The ESR spectrum of complex one was recorded in DMSO at 300 and 77K (LNT). The range (S:5a and 5b) Shows a well-resolved four-line spectrum and no characteristic features for the presence of a dinuclear complex. This is also supported by the magnetic moment of compound 1 (1.81 BM) which confirms the mononuclear nature of the mixture. The spin Hamiltonian parameters, calculated for the complex one from the spectra, are given in Table 2. The g tensor values of complex one can be used to derive the ground state.

In square planar complexes, the unpaired electron lies in the dx2-y2 orbital giving gll> g⊥> 2 while the unpaired electron lies in the dz2 orbital giving⊥>gll>2. From the observed values, it is clear that gll> g⊥> 2 was suggesting that the complex is square –planar. This is also supported by the fact that the unpaired electron lies predominantly in the dx2-y2 orbital, as evident from the value of the exchange interaction term G, estimated from the expression Eq. (4).

G = (gll- 2) / (g⊥- 2) (4)

According to Hathaway, if G > 4.0, the local tetragonal axes are aligned parallel or only slightly misaligned. If G A = 44.9; g = 2.23 > g = 2.05) indicates that the unpaired electron is present in the dx2-y2 orbital with square- planar geometry around the complex 1.

The in-plane bonding covalence parameters, 2 are related to g║ and g┴ according to Eq. (5).

2= – (A║/0.036) + (g║ – 2.0036) + 3/7 (g – 2.0036) + 0.04 (5)

The 2 value of 0.5 indicates complete covalent bonding, while that of 1.0 suggests complete ionic bonding. The out-of-plane bonding (γ2) and in-plane -bonding (2) parameters are calculated using Eq. (6) and Eq. (7).

2 = (g – 2.0036) E/ -8λ 2 (6)

γ2 = (g = 2.0036) E / -2λ 2 (7)

Here λ = 828cm-1 for free Cu (II) ion and E is the electronic energy for 2BIg →2A1g

Transition. This is also confirmed by orbital reduction factor K, which can be estimated using Eq. 8 & 9.

K = 22 (8)

K = 2γ2 (9)

Significant information about the nature of bonding in the complex one can be derived from the relative magnitudes of K|| and K⟘ Eq. (8) and Eq. (9). In the case of pure -bonding. K||≈K⟘ = 0.77, whereas K|| K⟘. Molecular orbital coefficients 2 (in-plane -bonding ), 2 (in-plane π-bonding) and γ2 (out-plane π-bonding) were calculated using the Eq. (5) – Eq. (7). The observed value 2 (0.732) indicates complex 1 is predominantly ionic. The observed two value (1.59) and γ2 value (1.34) shows that there is interaction in the out-of-plane -bonding, whereas the in-plane bonding is predominantly ionic. This is also confirmed by orbital reduction factors which were estimated from the simple relations. For the present complex, the observed order K|| (1.16) > K⟘ (0.98) implies a greater contribution from out of plane π-bonding than for in-plane π-bonding in metal-ligand π-bonding. Thus, the ESR study of the copper complex has provided supporting evidence for the optimal results.

3.8. Electronic spectra:

The electronic spectra and magnetic moment of the ligand and 1, 2, 3 and four complexes have been measured at room temperature. The complex 1 showed the magnetic moments 1.81 BM

indicating the presence of one unpaired electron. The electronic spectra (S: 6) of complex 1 exhibit absorption in the region 16,630 cm-1 has been assigned to 2B1g →2Aig transitions, and the bands in the region 30,211 and 36,211cm-1 correspond to charge transfer bands which is consistent with the presence of square planar geometry around the complex 1. The complex two at room temperature showed the magnetic moment 4.19BM indicating the presence of three unpaired electrons. The electronic spectra of the complex 2 showed absorption bands at 11,876; 15,313 and 19,696 cm-1 and these bands were assigned to 4T1g(F)→ 4T2g(F)(υ1); 4T1g(F)→ 4A2g(F)(υ2) and 4T1g(F)→ 4T2g(P)(υ3) transitions respectively.

The position of these bands is consistent with octahedral geometry around the Co (II) ion in complex 2 showed three absorption bands in the region 17,605; 25,794 and 38,461 cm-1 which have been assigned to 4A2g(F)→ 4T1g(P)(υ1); 4A2g(F)→ 4T1g(F)(υ2) and 4A2g(F)→ 4T2g(P)(υ3) respectively. The ligand field parameters (Dq, B, b) have also been calculated (Table 3) for the complexes 2 and three by using Konig’s method. The calculated value of B for the complexes 2 and 3 shows that the M-L bond is appreciably covalent. The value of B, which is lower than the free ion value of 971cm-1 for complex 2 and 918cm-1 for complex 3, indicates overlapping of ligand-metal orbitals. These parameters indicated the significant covalent character of the metal-ligand bonds and overlapping of ligand-metal orbitals.

The value of b lies in the range of 0.32-0.66, which indicates that the complexes 2 and 3 have significant covalent character. The complex four is found to be diamagnetic which is consistent with the d10 configuration, and electronic spectrum showed an absorption band at 24,635 cm-1 assigned to the ligand to metal charge transfer transition, which is compatible to an octahedral geometry.