Binary salt of a palladium(II) complex with (phosphonomethyl)phosphonic (medronic) acid comprising 'handbell-like' [Pd{μ-CH2(PO3)2}]3 units.

The asymmetric unit of the title compound, dipotassium bis[hexaaquanickel(II)] tris(μ(2)-methylenediphosphonato)tripalladium(II) hexahydrate, K(2)[Ni(H(2)O)(6)](2)[Pd(3){CH(2)(PO(3))(2)}(3)]·6H(2)O, consists of half a {[Pd{CH(2)(PO(3))(2)}](3)}(6-) anion [one Pd atom (4e) and a methylene C atom (4e) occupy positions on a twofold axis] in a rare 'handbell-like' arrangement, with K(+) and [Ni(H(2)O)(6)](2+) cations to form the neutral complex, completed by three solvent water molecules. The {[Pd{CH(2)(PO(3))(2)}](3)}(6-) units exhibit close Pd···Pd separations of 3.0469 (4) Å and are packed via intermolecular C-H···Pd hydrogen bonds. The [KO(9)] and [NiO(6)] units are assembled into sheets coplanar with (011) and stacked along the [100] direction. Within these sheets there are [K(4)Ni(4)O(8)] and [K(2)Ni(2)O(4)] loops. Successive alternation of the sheets and [Pd{CH(2)(PO(3))(2)}](3) units parallel to [001] produces the three-dimensional packing, which is also supported by a dense network of hydrogen bonds involving the solvent water molecules.