Many nitrite nitrate compounds are coordination complexes of cobalt.
Such a substance was discovered by Wolcott Gibbs and Frederick Genth in 1857.
[citation needed] Mercury(II) nitrate and potassium nitrate in water solution produce the salt tripotassium tetranitratomercurate(II) nitrate K3[Hg(NO2)4]NO3.
[1] On heating, nitrate nitrites lose NO2 and NO and yield metal oxides.
Other compounds having an element in two different anion states include the sulfate sulfites, the phosphate phosphites, arsenate arsenites and the selenate selenites.