Unusual adsorption behavior of a highly flexible copper-based MOF

Due to their network flexibility, metal-organic frameworks (MOFs) may respond to external stimuli such as guest molecules, heat, pressure, humidity and so on by a dynamical transformation of their structure. In this work we present experimental studies by means of nitrogen and argon physisorption at cryogenic temperature concerning the influence of handling and storage on the recently synthesized highly flexible copper-based MOF (3)(infinity)[(Cu-4(mu(4)-O)(mu(2)-OH)(2)(Me(2)trzpba)(4)]. Unusual adsorption isotherms with up to three distinct steps in the adsorbed volume have been found substantiating once more: (i) the high sensitivity of flexible network structures for environmental influences, (ii) the high diversity of physisorption isotherm types for flexible materials including isotherms with several steps and large hysteresis loops, and last but not least (iii) that theoretical methods assuming inert solids cannot be applied to highly flexible materials for calculating pore sizes and other solid state parameters. (C) 2011 Elsevier Inc. All rights reserved.