Two new metal–organic complexes formulated as {M₂(μ₈-bta)(μ₂-C₂O₄)·(H₃O)₂(H₂O)₂}_n (1: M = Co^II; 2: M = Fe^II; bta = benzene-1,2,4,5-tetracarboxylate) have been hydrothermally synthesized at 160 °C for 120 h. Their structures were determined by single-crystal X-ray diffraction analysis and characterized by XPS, IR, ICP, elemental, TG and magnetic analysis. Complexes 1 and 2 are isostructural and represent the first coordination network structure constructed by bridging oxalate and bta mixed ligands. In the crystallographic independent unit each metal ion center is in a distorted octahedral geometry and coordinated by four O atoms from the four COO groups of four bta ligands and by two other O atoms from a bis-chelating oxalate ligand. The interconnected independent units create different types of channels running in different directions. The complexes 1 and 2 contain helical chains composed of left-handed and right-handed helices interlaced in pairs. Uncoordinated water molecules occupy the channels in the two complexes. Both of the complexes have intramolecular antiferromagnetic interactions.