Single-molecule magnet behavior in a CuII-decorated {Dy III2} complex with nitronyl nitroxide biradicals

Abstract

Herein, based on a novel nitronyl nitroxide biradical ligand NITPhPyoebis (1) (5-(4-pyridinone)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene), four 3d–4f heterometallic polynuclear compounds, namely [Ln₂Cu₂(hfac)₁₀(NITPhOPybis)₂] (Ln^III = Gd 2, Tb 3, Dy 4 and Ho 5; hfac = hexafluoroacetylacetonate; NITPhOPybis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene) were synthesized successfully. In these 3d–4f compounds, two NITPhOPybis biradical ligands acted as bridge ligands with the μ₃-η¹:η² coordination mode to bind two Ln^III ions and two Cu^II ions, generating octa-spin 2p–3d–4f systems. Strong antiferromagnetic coupling was observed between the Cu^II ion and the coordinated NO group while there is weak antiferromagnetic interaction between the two Gd^III ions bridged by double oxygen atoms. The frequency-dependent out-of-phase signals associated with the slow relaxation of magnetization confirm the single-molecule magnet behavior of the Dy complex.