New outstanding possibilities are emerging by the synthesis of organo-inorganic polymeric materials from a buildingblock
approach. Our approach has been to assemble extended solids from bent flexible arenedicarboxylate linkers that
offer totally new topologies with helical channels. A new family of Rare-earth Polymeric Framework (RPF-4) has been
obtained and its structure solved. The framework is formed by a Lanthanide (Ln) matrix, with the Ln atoms well
separated in two directions. The crystals are highly stable in air and the decomposition temperature is above 350°C.
Under UV excitation, the linker presents a bluish-white emission peaking around 450 nm. The emission corresponding to
the different crystals either present an emission similar to the linker, slightly modified depending on R, or an intense
emission due to Ln localized crystal field transitions. In the second case, an energy transfer from the linker to the Ln
ions, which relax radiatively with a very efficient emission, seems to occur. The observed emission properties and crystal
stability are of interest for applications as light emitting materials. The peculiarities of the structure may avoid the
concentration quenching of the luminescence since Ln ions form well separated chains along a-axis with interchain
distances around 12.5 Å.
|