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

The divalent metallocene complexes Ln-(Cp-iPr5)(2) (Ln = Tb, Dy) were synthesized through the KC8 reduction of Ln(Cp-iPr5)(2)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 4f(n)5d(1) 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-iPr5)(2)] [B(C6F5)(4)] reveals that lanthanide reduction has opposing effects for dysprosium and terbium, with magnetic relaxation times increasing from Tb-III to Tb-II and decreasing from Dy-III to Dy-II. The impact of this effect is most notably evident for Tb(Cp-iPr5)(2), which displays an effective thermal barrier to magnetic relaxation of 1205 cm(-1) and a 100-s blocking temperature of 52 K, the highest values yet observed for any nondysprosium single-molecule magnet.