Blue dimetallic complexes of two heavy metal ions Cd^|| and Hg^|| with an extended nitrogen donor ligand. Preparation, spectral characterization, and crystallographic studies

Abstract

In methanol, the metal salts CdCl₂·H₂O and HgCl₂ react instantaneously with the deprotonated ligand, L^-, producing molecular dimetallic ink-blue complexes of general formula M₂Cl₂L₂, M=Cd(II), (1) and Hg(II), (2) (HL=2-[2-(pyridylamino)phenylazo]pyridine). Crystal structures of these two complexes are reported. The coordination sphere around each Cd(II) ion in 1 is a distorted square pyramidal. The metal ion (Cd1) sits above the basal plane of three nitrogen atoms, N(1), N(3), and N(4). The second cadmium ion (Cd2) in this compound lies below the plane of three nitrogen atoms, N(6), N(8), and N(9). The apical positions are occupied by two Cl atoms. Secondary intramolecular interactions between the metal ions and the anionic secondary amine nitrogen atoms (N(4) and N(9)) are noted. The geometry of each Hg(II) ion in the mercury complex, Hg₂Cl₂L₂·0.5H₂O, is also distorted square based pyramid with the metal ions lying out of planes of the three nitrogen atoms of the chelating ligands. Secondary Hg(1)···N(1A) (deprotonated amine) interactions are noted. The separation between the two Hg(II) ions in this complex is within the sum of their van der Waals radii. Solution properties of these blue complexes are reported. The origin of the intense blue color in these complexes is the intraligand transitions that occur near 615 nm. ¹H NMR of Hg₂Cl₂L₂·0.5H₂O indicates that it undergoes exchange in solution with the coordinated ligands.