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SM ISO690:2012 KOCHUBEY, Dmitry, KAICHEV, Vasiliy, SARAEV, Andrey, TOMYN, Stefania, FRITSKII, I., BELOV, Alexander, VOLOSHIN, Yan. XANES and XPS study of the electronic structure of electrocatalytically active cobalt(I) cage complexes and their clathrochelate cobalt(II)- and cobalt(III)-containing precursors and analogs. In: Physical Methods in Coordination and Supramolecular Chemistry, 24-26 octombrie 2012, Chişinău. Chisinau, Republic of Moldova: 2012, XVII, p. 34. |
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Physical Methods in Coordination and Supramolecular Chemistry XVII, 2012 |
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Conferința ""Physical Methods in Coordination and Supramolecular Chemistry"" Chişinău, Moldova, 24-26 octombrie 2012 | ||||||
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Pag. 34-34 | ||||||
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Nowadays, the great attention is paid to the evolution of the traditional methods of generating of the heat and electricity into the modern hydrogen energetics. One of the most rapidly developing areas is the search for the highly efficient catalytic systems that can generate H2 from aqueous solutions. As electrocatalysts for H2 production, we used cheap and synthetically available cobalt(I, II and III) clathrochelates, which demonstrate unusually high stability in time, may easily be functionalized with up to eight substituents [1,2] and immobilized on a working electrode [3, 4]. The catalytic cycle for H2 generation (Scheme) includes the fast transfer of H+ to the basic encapsulated cobalt(I)- containing metallocenter resulting from the Co2+/+ reduction and the formation of the corresponding Co – H hydride complex as the most probable intermediate of this electrocatalytic process. This hydride clathrochelate then easily undergoes a protonation with a fast intramolecular formation of the H – H bond and an evolution of H2 molecule. The cobalt(III) cage complex formed undergoes the Co3+/2+ reduction to the initial cobalt(II)-containing clathrochelate electrocatalyst. Hence, the cobalt(I, II and III) clathrochelates are involved in this cycle, and the detailed investigation of their electronic structure by the modern physical methods seems to be of great importance. As the XPS data showed, the Co2p3/2 binding energy increases with a formal oxidation state of an encapsulated cobalt ion; for the cobalt(I), cobalt(II), and cobalt(III) clathrochelates this energy is in the ranges 780.5 – 780.8, 780.9 – 781.2, and 781.8 – 782.2 eV, respectively. The Co2p core-level spectra of all the clathrochelates studied contain very weak electron shake-up satellites suggesting of a low hybridization of the metal-localized Co3d orbitals and the valent ones of the cage encapsulating ligands. XANESs (Fig.) demonstrate a lowering of the Co1s ionization potentials from the cobalt(III) complexes to their cobalt(II)-containing analogs and then to the cobalt(I) clathrochelates; an absence of the pre-edge structure and the specific peculiarities of its spectra suggest a high symmetry of the N6-coordination polyhedra of an encapsulated cobalt(I) ion with electronic configuration d 8 . This study was supported by RFBR (grants 10- 03-00837 and 12-03-00961) and DESY (HASYLab project I-20110163). |
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