Synthesis and Magnetism of Neutral, Linear Metallocene Complexes of Terbium(II) and Dysprosium(II).

The divalent metallocene complexes Ln(Cp) (Ln = Tb, Dy) were synthesized through the KC reduction of Ln(Cp)I intermediates and represent the first examples of neutral, linear metallocenes for these elements. X-ray diffraction analysis, density functional theory calculations, and magnetic susceptibility measurements indicate a 4f5d electron configuration with strong s/d mixing that supports the linear coordination geometry. A comparison of the magnetic relaxation behavior of the two divalent metallocenes relative to salts of their trivalent counterparts, [Ln(Cp)][B(CF)], reveals that lanthanide reduction has opposing effects for dysprosium and terbium, with magnetic relaxation times increasing from Tb to Tb and decreasing from Dy to Dy. The impact of this effect is most notably evident for Tb(Cp), which displays an effective thermal barrier to magnetic relaxation of 1205 cm and a 100-s blocking temperature of 52 K, the highest values yet observed for any nondysprosium single-molecule magnet.