Pressure-induced New Oxidation States

The formalism of the oxidation state of atoms in compounds is a key concept in chemistry. Finding novel compounds containing elements with unusually high oxidation states allows a deeper understanding of chemical behavior of elements. On the other hand, high oxidation state compounds usually bring new types of bonds with interesting physical and chemical properties. Thus, the preparation of compounds with unusual oxidation states becomes an attractive topic in chemistry and condensed-matter physics. Gold (Au) is a well-known fascinating element, but still hides interesting surprises to be discovered, especially for oxidation state. Here, we propose that high pressure becomes a controllable method for preparing high negative oxidation state of Au through its reaction with lithium. Au acts as a 6p-element in dense lithium aurides. Moreover, we identify two hitherto unknown stoichiometric compounds, AuF4 and AuF6, exhibiting typical molecular crystal character, in which Au demonstrates +4 and +6 oxidation states. On other hand, we also achieve several compounds with unusual stoichiometry such as IrF₈, IF₈, and BaF₅.