Water-stable LnIII-based coordination polymers displaying slow magnetic relaxation and luminescence sensing properties

Six new two-dimensional isostructural lanthanide coordination polymers (Ln(III)-CPs), [Ln(2)(L)(3)(H2O)(3)]center dot DMF (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5) and Ho (6), H2L = 3-(3,5-dicarboxylphenoxy)pyridine), have been fabricated successfully under solvothermal conditions. In these compounds, Ln(III) ions are linked by the mixed (mu-O-carboxylate)(COO)(2) triple bridges to give dinuclear motifs. The motifs are connected through single carboxylate bridges to give alternating chains, and the chains are interlinked by the L ligands to produce 2D layers. Their structures with accessible Lewis-base sites and coordinated water molecules could easily recognize various analytes. The dc magnetic susceptibility studies for Gd-CP (3) and Ho-CP (6) reveal the occurrence of probable antiferromagnetic interactions, but for Dy-CP (5) show ferromagnetic interactions. Further investigations suggest that Dy-CP (5) displays slow magnetic relaxation behavior with an energy barrier (Delta U-eff) and a pre-exponential factor (tau(0)) of 25.47 K and 1.25 x 10(-6) s at 1200 Oe dc field, respectively. The luminescence explorations suggest that Eu-CP (2) and Tb-CP (4) can exhibit high quenching efficiency and low detection limit for sensing Fe3+, MnO4-, Cr-VI-anions (CrO42-, Cr2O72-) and 2,4,6-trinitrophenol (TNP) in water systems. Moreover, in the process of detecting analytes, Eu-CP (2) and Tb-CP (4) not only exhibit excellent water stability and strong luminescence, but also show remarkable recyclability and regeneration. Especially, Eu/Tb-CP can detect Fe3+, MnO4-, CrO42- and Cr2O72- simultaneously, which is rarely reported in the past.