4f-Block Metal Complexes as Secondary Building Units in Preparing 4d–4f Coordination Polymers: Preparation, Structures, and Luminescent Properties of [Ln2L6(H2O)4]·{[Ln2L4(H2O)6](NO3)2} and {[AgLnL2(H2O)3](NO3)2(H2O)4} (L = 3-Pyridinepropinoate, Ln = Eu, Tb, Nd)

Abstract

Three new 4d–4f metal–organic coordination polymers were prepared by using 4f-block metal complexes as secondary building units. Discrete 4f complexes, [Ln2L6(H2O)4]·{[Ln2L4(H2O)8](NO3)2} {Ln = Eu (1), Tb (2), Nd (3)}, were prepared by microwave-heating a mixture of Ln(NO3)3·nH2O, 3-pyridinepropionic acid (HL), and NaOH in water for 1 min. Compounds 1–3 were subsequently treated with AgNO3 to form three-dimensional Ag–Ln coordination polymers, [AgLnL2(H2O)3](NO3)2(H2O)4 {Ln = Eu (4), Tb (5), Nd (6)}. Compounds 1–3 are isostructural and consist of two dimers: a neural dimer and an ionic dimer. In these compounds, the pyridyl N atoms of ligands do not coordinate to the Ln3+ ions. In isostructural coordination polymers 4–6, the pyridyl N atoms are bonded to soft Ag+ ions, and carboxylate oxygen atoms are bonded to hard Ln3+ ions. Compounds 1 and 4 exhibit practically the same red luminescence in the solid state, and compounds 2 and 5 exhibit the green luminescence, but compounds 3 and 6 do not exhibit photoluminescence in the visible region.