The asymmetric unit of the title coordination polymer, [Co(C9H4N2O4)(C2H4N4)]
n
or [Co(L
1)(L
2)]
n
, consists of one crystallographically independent Co2+ centre, one L
1
2− ligand and one L
2 ligand (L
1 = 1H-benzimidazole-5,6-dicarboxylic acid, L
2 = 3-amino-1,2,4-triazole). The Co2+ centre is coordinated by two carboxylato-O atoms from two independent L
1
2− ligands and two nitrogen atoms from L
2 and another L
1 ligand. Thus, the metal center adopts a four-coordinate mode, forming a tetrahedral geometry. Interestingly, through the combination of two L
1
2−, two L
2 ligands and two Co2+ ions, a basic repeating unit is constructed, resulting in the formation of a one-dimensional straight chain structure. These chains are further expanded to the final three-dimensional framework via N—H...O hydrogen-bonding interactions.