Two isostructural ID coordination polymers {[Ln(OAc)(2)(H2O)(OBPT)]center dot 3H(2)O} (HOBPT = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol, Ln = Eu3+, 1; Tb3+, 3) and two discrete complexes [Ln(OAc)(2)(DMF)(2)(OBPT)] (Ln = Eu3+, 2; Tb3+, 4) have been synthesized in H2O-MeOH or DMF solvents, respectively. Their structures were identified by powder X-ray diffraction. Single crystal X-ray studies for complexes 1 and 2 revealed that the coordination geometries of the Eu3+ ions are similar and can be described as a distorted tricapped trigonal prism with six oxygen atoms and three nitrogen atoms. The difference between them is that one aqua ligand and one oxygen atom from the OBPT ligand complete the coordination sphere in complex 1, whereas two DMF molecules complete the coordination sphere in complex 2. Interestingly, the solvent mediated, reversible crystal-to-crystal transformation between them was achieved by immersing the crystalline samples in the corresponding solvent (H2O or DMF) or by exposing them to solvent vapor. Complex 1 shows a highly selective luminescence enhancement in response to DMF in comparison to that observed in response to other examined solvents such as acetone, ethyl acetate, ethanol, acetonitrile, methanol, and THF.