HIGH OXYGEN PRESSURES AND THE STABILIZATION OF THE HIGHEST OXIDATION-STATE OF IRIDIUM

High oxygen pressures appear to be a powerful tool for stabilizing unu sual oxidation states of transition elements. During the last twenty f ive years numerous new oxides containing 3d elements with a high valen cy have been prepared [1]. This paper presents the main results concer ning the synthesis, the structural determinations, and the magnetic an d electrical characterizations of a new series of oxides A(2)MIr(VI)O- 6 (A=Ba,Sr; M=Sr,Ca,Mg,Zn) with the (VI) oxidation state for iridium. The influence of the oxygen pressure on the stabilization of Ir(VI) is emphasized. The study underlined the strong increase of the Me-O (Me : transition metal) covalency with the increasing Me-oxidation state a nd the change from 3d to 5d in the same column of the Periodic Table.