Photoswitching of Co(ii)-based coordination cages containing azobenzene backbones

Abstract

Inclusion of photoswitchable azobenzene units as spacers into ditopic bridging ligands Lm and Lp, containing two chelating pyrazolyl-pyridine termini, allows formation of metal complex assemblies with Co(II) that undergo a range of light-induced structural transformations. One notable result is the light-induced conversion of a Co2(Lp)3 dinuclear triple helicate (based on the E ligand isomer) to a C3-symmetric Co4(Lp)6 assembly, assumed to be an edge-bridged tetrahedral cage, based on the Z ligand isomer. Another is the preparation of a series of Co4(Lm)6 complexes, of which Co4(E-Lm)6 was crystallographically characterised and consists of a pair of Co2(Lm)2 double helicates connected by an additional two bridging ligands which span the pair of helicate units, giving a cyclic Co4 array in which one and then two bridging ligands alternate around the periphery. A set of Co4(Lm)6 complexes could be prepared containing different ratios of Z : E ligand isomers (0 : 6, 2 : 4, 4 : 2 and 6 : 0) of which Co4(Z-Lm)2(E-Lm)4 was particularly stable and dominated the speciation behaviour, either during light-induced switching of the ligand geometry in pre-formed complexes, or when ligand isomers were combined in different proportions during the preparation. These examples of (i) interconversion between Co2L3 (helicate) and (ii) Co4L6 (cage) assemblies with Lp, and the interconversion between a series of Co4L6 assemblies Co4(Z-Lm)n(E-Lm)6−n with Lm, constitute significant advances in the field of photoswitchable supramolecular assemblies.

Graphical abstract: Photoswitching of Co(ii)-based coordination cages containing azobenzene backbones

Supplementary files

Article information

Article type
Edge Article
Submitted
06 Mar 2024
Accepted
02 May 2024
First published
03 May 2024
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2024, Advance Article

Photoswitching of Co(II)-based coordination cages containing azobenzene backbones

M. B. Tipping, L. Pruñonosa Lara, A. B. Solea, L. K. S. von Krbek and M. D. Ward, Chem. Sci., 2024, Advance Article , DOI: 10.1039/D4SC01575D

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