Issue 4, 2023

Catalytic reactions in a Co12 cuboctahedral cage arising from guest encapsulation and cage-based redox activation

Abstract

A Co12 coordination cage with a cuboctahedral architecture, and incorporating a mixture of tritopic (face-capping) and ditopic (edge-bridging) ligands, shows strong guest binding of large aromatic fluorophores (fluorescein and its derivatives 6-carboxyfluorescein and Eosin-Y) with 1 : 1 binding constants in water in the range log K = 6.7–7.9; its large central cavity (>1000 Å3) facilitates binding of much larger guests than was possible with the smaller Co8 cage that we have reported previously. Guest binding is accompanied by catalysed reactions of bound guests because the high positive charge on the cage surface (24+) also attracts anions, allowing the organic guests and anionic reaction partners to be co-located, resulting for example in cage-catalysed hydrolysis of phosphate esters (the insecticides Me-paraoxon and Et-paraoxon) and conversion of diacetyl fluorescein to fluorescein. In addition, we demonstrate a new type of cage-based catalysis which relies on the redox activity of the Co(II)/Co(III) couple in the cage to activate the peroxymonosulfate (PMS) anion by converting it to the highly reactive SO4˙ radical ion, which bleaches cavity-bound fluorescein by complete oxidation. This is an example of an ‘advanced oxidation process’ in which the host cage not only brings the fluorescein and the PMS together via orthogonal hydrophobic and electrostatic interactions, but also provides redox activation of the PMS via a Co(II)/Co(III) couple, with the cage taking an active role in the catalytic process rather than acting simply as a passive reaction vessel.

Graphical abstract: Catalytic reactions in a Co12 cuboctahedral cage arising from guest encapsulation and cage-based redox activation

Supplementary files

Article information

Article type
Research Article
Submitted
19 out 2022
Accepted
06 jan 2023
First published
09 jan 2023
This article is Open Access
Creative Commons BY license

Inorg. Chem. Front., 2023,10, 1270-1278

Catalytic reactions in a Co12 cuboctahedral cage arising from guest encapsulation and cage-based redox activation

X. Zhang, B. Sudittapong and M. D. Ward, Inorg. Chem. Front., 2023, 10, 1270 DOI: 10.1039/D2QI02223K

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