Solvatochromism and the effect of solvent on properties in a two-dimensional coordination polymer of cobalt-trimesate

Abstract

Stimuli responsive porous materials are being investigated for a plethora of potential applications. These materials have the ability to respond to their physical and chemical environment and thus provide an opportunity to study supramolecular type interactions. We present an investigation into the effects of guest inclusion on framework flexibility in a two-dimensional polymer network, {[Co(btc)(DMF)₂]·xDMF}_n (1) where btc is benzene-1,3,5-tricarboxylate (trimesate) and DMF N,N-dimethylformamide. Solvents for guest exchange were selected to explore different potential interactions, such as hydrogen bonding (water and alcohols) and π-stacking (benzonitrile) and to cover a wide range of polarities and molecular sizes. Results showed that all solvents used could be exchanged directly for the guest DMF with accompanying visible colour changes. The incorporation of the new guest solvent was confirmed by PXRD and thermal analysis. This process is reversible for most solvents. On removal of the guest DMF, the framework (1-f) is retained, but layers collapse to a less crystalline material. Only water and methanol are capable of penetrating the material to reconstitute the layers. The crystal structure of the guest-exchanged system with benzonitrile (2) showed that the coordination polymer framework is retained, albeit with a change in symmetry and interlayer spacing, making 1 an example of a ‘breathing’ coordination polymer. A survey of related structures in the CSD found that there are four common motifs, which cannot be predicted from either the composition or space group symmetry of the compound.