Hexanuclear Molecular Precursors as Tools to Design Luminescent Coordination Polymers with Lanthanide Segregation.

Solvothermal reactions between hexanuclear complexes with the general chemical formula [Ln6(μ6-O)(μ3-OH)8(NO3)6(H2O)12]·2NO3·2H2O and 2-bromobenzoic acid (2-bbH) lead to a series of isostructural one-dimensional coordination polymers with the general chemical formula [Ln2(2-bb)6]∞ with Ln = Sm, Eu, Tb, Dy, and Y. These coordination polymers crystallize in the orthorhombic space group Fdd2 (No. 43) with the following cell parameters: a = 29.810(3) Å, b = 51.185(6) Å, c = 11.7913(14) Å, V = 17992(4) Å3, and Z = 16. The europium- and terbium-based derivatives show sizable luminescence intensities under UV excitation. Isostructural heterolanthanide coordination polymers have also been prepared. Their luminescent properties suggest that during the synthetic process the starting hexanuclear complexes are destroyed but strongly influence the distribution of the different lanthanide ions over the metallic sites of the crystal structure. Indeed, it is possible to prepare heterolanthanide coordination polymers in which lanthanide-ion segregation is controlled.