Hassium tetroxide

Hassium tetroxide (also hassium(VIII) oxide) is the inorganic compound with the formula HsO4. It is the highest oxide of hassium, a transactinide transition metal. It has little use outside of scientific interest, where it is often studied in comparison to osmium tetroxide and ruthenium tetroxide, its lighter octavalent group 8 element analogs.

Physical properties
Because of the extreme cost and difficulty of producing hassium, hassium tetroxide has never been obtained in macroscopic amounts, as only a few molecules have ever been synthesized. As a result, many of its physical properties are experimentally uncharacterized and unknown. However, most research available generally shows hassium tetroxide to behave like a typical congener to osmium tetroxide. Hassium tetroxide is less volatile than osmium tetroxide.

Synthesis
Hassium tetroxide can be obtained by reacting atomic hassium with oxygen at 600 °C.
 * Hs + 2 O2 → HsO4

Reactions
Hassium tetroxide can be combined with sodium hydroxide in an acid-base reaction, in which case it acts like the acid, to form sodium hassate(VIII):
 * HsO4 + 2 NaOH -> Na2[HsO4(OH)2]