The mercury-mercury bond in inorganic and organometallic compounds. A theoretical study

Abstract

The effects of relativity and electron correlation in diatomic mercury HgX compounds and in linear HgX 2 and Hg 2X 2 compounds (X=H, F, Cl, CH3 and CF 3) are investigated using relativistic pseudopotential and local density approximation calculations. The stability of the HgHg bond in Hg 2X 2 is found to be influenced significantly by the electronegativity of the ligand X. Electronegative ligands such as fluorine (X=F) lead to strong mercury based radical character in the HgX monomer unit supporting an HgHg bond to form a stable Hg 2X 2. This effect diminishes for less electronegative ligands such as X=H or CH 3 where the unpaired electron is localized more towards the ligand X. As a consequence, HgHg bonding in Hg 2(CH 3) 2 is very weak which may explain why organomercury compounds of the form Hg 2R 2 (R=any organic group) have not yet been observed. Among these organomercury compounds Hg 2(CF 3) 2 will be most stable. Relativistic and electron correlations effects are shown to have a significant influence on this trend. Hg 2(CR 3) 2 is isolobal to Au 2(PR 3) 2 and it is proposed that the Hg 2(CR 3) 2 unit may be stabilized at other metal centres.