A facile route for tuning emission and magnetic properties by controlling lanthanide ions in coordination polymers incorporating mixed aromatic carboxylate ligands

Abstract

A series of lanthanide coordination polymers, [Ln (Btca) (Pimda)·2H2O]n (Ln = Nd(1), Sm(2), Eu(3), Gd(4), Tb(5), Dy(6)), (HBtca = 1H-benzo[d][1, 2, 3]triazole-5-carboxylic acid and H3Pimda = 2-propyl-1H-imidazole-4,5-dicarboxylic acid) have been obtained through moderate temperature hydrothermal syntheses. Single crystal X-ray analyses reveal the family of polymers exhibit same 1D chains composed by binuclear units, and further being extended into 2D layer connected by H3Pimda. The 2D layers are further interlinked by strong intermolecular hydrogen bonds interactions, resulting in the 3D supramolecular architectures. The solid state of 4 shows ligand based fluorescence, while 1, 2, 3, 5 and 6 exhibit strong/moderate photoluminescence emissions in the NIR/visible regions based on characteristic Ln3+ emission selected. Importantly, by in situ doping different concentrations of Eu3+ and Tb3+ cations, series of Eu3+/Tb3+ binary polymers were fabricated, showing a tunable emission color from green, yellow, orange to red. Moreover, the magnetic studies reveal the presence of very weak ferromagnetic Gd···Gd coupling within the binuclear units of 4. The depopulation of Stark components at low temperature and possible weak anti-ferromagnetic interactions were observed within polymers 2 and 5. Remarkably, ac magnetic susceptibility study reveals the Dy3+ polymer is a candidate for elucidation of slow relaxation of the magnetization in lanthanide carboxylate system.