Study on the construction of photoresponsive single-molecule magnets in frozen solutions

对于单金属单分子磁体（SMMs）的构建，我们提出使用由2p有机自旋和3d金属离子组成的异自旋体系。在我们的异旋体系中，吡啶配体分别携带单、二、三苯（S=2/2,4/ 2,6 /2）和高自旋Co（II）离子CoCl_2和Co(p-tolsal)_2，分别作为有机自旋的2p和金属离子的3d。重氮吡啶配体和Co（II）离子在溶液中以适当的比例混合。为了避免分子间的磁相互作用，采用冷冻溶液条件作为SQUID测量的样品。对六个配合物样品进行了辐照前后的交直流磁化率测定。在6个样品辐照后的交流磁化率测量中，观察到与辐照频率相关的钴配合物的相内和相外分量（分别为χ’和χ”），表明钴配合物具有缓慢的磁弛豫。6种配合物翻转自旋的激活势垒U_<eff>值估计在40 ~ 93 K之间。在1.9 K的直流磁场依赖性下，6种配合物的磁滞环相对较大，矫顽力H_c=7 ~ 10 kOe。将得到的U_<eff>、τ_0和H_c的值与相关配合物的值进行汇总。在这项工作中，我们成功地在冷冻溶液中制备了单金属单分子磁体。此外，通过系统地改变配合物的S值，得出自旋翻转的激活势垒U_<eff>和共振量子隧道效应引起的弛豫时间分别随着配合物S值的增加而增加和减少的结论。

For the construction of monometallic single-molecule magnets (SMMs), We proposed to use the heterospin systems consisting of the 2p organic spins and the 3d metal ions. In our heterospin systems, pyridine ligands carrying mono-, di-, and tricarbene (S=2/2,4/2, and 6/2, respectively) and high-spin Co(II) ions, CoCl_2 and Co(p-tolsal)_2, were employed as the 2p organic spins and the 3d metal ions, respectively. Various combinations of two components, diazo-pyridine ligands and Co(II) ions, in solutions were mixed in appropriate ratios. To avoid the intermolecular magnetic interaction, the frozen solution conditions were used as the samples for SQUID measurements. The ac and dc magnetic susceptibility measurements for six samples of the complexes were carried out before and after irradiation. In ac magnetic susceptibility measurements after irradiation of six samples, the in-phase and out-of phase components (χ' and χ", respectively) with the applying frequency dependence were observed, indicating that the cobalt complexes have slow magnetic relaxations. The values of the activation barriers, U_<eff>, for flipping the spin were estimated to be 40- 93 K for the six complexes. In the dc field dependence of magnetization at 1.9 K, relatively large hysteresis loops with coercive force, H_c=7-10 kOe for the six complexes were observed. Obtained values of U_<eff>, τ_0, and H_c, for all six complexes were summarized together with those for the related complexes. In this work, we successfully prepared the monometallic single-molecule magnets in frozen solution. Furthermore, by changing the S values of the complexes systematically, it was concluded that the activation barrier, U_<eff>, for flipping the spin and the relaxation time due to the resonant quantum tunneling effect increased and decreased, respectively, with increasing S value of the complex.