Mercury-199 NMR of mercury-bridged transition metal clusters.

The 199Hg NMR data for the series of complexes (.mu.3-.eta.2-C2CMe3)(CO)9Ru3(.mu.-Hg)X (X = Cl, Br, iodo) and (.mu.3-.eta.2-C2CMe3)Ru(.mu.3-Hg)M [M = MoC5H5(CO)3, Mn(CO)5, Re(CO)5, FeC5H5(CO)2, RuC5H5(CO)2, Co(CO)4] and the phosphine deriv. P(C6H5)3(CO)8(.mu.3-.eta.2-C2CMe3)Ru3(.mu.3-Hg)MoC5H5(CO)3 are reported. The 199Hg chem. shifts vary over a relatively large range for the series (.apprx.1500 ppm) with some of the mixed transition series showing the largest downfield shifts (relative to HgMe2) reported to date. The data are discussed in light of previously reported 199Hg shifts for related complexes and although there is no correlation between Hg-M bond lengths in this isostructural series some general correlations of the chem. shifts with the expected polarity of the Hg-M bond based on the reactivity of the complexes and the qual. theory of 199Hg chem. shifts can be made. A very large variation in line width is also obsd. which correlates well with the expected efficiency of quadrupole relaxation mechanisms.