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

Iñigo J Vitórica-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

doi:10.1002/chem.201500514

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

Chemistry. 2015 Jun 8;21(24):8799-811. doi: 10.1002/chem.201500514. Epub 2015 May 11.

Authors

Affiliations

¹ Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF (UK), Fax: (+44) 114-222-9536 http://www.sheffield.ac.uk/chemistry/staff/profiles/lee_brammer.
² Current address: School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL (UK).
³ Instituto de Ciencia Molecular (ICMol), Universidad de Valencia c/Catedrático José Beltrán 2, 46980 Paterna (Spain).
⁴ Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose St, Glasgow G1 1XJ (Scotland).
⁵ Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxon OX11 0DE (UK).
⁶ School of Materials, University of Manchester, Manchester M13 9PL (UK).
⁷ Molecular Design Institute, NYU Department of Chemistry, 100 Washington Square East, New York, NY 10003 (USA).
⁸ Current address: Department of Chemistry, York College of The City University of New York, 94-20 Guy R. Brewer Blvd, Jamaica, New York, NY 11451 (USA).
⁹ Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF (UK), Fax: (+44) 114-222-9536 http://www.sheffield.ac.uk/chemistry/staff/profiles/lee_brammer. lee.brammer@sheffield.ac.uk.

Abstract

Despite an absence of conventional porosity, the 1D coordination polymer [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)3 ] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into AgO bonds to yield coordination polymers [Ag4 (O2 C(CF2 )2 CF3 )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-ROH→1→2, in which 2 is the 2D coordination polymer [Ag4 (O2 C(CF2 )2 CF3 )4 (TMP)2 ] formed by loss of TMP ligands exclusively from singly-bridging sites. Four polymorphic forms of 1 (1-A(LT) , 1-A(HT) , 1-B(LT) and 1-B(HT) ; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X-ray diffraction (PXRD) studies of the 1-ROH→1→2 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-A(HT) show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.

Keywords: coordination polymers; gas-phase spectroscopy; in situ diffraction; microscopy; polymorphism; porosity; solid-state reactions; thermal analysis.