Self-assembly of 2D zinc metal-organic frameworks based on mixed organic ligands

Self-assembly of Zn(NO₃)₂·6H₂O, 5-amino-2,4,6-triiodoisophthalic acid (H₂atiip) and 4,4′-bipyridine (bpy) or 1,3-di(4-pyridyl)propane (dpp) gave rise to three unusual zinc metal-organic frameworks, Zn₂(bpy)₂(atiip)₂·3H₂O·2dmf (1), Zn₈(dpp)₈(atiip)₈·4H₂O (2), Zn(dpp)(atiip)·(dmf)·(H₂O) (3). All complexes possess 2D layer frameworks constructed from 1D Zn-carboxylate tubular unit for 1, 1D Zn-carboxylate helical chain for 2 and 3. In 1 and 2, the bpy or dpp act as both bridging and blocking ligands and the blocking ligands play an important role in the formation of the 2D layer frameworks. Both 2 and 3 contain two different large metallomacrocycles. Photoluminescence measurements of 1-3 in the solid state at room temperature show that all complexes exhibit luminescence, which can be assigned to an intraligand π → π^∗ transition or ligand-to-metal charge transfer (LMCT).