Lanthanide Sulfate Frameworks: Synthesis, Structure, and Optical Properties

Layered lanthanide sulfate compounds with three different structures have been prepared and characterized. The compounds [C10H10N2][La(SO4)2]·2H2O (I), [C10H10N2][La(SO4)2(H2O)2]2 (IIa), [C10H10N2][Pr(SO4)2(H2O)2]2 (IIb), [C10H10N2][Nd2(SO4)4(H2O)2]2 (IIIa), [C10H10N2][Sm2(SO4)4(H2O)2]2 (IIIb), and [C10H10N2][Eu2(SO4)4(H2O)2]2 (IIIc) have anionic lanthanide sulfate layers separated by protonated bipyridine molecules. The layers are formed by the connectivity between the lanthanide polyhedra and sulfate tetrahedra. The formation of a two-dimensional La−O−La layer (Ia), Pr−O−Pr chains (IIb), and a tetramer cluster (IIIa) is noteworthy. The compounds exhibit honeycomb (I), square (IIa, IIb), and honeycomb (IIIa−IIIc) net arrangements, when the connectivity between the lanthanide ions is considered. Optical studies indicate the observation of characteristic metal-centered emission at room temperature. The Nd compound (IIIa) exhibits a two-photon upconversion behavior.