X-Ray K Absorption Edge Structures of Ligand Chlorine Ion in Some Cobalt Coordination Compounds

Abstract

The X-ray Cl K absorption spectra in [Co(NH₃)₆]Cl₃, [Co(NH₃)₅Cl]Cl₂, trans-[Co(NH₃)₄Cl₂]Cl and Cs₂[CoCl₄] are measured with a high-resolution vacuum two-crystal spectrometer. The spectra, except that of [Co(NH₃)₆]Cl₃, show an extremely narrow absorption line at the absorption threshold. The result is interpreted on the basis of molecular orbital theory and it is proposed that the intensity of these narrow absorption lines depends on the chemical state between the cobalt and ligand chlorine ions. The narrow absorption line may well be attributed to transitions of the Cl 1s electron into the e_g^* antibonding orbitals having partially the 3p character of chlorine in [Co(NH₃)₅Cl]Cl₂ and trans-[Co(NH₃)₄Cl₂]Cl. In Cs₂[CoCl₄] it may be ascribed to the Cl 1s-t₂^* transitions.