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Coordination Polymer Flexibility Leads to Polymorphism and Enables a Crystalline Solid–Vapour Reaction: A Multi-technique Mechanistic Study

DOI: 10.1002/chem.201500514 DOI Help
PMID: 25962844 PMID Help

Authors: Inigo Vitorica (The University of Sheffield) , Stefano Libri (University of Sheffield) , Jason Loader (University of Sheffield) , Guillermo Minguez Espallargas (Universidad de Valencia) , Michael Hippler (University of Sheffield) , Ashleigh J. Fletcher (University of Strathclyde) , Stephen Thompson (Diamond Light Source) , John E. Warren (University of Manchester) , Daniele Musumeci (New York University) , Michael D. Ward (New York University) , Lee Brammer (University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry - A European Journal , VOL 21 (24) , PAGES 8799–8811

State: Published (Approved)
Published: June 2015

Open Access Open Access

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.

Journal Keywords: Coordination Polymers; Gas-Phase Spectroscopy; In Situ Diffraction; Microscopy; Polymorphism; Porosity; Solid-State Reactions; Thermal Analysis

Subject Areas: Chemistry, Materials

Instruments: I11-High Resolution Powder Diffraction

Other Facilities: SRS Daresbury station 9.8

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