Syntheses, Structures, and Photoluminescent Properties of Lanthanide Coordination Polymers Based on a Zwitterionic Aromatic Polycarboxylate Ligand

Abstract

Three series of lanthanide coordination polymers, {[Ln(L)(H2O)2]·NO3·2H2O }n (Ln = La 1, Pr 2), {[Ln2(L)2(NO3)(H2O)2]·Cl·6H2O}n (Ln = Nd 3), {[Ln(L)(H2O)2]·Cl·3H2O}n (Ln = Sm 4, Eu 5, Gd 6, Tb 7, Dy 8, Ho 9, Er 10, Tm 11, Yb 12, and Lu 13) (H3L = 4-carboxy-1-(3,5-dicarboxy-benzyl)-pyridinium chloride), have been successfully synthesized under hydro(solvo)thermally conditions. Single-crystal X-ray diffraction analyses revealed that compounds 1–3 all crystallize in triclinic space group P1̅, but they display different three-dimensional structures with diverse dinuclear subunits. In contrast, compounds 4–13 display the same layer structures in the triclinic space group P1̅. The structural difference of these two classes of compounds is derived from the effect of lanthanide contraction. Powder X-ray diffraction (PXRD) and thermogravimetric analyses of compounds 1–13 have also been investigated and discussed in detail. The solid-state luminescent properties of compounds 4, 5, 7, and 8 were characterized, and the results revealed that they exhibit characteristic Sm(III), Eu(III), Tb(III), and Dy(III) emissions in the pink, red, green, and yellow light regions, respectively. More interestingly, the luminescence colors of the Tb(1–x)(L):xEu can easily be tuned from green to green-yellow, yellow, orange, and red-orange due to the energy transfer from Tb3+ to Eu3+ ions by adjusting the doping concentration of Eu3+ ions.