Supramolecular heptanuclear Ln–Cu complexes involving nitronyl nitroxide biradicals: structure and magnetic behavior

Abstract

Four novel heptanuclear Ln–Cu complexes with the formula [Ln₂Cu(hfac)₈(NITPhTzbis)₂][LnCu(hfac)₅(NITPhTzbis)]₂ (LnCu = YCu 1, TbCu 2, DyCu 3 and HoCu 4; hfac = hexafluoroacetylacetonate) were successfully constructed by employing the triazole functionalized nitronyl nitroxide biradical ligand NITPh-Tzbis (NITPh-Tzbis = 5-(1,2,4-triazolyl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene). These hetero-tri-spin complexes are composed of two biradical-bridged dinuclear [(LnCu(hfac)₅(NITPhTzbis)] units and one trinuclear [Ln₂Cu(hfac)₈(NITPhTzbis)₂] unit which form a heptanuclear supramolecular structure through π–π interactions. Magnetic susceptibility investigations indicate that ferromagnetic exchange interactions dominate at low temperature for this supramolecular system which can be attributed to the Ln–nitroxide exchange and intramolecular NIT⋯NIT coupling mediated by the m-phenylene moiety. The DyCu derivative was found to exhibit a slow magnetic relaxation behavior.