Two flexible triazine-based polycarboxylate ligands, 1,3,5-triazine-2-iminodiacetic acid-4,6-bis(L-alanine) (H4L1) and 1,3,5-triazine-2-iminodiacetic acid-4,6-biglycine (H4L2), have been designed and used to construct a series of luminescent lanthanide coordination polymers {[Ln(HL1)](H2O)5}n (Ln = 1, Tb; 2, Eu; 3, Gd) and {[Ln(HL2)(H2O)](H2O)2}n (Ln = 4, Tb; 5, Eu; 6, Gd). The complexes were structurally authenticated by single-crystal X-ray diffraction, revealing that isostructural complexes 1–3, derived from H4L1, possess a 2-D framework with the monoclinic space group C2/c, whereas isostructural complexes 4–6, based on H4L2, exhibit a 2-D layer structure with the monoclinic space group P2(1)/c. Solid-state photoluminescence properties of the complexes were investigated. Complexes 1 and 2 exhibit remarkable green and red luminescence emissions with high quantum yields up to 67% and 68%, respectively, and millisecond-level lifetimes. Nevertheless, complexes 4 and 5 feature weak quantum yields (9.9% for 4; and 30% for 5).