Synthesis, structure and luminescence properties of metal-organic frameworks based on benzo-bis(imidazole)

Metal-organic frameworks (MOFs) constructed from conjugated organic ligands are candidates for hybrid photoactive materials with potential applications. Compared to that from the ligands only, the intensity and wavelength of the luminescence could be tuned after they were incorporated in extended framework. In this report, by using an organic ligand with azolate moiety, benzo-bis(imidazole) (H2BBI), we synthesized two new MOF structures. Framework 1 ([Co(H2BBI)(DMSO)2Cl2]n, DMSO = dimethyl sulfoxide), constructed from tetrahedral Co(II) and H2BBI, exhibits zigzag 1D structure. Meanwhile, framework 2 ([Cu2(H2BBI)3(DMSO)6(NO3)4]n), a layered structure with hcb topology, was assembled from tetragonal pyramidal Cu(II) and H2BBI. Furthermore, 2 exhibits strong luminescence emission (λex = 280 nm). A blue shift of 40 nm (from 359 nm to 319 nm) was observed in framework 2 compared to the free ligand, which could be explained by the ligand-to-metal charge transfer in the network.