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).