Single-molecule magnet behavior in a CuII-decorated {Dy2III} complex with nitronyl nitroxide biradicals

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 [Ln(2)Cu(2)(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 (3)-(1):(2) 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.