A New Class of Lanthanide Complexes with Three Ligand Centered Radicals: NMR Evaluation of Ligand Field Energy Splitting and Magnetic Coupling. Issue 45 (3rd July 2019)

• Record Type: Journal Article
• Authors: Hiller, Markus; Sittel, Thomas; Wadepohl, Hubert; Enders, Markus
• Is Part Of: Chemistry. Volume 25:Issue 45(2019)
• Page Start: 10668
• Page End: 10677
• Publication Date: 2019-07-03
• Subjects: ligand-field parameter -- magnetic anisotropy -- molecular magnetism -- paramagnetic NMR spectroscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201901388
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Combination of three radical anionic Ph‐BIAN ligands (Ph‐BIAN=bis‐(phenylimino)‐acenaphthenequinone) with lanthanoid ions leads to a series of homoleptic, six‐coordinate complexes of the type Ln(Ph‐BIAN)3 . Magnetic coupling data were measured by paramagnetic solution NMR spectroscopy. Combining 1 H NMR with 2 H NMR of partially deuterated compounds allowed a detailed study of the magnetic susceptibility anisotropies over a large temperature range. The observed chemical shifts were separated into ligand‐ and metal‐centered contributions by comparison with the Y analogue (diamagnetic at the metal). The metal‐centered contributions of the complexes with the paramagnetic ions could then be separated into pseudocontact and Fermi contact shifts. The latter is large within the Ph‐BIAN scaffold, which shows that magnetic coupling is significant between the lanthanide ion and the radical ligand. Pseudocontact shifts were further correlated to structural data obtained from X‐ray diffraction experiments. Ligand‐field parameters were determined by fitting the temperature dependence of the observed magnetic susceptibility anisotropies. The electronic structure determined by this approach shows, that the Er and Tm analogues are candidates for single molecule magnets (SMM). These results demonstrate the possibilities for the application of NMR spectroscopy in investigations of paramagnetic systems in general and single molecule magnets in particular. Abstract : 3π+nf‐electrons+ligand field : Magnetic anisotropy and J‐coupling was measured by NMR spectroscopy in a new series of homoleptic lanthanide complexes. Temperature dependent quadrupolar NMR splitting (RQC) and subsequent mathematical analysis describe the ligand field as equatorial with energy splitting of the mJ manifold up to 1000 cm −1 .