bands with 2A1g(dx2-y2) as the ground state. Using the EPR results, the dipolar term (P) and the Fermi contact term (k) are calculated as 0.38 cm-1 and k = 0.3 respectively. The bonding parameter, α2 is found to be 0.28 indicating reasonably high degree of covalent bonding between metal and ligands.

Synthetic copper doped *zinc potassium phosphate hexahydrate* (ZPPH), ZnKPO4 6H2O: It is similar to strubite, a bio-mineral. The g values are: g1 = 2.372, g2 =2.188 and g3 = 2.032. The hyperfine structure constants are A1 = 78 x 10-4 cm-1, A2 = 48 x 10-4 cm-1 and A3 = 63 x 10-4 cm-1respectively. It is seen that g1 > g2 > g3 and the quantity R = (g2 –g3)/(g1-g2) = 0.85. This confirms that the ground state for Cu(II) is 2A1g(dx2-y2) ( elongated rhombic field ). Using the EPR data and substituting free ion dipolar term [P= 0.036 cm-1] for Cu(II) and ge value in equation (57), the bonding parameter, α<sup>2</sup> = 0.55, is obtained. It indicates a predominant covalency in compound.

**Figure 12.** EPR spectrum of atacamite at RT

**Figure 11.** EPR spectrum of CuO-ZnO nano composite.

predominant covalency in compound.

suggests that the composite has some covalent character.

*CuO-ZnO nano composite:* EPR spectrum of CuO-ZnO nano composite recorded at room temperature is shown in Fig-11. The calculated g values are 1.76, 2.31 and 2.05. The g value of 1.76 is assigned to free radical of O2-. Further gII value of 2.31, g┴value of 2.05 are due to Cu(II) in tetragonal distortion. Also it has A11 =13.3 mT. These results show that the ground state of Cu(II) as dx2- y2. Further, the covalency parameter, α2 (0.74)

3. *Atacamite* [Cu2(OH)3Cl]: The EPR spectrum is shown in Fig.12. The g values corresponding to three sets of the resolved four lines in low, mid and high fields are g1 = 2.191, g2 =2.010 and g3 = 1.92. The corresponding hyperfine structure constants are A1 = 11.0 mT, A2 = 3,0 mT and A3 = 5.0 mT respectively. Since g1 > g2 > g3, the quantity R = (g2 –g3)/(g1-g2) = 0.50 which is less than unity. This indicates 2A1g(dx2-y2) is the ground state for Cu(II) which is in an elongated rhombic field. The optical absorption spectrum of the compound at RT shown in Fig-13 shows bands at 15380, 11083, 10296 and 8049 cm-1. Using the EPR results, the energy states are ordered as 2A1g(dx2-y2) < 2A2g(dz2) < 2B1g(dxy) < 2B2g(dxz) < 2B2g(dyz). Thus we have four bands with 2A1g(dx2-y2) as the ground state. Using the EPR results, the dipolar term (P) and the Fermi contact term (k) are calculated as 0.38 cm-1 and k = 0.3 respectively. The bonding parameter, α2 is found to be 0.28 indicating reasonably high degree of covalent bonding between metal and ligands. Synthetic copper doped *zinc potassium phosphate hexahydrate* (ZPPH), ZnKPO4 6H2O: It is similar to strubite, a bio-mineral. The g values are: g1 = 2.372, g2 =2.188 and g3 = 2.032. The hyperfine structure constants are A1 = 78 x 10-4 cm-1, A2 = 48 x 10-4 cm-1 and A3 = 63 x 10-4 cm-1respectively. It is seen that g1 > g2 > g3 and the quantity R = (g2 –g3)/(g1-g2) = 0.85. This confirms that the ground state for Cu(II) is 2A1g(dx2-y2) ( elongated rhombic field ). Using the EPR data and substituting free ion dipolar term [P= 0.036 cm-1] for Cu(II) and ge value in equation (57), the bonding parameter, α<sup>2</sup> = 0.55, is obtained. It indicates a

**Figure 13.** Optical absorption spectrum of atacamite

#### **Author details**

S.Lakshmi Reddy *Dept. of Physics, S.V.D.College, Kadapa, India* 

Tamio Endo *Dept. of Electrical and Electronics Engineering, Graduate School of Engineering, Mie University, Mie, Japan* 

G. Siva Reddy *Dept. of Chemistry, Sri Venkateswara University, Tirupati, India* 

## **21. References**

