Magnetic relaxation in unique nitronyl nitroxide biradical-Ln–Cu chains with Ln-bis(NIT)–Cu-bis(NIT)–Ln units

Abstract

Utilizing a nitronyl nitroxide biradical NITPhPybis [5-(4-pyridyl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)-benzene], a new family of isomorphic 2p–3d–4f chains {[LnCu(hfac)₅(NITPhPybis)]·CHCl₃}_n (hfac: hexafluoroacetylacetonate; Ln^III: Gd 1; Dy 2; Ho 3; Tb 4) have been successfully produced. In complexes 1–4, the NITPhPybis biradical chelates one Ln^III ion through its bis(NIT) moiety while the N donor of pyridine and another uncoordinated NO group of the biradical, respectively, bind one Cu^II ion, yielding a biradical-Ln–Cu 1D zigzag chain with a unique [Ln-bis(NIT)–Cu-bis(NIT)–Ln] structural motif. DC magnetic studies reveal that ferromagnetic exchanges dominate in these Cu–Ln-biradical chains, originating from the ferromagnetic Ln–NO and NO_axial–Cu exchanges. Non-zero χ′′ signals were observed for Dy/Tb–Cu derivatives implying slow magnetic relaxation behavior. The obtained effective energy barrier is U_eff = 18.0 K and τ₀ = 2.0 × 10⁻⁸ s for the DyCu derivative.