Poly[diaquabis(μ4-fumarato-κ4O1:O1′:O4:O4′)(μ4-fumarato-κ6O1:O1,O1′:O4:O4,O4′)(μ2-fumaric acid-κ2O1:O4)dipraseodymium(III)]

The title complex, [Pr2(C4H2O4)3(C4H4O4)(H2O)2]n, was synthesized by reaction of praseodymium(III) nitrate hexahydrate with fumaric acid in a water–ethanol (4:1) solution. The asymmetric unit comprises a Pr3+ cation, one and a half fumarate dianions (L2−), one half-molecule of fumaric acid (H2L) and one coordinated water molecule. The carboxylate groups of the fumarate dianion and fumaric acid exhibit different coordination modes. In one fumarate dianion, two carboxylate groups are chelating with two Pr3+ cations, and the other two O atoms each coordinate a Pr3+ cation. Each O atom of the second fumarate dianion binds to a different Pr3+ cation. The fumaric acid employs one O atom at each end to bridge two Pr3+ cations. The Pr3+ cation is coordinated in a distorted tricapped trigonal–prismatic environment by eight O atoms of fumarate dianion or fumaric acid ligands and one water O atom. The PrO9 coordination polyhedra are edge-shared through one carboxylate O atom and two carboxylate groups, generating infinite praseodymium–oxygen chains, which are further connected by the ligands into a three-dimensional framework. The crystal structure is stabilized by O—H...O hydrogen-bond interactions between the coordinated water molecule and the carboxylate O atoms.