Coordination polymer flexibility leads to polymorphism and enables a crystalline solid-vapour reaction: a multi-technique mechanistic study

Iñigo J. Vitõrica-Yrezábal, Stefano Libri, Jason R. Loader, Guillermo Mínguez Espallargas, Michael Hippler, Ashleigh J. Fletcher, Stephen P. Thompson, John E. Warren, Daniele Musumeci, Michael D. Ward, Lee Brammer

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Abstract

Despite an absence of conventional porosity, the 1D coordination polymer [Ag4(O2C(CF2)2CF3)4(TMP)3] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into AgO bonds to yield coordination polymers [Ag4(O2C(CF2)2CF3)4(TMP)3(ROH)2] (1-ROH; R=Me, Et, iPr). The reactions are reversible single-crystal-to-single-crystal transformations. Vapour-solid equilibria have been examined by gas-phase IR spectroscopy (K=5.68(9)×10−5 (MeOH), 9.5(3)×10−6 (EtOH), 6.14(5)×10−5 (iPrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two-step reactions 1-ROH12, in which 2 is the 2D coordination polymer [Ag4(O2C(CF2)2CF3)4(TMP)2] formed by loss of TMP ligands exclusively from singly-bridging sites. Four polymorphic forms of 1 (1-ALT, 1-AHT, 1-BLT and 1-BHT; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X-ray diffraction (PXRD) studies of the 1-ROH12 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 1-MeOH/1-AHT show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.

Original languageEnglish
Pages (from-to)8799-8811
Number of pages13
JournalChemistry - A European Journal
Volume21
Issue number24
Early online date11 May 2015
DOIs
Publication statusPublished - 28 May 2015

Keywords

  • coordination polymers
  • gas-phase spectroscopy
  • in situ diffraction
  • microscopy
  • polymorphism
  • porosity
  • solid-state reactions
  • thermal analysis

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