Correlation of a Solution-State Conformational Change between Mercuric Chloride Complexes of Tris[(2-(6-methylpyridyl))methyl]amine with X-ray Crystallographic Structures

Solution-state NMR and X-ray crystallography were used to investigate the complexation of HgCl₂ by the potentially tetradentate ligand tris[(6-methyl-2-pyridyl)methyl]amine (TLA) in acetonitrile. A change in the ligand conformation as a function of the metal-to-ligand ratio could be indirectly monitored through large changes in ³J(¹H¹⁹⁹Hg) to the methylene protons at −40 °C. The solution-state NMR were correlated with two solid-state structures. The five-coordinate complex [Hg(TLA)Cl₂] (1) crystallizes in the triclinic space group P1̄ with a = 8.663(3) Å, b = 11.539(4) Å, c = 13.739(3) Å, α = 80.81(2)°, β = 75.84(2)°, γ = 80.97(3)°, and Z = 2. The Hg−N_amine distance of 2.505(7) Å for the tridentate ligand is the same as the average Hg−N_lutidyl distance of 2.50(3) Å for the two bound lutidyl nitrogens. [Hg(TLA)Cl]₂(Hg₂Cl₆) (2) also crystallizes in P1̄ with a = 10.606(2) Å, b = 15.104(3) Å, c = 17.785(4) Å, α = 67.46(3)°, β = 83.52(3)°, γ = 80.29(3)°, and Z = 2. The ligand is tetradentate in the two crystallographically unique cations which are arranged in a dimer-like orientation. The average Hg−Cl distance is 2.37 (1) Å, and the average interionic Hg−Cl distance is 3.51(1) Å. The Hg− N_lutidyl distances are of two types:  two have an average distance of 2.36(3) Å, nearly the same as the Hg−N_amine distance of 2.35(2) Å. The remaining four N_lutidyl distances have an average distance of 2.56(5) Å.