(μ-Methylenediphosphonato-κ<sup>4</sup> <i>O</i>,<i>O</i>′:<i>O</i>′′,<i>O</i>′′′)bis[(ethylenediamine-κ<sup>2</sup> <i>N</i>,<i>N</i>′)palladium(II)] tetrahydrate
Acta crystallographica. Section E, Crystallographic communications