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

• Published in: Journal of molecular structure Vol. 1263; p. 133125
• Main Authors: Sarmah, Nirupamjit, Sharma, Deepa, Mehta, B.K., Shrivastava, B.D., Das, B.K., Zimina, A., Gaur, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.09.2022
• Subjects: Ab initio XANES calculations; Density of states; EXAFS; Octa-nuclear cobalt complexes; Planar ring structure; Density of states; XANES; Octa-nuclear cobalt complexes; EXAFS; Planar ring structure; Ab initio XANES calculations
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2022.133125

•Electronic nature of octanuclear cobalt complexes probed by XANES fingerprinting, EXAFS fitting and theoretical XANES simulations.•XANES indicated mixed nature Co2+/ Co3+ in 1 and Co3+ nature in 2 and 3.•EXAFS analysis confirmed octahedral nature of Co centres and indicated octanuclear nature of complexes 1-3.•XANES simulations showed Co ions present at vertices of octanuclear ring have different electronic structure.•Corresponding DOS curves calculated simultaneously for these sites correlate well to the XANES features. 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. [Display omitted]