Coordination chemistry of methylmercury(II). Synthesis, hydrogen-1 NMR, and crystallographic studies of cationic complexes of MeHg(II) with ambidentate and polydentate ligands containing pyridyl and N-substituted imidazolyl donors and involving unusual coordination geometries

Abstract

Complexes [MeHgL]N03 (L = 4,4’,4’’-triethyL2,2':6’,2”-terpyridyl (Et3terpy), terpy, bis(2-pyridy1)methanes ((py)CH2's), (py)2CMe2, (py)2CEt2, tris(2-pyridyl)methane, several N-alkylimidazoles, N-(2-pyridyl)imidazole, and N-methyl-2-(2-pyridy1)imidazoles) are obtained from addition reactions in acetone. Proton magnetic resonance spectroscopy is used to deduce coordination behavior of potential uni- or polydentate ligands in methanol, indicating that Et3terpy, terpy, (py)2CH2's, and N-methyl-2-(2-pyridyl)imidazoles act as bidentates to give three-coordinate mercury, but (py)2CR2 (R = Me, Et) are present as unidentates. A linear relation is obtained between 2J(1H-199Hg) for [MeHgL]+ and protonation constants for L, where L = N-alkylimidazoles, and the relation is similar to that obtained previously for L = pyridines. The ambidentate ligand N-(2-pyridyl)imidazole binds to mercury via the imidazole ring. Crystalline [MeHg((py)2CH2)]N03 has (py)CH2 present as a bidentate ligand with “T-shape” coordination geometry based on a dominant C-Hg-N moiety [Hg-N = 2.16(1) A, C-Hg-N = 172 (1) and a weaker Hg-N’ bond [2.75(2) A]. Crystalline [MeHg(Et3terpy)]N03 has Et3terpy present as a tridentate ligand with MeHg(II) bonded strongly to the central nitrogen [2.26(2) A, C-Hg-N = 171(1) and weakly to the terminal nitrogens [2.51(2), 2.61(2) A]. Syntheses of new ligands containing pyridyl and N-methylimidazolyl donor groups are described.