Temperature-dependent 3D structures of lanthanide coordination polymers based on dicarboxylate mixed ligands

Abstract

Fourteen three-dimensional (3D) lanthanide coordination polymers (CPs) with dicarboxylate mixed ligands, [Ln(fum)_1.5(H₂O)₂]·0.5(H₂bdc)·H₂O (Ln = Sm (1), Tb (2)), [Ln₂(fum)₂(bdc)(H₂O)₄]·2H₂O (Ln = Sm (3), Eu (4), Tb (5), Er (6)), [Ln(fum)_0.5(bdc)] (Ln = Sm (7), Eu (8), Tb (9), Er (10)), and [Ln₂(bdc)₂(ox)(H₂O)₄]·0.7H₂O (Ln = Sm (11), Gd (12), Tb (13), Dy (14)), have been synthesized hydrothermally from the self-assembly of lanthanide(III) ions (Ln³⁺), fumaric acid (H₂fum), and terephthalic acid (H₂bdc) in the presence of potassium hydroxide at different temperatures. The compounds fall into four classes. Compounds 1 and 2 were isolated from hydrothermal reactions performed at a relatively low temperature of 100 °C and found to crystallize in the triclinic space group P. The 3D framework is assembled from 2D layers of [Ln(fum)(H₂O)₂] units pillared by the chelating fum ligands and has 1D rhombic channels templated by H₂bdc and lattice H₂O molecules. The framework presents a binodal (4,5)-connected tcs topology with the point symbol (4⁴·6²)(4⁴·6⁶). Raising the reaction temperature to 140 °C resulted in the formation of compounds 3–6. These materials crystallize in the monoclinic system with the polar space group P2₁ and feature a 3D network constructed from dinuclear {Ln₂(OCO)₆(H₂O)₄} units interlinked by fum and bdc ligands, showing a uninodal 6-connected two-fold interpenetrated pcu topology. The small channels of the framework are occupied by lattice H₂O molecules. Further increase of the reaction temperature to 160 °C gave rise to the formation of compounds 7–10, crystallizing in the orthorhombic space group Pbca. The 3D framework is generated from 2D corrugated sheets of [Ln(fum)]²⁺ bound by bdc ligands and contains no intercalated H₂O molecules in the lattice. The framework possesses a trinodal (4,6,7)-connected net with the point symbol (4²·6⁴)₂(4⁶·6⁸·8)(4¹²·6⁹)₂. Finally, compounds 11–14 contained an in situ generated oxalate (ox) ligand formed under hydrothermal conditions conducted at a high reaction temperature of 180 °C. These compounds crystallize in the monoclinic space group P2₁/c and possess a 3D open framework consisting of a dinuclear [Ln₂(ox)(H₂O)₄]²⁺ unit linked by bridging bdc ligands and has small void channels occupied by lattice H₂O molecules. The frameworks were topologically simplified as a binodal (4,5)-connected tcj/hc net with a total point symbol of (4²·5²·7²)(4²·5³·7⁵). In the solid state at room temperature, the Tb (2, 5, 9, and 13) and Eu (4 and 8) compounds emit green and red light, respectively.