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

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 Ln(3+) 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 Ln(3+) metal centers each with a bound water molecule. Structure type II (Eu3+-Ho3+) features a nine and an eight coordinate Ln(3+) metal along with one bound and one solvent water molecule. Structure type III (Er3+-Lu3+) includes two eight-coordinate Ln(3+) metal centers with both water molecules residing in the lattice. Assembly into supramolecular 3D networks via p-p 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 center dot center dot center dot O and O-H center dot center dot center dot 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.