However, a structurally very comparable Dy(II) metallocene complex has been reported by Gould et al in 2019. The complex [Dy(Cp iPr5 )2] showed a similar formation of a perfectly straight geometry compared to the bent Dy(III) precursor. We have investigated the Tdependent susceptibility of 4-Dy upon cooling the sample in an external field of 1000 Oe. The obtained room temperature χT value was 10.95 cm 3 K mol -1 , which is surprisingly low compared to the theoretical values of either 14.07 cm 3 K mol -1 (Dy II , assuming 4f 10 5d 0 ) or 17.01 / 14.51 cm 3 K mol -1 (Dy II , assuming 4f 9 5d 1 and applying an L-S or j-j coupling scheme). Performing AC susceptibility measurements of 4-Dy without the application of an external field did not give any signal in the out-of-phase component. Only under the application of an external field a frequency-dependent maximum could be observed. Under the optimal field of 900 Oe, a signal was reliably detectable in the temperature range of 2 K -6 K, during which it shifts from approximately 200 Hz to 1500 Hz (Fig. ). Due to the application of the external field QTM is suppressed, vide supra, and the temperature dependent relaxation times were fitted with Orbach and Raman relaxation using equation (2) (Fig. ). The obtained best fit parameters the usual approach of designing high performance SMMs is no longer applicable. It should be noted that in the mixed valence compound [(Cp iPr5 )2Dy2I3] an additional electron facilitates the exchange between two Dy ions leading to huge magnetic hysteresis even at relatively high temperatures. However, the electron in this case is not located at the Dy and the magnetism is not arising from a Dy(II) species. The previously mentioned complex [Dy(Cp iPr5 )2] was reported with an energy barrier Ueff of 37.4 cm -1 , 42 very comparable to our observation for 4-Dy.