Coordination network that reversibly switches between two nonporous polymorphs and a high surface area porous phase

Abstract

We report a 2-fold interpenetrated primitive cubic (pcu) network X-pcu-5-Zn, [Zn-2(DMTDC)(2)(dpe)] (H2DMTDC = 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid, dpe = 1,2-di(4-pyridyl)ethylene), that exhibits reversible switching between an as-synthesized "open"phase, X-pcu-S-Zn-alpha, and two nonporous or "closed" polymorphs, X-pcu-5-Zn-beta and X-pcu-S-Zn-gamma. There are two unusual features of X-pcu-SZn. The first relates to its sorption properties, which reveal that the alpha form exhibits high CO2 uptake (ca. 255 cm(3)/g at 195 K) via reversible closed-to-open switching (type F-IV isotherm) of the type desirable for gas and vapor storage; there are only three other reports of porous materials that combine these two features. Second, we could only isolate the beta form by activation of the CO2 loaded a form and it persists through multiple CO2 adsorption/desorption cycles. We are unaware of a new polymorph having been isolated in such a manner. That the observed phase changes of X-pcu-S-Zn-alpha occur in single-crystal-to-single-crystal fashion enabled structural characterization of the three forms; gamma is a coordination isomer of a and beta both of which are based upon "paddlewheel" clusters.