Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
J Am Chem Soc. 2011 Oct 12;133(40):15806-9. doi: 10.1021/ja203845x. Epub 2011 Sep 15.
Two mononuclear high-spin Fe(II) complexes with trigonal planar ([Fe(II)(N(TMS)(2))(2)(PCy(3))] (1) and distorted tetrahedral ([Fe(II)(N(TMS)(2))(2)(depe)] (2) geometries are reported (TMS = SiMe(3), Cy = cyclohexyl, depe = 1,2-bis(diethylphosphino)ethane). The magnetic properties of 1 and 2 reveal the profound effect of out-of-state spin-orbit coupling (SOC) on slow magnetic relaxation. Complex 1 exhibits slow relaxation of the magnetization under an applied optimal dc field of 600 Oe due to the presence of low-lying electronic excited states that mix with the ground electronic state. This mixing re-introduces orbital angular momentum into the electronic ground state via SOC, and 1 thus behaves as a field-induced single-molecule magnet. In complex 2, the lowest-energy excited states have higher energy due to the ligand field of the distorted tetrahedral geometry. This higher energy gap minimizes out-of-state SOC mixing and zero-field splitting, thus precluding slow relaxation of the magnetization for 2.
报道了两个单核高自旋 Fe(II) 配合物，具有三角平面 ([Fe(II)(N(TMS)(2))(2)(PCy(3))] (1) 和变形四面体 ([Fe(II)(N(TMS)(2))(2)(depe)] (2) 几何构型（TMS = SiMe(3)，Cy = 环己基，depe = 1,2-双(二乙基膦基)乙烷)。1 和 2 的磁性性质揭示了外态自旋轨道耦合 (SOC) 对缓慢磁弛豫的深远影响。由于存在与基态电子激发态混合的低能电子激发态，配合物 1 在施加的最佳直流磁场 600 Oe 下表现出缓慢的磁化弛豫。这种混合通过 SOC 将轨道角动量重新引入到电子基态中，因此 1 表现为场诱导的单分子磁体。在配合物 2 中，由于变形四面体几何形状的配体场，最低能量激发态具有更高的能量。这个更高的能隙最小化了外态 SOC 混合和零场分裂，从而阻止了 2 的磁化缓慢弛豫。
