Combined X-ray Absorption Near-Edge Structure and X-ray Photoelectron Study of the Electrocatalytically Active Cobalt(I) Cage Complexes and the Clathrochelate Cobalt(II)- and Cobalt(III)-Containing Precursors and Analogs

Abstract

As the catalytic cycle for electrochemical hydrogen generation includes cobalt(I, II, and III)-containing clathrochelate species, we performed a detailed study of their electronic structure. The Co K-edge spectra demonstrated a lowering of the Co 1s ionization potentials from cobalt(III) complexes to their cobalt(II)-containing analogs and then to the cobalt(I) clathrochelates. The absence of pre-edge structure and specific peculiarities suggested a high symmetry of the N6-coordination polyhedra of an encapsulated cobalt(I) ion. The Co 2p core-level spectra contained very weak shakeup satellites, suggesting a hybridization of the cobalt-localized 3d orbitals and the valent orbitals of their encapsulating ligands, while the binding energy Co 2p3/2 increased with a formal oxidation state of an encapsulated cobalt ion(I, II, or III) from 780.5–780.8 eV and 780.9–781.2 eV to 781.8–782.2 eV. The Cl 2p, C 1s, N 1s, O 1s, B 1s, and Co 2p core-level spectra and data of X-ray absorption near edge structure (XANES) proved that both the electronic and spatial structures of the highly conjugated polyene macrobicyclic ligands are affected by the metal-localized redox processes. The nature of these encapsulating ligands influenced the redox characteristics of the caged metallocenters, allowing them to adopt unusual catalytically active oxidation state.

Ionic Polymer Microspheres Bearing a CoIII–Salen Moiety as a Bifunctional Heterogeneous Catalyst for the Efficient Cycloaddition of CO2 and Epoxides

“…The peak at BE=67 eV is assigned to Br 3d and that at BE=780 eV is for Co 2p. The peaks in the spectrum of Co 2p (Co 2p 1/2 : BE=796 eV; Co 2p 3/2 : BE=781 eV; Figure b) matched well with those of reported Co III –salen complexes …”

“…The peaks in the spectrum of Co 2p (Co 2p 1/2 :B E = 796 eV;C o2p 3/2 :B E = 781 eV;F igure 2b)m atched well with those of reported Co III -salen complexes. [17,42,43] The thermal stabilityo fT BB-Bpy and TBB-Bpy@Salen-Cow as analyzed by thermogravimetric/derivative thermogravimetric (TG-DTG) analysis ( Figure 3). TBB-Bpy is quite stable up to 280 8C.…”

Approach to the Mechanism of Hydrogen Evolution Electrocatalyzed by a Model Co Clathrochelate: A Theoretical Study by Density Functional Theory

“…Figure a in reference [13]) suggests that the catalytically active species is a reduced form of the complex [Co II ] 0 . This fact had been expressed before,,,, and the monomolecular catalytic pathway depicted in Figure b (black and red color) has been explicitly proposed elsewhere,, consisting in a typical ECCE mechanism. In the acronym ECCE and from here on, the capital letter E stands for an electrochemical step, while the capital letter C represents a chemical step.…”

“…However, the energetic barrier calculated for the HER is far too high, since typical barriers for the HER catalyzed by organometallic complexes are around 90 kJ mol −1 , which is in open contrast to the calculated barrier of 691.65 kJ mol −1 found in this work. A thorough revision of the literature indicates that the ECCE mechanism in Figure b (black and red color) is the most abundantly proposed for clathrochelates,, therefore it is tacitly assumed that this is the actual operating mechanism. Though, our structural and mechanistic analyses suggest that, at least for the Co(Cl 2 Gm) 3 (B−CH 3 ) 2 complex, such mechanism is neither structurally nor energetically favored.…”

“…The three redox states of the clathrochelate and their high and low spin configurations were explored. The ECCE mechanism of HER first calculated here was based on a proposition made in previous publications ,. The explored mechanism consisted in the activation of a [Co] 0 clathrochelate by one‐electron reduction to yield the catalytically active [Co] 1− .…”