Lanthanide oxalatophosphonates with two types of layered structures: syntheses, structures, luminescence and magnetic properties

Abstract

Two types of lanthanide(III) oxalatophosphonates, namely, [Ln(H₂L)(C₂O₄)]·H₂O [Ln = La (1), Ce (2), Pr (3)] and [Ln₂(H₃L)(C₂O₄)₃(H₂O)₄]·2H₂O [Ln = Eu (4) and Dy (5)] have been hydrothermally obtained by using (4-carboxypiperidyl)-N-methylenephosphonic acid (H₃L) as the phosphonate ligand and oxalate as the second ligand. These five compounds have the same precursor, but they exhibit two different 2D layered structures. Compounds 1–3 are isostructural and exhibit a 2D layered structure in which {Ln(1)O₉}, {Ln(2)O₉} and {CPO₃} polyhedra via corner-sharing and edge-sharing are interconnected into a 1D chain. These chains are further cross-linked by oxalate anions into a 2D layered structure, and the uncoordinated carboxylate groups are oriented toward the interlayer space. Compounds 4 and 5 are isostructural and also show a 2D layered structure. Lanthanide ions are interconnected by oxalate anions forming a 2D layered structure, and the carboxyl groups of H₃L are grafted on the two sides of the layer. The structure variations are attributed to the effect of lanthanide contraction. In addition, the luminescence properties of compounds 4 and 5, and the magnetic properties of compound 5 have been studied.