Sensitization of Ho-III and Sm-III luminescence by efficient energy transfer from antenna ligands: Magnetic, visible and NIR photoluminescence properties of Gd-III, Ho-III and Sm-III coordination polymers

Abstract

Hydrothermal reactions of lanthanide metal salts with 2-sulfoterephthalate (2-stp) and 4,4'-bipyridine (4,4'-bipy) led to three coordination polymers, {[Ln(2-stp)(4,4'-bipy)(H2O)]center dot(H2O)), [Ln = Gd (1), Ho (2) and Sm (3)]. Their structures have been established by X-ray single crystal diffraction. Complexes 1-3 are isostructural with 2D framework in which all Ln(III) atoms are nine-coordinated. All these 2D layers are further interlinked via hydrogen bonds resulting in 3D architecture. The solid-state photoluminescence measurements display the characteristic luminescence of Ho (2) and Sm (3), which is due to efficient energy transfer from the ligands to the central Ln(III) ions via an "antenna effect". Variable temperature magnetic susceptibility and isothermal magnetization as function of external magnetic field for 1-3 is studied which reveal mainly the presence of antiferromagnetic interactions and the thermal depopulation of Stark sublevels together with crystal field affects.