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-N-imidazoyl bonds ranging from 2.257(5) to 2.631(6) Angstrom. Ligand geometry suggests the Hg-N-(NR3) distances of 2.959(6) Angstrom in 1 reflects weak bonding interactions. This complex has a Hg-199 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-N-imidazoyl and Hg-N-acetonitrile bond lengths of 2.642(8), 2.198(5) and 2.264(11) Angstrom, respectively. Complex 3 is also five coordinate, with Hg-N-(NR3), Hg - Cl and average Hg - N-imidazoyl distances in the cations of 2.758(7), 2.424(2) and 2.29(4) Angstrom, respectively. Conditions for slow exchange on the J(HgH) coupling time-scale were found for both 1 : 1 metal-to-ligand complexes in acetonitrile-d(3). 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 Hg-199 NMR as a metallobioprobe is discussed.