NIR emission and luminescent sensing of a lanthanide-organic framework with Lewis basic imidazole and pyridyl sites

A series of lanthanide-organic frameworks [Ln(Himdc)(ina)(H₂O)]_n (Ln = Eu 1a; Sm 1b; and Nd 1c, H₃imdc = imidazole-4,5-dicarboxylic acid, Hina = isonicotinic acid) were synthesized under hydrothermal conditions. All compounds 1a-1c consist of a 3D microporous lanthanide carboxylate ([Eu(COO)₃]_n) framework and uncoordinated Lewis basic pyridyl and imidazole groups hung in the channels. The luminescence investigations show that the compound 1c displays an interesting NIR luminescence property. The compound 1a exhibits a good potential as a luminescent multi-responsive sensing material for Fe³⁺ ions and Cr₂O₇^2- anions.