Slow magnetic relaxation in CoII–LnIII heterodinuclear complexes achieved through a functionalized nitronyl nitroxide biradical

A new nitronyl nitroxide biradical ligand NITPh-PyPzbis (5-(3-(2-pyridinyl)-1H-pyrazol-1-yl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene) has been successfully applied for constructing a 3d–4f CoII–LnIII system, giving rise to a family of novel hetero-tri-spin complexes, namely, [LnCo(hfac)5(NITPh-PyPzbis)]·CH2Cl2 (LnCo = YCo 1, GdCo 2, TbCo 3, DyCo 4, and HoCo 5; hfac = hexafluoroacetylacetonate). In these hetero-tri-spin complexes, the NITPh-PyPzbis biradical chelates one LnIII and one CoII simultaneously by means of its adjacent aminoxyl moieties and two N donors from the 3-(2-pyridinyl)-1H-pyrazol-1-yl unit, respectively, realizing the unique biradical-Co–Ln heterodinuclear structure. Direct-current magnetic susceptibility investigations show that antiferromagnetic coupling is predominant in the YCo derivative, while the leading magnetic interaction in the GdCo analogue is ferromagnetic. Alternating-current data for the DyCo complex display visible temperature/frequency-dependent χ′′ peaks, indicating the SMM behavior. In the fluorescence spectra, four characteristic emission bands of the TbIII ion have been detected for the TbCo analogue.