Phosphonium-based tetrakis dibenzoylmethane Eu(III) and Sm(III) complexes: Synthesis, crystal structure and photoluminescence properties in a weakly coordinating phosphonium ionic liquid

Highly luminescent anionic Ln(III) ?-diketonate complexes of the formula [P<inf>8,8,8,1</inf>][Ln(dbm)<inf>4</inf>], with Ln = Eu³⁺ and Sm³⁺, [P<inf>8,8,8,1</inf>] = trioctylmethylphosphonium and dbm = 1,3-diphenylpropane-1,3-dione were synthesized. The single crystal X-ray structure of the samarium and europium complexes showed that the metal ion was surrounded by four ligands and that no water or solvent molecules were coordinated. The solid complexes showed good thermal stability up to 250 °C. The complexes easily dissolved in the ionic liquid trioctylmethylphosphonium bis(trifluoromethylsulfonyl)imide [P<inf>8,8,8,1</inf>][Tf<inf>2</inf>N], due to the presence of a common phosphonium countercation in the ionic liquid and in the Eu(III) and Sm(III) complexes. The photoluminescence of the complexes was studied in the solid state and in an ionic liquid as well as in acetonitrile (MeCN) as a solvent.