Coordination Polymer Flexibility Leads to Polymorphism and Enables a Crystalline Solid–Vapour Reaction: A Multi‐technique Mechanistic Study. Issue 24 (11th May 2015)

• Record Type: Journal Article
• Authors: Vitórica‐Yrezábal, Iñigo J.; Libri, Stefano; Loader, Jason R.; Mínguez Espallargas, Guillermo; Hippler, Michael; Fletcher, Ashleigh J.; Thompson, Stephen P.; Warren, John E.; Musumeci, Daniele; Ward, Michael D.; Brammer, Lee
• Is Part Of: Chemistry. Volume 21:Issue 24(2015)
• Page Start: 8799
• Page End: 8811
• Publication Date: 2015-05-11
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201500514
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Despite an absence of conventional porosity, the 1D coordination polymer [Ag<sub>4</sub>(O<sub>2</sub>C(CF<sub>2</sub>)<sub>2</sub>CF<sub>3</sub>)<sub>4</sub>(TMP)<sub>3</sub>] (<bold>1</bold>; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into AgO bonds to yield coordination polymers [Ag<sub>4</sub>(O<sub>2</sub>C(CF<sub>2</sub>)<sub>2</sub>CF<sub>3</sub>)<sub>4</sub>(TMP)<sub>3</sub>(ROH)<sub>2</sub>] (<bold>1‐ROH</bold>; R=Me, Et, <italic>i</italic>Pr). The reactions are reversible single‐crystal‐to‐single‐crystal transformations. Vapour‐solid equilibria have been examined by gas‐phase IR spectroscopy (<italic>K</italic>=5.68(9)×10<sup>−5</sup> (MeOH), 9.5(3)×10<sup>−6</sup> (EtOH), 6.14(5)×10<sup>−5</sup> (<italic>i</italic>PrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two‐step reactions <bold>1‐ROH</bold>→<bold>1</bold>→<bold>2</bold>, in which <bold>2</bold> is the 2D coordination polymer [Ag<sub>4</sub>(O<sub>2</sub>C(CF<sub>2</sub>)<sub>2</sub>CF<sub>3</sub>)<sub>4</sub>(TMP)<sub>2</sub>] formed by loss of TMP ligands exclusively from singly‐bridging sites. Four polymorphic forms of <bold>1</bold> (<bold>1‐A<sup>LT</sup></bold>, <bold>1‐A<sup>HT</sup></bold>, <bold>1‐B<sup>LT</sup></bold> and <bold>1‐B<sup>HT</sup></bold>; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X‐ray diffraction (PXRD) studies of the <bold>1‐ROH</bold>→<bold>1</bold>→<bold>2</bold> transformations indicate the role of the HT polymorphs in these reactions. The structural relationship between polymorphs, involving changes in conformation of perfluoroalkyl chains and a change in orientation of entire polymers (A versus B forms), suggests a mechanism for the observed reactions and a pathway for guest transport within the fluorous layers. Consistent with this pathway, optical microscopy and AFM studies on single crystals of <bold>1‐MeOH</bold>/<bold>1‐A<sup>HT</sup></bold> show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.</p> </abstract>