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

Six three-dimensional nanoporous lanthanide coordination polymers, [Ln(2)(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 (H(2)bpdc) in DMF solution. Crystallographic data show that compounds 1-6 are isomorphous and crystallize in monoclinic, space group C-2. Each Ln(III) is eight-coordinated to seven O atoms from six bpdc(2-) 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 bpdc(2-) 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 x 27.05 angstrom rhombic channels along the b axis and 8.66 x 15.91 angstrom 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 bpdc(2-) ligand to the LnIII 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.