Three cobalt (II) complexes with triethylenetetraaminehexaacetic acid: From binuclear complex to 3d-4f coordination polymers

► Three novel complexes with H6TTHA have been synthesized and characterized. ► Complex 2 and 3 are 3d-4f coordination polymers with 3D framework. ► The 3D framework comprise an infinite 1D chain based on heterometallic Ln2Co2. ► This report provides an available way of the construction of 3d-4f complexes.