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

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 5D0→7F0-4 and 5D1→7F1,2,4 transitions. No emission of polyether ligands is observed, indicating that the energy transfer from the polyether ligands to the Eu3+ ion is quite efficient. The PL spectra of [Eu(Pic)2(OH2)6]+(Pic)−·6H2O III, [Eu(NO3)3(OH2)3]·(18C6) IV, [Eu(NO3)3·6H2O] V and Eu2O3VI are also observed. Compounds I-IV exhibited high Ω2 intensity parameter values, namely 16.93, 10.23, 17.10 and 12.35 (in units of 10−20 cm2), respectively. These relatively high values reflect the hypersensitive behaviour of the 5D0→7F2 transition and indicate that the Eu3+ ion is located in a highly polarisable chemical environment.