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

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).