Syntheses, structures, photoluminescence, and magnetic properties of nanoporous 3D lanthanide coordination polymers with 4,4′-biphenyldicarboxylate ligand

Abstract

Six three-dimensional nanoporous lanthanide coordination polymers, [Ln₂(bpdc)₃(HCOOH)₂]_n [Ln = Eu (1), Sm (2), La (3), Ce (4), Gd (5) and Nd (6)], were prepared by the solvothermal reactions of the Ln^III ions with 4,4′-biphenyldicarboxylate (H₂bpdc) in DMF solution. Crystallographic data show that compounds 1–6 are isomorphous and crystallize in monoclinic, space groupC₂. Each Ln^III is eight-coordinated to seven O atoms from six bpdc²⁻ ligands and one O atom from HCOOH molecule in distorted bisdisphenoid coordination geometry. The adjacent Ln^III ions are intraconnected by the carboxylate groups of the bpdc²⁻ ligands to form a 1D inorganic rod-shaped chain [Ln(CO₂)₃]_n. The inorganic chains are interconnected by the biphenyl groups, giving rise to a 3D framework that consists in two types of 1D open channels, with 15.11 × 27.05 Å rhombic channels along the b axis and 8.66 × 15.91 Å quadrate channels along the c axis without interpenetration. Compounds 1 and 6 are strong luminescent materials which exhibit characteristic Eu^III emission bands in the visible region for 1 and Nd^III emission bands in the near IR region for 6 upon excitation at 360 nm. The absence of the ligand emission can be ascribed to the energy transfer from the bpdc²⁻ ligand to the Ln^III ion during photoluminescence. The magnetic properties of compounds 1, 4, 5 and 6 have been investigated through the measurement of their magnetic susceptibilities over the temperature range of 1.8–300 K.