A new Co-nitroimidazolate–dicarboxylate pillared-layer network with various types of channels and ultra-large cages for gas uptake

Abstract

A novel porous coordination polymer based on a Co-nitroimidazolate–dicarboxylate pillared-layer network, namely, [Co₇(bdc)₆(nIm)₂(H₂O)₆]·3H₂O·3DMF, (1, H₂bdc = 1,4-benzenedicarboxylic acid, nIm = 2-nitroimidazole), has been synthesized by a solvothermal reaction. The microporous layers of 1 consisted of two kinds of SBUs, six-connected Co₃(O₂CR)₆ and three-connected [Co₂(O₂CR)₃]⁺, forming unprecedented Co₃-Co₂-bdc-based layers with three types of diamonded grids in the bc plane. The layers are further linked by bidentate-bridging nIm ligands as pillars into a 3-D metal–organic framework with two kinds of rectangular channels parallel to the c axis. It is worth mentioning that compound 1 also exhibits uniquely polyhedral cages with a maximum diagonal dimension of up to 31.019 Å, which has fallen in the scope of mesoporous (2–50 nm). To systematically evaluate the channels and special cages, the adsorption ability of 1 was measured by N₂, H₂ and CO₂ sorption experiments. Topological analysis indicates that compound 1 adopts a new topological structure with a point symbol of {4¹²·6¹⁴·8²}{4⁶}₂. Moreover, thermal gravimetric analysis (TGA) of as-synthesized 1 reveals a stability range up to 311 °C.