Probing the electronic nature of Co centers forming the planar ring in octa-nuclear Co complexes using X-ray absorption spectroscopy

The formation of octanuclear cobalt core has been studied in the Co complexes Na[Co8{O2CCH3}8(OCH3)16]NO3(1), Na[Co8{O2CC(CH3)3}8(OCH3)16]NO3(2), Na[Co8{O2CC(CH3)3}8 (OC2H5)16]NO3(3) by analysing the X-ray absorption spectra at the Co K-edge. Analysis of EXAFS confirmed octahedral coordination around the Co atoms. The presence of neighbouring Co atoms has been associated to the octanuclear nature of the complexes. The XANES features have been correlated with the oxidation state of the absorbing Co atoms and their coordination in the complexes. XANES spectra have been simulated by ab-initio XANES calculations performed for the Co centres forming the planar ring in order to investigate and compare the electronic nature of these metal centres. Co density of states (DOS), i.e., s-, p- and d-DOS have also been calculated to explain the different features of XANES spectra. The simulated XANES spectra are further compared with the experimental spectra to probe the effect of different ligands present in the complexes.