A CORRELATION BETWEEN RELATIVISTIC EFFECTS AND THE FORMAL CHARGE OF THE Hg ION AND LIGAND NATURE. THE STRUCTURE OF POLYATOMIC Hg IONS

L.M. Volkova ¹, S.A. Magarill ²

¹Institute of Chemistry, FE Branch of RAS, Av. Stoletiya Vladivostoka, 159, 690022 Vladivostok, Russia
²Institute of Inorganic Chemistry, Sib Branch of RAS, Akad. Lavrentiev Av., 3, 630090 Novosibirsk, Russia

An analysis of clearly defined correlation between a relativistic (R) contraction of the 6s- and 6p-shells and the expansion of the 5d-shell of the Hg ions allowed us to discuss the known crystal chemical regularities in the mercury compounds with the formal charge of Hg smaller than 2. Obviously the removal of a part of electron density from the s-orbitals in the Hg ion will result in the contraction of the 5d-orbitals (a decrease in the R-expansion) relative to their state in metallic Hg due to a decrease in the nucleus shielding by the 6s-electrons. An addition of electrons on the unoccupied 6p-orbitals will prevent the R-expansion of the 5d-layer due to the Coulomb and Pauli expansion of the 6s- and 6p-layers. Consideration is being given to the influence of ligand nature and an interaction type of mercury ions with ligands on the R-contraction of the 6s-and 6p-orbitals and the R-expansion of the 5d-orbitals. It is shown that the R-contraction and the R-expansion extent of the 6s-, 6p- and 5d-orbitals correlate with a number of the interbonded Hg ions, a geometric form of these Hg combinations, the Hg-Hg distances, ability of Hg to be bonded with d-elements and conductivity of Hg-compounds. We suppose that the highly electronegative ligands, capable of taking strongly the electron density from the 6s-orbitals (to expansion the 6s-orbitals through their increased contribution to the bonding), will cause the R-expansion of the 5d-orbitals and their contribution to the bonding to decrease. This explains the disruption of the large polyatomic Hg ions in the presence of the highly electronegative unbounded anions. In linear X-Hg-Hg-X groups a shortening of the Hg-Hg distances with a lengthening of the Hg-X bonds (a decrease in the covalence share of the Hg-X bonds) is caused perhaps, by an increase in the contraction of the 5d-layer with removing the 6s-electrons density maximum from the Hg nucleus.

This work was financially supported by the Russian Fundamental Research Fund (grant 98-05-65223).