Deborah C. Bebout

Investigation of the mercury(II) coordination chemistry of tris[(1-methylimidazol-2-yl)methyl]amine by X-ray crystallography and NMR

The coordination chemistry of Hg(II) with tris[(1-methylimidazol-2-yl)methyl]amine (TMIMA) was investigated. The structures of [Hg(TMIMA)2](ClO4)2 (1), [Hg(TMIMA)(NCCH3)](ClO4)2 (2) and [Hg(TMIMA)Cl]2(HgCl4) (3) were characterized by X-ray crystallography. Complex 1 has six strong Hg–Nimidazoyl bonds ranging from 2.257(5) to 2.631(6) A. Ligand geometry suggests the Hg–N(NR3) distances of 2.959(6) A in 1 reflects weak bonding interactions. This complex has a 199Hg chemical shift of −1496 ppm, significantly upfield from nitrogen coordination complexes with lower coordination numbers. The five-coordinate complex 2 has Hg–N(NR3), Hg–Nimidazoyl and Hg–Nacetonitrile bond lengths of 2.642(8), 2.198(5) and 2.264(11) A, respectively. Complex 3 is also five coordinate, with Hg–N(NR3), Hg–Cl and average Hg–Nimidazoyl distances in the cations of 2.758(7), 2.424(2) and 2.29(4) A, respectively. Conditions for slow exchange on the J(HgH) coupling time-scale were found for both 1 ∶ 1 metal-to-ligand complexes in acetonitrile-d3. Observed heteronuclear coupling constants were similar to those associated with Hg(II) substituted proteins with histidine–metal bonds. Solution and solid-state comparisons to the Hg(II) coordination chemistry of tetradenate pyridyl ligands are made. Relevance to development of 199Hg NMR as a metallobioprobe is discussed.

Structure and isomerization comparison of Zn(ii), Cd(ii) and Hg(ii) perchlorate complexes of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine

The divalent zinc triad perchlorate coordination chemistry of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine (L) was investigated by X-ray crystallography and solution state (1)H NMR. New complexes [HgL(ClO4)2] (1) and [CdL(ClO4)2] (2) were isolated as bicapped distorted square pyramidal racemates, contrasting with the approximate trigonal bipyramidal structure of [ZnL](ClO4)2 (3). Although rapid inter- and intramolecular exchange is common for simple complexes of zinc triad metal ions, conditions for slow intramolecular isomerization on both the δ and J(HH) time scales were established for 1, 2 and 3. Trends in geminal (1)H coupling suggested that an asymmetric structure was favored for all three metal ions at or below 40 °C. Contributions of a symmetric structure to solution equilibria were both temperature- and metal ion-dependent. Spectral trends were consistent with interconversion of a pair of enantiomeric square pyramidal ligand conformers through a symmetric trigonal bipyramidal ligand conformer by M-N bond cleavage and nitrogen inversion. Racemization was slower than the coupling constant time scale up to 40 °C for all complexes. Differential stabilization of specific small ligand conformations in solution has potential toxicological significance.

Caging the mercurous ion: a tetradentate tripodal nitrogen ligand enhances stability and J(1H199Hg)

AbstractThe dimeric mercurous ion has been encapsulated by a pair of the tetradentate tripodal nitrogen ligands tris[(2-(6-methylpyridyl))methyl]amine (TLA). The complex [Hg2(TLA)2](ClO4)2 (1) was isolated directly from an acetonitrile solution of Hg(ClO4)2 ⋅ 3H2O and TLA. Complex 1 crystallizes in the triclinic space group

Mercury coordination chemistry of a nitrogen/thioether sulfur ligand having an internal hydrogen bond donor: Generation of a thioether-coordinated dimercurous complex

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

with a = 10.537(2) Å, b = 10.751(2) Å, c = 10.907(2) Å, α = 75.20(3)○, β = 73.73(3)○, γ = 75.73(3)○, and Z = 1. The cation is located an inversion center. The Hg–Hg and Hg–Namine bond distances are 2.5469(8) and 2.297(6) Å, respectively, and the average Hg–Npyridyl bond length is 2.75(7) Å. Complex 1 was stable indefinitely in acetonitrile-d3 solution, permitting detection of 13 and 22 Hz heteronuclear couplings between the Hg(I) ions and the methylene protons of the ligand. Comparisons with the structures and spectroscopic properties of related mercuric and mercurous complexes are made.

COMPARISON OF HETERONUCLEAR COUPLING CONSTANTS FOR ISOSTRUCTURAL NITROGEN COORDINATION COMPOUNDS OF 111/113CD AND 199HG

Tridentate ligand N-(2-pyridylmethyl)-N-(2-(ethylthiolato)amine (L) forms the novel complex [Hg(5)(L)(6)](ClO(4))(4).toluene () with a bicyclo[3.3.3] Hg(5)S(6) core and 4-, 5- and 6-coordinate metal centers; characterization of a solution of by ESI-MS revealed elaborate speciation involving [Hg(n)L(n+1)(ClO(4))(n-2)](+), [Hg(n)L(n)(ClO(4))(n-1)](+) and [Hg(n)L(n-1)(ClO(4))(n)](+) ion families.

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

Admixture of the chelate ligand bmnpa (N,N-bis(2-methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine) with an equimolar amount of Hg(ClO4)2·3H2 Oi n CH 3OH/CH2Cl2, followed by recrystallization from CH3CN/Et2O, yielded the Hg(II) perchlorate complex ((bmnpa)Hg(ClO4)2 )( 1). Addition of an equimolar amount of Me4NOH·5H2 Ot o aC H 3CN solution of 1, followed by recrystallization from CH3OH/Et2O, yielded the dinuclear Hg2 2+ complex ((bmnpaHg)2)(ClO4)2 (4). X-ray crystallographic characterization of 1·0.5CH3CN revealed a mononuclear structure having a primary coordination number of two with a distorted linear geometry, and four secondary bonds for an effective coordination number of six. The 1 H NMR spectrum of 1 in CD3CN shows distinctive 3 J199Hg−1H coupling in the benzylic -CH2 - and thioether −SCH3 resonances. Complex 4·CH3OH exhibits a structure in the solid state wherein each mercury center of the Hg2 2+ ion displays thioether coordination and a distorted tetrahedral geometry. Complex 4 is the first dimercurous complex for which J199Hg−1H coupling involving a -SCH3 appendage is reported.