Solvent induced reversible single-crystal-to-single-crystal structural transformation in dynamic metal organic frameworks: a case of enhanced hydrogen sorption in polycatenated framework

Abstract

Two d¹⁰ metal complexes {[Zn₂(fum)₂(dim)₂](H₂O)(MeOH)}_n (1) and {[Cd₂(fum)₂(dim)₂(H₂O)](MeOH)}_n (2) have been prepared by using fumarate (fum) and di(1H-imidazol-1-yl)methane (dim) in methanol and water solutions. They have different structural architectures and interactions with lattice solvent methanol. A single crystal of complex 1 transforms to {[Zn(fum)(dim)](H₂O)}_n (1a) by selective elimination of lattice methanol in a reversible fashion at room temperature. On the other hand, a polycatenated framework of complex 2 does not undergo such solvent induced transformation at room temperature; rather it shows reversible dissolution–recrystallization structural transformation (DRST) by slow evaporation of methanol molecules, forming {[Cd(dim)₂(H₂O)₂](fum)(H₂O)₂}_n (2a). This selective solvent induced reversible SCSC structural transformation of complex 1 and reversible DRST of complex 2 at room temperature have been also established by PXRD and luminescence studies. Gas sorption studies (H₂, N₂, and CO₂) have been performed for the compounds, and the hydrogen uptake was found to be higher in the case of the polycatenated framework.