OXIDATION-STATE - AB-INITIO STUDY OF ZINC(IV), CADMIUM(IV), AND MERCURY(IV) FLUORIDES(IV IN GROUP 12 CHEMISTRY )

Mercury(IV) fluoride, HgF4, is thermodynamically stable or only slight ly endothermic with respect to gaseous HgF2 + F2 and might be accessib le via fluorination of HgF2, e.g. by KrF2. This is the result of high- level quasirelativistic pseudopotential QCISD(T) calculations. In cont rast, the existence of CdF4 is unlikely and that of ZnF4 even more so. The easier oxidation of HgF2, compared to CdF2 or ZnF2, is due to a r elativistic destabilization of the Hg(II)-F bonds rather than to a rel ativistic stabilization of HgF4. Spin-orbit coupling also contributes to a stabilization of HgF4 vs HgF2 + F2, but only slightly. The perfor mance of various computational levels to treat electron correlation an d of a general basis-set contraction scheme based on atomic natural or bitals have been evaluated. The characterization of molecular HgF4 sho uld be possible via vibrational spectroscopy, as the calculated harmon ic frequencies differ considerably from those of other possible specie s that might be present in the reaction mixture. Calculations on anion ic model complexes and on the dimers (HgF4)2 and (HgF2)2 show that HgF 4 gains only limited additional stability by anionic complexation or b y aggregation. Thus, any successful synthesis should involve condition s where the lattice energy of HgF2 is not relevant (e.g. gas-phase mol ecular beam experiments or reactions in solution).