Lanthanide-based metal–peptide frameworks prepared by ionothermal method: Anion direct effect, DFT calculation and luminescence property

• Four new lanthanide-based MPFs were obtained by ionothermal method.
• DFT calculation reveals that bromine ions play an important role in their structure.
• Luminescence analysis shows that 3 and 4 behave good fluorescence properties.

A series of new isomorphic lanthanide-based metal–peptide frameworks, [Ln(PODC)(H2O)2]Br (Ln = La(1), Nd(2), Eu(3), Tb(4), H2PODC = 2, 5-piperazinedione-1, 4-diacetic acid), were synthesized under the ionic liquid medium. Crystal structure measure results exhibit that they are new three-dimensional frameworks, where bromine anions of ionic liquid are enveloped in the pore. Interestingly, it is found that bromine anions can effectively counteract the effects of lanthanide ions (e.g. lanthanide contraction). Via the first-principles DFT calculation, it is obtained that bromine anions of ion liquid influence the electronic properties of PODC2 − ligand and thereby directly control the structure. Luminescence analysis demonstrates that compounds 3 and 4 have good fluorescence properties, where the emission peaks can be ascribed to the transitions of 5D0 → 7FJ (J = 0, 1, 2, 3, 4) for 3 and 5D4 → 7FJ (J = 6, 5, 4, 3) for 4.

Four lanthanide-based metal–peptide frameworks under ionothermal condition exhibit new three-dimensional framework and further reveal that anion of ion liquid plays an important role in structure by DFT calculation.Figure optionsDownload as PowerPoint slide