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Electron spin resonance of X- and Y- irradiated potassium difluoromalonate and electron paramagnetic resonance of copper (II) complex with trifluoroacetate ligands Mustafa, Mohammed Rafi

Abstract

In Part I of this thesis an irradiated single crystal of dipotassium difluoromalonate monohydrate has been studied by Electron Spin Resonance. On X-irradiation the crystal yields CF(COO¯)2 radical with a highly anisotropic hyperfine tensor, characteristic of a (19)F nucleus. In addition, some other lines were also observed which were too weak to be analyzed. On γ-irradiation, the crystal yields mainly the same radical in addition to two types of CF(2)COO¯ radicals. In one type, the carboxyl group was found to be nearly coplanar with the CF(2) fragment while in the other, it was nearly perpendicular. A broad central line in each spectrum indicated also the possibility of the presence of CO(2)¯ radical. An unrestricted Hartree-Fock calculation, using the approximation of Intermediate Neglect of Differential Overlap was carried out on a number of fluorinated radicals to correlate the (19)F hyperfine tensors obtained in the present study with those obtained previously. The theory was used to calculate the theoretical hyperfine tensors for various radicals and was found to give a reasonably good agreement with the experimental results. On this basis the hyperfine tensor for CHFCOO¯ radical was predicted. The calculation also showed that one of the carboxyl groups in CF(COO¯)2 radicals is co-planar with the radical plane while the other makes an angle of 85°. In Part II, a crystal of zinc trifluoroacetate dihydrate, containing small amounts of Cu++ has been studied at 77°K and it was found that the Cu++ ion resides in an approximately tetragonal environment with the ground state consisting of mainly d(z2) orbital which is coupled to d(x2)-(y2) orbital, perhaps through vibronic interactions. Also a solution of copper trifluoroacetate in trifluoroacetic acid was studied at room temperature and at 77°K and the results were interpreted by assuming a tetragonal symmetry with the ground state being pure d(x2)-(y2).

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