Lanthanide metal-organic frameworks based on octahedral secondary building units: Rare net topology and luminescence

Three isomorphous three-dimensional (3D) lanthanide metal-organic frameworks, [Ln₂(DBTDC-O₂)₃(DMF)₄] · 3DMF · 2H₂O (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 [Ln₂(COO) ₆] dinuclear moiety, which serves as octahedral secondary building units (SBUs) to produce the rare sxb 3D net (4⁸5⁴6 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.