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 (Cr units), cage symmetries, and packing motifs enable these materials to achieve Brunauer-Emmett-Teller surface areas of up to 1000 m/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 (m/mol cage) rather than gravimetric (m/g) basis is proposed as a rational method of comparing members of a family of related molecular materials.