Sieber Andreas, Boskovic Colette, Bircher Roland, Waldmann Oliver, Ochsenbein Stefan T, Chaboussant Grégory, Güdel Hans U, Kirchner Nadeschda, van Slageren Joris, Wernsdorfer Wolfgang, Neels Antonia, Stoeckli-Evans Helen, Janssen Stefan, Juranyi Fanni, Mutka Hannu
Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
Inorg Chem. 2005 Jun 13;44(12):4315-25. doi: 10.1021/ic050134j.
A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1.
已合成并研究了一个新的四核镍配合物家族[Ni(4)(ROH)(4)L(4)]（H(2)L = 水杨醛-2-乙醇胺；R = 甲基（1）或乙基（2））。配合物1和2具有一个由扭曲的立方烷排列组成的[Ni(4)O(4)]核心。磁化率和非弹性中子散射研究表明，四个Ni(II)中心之间存在铁磁和反铁磁成对交换相互作用的组合，导致基态自旋S = 4。磁化测量显示，两种配合物均具有易轴型磁各向异性，D约为-0.93 cm(-)(1)。尽管磁各向异性较大，但在低至40 mK的温度下未观察到磁化强度的缓慢弛豫。为了确定低温磁行为的起源，使用非弹性中子散射和频域磁共振光谱对配合物1的磁各向异性进行了详细探测。光谱研究证实了易轴型各向异性，并表明存在强横向相互作用。这些导致了磁化强度的快速量子隧穿，解释了配合物1意外不存在缓慢磁化弛豫的现象。
