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Complex Definition Chemistry Essay Sample

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Complex Definition Chemistry Essay Sample

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[66], 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[67], 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[69].

The in-plane  bonding covalence parameters[70], 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[71] 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[72-74]. 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.

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