Characterization of Mercury(II) Complexes of Bis[(2-pyridyl)methyl]amine by X-ray Crystallography and NMR Spectroscopy

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Abstract

Solution-state NMR and X-ray crystallography were used to investigate the complexation of Hg(II) by the tridentate ligand bis[(2-pyridyl)methyl]amine (BMPA). Mercury coordination compounds exhibiting rarely observed solution-state NMR 1H199Hg satellites were characterized. Temperature and concentration effects on solution-state NMR properties were investigated. The solution-state NMR were correlated with two solid-state structures. The distorted trigonal prismatic complex [Hg(BMPA)2](ClO4)2·0.5toluene (1) crystallizes in the triclinic space group P1̄ with a = 10.953(5) Å, b = 12.812(5) Å, c = 13.006(5) Å, α = 67.50(3)°, β = 82.74(3)°, γ = 67.88(3)°, and Z = 2. The Hg−Namine bonds are 2.404(4) and 2.350(4) Å and the Hg−Npyridyl bond lengths are similar, ranging from 2.352(4) to 2.557(5) Å. Solution NMR studies are consistent with rapid equilibrium between isomeric trigonal prismatic and facial octahedral forms of this complex. A twisting mechanism is proposed to mediate interconversion. The distorted square planar complex [Hg(BMPA)NCCH3](ClO4)2 (7) crystallizes in the monoclinic space group P21/c with a = 12.987(2) Å, b = 17.469(4) Å, c = 8.886(2) Å, β = 95.200(12)°, and Z = 4. The Hg−Namine distance is 2.403 Å, the average Hg−Npyridyl distance is 2.23 Å, and the Hg−Nnitrile distance is 2.229 Å. The BMPA ligand is bound to Hg(II) in a meridional fashion with a solvent molecule in the same plane and close associations to two axial perchlorates with Hg−O distances of 2.707(7) and 2.90(2) Å. Solution NMR studies support limited dynamics for a cation with similar interactions between BMPA and Hg(II).

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