Two novel 3D lanthanide metal-organic frameworks [Ln(pydc)(pip)(1/2)(H2O] (Ln=Ce (1) and Pr (2), H(2)pydc=2,5-pyridinedicarboxylic acid, H(2)pip=2,5-piperazinedicarboxylic acid have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, thermogravi-metric analysis (TGA), powder X-ray diffractions (PXRD), and single-crystal X-ray diffractions. Field emission scanning electron microscopy (FESEM) was used for morphological analysis. Complexes are isostructural and feature interesting 3D frameworks. Both compounds crystallize in the monoclinic system, space group P2(1)/c. Structural analyses of I and 2 show that Ln(3+) ions connect with each other through H(2)pydc and H(2)pip. To the best of our knowledge, they are the first heteroleptic lanthanide polymers obtained through in situ 2,5-piperazinedicarboxylic acid syntheses. Moreover, thermal and luminescent properties of the compounds have been investigated. (C) 2015 Elsevier Inc. All rights reserved.