Poly[[di-μ2-aqua-di-μ5-croconato(2–)-nickel(II)dipotassium(I)] tetra­hydrate].

In the title compound, {[K2Ni(C5O5)2(H2O)2]·4H2O} n, the Ni atom lies on an inversion centre. Two inversion-related croconate [4,5-dihydroxy-4-cyclo­pentene-1,2,3-trionate(2−)] ligands and an NiII ion form a near-planar symmetrical [Ni(C5O5)2]2− moiety. The near-square coordination centre of the moiety is then extended to an octa­hedral core by vertically bonding two water mol­ecules in the [Ni(C5O5)2(H2O)2]2− coordination anion. The crystal structure is characterized by a three-dimensional network, involving strong K⋯O⋯K binding, K⋯O—Ni binding and hydrogen bonding. [ABSTRACT FROM AUTHOR]