Abstract: Nitroxyl radicals functionalized with aryl heterocycles (Rad5-6) (see picture) are promising in design of molecular magnets due to directly linked N—O group bearing spin density and predictable coordination mode. This is critical to obtain magnetically anisotropic Ln3+ complexes with prescribed geometry and ligand field strength. This is crucial to suppress magnetization tunnelling in SMMs. The recently obtained complexes [Ln(Rad5-6)(NO3)3] (1) possess strong magnetic exchange coupling in a {Ln←O—N} fragment [1], which also contributes to the suppression of the tunnelling effect. The latter is the higher than the lower a polyhedron symmetry, which is typical for coordination-capacious lanthanides. Therefore, rational design of paramagnetic ligands for the complexes with a geometry suitable for either prolate or oblate type of Ln3+-ions is a challenging task. In the sandwich-like complexes [Ln(Rad5-6)2(OTf)3] (2) [2], the equatorial anions are well suited for oblate Ln3+-ions, while their absence fits better prolate ones. Magnetic behaviour of 2 can be tuned: tripod should be more sterically demanding and symmetrical. It is possible by varying tripod’s organization: combination of 5-membered cycle of oxazolidine-N-oxide with 2-imidazoline-1-methyl as Ar (5-5 arrangement) or 6-membered cycle of oxazinane-N-oxide with 2-pyridyls (6-6 arrangement). The methyl addition to Ar should lead to the formation of 6-coordinate complexes.

Cite: Vostrikova K.E.
Design of the lanthanide(III) complexes with tripodal nitroxyl radicals
9th Asian Conference on Coordination Chemistry 19-22 Feb 2024