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Key indicators: single-crystal X-ray study; T = 298 K; mean (C-C) = 0.008 Å; R factor = 0.036; wR factor = 0.097; data-to-parameter ratio = 11.5. 6 ]Á6H 2 O} n , the 1H,3H-benzimidazol-3-ium-5,6-dicarboxylate ligand is protonated at the imidazole group (H 2 bdc). The Eu III ion is coordinated by nine O atoms from two H 2 bdc ligands, two sulfate anions and three water molecules, displaying a bicapped trigonal prismatic geometry. The carboxylate groups of the H 2 bdc ligands and the sulfate anions link the Eu III ions, forming a chain along [010]. These chains are further connected by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds and -interactions between the imidazole and benzene rings [centroid-centroid distances = 3.997 (4), 3.829 (4) and 3.573 (4) Å ] into a three-dimensional supramolecular network. In the title coordination polymer Related literature

The asymmetric unit of the title compound, [Cd3(C8H5N2O2)2(SO4)2(H2O)3]n, contains three CdII ions, two sulfate anions, two 1H-benzimidazole-5-carboxyl­ate (H2bic) ligands and three coordinated water mol­ecules. One CdII ion is six-coordinated and exhibits a distorted octa­hedral geometry, while the other two CdII ions are seven-coordinated, displaying a distorted penta­gonal–bipyramidal geometry. The CdII ions are bridged by two types of sulfate anions, producing inorganic chains along [100]. These chains are further connected by the H2bic ligands, leading to a three-dimensional framework. N—H⋯O and O—H⋯O hydrogen bonds and π–π inter­actions between the imidazole and benzene rings [centroid–centroid distances = 3.953 (2), 3.507 (2), 3.407 (2) and 3.561 (2) Å] further stabilize the crystal structure.