Three novel heterometal-organic frameworks {[CoCdLn(HCAM)(2)(CAM)(H(2)O)(7)].7H(2)O}(n) (Ln = Dy (); Eu (); Sm ()) have been successfully synthesized under hydrothermal condition using 4-hydroxyl-pyridine-2,6-dicarboxylic acid (H(3)CAM) as ligand, and display a fascinating 3D structure constructed by double-stranded helical motifs and exhibit luminescent properties.