Synonyms: Nickelate(6-), (((1,2-ethanediylbis((nitrilo-kappaN)bis(methylene)))tetrakis(phosphonato-kappaO))(8-))-, potassium hydrogen (1:5:1), (OC-6-21)-;Pentapotassium nickelous 1,2-ethane di(nitrilodi(methylene phosphonate));Hydrogen pentapotassium (((ethylenebis(nitrilobis(methylene)))tetrakis(phosphonato))(8-))nickelate(6-);Nickelate(6-), (((1,2-ethanediylbis((nitrilo-kappaN)bis(methylene)))tetrakis(phosphonato-kappaO))(8-))-, pentapotassium hydrogen, (OC-6-21)-;nickel(2+) potassium hydrogen [ethane-1,2-diylbis(nitrilodimethanediyl)]tetrakis(phosphonate) (1:5:1:1)