Structural and luminescence studies of trivalent europium complexes with pentaethylene glycol and 18-crown-6 ligands in the presence of picrate anion

摘要

Two new isostructural complexes of europium picrate (Eu-Pic) with pentaethylene glycol (EO5) and 18-crown-6 (18C6) ligands formed complexes of molecular formula [Eu(Pic)_2(18C6)]~+ (Pic)~- Ⅰ and [Eu(Pic)_2(EO5)]~+ (Pic)~~-Ⅱ have been isolated and characterised. Compound Ⅰ showed 10-coordination number through six oxygen atoms from the 18C6 ligand and two bidentate picrate anions. Meanwhile, compound Ⅱ exhibited 9-coordination number via six oxygen atoms from EO5 ligand, two oxygen atoms from a bidentate and one oxygen atom from monodentate picrate anions. Photoluminescence (PL) spectra of the solid-state europium complexes display sharp lines which are assigned to ~5D_0→~7F_(0-4) and ~5D_1→~7F_(1,2,4) transitions. No emission of polyether ligands is observed, indicating that the energy transfer from the polyether ligands to the Eu~(3+) ion is quite efficient. The PL spectra of [Eu(Pic)_2(OH_2)_6]~+ (Pic)~- • 6H_2O Ⅲ, [Eu(NO_3)_3(OH_2)_3]·(18C6) Ⅳ, [Eu(NO_3)_3 · 6H_2O] V and Eu_2O_3 Ⅵ are also observed. Compounds Ⅰ-Ⅳ exhibited high Ω_2 intensity parameter values, namely 16.93, 10.23, 17.10 and 12.35 (in units of 10~(-20)cm~2), respectively. These relatively high values reflect the hypersensitive behaviour of the ~5D_0→~7F_2 transition and indicate that the Eu~(3+) ion is located in a highly polarisable chemical environment.