pH-Dependent Interpenetrated, Polymorphic, Cd2+- and BTB-based Porous Coordination Polymers with Open Metal Sites

Two polymorphic porous coordination polymers constructed from Cd2+ and benzene-1,3,5-tribenzoate and having interpenetrated two-dimensional (2D) (6,3) net topology and three-dimensional (3D) (10,3)-b net topology structures were synthesized. The number of single honeycomb-type layers interpenetrated dictates the dimensionality of the crystal structures of these two phases. The 2D structure has two interpenetrated layers, whereas the 3D structure has four interpenetrated layers. Interestingly, these two polymorphic forms selectively adsorb CO2 over N2, C2H4, and C2H6. Moreover, diffuse reflectance Fourier-transform infrared spectroscopy of CO2 adsorbed on these two polymorphic phases indicates strong interaction between CO2 and the open metal sites present on Cd2+ ions.