The ESR spectrum of complex 1 was recorded in DMSO at 300 and 77K (LNT). The spectrum (S:5a and 5b) Shows a well-resolved four-line spectrum and no characteristic features for the presence of a di nuclear complex. This is also supported by the magnetic moment of complex 1 (1.81 BM) which confirms the mononuclear nature of the complex. The spin Hamiltonian parameters, calculated for the complex 1 from the spectra, are given in Table 2. The g tensor values of complex 1 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 suggesting that the complex is square –planar. This is also supported by the fact that the unpaired electron lies predominantly in the dx2-y2 orbital66, 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 Hathaway67, 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 169.
The in-plane ? bonding covalence parameters70, ?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 (?2) and in-plane ?-bonding (?2) parameters are calculated using Eq. (6) and Eq. (7).
?2 = (g – 2.0036) E/ -8? ?2 (6)
?2 = (g = 2.0036) E / -2? ?2 (7)
Here ? = 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 = ?2?2 (8)
K = ?2?2 (9)
Significant information about the nature of bonding in the complex 1 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 ?-bonding) and ?2 (out-plane ?-bonding) were calculated using the Eq. (5) – Eq. (7). The observed value ?2 (0.732) indicates complex 1 is predominantly ionic in character. The observed ?2 value (1.59) and ?2 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 factors71 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 ?-bonding than for in-plane ?-bonding in metal ligand ?-bonding. Thus, the ESR study of the copper complex has provided supporting evidence for the optical results.
3.8. Electronic spectra:
The electronic spectra and magnetic moment of the ligand and 1, 2, 3 and 4 complexes have been measured at room temperature. The complex 1 showed the magnetic moments 1.81 BM indicaing presence of one unpaired elexctron. 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 corresponds to charge transfer bands which is consistent with the presence of square planar geometry around the complex 172-74 . The complex 2 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)(?1); 4T1g(F)? 4A2g(F)(?2) and 4T1g(F)? 4T2g(P)(?3) 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 whichh have been assigned to 4A2g(F)? 4T1g(P)(?1); 4A2g(F)? 4T1g(F)(?2) and 4A2g(F)? 4T2g(P)(?3) respectively. The ligand field parameters (Dq, B, b) have also been calculated (Table 3) for the complexes 2 and 3 by using Konig’s method. The calculated value of B for the complexes 2 and 3 shows that 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 significant covalent character of the metal-ligand bonds and an 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 appreciable covalent character. The complex 4 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 ligand to metal charge transfer transition, which is compatible to an octahedral geometry.