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 () 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 ( and ) were made with Ce(3+) and Pr(3+) 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 Ln(3+) coordination number as well as the number of bound and solvent water molecules within the crystal lattice. Structure type I (Ce(3+)-Sm(3+)) contains two nine-coordinate Ln(3+) metal centers each with a bound water molecule. Structure type II (Eu(3+)-Ho(3+)) features a nine and an eight coordinate Ln(3+) metal along with one bound and one solvent water molecule. Structure type III (Er(3+)-Lu(3+)) includes two eight-coordinate Ln(3+) 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-HO and O-HO synthons. Visible and near-IR luminescence studies were performed on compounds , , , and at room temperature. As a result characteristic near-IR luminescent bands of Pr(3+), Nd(3+), Sm(3+), and Yb(3+) as well as visible bands of Sm(3+) were observed.