A novel third-generation Cu-PCP with unprecedented m-OH2 bridge

Soft porous coordination polymers (Soft-PCPs) also known as third-generation porous materials (i.e. undergoing reversible transformations accompanied by structural modifications) are the subject of high interest as a consequence of their unique properties. These materials have a kind of “soft” periodic network with bistability associated to a contracted or expanded phase, as a response to external stimuli. In this communication, we present the new Cu-PCP of formulation ([Cu2(dmcapz)2(OH2)]DMF1.5)n (1) easily obtained in the reaction of CuCl2 with 3,5-dimethyl-4-carboxypyrazole (H2dmcapz). 1 shows an unprecedented H2O bridge between the two metal atoms. The removal of this water molecule gives rise to a metastable evacuated phase (1b) that transforms into an empty and extremely stable material (1c) after freezing at liquid nitrogen temperature (see Scheme). The soaking of 1c into water, allows the complete and instantaneous recover of the water exchanged material 1a. Noteworthy, 1c is very stable in air since ambient moisture cannot transform it into 1a, due to the need of high water pressures to achieve the gate opening. The key factor of these reversible phase changes in 1 is the flexible nature of Cu(II) coordination polyhedron which is able to adapt to various coordination numbers and geometries. Noteworthy, the changes in the coordination sphere of Cu are confirmed by marked colour changes. The relation between the Cu coordination geometries and the 3D structure are under investigation, as well as the differences in gas adsorption properties of 1b and 1c evacuated materials.