Use of magnetic spectroscopies to unveil an unexpected Dy-anionic radical coordination compound

Abstract

We report the synthesis, the magnetic, electronic and spatial characterization of the novel compound [Dy(HDPA)2(H2DPA)]·1.5 H2O (H2DPA = dipicolinic acid), 1. The reaction yields ca. 76 % of a nonacoordinated formally Dy3+ compound possessing a rare tricapped trigonal prismatic geometry whose spectroscopic analyses by X-ray crystallography, 1H NMR, UV–Vis, and ESR are presented herein. The bond distances and angles coincide with most Dy3+ reports. DFT description of 1 suggests a non-innocent Dy3+ coordinated to a radical anion ligand, and other 2 non radical ligands and CASSCF/CASPT2 description support this description. Specifically, ESR confirms the presence of such a free radical system. At low temperatures (T ≈ 2 K), the ESR spectrum shows a similar free radical signal with a g value of 2.006, suggesting the delocalization of the electron in the π system. Moreover, the comparison of results with the equivalent Dy3+ with no free radical interaction is also included as a Dy3+ counterpart, [Dy3+(HDPA)3] 2.