Synthesis and Crystal Structures of Various Phases of the Microporous Three-Dimensional Coordination Polymer [Zr(OH)2(C2O4)]n

A homometallic Zr­(IV)-oxalate three-dimensional (3-D) coordination polymer of formula [Zr­(OH)2(C2O4)­·0.5H2O] is reported. This compound was found to be a microporous solid with reversible sorption abilities. Upon guest release and sorption, the crystalline material undergoes single crystal to single crystal transitions. The crystal structures for three phases have been solved from single crystal diffraction studies. They consist of the guest containing frameworks [Zr­(OH)2(C2O4)­·0.5H2O], 1, 3, and the guest-free porous phase [Zr­(OH)2(C2O4)], 2; all are found with tetragonal space group I4/m. Phase 1 has been obtained by controlled diffusion of the reagents (ZrO­(NO3)2 and H2C2O4) in a silica gel medium; the other phases have been formed from 1 by thermal activation (2) and re-adsorption of H2O (3).