Metal–organic frameworks of lanthanide iminodiacetates and tartrates: Synthesis, structural characterization and luminescence properties — Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

Two series of lanthanide-containing metal–organic frameworks (Ln-MOFs) of the general formula {[Ln(HIDA)₂H₂O]ClO₄·H₂O}_n (Ln = La (1), Nd (2), Eu (3), Gd (4), Tb (5), Eu:Tb (6); H₂IDA = iminodiacetic acid) and [Ln(TT) (HTT) (H₂O)₃]_n (Ln = Eu (7), Gd (8), Tb (9), Dy (10), and Eu:Tb (11); H₂TT = tartaric acid) were synthesized by reacting Ln(ClO₄)₃ with iminodiacetic acid and L-tartaric acid, respectively. All compounds were structurally characterized by single-crystal X-ray diffraction. Elemental analyses are consistent with the corresponding crystallographically generated formulas. Moreover, the luminescence properties of both the single and mixed-lanthanide complexes were studied. Near infrared, red, and green emissions that are characteristic of Nd(III), Eu(III), and Tb(III) are observed for 2, 3/7, and 5/9, respectively. For the two mixed-lanthanide complex systems 6 and 11, depending on the relative amount of Eu(III) and Tb(III), the color of emission can be fine-tuned. It is found that a small amount of Eu(III) is adequate for the observation of the most intense transition of Eu(III). This is believed to be a result of energy transfer from Tb(III) to Eu(III) within the same complex - a conclusion supported by the significantly shortened lifetime of Tb(III) and the accompanying enhanced lifetime of Eu(III) in the mixed-lanthanide complex with respect to the corresponding values for the pure Tb(III) and Eu(III) complexes with the same ligand.