The effect of 4-halogenobenzoate ligands on luminescent and structural properties of lanthanide complexes: experimental and theoretical approaches

Abstract

The ligands 4-fluorobenzoate (4-fba), 4-chlorobenzoate (4-cba), 4-bromobenzoate (4-bba) and 4-iodobenzoate (4-iba) were chosen to synthesize europium(III), gadolinium(III) and terbium(III) complexes and compare the effect of halogens on their phys. chem. and luminescent properties. The prepd. complexes are [Eu(4-fba)3(H2O)2] (1), [Gd(4-fba)3(H2O)2].0.5H2O (2), [Tb(4-fba)3(H2O)2].0.5H2O (3), [Eu(4-cba)3].2H2O (4), [Gd(4-cba)3(H2O)] (5), [Tb(4-cba)3(H2O)2] (6), [Eu(4-bba)3].2.5H2O (7), [Gd(4-bba)3(H2O)2] (8), [Tb(4-bba)3(H2O)] (9), [Eu(4-iba)3(H2O)2] (11), [Gd(4-iba)3(H2O)2] (12), [Tb(4-iba)3(H2O)2] (13). The homobimetallic complex [Eu(4-iba)3(H2O)(DMF)]2 (10) crystallizes in the monoclinic P21/c space group with a 8.3987(9), b 25.314(3), c 14.1255(17) �, and ? 105.347(2)�. FTIR spectroscopy indicates that the bidentate bridging mode of the carboxylato ligand was present in all complexes while bidentate chelate and a mixt. of bidentate bridging and chelate modes were also found. According to emission spectra profiles and the Judd-Ofelt parameters the halogen of ligand mols. modifies the chem. environment symmetry around the europium(III) ion in their resp. complexes. The complexes [Eu(4-fba)3(H2O)2] and [Eu(4-iba)3(H2O)2] have the highest symmetry around the europium(III) while the complexes [Eu(4-cba)3]�2O, [Eu(4-bba)3]�2H2O and [Eu(4-iba)3(H2O)(DMF)]2 have the lowest. The different halogens at the para position do not change the covalence degree of Eu-O bonds significantly, however they play a role in the ligand to metal charge transfer energies. The highest non-radiative energy transfer rates from ligand to europium(III) were found for the complexes [Eu(4-cba)3]�2O and [Eu(4-bba)3]�2H2O. [on SciFinder(R)]