A series of lanthanide coordination polymers have been synthesized through the hydrothermal reaction of 2,5-piperazinedione-1,4-diacetic acid (H₂PODC) and Ln(NO₃)₃ (Ln = La, 1; Pr, 2; Sm, 3; Ho, 4 and Er, 5). Crystal structure analysis reveals that their structural variations are attributed to the effect of lanthanide contraction.