Synthesis, Structure, and Luminescence of Mixed-Ligand Lanthanide Trifluoroacetates.

A series of new mixed-ligand lanthanide trifluoroacetates of formula Ln(4-cpno)(tfa)(HO)·HO (Ln = Sm, Eu, Gd, Tb, Dy; 4-cpno = 4-cyanopyridine -oxide; tfa = trifluoroacetate) is reported. Trifluoroacetates were synthesized as chemically pure polycrystalline solids and their crystal structures were probed using single-crystal and powder X-ray diffraction. Ln(4-cpno)(tfa)(HO)·HO solids make up an isostructural series in which LnO polyhedra are bridged by 4-cpno to form edge-sharing dimers. Trifluoroacetato connects these dimers to yield chains whose three-dimensional packing is governed by hydrogen bonds established between 4-cpno, trifluoroacetato, and water. 4-cpno serves as an efficient sensitizer of lanthanide-centered luminescence. UV excitation of its singlet manifold and subsequent energy transfer to the 4 levels of the lanthanides yield orange (Sm), red (Eu), green (Tb), and yellow (Dy) emissions. Sensitization efficiencies reach 81 and 64% for Eu and Tb hybrids, respectively. Tb(4-cpno)(tfa)(HO)·HO displays a quantum yield of 52%, which coupled to the high absorptivity of 4-cpno, makes it a bright-green emitter under 292 nm excitation. Lanthanide trifluoroacetates may therefore serve as hybrid solid-state light emitters provided that adequate sensitizers are identified.