Effects of structures of HgX_2 complexes (X = CF _3SO_3 and Cl) with chiral bidentate ligands on circular dichroism spectra

摘要

The effects of the structures of HgX_2 complexes (X = CF _3SO_3 and Cl) with chiral bidentate ligands [(R)-(-)-1-(1-naphthyl)-N,N-bis(pyridin-4-ylmethyl)ethanamine, (R)-(+)-1-phenyl-N,N-bis(pyridin-4-ylmethyl)ethanamine, (R)-(-)-1-(1-naphthyl)- N,N-bis(pyridin-3-ylmethyl)ethanamine, and (R)-(+)-1-phenyl-N,N-bis(pyridin-4- ylmethyl)ethanamine] on circular dichroism (CD) spectra are reported. The CD spectra of free (R)-(-)-1a and (R)-(+)-1b, which have 4-pyridyl groups, are similar to those of (R)-(-)-2a and (R)-(+)-2b, which have 3-pyridyl groups. When equimolar amounts of Hg(CF_3SO_3)_2 are added to these ligands, a decrease in the CD intensity of (R)-(-)-2a is observed, and significant spectral changes (intensity and shape) are observed in (R)-(-)-1a, (R)-(+)-1b, and (R)-(+)-2b. X-ray crystal structures suggest that the (R)-(-)-2a/Hg(CF_3SO_3)_2 complex is a coordination polymer with no bridging CF_3SO_3 anions, whereas the (R)-(-)-1a/Hg(CF_3SO_3)_2 and (R)-(+)-1b/Hg(CF_3SO_3)_2 complexes are coordination polymers with CF_3SO_3 anion bridges, and the (R)-(+)-2b/Hg(CF_3SO_3)_2 complex has a tricyclic structure bridged by CF_3SO_3 anions. Two different conformers, which have clockwise and counter-clockwise screw senses between the naphthalene axis and the pyridine axis, are observed in the ligand components of the (R)-(-)-2a/Hg(CF_3SO_3)_2 complex. In contrast, the X-ray structures of the (R)-(-)-2a/HgCl_2 and (R)-(+)-2b/HgCl_2 complexes are one-dimensional coordination polymers without bridging Cl anions. The significant CD spectral changes in the HgX _2 complexes with different chiral bidentate ligands require formation of rigid structures and a single-directional screw sense between chromophores.