The coordination chemistry of Hg() with tris[(1-methylimidazol-2-yl)methyl]amine (TMIMA) was investigated. The structures of [Hg(TMIMA) 2 ](ClO 4 ) 2 (1), [Hg(TMIMA)(NCCH 3 )](ClO 4 ) 2 (2) and [Hg(TMIMA)Cl] 2 (HgCl 4 ) (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) Å. Ligand geometry suggests the Hg-N (NR 3 ) distances of 2.959(6) Å in 1 reflects weak bonding interactions. This complex has a 199 Hg chemical shift of Ϫ1496 ppm, significantly upfield from nitrogen coordination complexes with lower coordination numbers. The five-coordinate complex 2 has Hg-N (NR 3 ) , Hg-N imidazoyl and Hg-N acetonitrile bond lengths of 2.642(8), 2.198(5) and 2.264(11) Å, respectively. Complex 3 is also five coordinate, with Hg-N (NR 3 ) , Hg-Cl and average Hg-N imidazoyl distances in the cations of 2.758(7), 2.424(2) and 2.29(4) Å, 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() substituted proteins with histidine-metal bonds. Solution and solid-state comparisons to the Hg() coordination chemistry of tetradenate pyridyl ligands are made. Relevance to development of 199 Hg NMR as a metallobioprobe is discussed.

Tripodal N4 ligands tris[(1-methylimidazol-2-yl)methyl]amine (L1), bis[(1-methylimidazol-2-yl)methyl][(2-pyridyl)methyl]amine (L2) and [(1-methylimidazol-2-yl)methyl]-bis-[(2-pyridyl)methyl]amine (L3) were used to prepare five new [ML2](ClO4)2 (M = Cd(II), Hg(II)) complexes. All complexes had N8 metal coordination and a trans-bicapped octahedral structure as determined by X-ray crystallography. Metal-nitrogen bond distances generally decreased in the order M-Namine > M-Npyridyl > M-Nimidazoyl, and the perchlorates were well separated from the metal ions. Variable temperature solution state (1)H NMR spectroscopy revealed conditions for slow intramolecular reorganization were more readily accessible for the Cd(II) complexes than for the Hg(II) complexes. Both protons of imidazoyl ring ligand components had large, comparable J((199)Hg(1)H) despite sizable differences in nuclear separation.

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