New neutral and anionic thiocyanate complexes of Y(III) and Eu(III) with 2,2′-bipyridine and 1,10-phenanthroline: Synthesis, structures, thermal behavior and photophysical properties

Abstract Neutral complexes [M(NCS)3(H2O)(bpy)2]·0.5(bpy)·H2O, [M(NCS)3(H2O)(phen)2]·phen·0.5H2O and anionic complexes [Hbpy][M(NCS)4(bpy)2]·H2O, [Hphen][M(NCS)4(phen)2] with M(III) = Y, Eu have been synthesized. In each pair, the yttrium and europium complexes are isostructural and the metal coordination number (CN) is 8. The thermal behavior of the compounds was studied in an inert atmosphere in the range of 30–500 °C. The thermal stability of the complexes is determined by the solvate molecules. Anionic complexes without solvate molecules are stable up to 250 °C. In solvates with phen, elimination of coordinated water is accompanied by transition of phen from outer-sphere to inner-sphere at 170–220 °C. The magnetic and photoluminescent properties of europium complexes have been determined. The absence of coordinated water in anionic complexes and in the intermediate obtained from the neutral complex [M(NCS)3(H2O)(phen)2]·phen·0.5H2O increases the luminescence lifetime of the 5D0 level of europium and the internal quantum yield, which ranges from 9 to 30%. A study of the photoluminescence of [Hphen][EuxY1−x(NCS)4(phen)2] solid solutions has shown that dilution decreases the radiationless deactivation of the 5D0 level.