Guest molecular guided syntheses of 2-dimensional uranyl complexes with rigid benzenedicarboxylate ligands

Abstract

Two new heterometallic uranyl-organic frameworks (UOFs), [Cd(phen)2(H2O)2][(UO2)2(BDC)3]·2H2O (1) and [Ni(phen)3][(UO2)2(BDC)3]·2H2O (2), were obtained under hydrothermal conditions. Both crystal structures were characterized by single-crystal X-ray diffraction analyses and the results indicate that both complexes feature a similar 2D honeycomb framework that is connected by rigid benzenedicarboxylate (BDC) ligands and uranyl units. BDC works as a linker to bridge neighboring UO2 2+ units, where UO2 2+ is tris-chelated. Different guest molecules guided the stacking of 2D layers and lead into their 3D supramolecular crystal structures with different space groups. As a result, 1 crystallized in a polar space group Cc, whereas 2 belongs to a chiral space group P6122. Thermogravimetric measurements were performed to study their thermal stability. UV-visible diffuse reflectance spectroscopy measurements indicate an experimental optical bandgap of 3.87 eV and 3.63 eV, respectively, for 1 and 2. Luminescent studies of both samples show strong green light emissions.