Bis-tetradentate complexes of Cd(ii) and Hg(ii) with N8 coordination: structural and NMR comparisons

Abstract

Tripodal N₄ ligands tris[(1-methylimidazol-2-yl)methyl]amine (L1), bis[(1-methylimidazol-2-yl)methyl][(2-pyridyl)methyl]amine (L2) and [(1-methylimidazol-2-yl)methyl]-bis-[(2-pyridyl)methyl]amine (L3) were used to prepare five new [ML₂](ClO₄)₂ (M = Cd(II), Hg(II)) complexes. All complexes had N₈ metal coordination and a trans-bicapped octahedral structure as determined by X-ray crystallography. Metal–nitrogen bond distances generally decreased in the order M–N_amine > M–N_pyridyl > M–N_imidazoyl, and the perchlorates were well separated from the metal ions. Variable temperature solution state ¹H NMR spectroscopy revealed conditions for slow intramolecular reorganization were more readily accessible for the Cd(II) complexes than for the Hg(II) complexes. Both protons of imidazoyl ring ligand components had large, comparable J(¹⁹⁹Hg¹H) despite sizable differences in nuclear separation.