Synthesis, structure and luminescence properties of europium and zinc ionic complexes

Abstract

Two europium and zinc ionic complexes [Eu 2(Hsal) 8][Zn(phen) 3] · (H 2sal)(H 2O) ( 1) and [Eu 2(TPA) 8][Zn(TPA)(Phen) 2] 2 · (H 2O) 2 ( 2) (where H 2sal=salicylic acid, TPA=α-thiophene carboxylic acid, phen=1,10-phenanthroline) have been synthesized by the rheological phase reaction method and structurally characterized by IR spectra and X-ray crystallography. The results show that in both complexes the carboxylate groups adopt three modes: bidentate bridging, bidentate chelating and tridentate chelating-bridging. Complex 1 consists of a discrete dinuclear [Eu 2(Hsal) 8] 2− anion, [Zn(phen) 3] 2+ cation, free salicylic acid and a lattice water molecule. Interestingly, in the unit cell there are two types of dimeric [Eu 2(Hsal) 8] 2− anions with inversion centers. The hydrogen bonds between the chelating carboxylate groups and the lattice water molecules link the dimeric Eu1 units into 1-D chains. Complex 2 comprises of a dimeric [Eu 2(TPA) 8] 2− anion, two [Zn(TPA)(Phen) 2] + cations and two lattice water molecules. One obvious difference from complex 1 is that besides phen ligands, the TPA − group also coordinates to the Zn 2+ ion. The C–H⋯O, O–H⋯O hydrogen bonds and π–π stacking interactions play an important role in the crystal structure. These two complexes emit strong red light when irradiated by UV light. The emission bands at about 590, 610 nm correspond to the characteristic 5D 0 → 7F 1, 5D 0 → 7F 2 transitions of Eu 3+ ions. The large intensity ratio of 5D 0 → 7F 2/ 5D 0 → 7F 1 indicates the low symmetry of Eu 3+ ion sites in both complexes, consistent with the results of the structure determination.