Langley Stuart K, Wielechowski Daniel P, Chilton Nicholas F, Moubaraki Boujemaa, Murray Keith S
School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
School of Science and the Environment, Chemistry Division, Manchester Metropolitan University , Manchester M15 6HB, England.
Inorg Chem. 2015 Nov 2;54(21):10497-503. doi: 10.1021/acs.inorgchem.5b01999. Epub 2015 Oct 21.
We report the synthesis of several heterometallic 3d-4f complexes which result from the replacement of the Dy(III) ions in the [Cr(III)2Dy(III)2(OMe)2(mdea)2(O2CPh)4(NO3)2] single-molecule magnet (SMM) by the trivalent Pr, Nd, Gd, Tb, Ho, and Er lanthanide ions. The parent {Cr2Dy(III)2} compound displayed an anisotropy barrier to magnetization reversal of 53 cm(-1), with magnetic hysteresis observed up to 3.5 K and with large coercive fields at low temperatures (2.7 T at 1.8 K). Magnetic studies for the new complexes revealed significantly different static and dynamic magnetic behavior in comparison to the parent {Cr(III)2Dy(III)2} complex. When Ln(III) = Pr, a complete loss of SMM behavior is found, but when Ln(III) = Nd or Er, frequency-dependent tails in the out-of-phase susceptibility at low temperatures are observed, indicative of slow magnetic relaxation, but with very small anisotropy barriers and fast relaxation times. When Ln(III) = Tb and Ho, SMM behavior is clearly revealed with anisotropy barriers of 44 and 36 cm(-1), respectively. Magnetic hysteresis is also observed up to 2.5 and 1.8 K (0.003 T/s) for the Tb and Ho complexes, respectively. A large loss of the magnetization is, however, observed at zero-field, and as a result, the large coercivity which is present in the {Cr2Dy2} example is lost. The {Cr2Tb2} and {Cr2Ho2} complexes are rare examples of Tb- and Ho-based SMMs which reveal both slow relaxation in the absence of a static dc field (ac susceptibility) and open hysteresis loops above 1.8 K.
我们报道了几种异金属3d - 4f配合物的合成，这些配合物是通过用三价镨、钕、钆、铽、钬和铒镧系离子取代[Cr(III)2Dy(III)2(OMe)2(mdea)2(O2CPh)4(NO3)2]单分子磁体（SMM）中的Dy(III)离子而得到的。母体{Cr2Dy(III)2}化合物表现出53 cm⁻¹的磁化反转各向异性势垒，在高达3.5 K时观察到磁滞现象，并且在低温下具有大的矫顽场（1.8 K时为2.7 T）。对新配合物的磁性研究表明，与母体{Cr(III)2Dy(III)2}配合物相比，其静态和动态磁性行为有显著差异。当Ln(III) = Pr时，发现SMM行为完全丧失，但当Ln(III) = Nd或Er时，在低温下观察到异相磁化率中的频率依赖性尾部，表明存在缓慢的磁弛豫，但各向异性势垒非常小且弛豫时间很快。当Ln(III) = Tb和Ho时，分别以44和36 cm⁻¹的各向异性势垒清楚地显示出SMM行为。对于Tb和Ho配合物，分别在高达2.5 K和1.8 K（0.003 T/s）时也观察到磁滞现象。然而，在零场下观察到大量的磁化损失，结果，{Cr2Dy2}示例中存在的大矫顽力丧失。{Cr2Tb2}和{Cr2Ho2}配合物是基于Tb和Ho的SMM的罕见示例，它们在没有静态直流场（交流磁化率）的情况下显示出缓慢弛豫，并且在高于1.8 K时显示出开放的磁滞回线。
