Anion-Controlled Circular Dichroism Spectral Changes in Hg²⁺ Complexes with a Chiral Bidentate Ligand

Anion-controlled circular dichroism (CD) spectral changes in Hg2+ complexes with a chiral bidentate ligand are reported. Although the Hg­(CF3SO3)2 and Hg­(CF3CO2)2 complexes with (R)-(−)-1-(naphthalen-1-yl)-N,N-bis­(pyridin-4-ylmethyl)­ethanamine, (R)-(−)-1, show significant CD spectral changes, no CD spectral changes were observed in the HgCl2, HgBr2, Hg­(CN)2, or Hg­(CH3CO2)2 complexes. X-ray analysis indicates that both the (R)-(−)-1-Hg­(CF3SO3)2 and (R)-(−)-1-HgCl2 complexes form a coordination polymer and a discrete 2:3 [=(R)-(−)-1/HgCl2] complex with a figure-eight structure. X-ray crystallography revealed that (i) the Hg–Hg distances bridged by anions vary depending on the anions used and (ii) a coordination polymer cannot be formed when the Hg–Hg distances are too short. Therefore, the formation of a coordination polymer is required to give the observed significant CD spectral changes.