Tetranuclear lanthanide-based silsesquioxanes: towards a combination of a slow relaxation of the magnetization and a luminescent thermometry.

Lanthanide-based silsesquioxanes constitute an emerging family of cage-like metallasilsesquioxanes with exciting optical and magnetic properties. We report here the synthesis, structures and luminescence properties of a series of tetranuclear lanthanide-silsesquioxane compounds of general formula [NEt][(PhSiO)(Ln/Ln')(NO)(EtOH)(MeCN)]·4(MeCN) with different lanthanide ions (where Ln/Ln' = Dy/Eu (1), Dy/Tb (2) and Eu/Tb/Y (3)) and investigate the impact of the lanthanide ions combination on magnetic and photo-luminescent properties. Compound 1 behaves as a field-induced Single Molecule Magnet (SMM) and presents temperature-dependent luminescence characteristics of Eu making it an emissive thermometer working in the temperature range 293-373 K with the maximum relative sensitivity of 1.15% K achieved at 293 K. Compounds 2 and 3 are paramagnets, which demonstrate a characteristic photoluminescence with Dy to Tb and Tb to Eu energy transfers, respectively.