Novel Polyoxometalate-Templated, 3-D Supramolecular Networks Based on Lanthanide Dimers: Synthesis, Structure, and Fluorescent Properties of [Ln2(DNBA)4(DMF)8][Mo6O19] (DNBA = 3,5-Dinitrobenzoate)

The spherical Lindquist type polyoxometalate, Mo6O192-, has been used as a noncoordinating anionic template for the construction of novel threedimensional lanthanide-aromatic monocarboxylate dimer supramolecular networks [Ln2(DNBA)4(DMF)8][Mo6O19] (Ln = La 1, Ce 2, and Eu 3, DNBA = 3,5-dinitrobenzoate, DMF = dimethylformamide). The title compounds are characterized by elemental analyses, IR, and single-crystal X-ray diffractions. X-ray diffraction experiments reveal that two Ln(III) ions are bridged by four 3,5-dinitrobenzoate anions as asymmetrically bridging ligands, leading to dimeric cores, [Ln2(DNBA)4(DMF)8]2+; [Ln2(DNBA)4(DMF)8]2+ groups are joined together by (pi)-(pi) stacking interactions between the aromatic groups to form a two-dimensional grid-like network; the 2-D supramolecular layers are further extended into 3-D supramolecular networks with 1-D box-like channels by hydrogen-bonding interactions, in which hexamolybdate polyanions reside. The compounds represent the first examples of 3-D carboxylate-bridged lanthanide dimer supramolecular "host" networks formed by (pi)-(pi) stacking and hydrogen-bonding interactions encapsulating noncoordinating "guest" polyoxoanion species. The fluorescent activity of compound 3 is reported.