SOLID-STATE HG-199 AND CD-113 NMR-STUDIES OF MERCURY THIOLATE AND CADMIUM THIOLATE COMPLEXES - SPECTROSCOPIC MODELS FOR [HG(SCYS)N] CENTERS IN THE BACTERIAL MERCURY RESISTANCE PROTEINS

Hg-199 CP/MAS-NMR spectra have been measured for representative examples of the major coordination geometries available to monomeric mercury thiolate complexes: [Hg(SR)2], [Hg(SR)3]1-, and [Hg(SR)4]2-. Solid-state Cd-113 NMR spectra have been measured for related [Cd(SR)3]1- compounds. [(n-Bu)4N] [Cd(S-2,4,6-i-Pr3C6H2)3] and [Ph4P][Hg(S-2,3,5,6-Me4C6H)3] were structurally characterized by X-ray crystallography. The metal ions in both compounds are three-coordinate with distorted Y-shaped, planar [MS3] units. These structures are discussed in relationship to a second conformational isomer, the symmetric C3h [M(SR)3]1- anion. The shielding tensor, isotropic chemical shift (sigma-iso), the chemical shielding anistropy (DELTA-sigma), and the asymmetry parameter (eta) vary in a systematic manner as a function of coordination number and coordination geometry. Hg-199 and Cd-113 CP/MAS-NMR data for selected compounds (sigma-iso, DELTA-sigma, eta) are as follows: [Hg(S-2,4,6-i-Pr3C6H2)2] (-1015, 4256, 0.16); [Ph4P][Hg(S-2,4,6 -i-Pr3C6H2)3] (-267, 1408, 0.30), [(n-Bu)4N][Hg(SPh)3] (-341, 1273, 0.97), [Et4N]2[Hg(S-2-PhC6H4)4] (-433, 86.5, 0.86), and [Ph4P][Cd(S-2,4,6-i-Pr3C6H2)3] (668, 483, 0.24). The implications of this study to solution and solid-state Hg-199 and Cd-113 NMR studies of Hg- and Cd-cysteine proteins are discussed.