Electron-Induced Spin Crossover of Single Molecules in a Bilayer on Gold
Electron-Induced Spin Crossover of Single Molecules in a Bilayer on Gold
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DOI：
10.1002/anie.201201203
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Berndt, Richard
中科院分区：
文献类型：
--
作者：
Gopakumar, Thiruvancheril G.;Matino, Francesca;Berndt, Richard
具有可切换磁性的分子是自旋电子学的有前途的构建块。这种系统可以基于自旋交叉（SCO）效应来实现。这种现象在d4-d 7构型的第一行过渡金属络合物中观察到，铁（II）的实例数量最多。根据周围配体的性质和场强，中心铁离子可以以两种不同的电子构型存在，低自旋（LS，S= 0）和高自旋（HS，S= 2）。诸如温度、光或压力的外部刺激可以用于在这些状态之间切换。[1-3]到目前为止，这种自旋态转换已经从块状材料和薄膜中报道。[4-9]或者，过渡金属离子的自旋可以通过配体的配位/解配位来切换。这种配位诱导的自旋态转换（CISSS）已经在室温下的溶液中得到了证实。[10在薄膜中已经证明了类似的效果。[12还报道了构象变化影响表面上分子的磁性。[14用溶液法在高取向热解石墨上制备了SCO分子的超薄层。[16虽然单分子分辨率不可用，但簇之间的光谱差异归因于高自旋和低自旋状态。[16]从铁（II）的复杂的电子传输实验中观察到的近藤效应已被解释的自旋交叉。[18]为了在单个SCO分子的水平上实现自旋状态切换，期望通过分子束外延在单晶表面上生长良好限定的非晶分子层。不幸的是，大多数SCO络合物的热稳定性对于这种方法是低的。然而，最近，已经报道了两种SCO体系[Fe-（phen）2（NCS）2]和[Fe（bpz）2 phen]（1;图1a）的成功真空沉积（phen= 1，10-菲咯啉，bpz=二氢双（吡唑基）硼酸盐）。[19，20]
Molecules with switchable magnetic properties are promising building blocks for spintronics. Such systems can be realized on the basis of the spin crossover (SCO) effect. This phenomenon is observed in first-row transition-metal complexes of d4–d7 configuration, the largest number of examples being available for iron (II). Depending on the nature and field strength of the surrounding ligands, the central iron ion may exist in two different electronic configurations, low spin (LS, S= 0) and high spin (HS, S= 2). External stimuli, such as temperature, light, or pressure, may be used to switch between these states.[1–3] To date, such spin-state switching has been reported from bulk materials and films.[4–9] Alternatively, the spin of a transition-metal ion may be switched by coordination/decoordination of a ligand. This coordinationinduced spin-state switching (CISSS) has been demonstrated at room temperature in solution.[10, 11] Similar effects have been evidenced in thin films.[12, 13] Conformational changes have also been reported to influence magnetic properties of molecules on surfaces.[14, 15] Ultrathin layers of SCO molecules have been prepared from solution on highly oriented pyrolytic graphite.[16, 17] While single-molecule resolution was not available, spectroscopic differences between clusters have been attributed to high-and low-spin states.[16] The observation of a Kondo effect from an iron (II)-containing complex in electron transport experiments has been interpreted in terms of spin crossover.[18]To achieve spin-state switching on the level of single SCO molecules, it is desirable to grow well-defined ultrathin molecular layers on single-crystal surfaces by molecularbeam epitaxy. Unfortunately, the thermal stability of most SCO complexes is low for this approach. Recently, however, successful vacuum deposition of two SCO systems,[Fe-(phen) 2 (NCS) 2] and [Fe (bpz) 2phen](1; Figure 1 a), have been reported (phen= 1, 10-phenanthroline, bpz= dihydrobis (pyrazolyl) borate).[19, 20]