On the stability and volatility of group 8 tetroxides, MO4 (M = ruthenium, osmium, and hassium (Z=108))

Recently, an experiment to chemically characterize for the first time a compound of the transactinide element hassium (Hs, Z = 108) has been performed. On the basis of the assumption that Hs will belong to group 8 of the periodic table and will thus be homologous to ruthenium (Ru) and osmium (Os), the presumably very volatile HsO(4) was isolated by gas adsorption chromatography. The experiment allowed the determination of the enthalpy of adsorption (-DeltaHa(0)((T))) of HsO(4) on a silicon nitride surface. In this work, the trend in standard enthalpies of sublimation (DeltaH(S0)((298))) of group 8 element tetroxides established by ruthenium tetroxide and osmium tetroxide was extrapolated to hassium tetroxide. The Delta(S)(0(298))(HsO(4)) was found to be very similar to DeltaH(S)(0(298))(OsO4). On the basis of an empirical correlation between the sublimation enthalpies and the enthalpies of adsorption of oxide (and oxyhydroxide) molecules on quartz surfaces, -DeltaH(a)(0(T))(HsO(4)) was predicted to be 46 +/- 15 U mol(-1). A trend for the values of the adsorption enthalpies of RuO4 approximate to OsO4 approximate to HsO(4) was found. A different theoretical approach makes use of the relation between the interaction distance of a physisorbed, nonpolar molecule on a dielectric surface and the interaction energy. From literature values of the adsorption of noble gases on metal surfaces, it was found that this distance is independent of the adsorbed species, as well as of the adsorbent material. With the use of this universal interaction distance, -DeltaH(a)(0(T))(OsO4) was calculated only from molecular geometries Of OsO4, the polarizability, and the first ionization potential and was found to agree with experimental results found in gas adsorption chromatography experiments, The -DeltaH(a)(0(T)) values of RuO4 and HsO4 were calculated using the same procedure; where no experimental values of molecular properties were available. these were extrapolated or published values obtained from density funcional calculations were used. A value of -DeltaH(a)(0(T))(HsO(4)) = 47 +/- 11 U mol(-1) is predicted, in agreement with the extrapolated value.