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 KC 8 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(C 6 F 5 ) 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.