Molecular design of cage iron(ii) and cobalt(ii,iii) complexes with a second fluorine-enriched superhydrophobic shell

Abstract

Pentafluorophenylboron-capped iron and cobalt(II) hexachloroclathrochelate precursors were obtained by the one-pot template condensation of dichloroglyoxime with pentafluorophenylboronic acid on iron and cobalt(II) ions under vigorous reaction conditions in trifluoroacetic acid media. These reactive precursors easily undergo nucleophilic substitution with (per)fluoroarylthiolate anions, giving (per)fluoroarylsulfide macrobicyclic complexes with encapsulated iron and cobalt(II) ions; nucleophilic substitution of the cobalt(II) hexachloroclathrochelate precursor with a pentafluorophenylsulfide anion gave the target hexasulfide monoclathrochelate and the mixed-valence Co(III)Co(II)Co(III) bis-clathrochelate as a side product. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, (57)Fe Mössbauer (for the X-rayed iron complexes), (1)H, (11)B, (13)C and (19)F NMR spectroscopies and by X-ray diffraction; their redox and electrocatalytic behaviors were studied using cyclic voltammetry and gas chromatography. As can be seen from the single-crystal X-ray diffraction data, the second superhydrophobic shell of such caged metal ions is formed by fluorine atoms of both the apical and ribbed (per)fluoroaryl peripheral groups. The main bond distances and chelate N=C-C=N angles in their molecules are similar, but rotational elongation (contraction) along the molecular C3-pseudoaxes, accompanied by changes in the geometry of the corresponding MN6-coordination polyhedra from a trigonal prism to a trigonal antiprism, allowed encapsulating Fe(2+), Co(2+) and Co(3+) ions. The nature of an encapsulated metal ion and its oxidation state affect the M-N bond lengths, and, for cobalt(ii) clathrochelate with an electronic configuration d(7) the Jahn-Teller structural effect is observed as an alternation of the Co-N distances. Pentafluorophenylboron-capped hexachloroclathrochelate precursors, giving stable catalytically active metal(I)-containing intermediates due to the electron-withdrawing effect of their six ribbed chlorine substituents, were found to show moderate electrocatalytic activity in a 2H(+)/H2 hydrogen-forming reaction. In the case of their ribbed-functionalized sulfide derivatives, the strong electron-withdrawing (per)fluoroaryl groups do not stabilize the reduced electrocatalytically active metal(i)-containing species as their mesomeric effect is absent or substantially decreased by steric hindrances between them.

A New Series of Cobalt and Iron Clathrochelates with Perfluorinated Ribbed Substituents

“…6 Indeed, (per)fluorinated iron and cobalt(II) clathrochelates with pendant (per)fluoroarylsulfide substituents are known to withstand harsh acidic conditions. 7 In these complexes, however, the presence of bridging sulfur atoms does not allow the (per)fluoroaryl groups to stabilize the reduced (and probably electrocatalytically active) metal(I)-containing intermediate. 7 Removing these atoms may potentially open a new pathway to better (more efficient and more stable) clathrochelate-based electrocatalysts for the HER, which are functional analogs of macrocyclic BF 2 -cross-linked iron(II) complexes of perfluoroaryl-substituted α-dioximates earlier used for this purpose.…”

“…7 In these complexes, however, the presence of bridging sulfur atoms does not allow the (per)fluoroaryl groups to stabilize the reduced (and probably electrocatalytically active) metal(I)-containing intermediate. 7 Removing these atoms may potentially open a new pathway to better (more efficient and more stable) clathrochelate-based electrocatalysts for the HER, which are functional analogs of macrocyclic BF 2 -cross-linked iron(II) complexes of perfluoroaryl-substituted α-dioximates earlier used for this purpose. 8 Here, we report iron and cobalt(II) (per)fluoroclathrochelates with inherent perfluoroaryl ribbed substituents, which can be obtained by a simple one-pot synthetic approach, and their behavior in the HER.…”

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

“…Tris‐glyoximate metal clathrochelates such as the cobalt species shown in Figure a are a family of metal complexes that have been shown to be efficient catalysts for the HER . Clathrochelates are basically cage compounds which are able to stabilize the low oxidation states of transition metals (e. g. Co or Fe), thereby offering interesting possibilities to act as hydrogen‐producing catalysts with an appealing potential as molecular electrocatalysts ,…”

“…Concerning the experimental cyclic voltammogram of clathrochelates, qualitative prove of electrocatalysis is well established . Some previous experimental work has been performed with inorganic acids dissolved in water ,. Consequently, any mechanistic analysis is obscured by the two proton sources present in the system.…”

Wettability evolution of different nanostructured cobalt films based on electrodeposition

“…Superhydrophobicity of Co has become an important research topic in recent years [9]. Researchers have recently fabricated a variety of superhydrophobic Co nanostructures [10][11][12][13][14]. However, the growth mechanism of these superhydrophobic films was not discussed in detail in any of these cases.…”