X-Ray K Absorption Edge Structures of Chlorine Ion in [CoCl₂(en)₂]NO₃, [CoCl₂(en)₂]Cl and [Co(en)₃]Cl₃·3H₂O

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X-ray K absorption edge structures of chlorine ion in trans-[CoCl₂(en)₂]NO₃, trans-[CoCl₂(en)₂]Cl and [Co(en)₃]Cl₃·3H₂O are measured with a high-resolution vacuum two-crystal spectrometer. The spectra, except that of [Co(en)₃]Cl₃·3H₂O having no ligand Cl⁻ ion, show an extremely narrow absorption line at the absorption threshold. All of the spectra show a broad absorption band extending to the higher energy region of the narrow absorption line. It is found that a characteristic of the respective spectra depends on the different chemical states between the cobalt and chlorine ions. The result is interpreted on the basis of molecular orbital theory.