摘要:
Two EDTA-based bichromophoric isomers form Zn(II) complexes that exhibit distinct fluorescent behaviors; the ligands are abbreviated as (edta1nap)H-2 and (edta(2)nap)H-2, each of which consists of an EDTA chain linked to two 1-naphthyl or 2-naphthyl groups. The coordination chemistry of these complexes was studied by UV-Vis, fluorescence and H-1 NMR. The formation constants and the inherent emission intensities were determined by the pH dependence of the emission spectra; the species of the most intense emission is ML(OH) for L = (edta1nap)(2-), and ML for (edta2nap)(2-). The H-1 NMR of Zn-(edta1nap)(2-) exhibits two sets of signals due to a slow exchange between two equivalent coordination geometries, whereas Zn-(edta2nap)(2-) undergoes a fast exchange to show a single set of NMR signals. The spin-lattice relaxation time T-1 determined for the isostructural Mn(II) complexes shows that the naphthyl proton closest to the metal ion is H(8) in the (edta1nap)(2-) complex, and H(3) in the (edta2nap)(2-) complex. The two ligands differ only in the substitution position of the naphthyl group, but this apparently small difference leads to the notable difference in structural, dynamic, and consequent emission-spectral properties of their metal complexes as a result of the steric and size effects of the aromatic rings. (C) 2010 Elsevier Ltd. All rights reserved.