Volume 225, 2021

Inclusion of viologen cations leads to switchable metal–organic frameworks

Abstract

The reactions of Zn(NO3)2·6H2O with the polycarboxylic acids 1,3-benzenedicarboxylic acid (H2mbdc), 1,4-benzenedicarboxylic acid (H2bdc), 1,3,5-benzenetricarboxylic acid (H3btc) and 4,4′-biphenyldicarboxylic acid (H2bpdc) in the presence of methyl viologen iodide ([MV]I2) in DMF gave anionic frameworks with methyl viologen species incorporated as counter-ions. When the reactions were carried out at 120 °C, the blue products [MV][Zn3(mbdc)4] (1-ht), [MV]0.44[H2MV]0.36[NMe2H2]0.4[Zn3(bdc)4]·0.6DMF (2-ht), [MV]0.5[Zn(btc)]·DMF (4-ht) and [MV][Zn4(bpdc)5]·8DMF·10H2O (5-ht) were formed, and these were shown to contain the radical cation [MV]˙+. In contrast, the same reactions carried out at 85 °C gave orange isostructural compounds containing the dication [MV]2+. Similar observations were made for reactions with ethyl viologen bromide. The compounds 1-ht, 2-ht and 4-ht contain similar framework topologies to analogues in which NMe2H2+ is the included cation. In contrast, 5-ht is based on a previously unreported interpenetrated network. Compound 2-ht contains the protonated species [H2MV]2+ in addition to [MV]˙+ and the crystal structure shows that the two rings in the former are staggered with respect to each other. This species is believed to form under the reaction conditions employed in the synthesis and the formation of [H2MV]2+ is suppressed by using an alternative approach in which methyl viologen is formed in situ from viologen diacetic acid. In the bdc-containing products, the radical cation is rapidly oxidised to the dication on exposure to air, as witnessed by the colour change from blue to orange. This change is reversed either by heating to 120 °C or exposure to UV radiation, both under nitrogen. This is in contrast to observations with the mbdc and btc analogues 1-ht and 4-ht, as in these compounds the blue colour persists for weeks. The difference can be related to the structures, with the channels present in 2-ht allowing oxygen to reach the radical cations.

Graphical abstract: Inclusion of viologen cations leads to switchable metal–organic frameworks

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
11 dic. 2019
Accepted
19 ago. 2020
First published
19 ago. 2020
This article is Open Access
Creative Commons BY-NC license

Faraday Discuss., 2021,225, 414-430

Inclusion of viologen cations leads to switchable metal–organic frameworks

L. K. Cadman, M. F. Mahon and A. D. Burrows, Faraday Discuss., 2021, 225, 414 DOI: 10.1039/C9FD00137A

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements