Controlling dimensionality via a dual ligand strategy in Ln-thiophene-2,5-dicarboxylic acid-terpyridine coordination polymers

Abstract

Eleven new lanthanide (Ln = Nd-Lu)-thiophene-2,5-dicarboxylic acid (25-TDC)-2,2′:6′,2′′-terpyridine (terpy) coordination polymers (1–11) which employ a dual ligand strategy have been synthesized hydrothermally and structurally characterized by single crystal and powder X-ray diffraction. Two additional members of the series (12 and 13) were made with Ce³⁺ and Pr³⁺ and characterized via powder X-ray diffraction only. The series is comprised of three similar structures wherein differences due to the lanthanide contraction manifest in Ln³⁺ coordination number as well as the number of bound and solvent water molecules within the crystal lattice. Structure type I (Ce³⁺–Sm³⁺) contains two nine-coordinate Ln³⁺ metal centers each with a bound water molecule. Structure type II (Eu³⁺–Ho³⁺) features a nine and an eight coordinate Ln³⁺ metal along with one bound and one solvent water molecule. Structure type III (Er³⁺–Lu³⁺) includes two eight-coordinate Ln³⁺ metal centers with both water molecules residing in the lattice. Assembly into supramolecular 3D networks via π–π interactions is observed for all three structure types, whereas structure types II and III also feature hydrogen-bonding interactions via the well-known C–H⋯O and O–H⋯O synthons. Visible and near-IR luminescence studies were performed on compounds 1, 2, 10, and 13 at room temperature. As a result characteristic near-IR luminescent bands of Pr³⁺, Nd³⁺, Sm³⁺, and Yb³⁺ as well as visible bands of Sm³⁺ were observed.