Photoluminescence Modulation in Lanthanide(III)/Pyrazine-2,5-dicarboxylato/Nitrato Frameworks

The solvent-free melt reactions between lanthanide(III) nitrates and pyrazine-2,5-dicarboxylic acid (H(2)pzdc) gave rise to four families of 3D compounds that differ from those accessible from conventional solvothermal synthesis, namely, {[Ln((4)-pzdc)(NO3)(H2O)(2)]2.33H(2)O}(n) (1-Ln; Ln = La, Ce), {[Ln(9)((4)-pzdc)(9)(NO3)(2)(H2O)(25)](NO3)(7)8H(2)O}(n) (2-Ln; Ln = Pr, Nd), {[Ln(6)((4)-pzdc)(5)((3)-pzdc)(2)(-pzdc)(H2O)(10)](NO3)(2)2H(2)O}(n) (3-Ln; Ln = Nd, Sm), and [Ln((4)-pzdc)(NO3)(H2O)](n) (4-Ln; Ln = Eu, Gd, Tb). This synthetic approach promotes the incorporation of nitrate anions into the final crystal structure as terminal ligands or counterions, which replace water molecules in the coordination sphere and enhance the photoluminescence properties of these compounds. The neodymium, samarium, europium, and terbium compounds exhibit their characteristic emissions in the infrared and visible regions. The pzdc ligand shows the highest sensitization towards Tb-III ions, and the photoluminescence intensity can be modulated by immersing the sample into different solvents and also by dehydrating it. Compounds 3-Ln have a topology named as jcr5, which has not been reported previously.