A Europium(II) Complex with Benzo‐15‐Crown‐5

Abstract

Keywords: Europium / Crown compounds / X-ray diffraction / Luminescence / LanthanidesThe present paper reports the crystal structure and luminescent properties of bis(benzo-15-crown-5)europium(II) diperchlorate. The structure is composed of complex bis(benzo-15-crown-5)europium(II) cations and perchlorate anions. The complex cation is centrosymmetric, and the metal ion is surrounded by 10 oxygen atoms of two ligand molecules. The

Developments in the Coordination Chemistry of Europium(II)

“…[86–87] Pyridine groups, known for exhibiting an antenna effect in Eu 3+ -containing complexes, were introduced into 18-crown-6. When bis(pyridino)-18-crown-6 was complexed with Eu 2+ , the emission of the complex in the solid state was quenched at room temperature, and only a weak emission at 430 nm was observed at 77 K, which is typical for Eu 2+ -containing crown ethers.…”

“…[86] However, a blue luminescence was observed when benzo-15-crown-5 84 and benzo-18-crown-6 85 were used as ligands. [54,87] The Eu 2+ -containing complex with benzo-15-crown-5 is characterized by a Eu 2+ metal center that is sandwiched by two benzo-15-crown-5 ligands. [86] In the solid state, Eu 2+ – 85 shows an emission peak that is similar to that observed in methanol at room temperature.…”

“…[87] This difference in excited state lifetime is likely due to the additional relaxation processes caused by the methanol O–H oscillators. [87] Furthermore, a phenyl moiety in the crown ether might contribute to a reduction in the lifetime, because this moiety can rigidify the crown ether and lead to structural changes to make Eu 2+ more exposed to luminescence quenchers relative to Eu 2+ bound to unmodified crown ethers. [6] Also, the cavity size of the crown ether affects the luminescence lifetime of the excited state.…”

“…A variety of functional groups have been used to study the contribution of antenna effects and conjugated π systems on the luminescence efficiency of Eu 2+ ‐containing complexes 86–87. Pyridine groups, known for exhibiting an antenna effect in Eu 3+ ‐containing complexes, were introduced into 18‐crown‐6.…”

“…This quenching is likely due to the energy transfer from the excited‐state, quasi‐5d energy level of Eu 2+ to the π* levels of pyridine, and this quenching was not observed when unfunctionalized 18‐crown‐6 ligand 83 was used 86. However, a blue luminescence was observed when benzo‐15‐crown‐5 84 and benzo‐18‐crown‐6 85 were used as ligands 54,87. The Eu 2+ ‐containing complex with benzo‐15‐crown‐5 is characterized by a Eu 2+ metal center that is sandwiched by two benzo‐15‐crown‐5 ligands 86.…”