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

The synthesis of fluoride-bridged tri-{[{(Cp'Dy-2}{mu-F)](3).tol, 1Dy, Cp' = C5H4Si(CH3)(3); tol = toluene), tetra([{Cp'Dy-2(mu-F)(2)}(2){(Cp')(THF)Dy(mu-F))(2)].hex, 2Dy, THF = tetrahydrofuran; hex = n-hexane), and heptanuclear (3Dy) dysprosium complexes is reported here and a hydroxy-bridged dinuclear dysprosium complex [Cp'Dy-2(mu-OH)](2)(4Dy) is synthesized for comparison. The nucleation number of the fluoridebridged 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'Dy-2) 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.