Solvent- and metal-directed lanthanide-organic frameworks based on pamoic acid: observation of slow magnetization relaxation, magnetocaloric effect and luminescent sensing

Abstract

Two types of lanthanide coordination polymers, namely, [Ln(PA)(NO3)(DMA)3] n (Ln=Gd (1), Dy (2), Eu (3), Tb (4)) (type I), and {[Ln2(PA)3(DMF)4]·2DMF} (Ln=Eu (5), Tb (6)) (type II) (PA=Pamoic acid, DMA=dimethylacetamide, DMF=N,N-dimethylformamide), have been synthesized by the reaction of Ln(NO3)3·6H2O with pamoic acid through layer diffusion method. These complexes were characterized by single crystal X-ray diffraction, infrared spectroscopy (IR), thermogravimetric analysis (TGA), fluorescence and magnetic measurements. Solvents and lanthanide atoms in the reaction play an important role in controlling different structures. Type I demonstrated 1-D linear chain structure connected by Ln atoms and PA ligands. Type II exhibited non-interpenetrating 3-D 6-connected 43612 nets based on binuclear [Ln2(CO2)6(DMF)4] cores. Magnetic properties of complexes 1–4 were investigated in details. Complex 1 shows significant magnetocaloric effect with–ΔSm=20.37 J kg–1 K–1 at 3.0 K and 7 T. Complex 2 exhibits slow relaxation of the magnetization. Complexes 3–6 exhibit both ligand- and metal-centered fluorescent properties. Complex 6 demonstrates fluorescent sensing of DMF and Cu2+ ion.