Spin-State Patterns in Surface-Grafted Beads of Iron(II) Complexes
Spin-State Patterns in Surface-Grafted Beads of Iron(II) Complexes
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DOI：
10.1002/anie.200905062
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Grohmann, Andreas
中科院分区：
文献类型：
--
作者：
Alam, Mohammad S.;Stocker, Michael;Grohmann, Andreas
随着光刻工艺的缩小（自上而下的方法）很快就会遇到小型化的基本物理极限，对功能材料设计的新策略的需求日益增加分子电子学的一个引人入胜的观点[2,3]是基于分子开关阵列的单分子水平的信息存储自旋交叉（SCO）化合物在这方面具有相当大的潜力。[5,6] SCO可以发生在八面体过渡金属配合物中，其中金属离子具有4到7个电子构型。[7,8]这种转变可能受到外界的刺激，如温度或压力的变化或照射。[7,8] SCO是熵驱动的，在固体状态下，受分子间相互作用（如氢键或π -π堆叠）的强烈影响。这种相互作用产生了SCO配合物之间的协同作用。高协同性可以导致自旋状态的变化伴随着滞后，这赋予系统双稳定性，从而产生记忆效应。[5,7]一个可行的读/写程序，即在单分子水平上可重复驱动的手段，是一个尚未满足的艰巨挑战，但通过这种方式，SCO化合物可以用于具有无与伦比的存储密度的设备。原则上，只要SCO系综内配合物的低自旋态和高自旋态之间的能量差足够大（约为几kT），即使没有迟滞，也可以实现可靠的信息存储。已知有大量的自旋交叉体系，其中含铁（II）配合物的[7]在溶液和固态中都是最多的。通常，亚铁处于准八面体N6配位环境，在低自旋状态（LS, 1A1g/t2g 6， S= 0）和高自旋状态（HS, 5T2g/t2g 4eg 2， S= 2）之间发生切换。
Novel strategies for the design of functional materials are in increasing demand, as the down-scaling of lithographic processes (the top-down approach) will soon encounter the fundamental physical limits of miniaturization.[1] One of the fascinating perspectives of molecular electronics [2, 3] is information storage at the single-molecule level, on the basis of arrays of molecular switches.[4] Spin-crossover (SCO) compounds hold considerable potential in this context.[5, 6] SCO can occur in octahedral transition-metal complexes in which the metal ion has ad 4 to d7 electron configuration.[7, 8] The transition may be stimulated externally, by a change in temperature or pressure, or by irradiation.[7, 8] SCO is entropydriven and, in the solid state, is influenced strongly by intermolecular interactions, such as hydrogen bonding or π–π stacking. Such interactions give rise to cooperativity between SCO complexes within the ensemble. High cooperativity can cause the change in spin state to be accompanied by hysteresis, which confers bistability on the system and thus a memory effect.[5, 7] A viable reading/writing procedure, that is, a means of reproducible actuation on the single-molecule level, is a formidable challenge that has yet to be met, but in this way SCO compounds could serve in devices of unsurpassable storage density. In principle, reliable information storage could be achieved even in the absence of hysteresis, provided the energy difference between low-spin state and high-spin state of the complexes within the SCO ensemble is sufficiently large (on the order of several kT). A large number of spin-crossover systems are known,[7] with complexes of iron (II) the most numerous, both in solution and in the solid state. Usually, ferrous iron is in a quasi-octahedral N6 coordination environment, and switching occurs between a low-spin (LS, 1A1g/t2g 6, S= 0) and a high-spin state (HS, 5T2g/t2g 4eg 2, S= 2).