Theoretical investigations of the reactivity of MO4 and the electronic structure of Na2[MO4(OH)2], where M=Ru, Os, and Hs (element 108)

Abstract

Abstract Fully relativistic, four-component, density functional theory calculations (4c-DFT) were performed for [MO4(OH)2]2- and Na2[MO4(OH)2], where M=Ru, Os, and Hs. The electronic structure of the Hs complex ion was shown to be similar to that of the Os complex ion, though [HsO4(OH)2]2- should be more covalent than the lighter congeners in group 8, by analogy with MO4. The calculations of the free energy change, Δ G r, of the [MO4(OH)2]2- and Na2[MO4(OH)2] formation reactions from the volatile tetroxides and NaOH have shown that HsO4 should be slightly less reactive than OsO4, with the difference in ΔG r being less than 52 kJ/mol. In the experimental study of the deposition of OsO4 and HsO4 on the surface of NaOH in the presence of water, such a difference in reactivity has not yet been clearly revealed. The anionic complex of Ru(VIII) was found to be much less stable than those of Os and Hs. Also, Delta;G r for the formation of [RuO4(OH)2]2- from RuO4 was found to be ∼300 kJ/mol more positive than ΔG r for analogous reactions of Os and Hs, which explains why the Ru(VIII) complex is not known. The ionic radii, IR(Hs8+)=0.454 Å for CN=4, IR(Os8+) = 0.49 Å and IR(Hs8+) = 0.54 Å for CN=6, have been obtained on the basis of the calculations of bond lengths in MO4, as well as via a correlation between R max of the outer np obitals and IR of the 5d and 6d elements, respectively.