Synthesis and Characterization of New Coordination Polymers with Tunable Luminescent Properties Generated from Bent 1,2,4-Triazole-Bridged <i>N</i>,<i>N</i>′-Dioxides and Ln(III) Salts

A new bent 1,2,4-triazole-bridged N,N′-dioxide ligand, namely, 3,5-bis(3-pyridyl-N-oxide)-4-amino-1,2,4-triazole (L2), was designed and synthesized by the oxidation of 3,5-bis(3-pyridyl)-4-amino-1,2,4-triazole with H2O2 in the presence of HOAc at ambient temperatures. Eleven Ln(III)-based coordination polymers have been successfully prepared by the solution reactions of L2 with various Ln(III)−perchlorates. The structures of these new Ln(III) polymers clearly reflect the effect of the lanthanide contraction. Compounds 1−6 feature a two-dimensional net, in which the Ln(III) atoms adopt a nine-coordinate {LnO9} sphere due to their larger ionic radii, whereas the Ln(III) centers in the one-dimensional double-stranded chains of 7−11 with smaller ionic radii lie in a {LnO8} coordination environment. In addition, the tunable emission intensity was realized on 7 by controlling the type of the involved counterion on the basis of a reversible solid-state anion exchange. Such reversible solid-state anion exchange might provide an alternative approach to tuning the luminescence.