Hydrothermal synthesis and characterization of the first oxalate–bta mixed-ligand three-dimensional frameworks: {[M2(mu8-bta)(mu2-C2O4)]·(H3O)2(H2O)2}n(M = CoII, FeII; bta = benzene-1,2,4,5tetracarboxylate)

Two new metal–organic complexes formulated as {M2(µ8-bta)(µ2-C2O4)·(H3O)2(H2O)2}n(1: M = CoII; 2: M = FeII; 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.