Dipotassium maleate with boric acid

In the title compound, poly[(μ₃-boric acid)-μ₄-maleato-dipotassium], [K₂(C₄H₂O₄){B(OH)₃}]_n, there are two independent K⁺ cations, one bonded to seven O atoms (three from boric acid and four from maleate), and the other eight-coordinate via three boric acid and four maleate O atoms and a weak η¹-type coordination to the C=C bond of the maleate central C atoms. Hydrogen bonding links the boric acid ligands and maleate dianions, completing the packing structure.