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

Abstract

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.