Lanthanide Cluster Organic Frameworks Derived from Pyridine-2,6-dicarboxylate and Oxalate: Syntheses, Structures and Luminescence

Two novel cluster organic frameworks derived from pyridine-2,6-dicarboxylate (PDA) and oxalate (ox2−) have been hydrothermally made: [Eu3(SO4)(PDA)3(ox)0.5(H2O)5]·4H2O (1) and Er(PDA)(ox)0.5(H2O) (2). Compound 1 possesses one-dimensional chain structure constructed from the alternate linkage of tetranuclear [Eu4(SO4)2]8+ (Eu4) and dinuclear [Eu2(ox)]4+ (Eu2) clusters. Compound 2 is a two-dimensional layer based on dimeric [Er2(COO)2]2+ (Er2) cluster units. Interestingly, such layer can be intuitively viewed as the linkages of helical chains and oxalate. In these two compounds, all anions are bivalent, and the ratio of trivalent lanthanide ions to these dianions is 2:3. Furthermore, compound 1 exhibits strong red luminescence upon 276 nm excitation.