Synthesis and structures of fluoride-bridged dysprosium clusters: influence of fluoride ions on magnetic relaxation behaviors

Abstract

The synthesis of fluoride-bridged tri-([{Cp′₂Dy}{μ-F}]₃·tol, 1Dy, Cp′ = C₅H₄Si(CH₃)₃; tol = toluene), tetra-([{Cp′₂Dy(μ-F)₂}₂{(Cp′)(THF)Dy(μ-F)}₂]·hex, 2Dy, THF = tetrahydrofuran; hex = n-hexane), and hepta-nuclear (3Dy) dysprosium complexes is reported here and a hydroxy-bridged dinuclear dysprosium complex [Cp′₂Dy(μ-OH)]₂(4Dy) is synthesized for comparison. The nucleation number of the fluoride-bridged complexes highly depends on the reaction solvents and the molar ratio of the dysprosium and fluoride precursors. The three Dy ions in 1Dy are arranged in a triangular fashion and the tetranuclear 2Dy displays a butterfly shape geometry. 3Dy shows a much more complicated structure with three types of fluoride bridges. 1Dy and 2Dy exhibit slow relaxation of magnetization with the energy barriers of 95 K and 98 K, respectively, while the dinuclear and heptanuclear dysprosium complexes barely show any behaviors of molecular nanomagnets. Ab initio calculations demonstrated that the thermo-assisted relaxation of magnetization of 1Dy and 2Dy originated from the {Cp′₂Dy} fragment. Analysis of magneto-structural correlation revealed that the fluoride ions had a great influence on the orientation of the easy axis of magnetization and the exchange interactions.