ESR studies can conveniently explain the ground state configuration of Cu (II) ion with an unpaired electron. The X-band ESR spectrum of complex one was recorded in DMSO at 300K and 77K (LNT). The spectrum (S: 5a and 5b) Shows a well-resolved four-line spectrum. The spin Hamiltonian parameters were calculated from the spectra, are given in Table 2. The g tensor values can be used to derive the ground state of the copper complex. In square planar complexes, the unpaired electron lies in the dx2-y2 orbital. For the complex 1, the g tensor values obtained are all = 2.23 > g⊥= 2.05 > 2.0023 respectively, which suggests that the complex is square planar. This also supports the fact that the unpaired electron predominantly lies in the dx2-y2 orbital , as evident from the value of the exchange interaction term G, estimated from the expression Eq. (4).
G = (all- 2.0023) / (g⊥- 2.0023) (4)
According to Hathaway , if the value of G is greater than 4.0, the local tetragonal axes are aligned parallel or only slightly misaligned. If G is lesser than 4.0, significant exchange coupling is present, and the misalignment is appreciable. For complex 1, the value of G = 4.77 which indicates that the local tetragonal axes aligned parallel or slightly misaligned with the presence of an unpaired electron in a dx2-y2 orbital. This result also suggests that the exchange coupling effects are not operative in the present complex.
The isotropic ESR parameters are = 2.11 and Also = 83.0 are calculated from the position spacing of the resonance lines from room temperature solution spectrum of the complex. The spectrum showed a typical eight-line pattern which indicates that single copper is present in the molecule which is a monomer. This is also supported by the magnetic moment of complex 1 (1.81 BM) which confirms the mononuclear nature of the complex. In the frozen solid state, two types of resonance components have been observed in the spectrum, one set due to parallel features and the other due to perpendicular features, which suggests axially symmetric anisotropy with well-resolved sixteen-line hyperfine splitting, characteristic of an interaction between the electron and copper nuclear spin. From the anisotropic ESR spectrum, the anisotropic parameters were calculated and the order of values are All = 160.8 > A⊥ = 44.9; all = 2.23 > g⊥ = 2.05 indicating that the unpaired electron is present in the dx2-y2 orbital with square- planar geometry of the complex 1.
The bonding parameters 2, 2, γ2 of the complex one was calculated. These bonding parameters may be considered a measure of covalency of in-plane bonding, out-of-plane bonding, in-plane bonding and out-of-plane bonding.
2, 2, γ2 parameters were calculated using the following equations. Eq. (5).
2= – (All/0.036) + (all – 2.0036) + 3/7 (g⊥ – 2.0036) + 0.04 (5)
2 = (all – 2.0036) E/ -8λ 2 (6)
γ2 = (all – 2.0036) E / -2λ 2 (7)
Here λ = 828cm-1 for free Cu (II) ion and E is the electric energy for the 2BIg →2A1g transition which is 16,630cm-1 for the complex 1. The λ value is calculated by using the following equation.
gav = 1/3 and gav = 2
The calculated λ for the compound 1 is 275cm-1 which is smaller than the free Cu (II) ion. This
reduction in λ value than compared to that of the free atom indicates the covalent character in M-L bond.**evil PV and the cost also indicate considerable mixing of ground and excited state terms.
The bonding parameter (2 = 0.81-0.99) considerable covalent character between metal-ligand. If the two value is 0.5, then it implies complete covalent bonding, while that of 1.0 implies complete ionic bonding. For the complex 1, the calculated the calculated two value is
0.732 which indicates that the complex has some covalent character. 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 completely ionic.
This is also confirmed by orbital reduction factor K which can be estimated using Eq. 8 & 9.
Kill = 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⟘. In the case of pure -bonding. K||≈K⟘ = 0.77, whereas K|| K⟘. 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.