The inert pair effect on heavy noble gases: insights from radon tetroxide

A quantum chemical survey of radon and xenon tetroxides (NgO₄, Ng = Xe, Rn) is reported herein. The intermediate species, which are formed in their explosive decomposition back to their elemental states (Ng and O₂), were also studied and their energetics were compared. While T_d symmetric RnO₄ has a minimum energy structure, its standard enthalpy of formation is 88.6 kJ mol^-1 higher than for XeO₄. The reason for this higher instability lies in what is known as the inert pair effect. This work establishes that the high-valent chemical trends of the sixth period of groups 13-15 are indeed extended to group 18.

Synthesis and Characterization of [XeOXe](2+) in the Adduct-Cation Salt, [CH3 CN- - -XeOXe- - -NCCH3 ][AsF6 ]2

Acetonitrile and [FXeOXe- - -FXeF][AsF6 ] react at -60 °C in anhydrous HF (aHF) to form the CH3 CN adduct of the previously unknown [XeOXe](2+) cation. The low-temperature X-ray structure of [CH3 CN- - -XeOXe- - -NCCH3 ][AsF6 ]2 exhibits a well-isolated adduct-cation that has among the shortest Xe-N distances obtained for an sp-hybridized nitrogen base adducted to xenon. The Raman spectrum was fully assigned by comparison with the calculated vibrational frequencies and with the aid of (18) O-enrichment studies. Natural bond orbital (NBO), atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses show that the Xe-O bonds are semi-ionic whereas the Xe-N bonds may be described as strong electrostatic (σ-hole) interactions.

On the Highest Oxidation States of Metal Elements in MO4 Molecules (M = Fe, Ru, Os, Hs, Sm, and Pu)

Metal tetraoxygen molecules (MO4, M = Fe, Ru, Os, Hs, Sm, Pu) of all metal atoms M with eight valence electrons are theoretically studied using density functional and correlated wave function approaches. The heavier d-block elements Ru, Os, Hs are confirmed to form stable tetraoxides of Td symmetry in (1)A1 electronic states with empty metal d(0) valence shell and closed-shell O(2-) ligands, while the 3d-, 4f-, and 5f-elements Fe, Sm, and Pu prefer partial occupation of their valence shells and peroxide or superoxide ligands at lower symmetry structures with various spin couplings. The different geometric and electronic structures and chemical bonding types of the six iso-stoichiometric species are explained in terms of atomic orbital energies and orbital radii. The variations found here contribute to our general understanding of the periodic trends of oxidation states across the periodic table.