Isomorphous Lanthanide Metal-Organic Frameworks Based on Biphenyldicarboxylate: Synthesis, Structure, and Photoluminescent Properties

We report the structures of six anionic, isomorphous metal-organic frameworks [Ln(bpdc)(2)(-)]-[NH2(CH3)(2)(+)], where Ln = La, Ce, Nd, Eu, Gd, Er, and bpdc(2-) = biphenyl-4,4'-dicarboxylate = -O2C(C6H4)(2)CO2-. The Ln(III) metal centers exhibit eight-coordinate binding to six different bpdc(2-) ligands (four of which are mu-2 bridging and two are bidentate) and the framework is charge-balanced by a dimethylammonium cation. The materials all possess the same 3D structure and crystallize in the orthorhombic space group Pbcn. All exhibit thermal stability up to ca. 300 degrees C and decompose to Ln(2)O(3) after 800 degrees C. The Eu-based structure exhibits strong fluorescence in the 612-620 nm range. These materials significantly expand the known chemistry and luminescence of the less studied f-block metal-organic frameworks.