Lanthanide Metal-Organic Frameworks Based on Octahedral Secondary Building Units: Rare Net Topology and Luminescence

Three isomorphous three-dimensional (3D) lanthanide metal-organic frameworks, [Ln(2)(DBTDC-O-2)(3)(DMF)(4)]center dot 3DMF center dot 2H(2)O (Ln = Nd, Eu, and Gd), have been solvothermally synthesized and characterized, where H2DBTDC-O-2 is a sulfone-functionalized bridging ligand, S,S-dioxodibenzothiophen-3,7-dicarboxylic acid. In the structures, two lanthanide(III) ions are bridged by four syn-syn carboxylate groups and chelated by another two carboxylate groups to generate a [Ln(2)(COO)(6)] dinuclear moiety, which serves as octahedral secondary building units (SBUs) to produce the rare sxb 3D net (4(8)5(4)6(3)), instead of the default primitive cubic (pcu) net. The frameworks possess relatively large solvent-occupied cavities despite the presence of 2-fold interpenetration. The Eu(III) compound displays intense luminescence as a result of the efficient ligand-to-metal energy transfer.