The complexation of Hg(II) by the tripodal ligand
tris[(2-pyridyl)methyl]amine (TMPA) was investigated
by
solution state NMR and X-ray crystallography. Mercury coordination
compounds exhibiting rarely observed
room-temperature solution state NMR
1H199Hg and
13C199Hg satellites were characterized.
Solvent, counterion,
temperature, and concentration effects on solution state NMR properties
were investigated. The solution state
NMR were correlated with two solid state structures. The
eight-coordinate complex
[Hg(TMPA)2](ClO4)2
(1)
crystallizes in the monoclinic space group
P21/n with a =
9.735(10) Å, b = 10.963(2) Å, c =
18.553(34) Å, β
= 103.81(12)°, and Z = 2. The mercury is at
the inversion center of a bicapped trigonal antiprism. The
Hg−Namine distance is 2.560(3) Å, and the average
Hg−Npyridyl distance is 2.58(2) Å. The
five-coordinate complex
[Hg(TMPA)Cl]2(HgCl4)
(2) crystallizes in the triclinic space group
P1̄ with a = 11.887(2) Å,
b = 13.260(2) Å,
c = 15.278(4) Å, α = 112.27(2)°, β =
109.39(2)°, γ = 90.670(10)°, and Z = 2.
The two crystallographically
unique cations are distorted trigonal bipyramids. The average
Hg−Cl distance is 2.355(12) Å, the average Hg−Namine distance is 2.43(2) Å, and the average
Hg−Npyridyl distance is 2.40(5) Å.
The solution state coordination chemistry of Hg(ClO 4 ) 2 with tris [(2-(6-methylpyridyl))methyl] amine (TLA) was investigated in acetonitrile-d 3 by proton NMR. Although Hg(II) is a d 10 metal ion commonly associated with notoriously rapid exchange between coordination environments, as many as six ligand environments were observed to be in slow exchange on the chemical shift time scale at select metal-to-ligand ratios. One of these ligand environments was associated with extensive heteronuclear coupling between protons and 199 Hg and was assigned to the complex [Hg(TLA)] 2+ . The 5 J( 1 H 199 Hg) = 8 Hz associated with this complex is the first example of five-bond coupling in a nitrogen coordination compound of Hg(II). The spectral complexity of related studies conducted in acetone-d 6 precluded analysis of coordination equilibria. Crystallographic characterization of the T-shaped complex [Hg(TLAH)(CH 2 COCH 3 )](ClO 4 ) 2 (1) in which two pyridyl rings are pendant suggested that the acidity of acetone combined with the poor coordinating abilities of the neutral solvent adds additional complexity to solution equilibria. The complex crystallizes in the triclinic space group P1 with a = 9.352(2) Å, b = 12.956(2) Å, c = 14.199(2) Å, α = 115.458(10)°, β = 90.286 (11)°, γ = 108.445(11)°, and Z = 2. The HgN amine , Hg-N pyridyl , and Hg-C bond lengths in the complex are 2.614(4), 2.159(4), and 2.080(6) Å, respectively. Relevance to development of 199 Hg NMR as a metallobioprobe is discussed.
Solution-state NMR and X-ray crystallography were used to investigate the complexation of HgCl(2) 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 (3)J((1)H(199)Hg) to the methylene protons at -40 degrees C. The solution-state NMR were correlated with two solid-state structures. The five-coordinate complex [Hg(TLA)Cl(2)] (1) crystallizes in the triclinic space group P&onemacr; with a = 8.663(3) Å, b = 11.539(4) Å, c = 13.739(3) Å, alpha = 80.81(2) degrees, beta = 75.84(2) degrees, gamma = 80.97(3) degrees, 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)(Hg(2)Cl(6)) (2) also crystallizes in P&onemacr; with a = 10.606(2) Å, b = 15.104(3) Å, c = 17.785(4) Å, alpha = 67.46(3) degrees, beta = 83.52(3) degrees, gamma = 80.29(3) degrees, 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.
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