Solution and solid-state NMR studies of MeHgII and RSHgII (R = Me, Et) complexes with pyrazolyl-containing ligands

The solid state and solution NMR spectra of the tetrakis(pyrazol-l-yl) borate (L a ) and tris(3,5-dimethylpyrazol-l-yl) hydroborate (L b ) ligands and their complexes with MeHg II and RSHg II (R = Me, Et) are reported. The solid state 13 C and 15 N solid state NMR spectra of the MeHgL a complex are consistent with the reported X-ray structure. The close similarity of the spectral data shown by MeHgL a and MeSHgL a suggests that the two species have the same structure. In order to confirm this hypothesis, the structure of MeSHgL a has been determined by single crystal X-ray diffraction. The chemical shift anisotropy (CSA) of 199 Hg resonance is too large in these T-shaped complexes and does not allow the observation of the 199 Hg resonance under cross polarisation-magic angle spinning (CPMAS) experimental mode. On the other hand 199 Hg CPMAS NMR spectra were obtained for the complexes with the L b ligand. The reduced 199 Hg CSA value together with the information gained from the 13 C and 15 N CPMAS NMR spectra suggest a tetra coordination around mercury in these complexes. The tight co-ordination mode shown by complexes with the L b ligand is reflected in a decrease in the thiol intermolecular exchange rate in solution. This decreased ligand lability allows the detection of 3 J Hg-H couplings (inside HgSCH 3 and HgSCH 2 CH 3 moieties) in the low temperature NMR limiting spectra.