1H and 199Hg NMR spectra of methylmercury(II)complexes. Effects of basicitv and ortho substitution in pyridines (L) in complexes [MeHgL]N03

Abstract

Linear complexes [MeHgL]NO3 (L = substituted pyridine) have been prepared and their 1H and 199Hg NMR spectra measured and compared with other complexes of this series reported previously. The coupling constant J(1H-199Hg) correlates directly with pKa and with the gas phase enthalpy of ionization [DGi(g) of LH+; with J(lH-199Hg) decreasing with increasing pKa or AGi(g). The chemical shift, delta, for 199Hg does not correlate with either pKa or AGi(g). Complexes without substituents in the 2 position of pyridine have delta l99Hg ca. 80-100 ppm downfield from MeHgN03, those with one methyl group in the 2 position ca. 125-150 ppm, and those with methyl groups in the 2 and 6 position (or benzyl or 3'-methylpyridyl groups in the 2 position) ca. 160-200 ppm downfield from MeHgN03. The coupling constant J(lH-l99Hg) is found to be more useful than delta 199Hg in determination of solution structures of MeHg(II) complexes of this type of ligand.