Coligand-Rigidity Induced Interpenetration in Flexible Bis-imidazolyl Type Linker Based Mixed Ligand Metal-Organic Frameworks

Interpenetration or catenation is well explored in the network structure of metal organic frameworks, but these kinds of networks were considered as not usable for normal applications of conventional open metal-organic frameworks (MOFs). Recently, flexibility in such networks was found to be an important factor to introduce functionality in the structures of MOFs, and also, the understanding of the factors that control interpenetration also become important. To date, there is no obvious root that has been found to have an interpenetrated network with successive flexibility. In search of such types of networks and to explore the avenue of understanding of growing interpenetration in a framework, six new metal-organic frameworks (MOFs) of Cu(II), Cd(II), and Zn(II) have been synthesized from three flexible dicarboxylates and two rigid dicarboxylates along with 2-methyl-1-(4-(2-methyl-1H-imidazole-1-yl)butyl)-1H-imidazole, as a coligand. All of these synthesized complexes have been characterized by single crystal and powder X-ray diffraction and were further characterized by elemental analysis, infrared spectroscopy (IR), and thermogravimetric analysis (TGA). N-2, CO2, H-2, and CH4 sorption studies were also done for all the MOFs, and the characteristic surface adsorptions were found in all cases. Here, from the studies of all these complexes, a common observation is found: flexible dicarboxylates give a noninterpenetrated framework whereas rigid linkers give an interpenetrated framework.