Construction of Zn(II) and Cd(II) metal-organic frameworks of diimidazole and dicarboxylate mixed ligands for the catalytic photodegradation of rhodamine B in water

A set of four metal-organic frameworks, namely, [Zn(1,3-BDC)(bmimb)](n) (1), [Zn(1,4-BDC)(bmimb)](n) (2), [Cd(1,3-BDC)(bmimb)](n) (3), and [Cd(1,4-BDC)(bmimb)](n) (4), have been prepared under solvothermal conditions (1,3-BDC = 1,3-benzenedicarboxylate; 1,4-BDC = 1,4-benzenedicarboxylate; bmimb = 4,4'-bis(4-methyl-1-imidazolyl)biphenyl). The long bmimb ligand (N center dot center dot center dot N separation of ca. 14.1 angstrom) induces interpenetration of 1, 2 and 4 to increase both the framework stability and the density of effective catalytic metal centers. Compounds 1, 2 and 4 are interpenetrated 3D structures while 3 features a 2D structure. Compound 1 exhibits a parallel 2D --> 3D polycatenation while 2 and 4 are isomorphous and feature 3D --> 3D interpenetration. Compounds 1-4 fluoresce in the range of 350-372 nm in the solid state, whereas compounds 2 and 3 catalyze the almost complete photodegradation of rhodamine B (RhB) in water within ca. 4 h and can be recycled at least five times without loss in their crystallinity.