Synthesis, characterization, and fluorescent properties of two Pb(II) complexes: {[Pb(hca)2·DMF]·DMF}∞ and [Pb(hca)2(phen)·DMF]2

Two novel Pb(II) complexes, {[Pb(hca)2·DMF]·DMF}∞ and [Pb(hca)2(phen)·DMF]2 (hca=trans-4-hydroxycinnamic group), were obtained by solid-phase reactions of PbAc2 and Hhca and PbAc2, Hhca, and phen, respectively, and characterized by spectroscopy. X-ray crystallography analysis reveals that complex 1, {[Pb(hca)2·DMF]·DMF}∞, adopts a 2-dimensional structure through the weak interactions of Pb and O atoms and that complex 2, [Pb(hca)2(phen)·DMF]2, shows a discrete dimeric structure, in which hydrogen bonds link the dimers into a 2D network. Both complexes 1 and 2 show visible fluorescence and the intensity is stronger than that of the ligand. More interestingly, the intensity of emission was increased at least fivefolds when the pH of the solution was adjusted to alkalinity. This can be attributed to that the deprotonization of phenolic group enhancing the conjugation of the ligand hca. These results indicate that this method may be an effective way to increase the emission intensity of similar complexes.