Characterization of HgCl₂ Tridentate Amine Complexes by X-ray Crystallography, NMR and ESI–MS

Abstract

Two new HgCl₂ complexes of tridentate nitrogen ligands were characterized by X-ray crystallography, proton NMR spectroscopy and ESI–MS. The five-coordinate complex [Hg(BMPA)Cl₂] (1) (BMPA = bis(2-pyridylmethyl)amine) crystallized from acetonitrile/m-xylene by slow evaporation in the monoclinic space group P2₁/n with a = 8.3896(8) Å, b = 12.8020(13) Å, c = 13.3526(13) Å, α = 90°, β = 90.480(2)°, γ = 90° and z = 4. The square pyramidal structure (τ = 0.009) has approximate C _s symmetry. Despite comparable Hg–N bond lengths in 1, inversion of the central nitrogen was rapid on the chemical shift time scale in dilute solution except at very low temperatures. The related complex [Hg(BEPA)Cl₂] (2) (BEPA = bis(2-{pyrid-2-yl}ethyl)amine) crystallized from acetonitrile/ethyl acetate/hexanes by slow diffusion in the orthorhombic space group Pnma with a = 13.424(3) Å, b = 14.854(3) Å, c = 8.118(2) Å, α = 90°, β = 90°, γ = 90° and z = 4. The mixed geometry structure (τ = 0.56) also has crystallographic mirror symmetry as well as C _s point group symmetry. In dilute acetonitrile solution, 1 was stable while 2 slowly converted to a more thermodynamically stable complex.

Graphical Abstract