P. Ray and B. Sarma obtained these dark purple double salts in 1949, mixing nickel sulfate with potassium or sodium periodate and (as oxidant) a boiling aqueous solution of an alkali persulfate salt.
[1] It is now known that ozone can replace the persulfate salt, and that similar solids exist for other alkali (RbNiIO6·0.5H2O, CsNiIO6·0.5H2O, and NH4NiIO6·0.5H2O), as well as certain other tetravalent metals (including manganese, germanium, tin and lead).
[2] The crystalline salts are insoluble in water, acid, or base.
[5][6] Diperiodatometalates with the same formula also exist for palladium and nickel, and similar diperiodatometalates can be made for Cu, Ag, Au, Ru and Os.
In the reaction, NiIV reduces to NiIII with the release of a hydroxyl radical.