Quasi-Relativistic Study of 199Hg Nuclear Magnetic Shielding Constants of Dimethylmercury, Disilylmercury and Digermylmercury

Abstract

Quasi-relativistic ab initio calculations were performed for 199Hg nuclear magnetic shielding constants and chemical shifts in a series of Hg(XH3)2 (X = C, Si, and Ge) compounds. The relativistic terms included were the spin-free relativistic (SFR) term, the one- and two-electron spin−orbit (SO) terms, and the relativistic magnetic interaction (RMI) term. The second-order Douglas−Kroll (D-K) form was adopted for the one-electron SO, SFR, and RMI terms, and the Breit−Pauli form for the two-electron SO term. The calculated results show that the SFR, SO, and RMI terms are all important for calculating the 199Hg shielding constants and chemical shifts of the compounds in question. The SFR and SO terms strongly couple with each other, and the RMI term also strongly affects the paramagnetic and Fermi-contact (FC) terms. The calculated 199Hg chemical shifts are in reasonable agreement with experimental data only if the SFR, SO, and RMI terms are included and tight s basis functions of mercury are used. We found that the total trend of the chemical shifts in Hg(XH3)2 (X = C, Si, and Ge) originates from the sum of the FC and paramagnetic terms, which are the effects of the relativity and the electronegativity of the ligand, respectively.