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; LnIII: Gd 1; Dy 2; Ho 3; Tb 4) have been successfully produced. In complexes 1-4, the NITPhPybis biradical chelates one LnIII ion through its bis(NIT) moiety while the N donor of pyridine and another uncoordinated NO group of the biradical, respectively, bind one CuII 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 NOaxial-Cu exchanges. Non-zero χ'' signals were observed for Dy/Tb-Cu derivatives implying slow magnetic relaxation behavior. The obtained effective energy barrier is Ueff = 18.0 K and τ0 = 2.0 × 10-8 s for the DyCu derivative.