Chromium(II) Metal-Organic Polyhedra as Highly Porous Materials

Herein we report for the first time the synthesis of Cr(II)-based metal-organic polyhedra (MOPs) and the characterization of their porosities. Unlike the isostructural Cu(II)- or Mo(II)-based MOPs, Cr(II)-based MOPs show unusually high gas uptakes and surface areas. The combination of comparatively robust dichromium paddlewheel units (Cr₂ units), cage symmetries, and packing motifs enable these materials to achieve Brunauer-Emmett-Teller surface areas of up to 1000 m²/g. Reducing the aggregation of the Cr(II)-based MOPs upon activation makes their pores more accessible than their Cu(II) or Mo(II) counterparts. Further comparisons of surface areas on a molar (m²/mol cage) rather than gravimetric (m²/g) basis is proposed as a rational method of comparing members of a family of related molecular materials.