Isostructural Oxamate Complexes with Visible Luminescence (Eu³⁺) and Field-Induced Single-Molecule Magnet (Nd³⁺)

The search for new metal-organic compounds as candidates for quantum information processing technologies is in the spotlight. Several metal ions and organic linkers have been used to obtain such compounds. Herein, we describe the synthesis, crystal structures, and cryomagnetic properties of two air-stable isostructural neodymium(III) and europium(III) one-dimensional (1D) coordination polymers of formula [Nd(Hmpa)₃(DMSO)₂]_n (1) and [Eu(Hmpa)₃(DMSO)₂]_n (2) [Hmpa=N-(4-methylphenyl)oxamate, and DMSO=dimethylsulfoxide]. These complexes were prepared by reacting n-Bu₄N(Hmpa) proligand [n-Bu₄N⁺=tetra-n-butylammonium] and the correspondent LnCl₃ ⋅ 6H₂O salt (Ln=Nd or Eu) in the open air and mild conditions. The crystal structures of 1 and 2 reveal the Ln³⁺ ion surrounded by two DMSO molecules and three oxamate ligands, one of them connecting to adjacent mononuclear entities through carboxylate bridges featuring a homometallic chain, while the other two establishing double N-H ⋅ ⋅ ⋅ O hydrogen bonds among adjacent polymers to give a resultant supramolecular 2D network. Cryomagnetic measurements in the static (dc) and dynamic current (ac) regimes reveal that 1 behaves as a field-induced single-molecule magnet below 8.8 K. A photoluminescence study shows that Hmpa ligands efficiently sensitize the luminescence of Eu³⁺ complex in the visible region in the solid state at room temperature.