Diversity of crystal structure with different lanthanide ions involving in situ oxidation–hydrolysis reaction

A series of lanthanide and lanthanide-transition metal compounds with isonicotinic acid (Hina) and oxalate ligands have been synthesized under hydrothermal reactions. X-Ray crystal structure analyses reveal that they have a rich structural chemistry. Three distinct structure types were exhibited with decreasing lanthanide radii: [LnCu(ina)₂(C₂O₄)]·H₂O (Ln = La 1, Pr 2, Nd 3) for type I, [Ln(ina)(C₂O₄)(H₂O)₂] (Ln = Sm 4, Eu 5, Gd 6) for type II, and [Ln(ina)(C₂O₄)_0.5(OH)] (Ln = Tb 7, Dy 8, Er 9) for type III. The structure of type I has a 3d–4f heterometallic structure and consists of 1D channels along the b axis, which filled with guest water molecules. They exhibit a first 3D uninodal eight-connected framework with a unique 3⁶·4¹⁸·5³·6 topology. Type II has 2D Ln–ina–C₂O₄ 4⁴-nets, the nitrogen donors of the ina ligand are not coordinated to any of the metal ions, inducing the lower dimensional networks. Type III consists of 2D Ln–C₂O₄ layers pillared by ina ligands to form a pillared-layer framework. The structure evolution is due to the versatile coordination modes of ina and oxalate ligands as well as the lanthanide contraction effect. Notably, the oxalate ligand was in situ synthesized from orotic acid through an oxidation–hydrolysis reaction. The type III materials show high thermal stability; luminescence properties of Nd 3, Sm 4, Eu 5, Tb 7 are also investigated.