Beyond the active-electron approximation: Origin of ferromagnetic exchange in donor-acceptor heterospin biradicals
Beyond the active-electron approximation: Origin of ferromagnetic exchange in donor-acceptor heterospin biradicals
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DOI：
10.1016/j.poly.2005.08.010
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发表时间：
2005-11-17
期刊：
影响因子：
2.6
通讯作者：
Depperman, EC
中科院分区：
文献类型：
--
作者：
Kirk, ML;Shultz, DA;Depperman, EC
该络合物(NNSQ)CuTp(CUM，Me)由三个不同的自旋携带单元组成。这三个S=1/2位点由铜(II)、硝基氮氧化物(NN)和5-叔丁基半喹酮(SQ)组成。由于铁磁相互作用，Cu(II)-SQ和SQ-NN成对相互作用都是强交换耦合的，导致S-T=3/2基态。低温EPR谱证实了由磁化率研究确定的S-T=3/2基态，并指出该四重态是由类似于0.5 cm(-1)的垂直条D垂直条分裂而成的零场。我们用电子吸收光谱和低温磁性圆二色谱相结合的方法，探讨了NNSQ异位旋双自由基配位体中强铁磁交换的起源。强排列内和NNSQ铁磁交换的起源被认为是具有明显的Sq pi->；NN pi*电荷转移特征的排列内电荷转移(ILCT)转变的结果。铁磁交换的大小与ILCT转变的能量、NN单位交换积分的大小以及连接SQ SOMO和NN LUMO的电子耦合矩阵元的大小有关。(C)2005爱思唯尔有限公司。保留所有权利。
The complex, (NNSQ)CuTp(Cum,Me), is comprised of three different spin carrying units. These three S = 1/2 sites are comprised of Cu(II), nitronyl nitroxide (NN), and 5-tert-butyl-semiquinone (SQ). Both the Cu(II)-SQ and SQ-NN pairwise interactions are strongly exchange coupled resulting an S-T = 3/2 ground state due to ferromagnetic interactions. Low-temperature EPR spectroscopy confirms the S-T = 3/2 ground state determined from magnetic susceptibility studies and indicates that the quartet is zero-field split by vertical bar D vertical bar similar to 0.5 cm(-1). We have probed the origin of the strong ferromagnetic exchange within the NNSQ heterospin biradical ligand by a combination of electronic absorption, and low-temperature magnetic circular dichroism spectroscopies. The origin of the strong intraligand NNSQ ferromagnetic exchange has been suggested to result from an intraligand charge transfer (ILCT) transition transition that possesses appreciable SQ pi -> NN pi* charge transfer character. The magnitude of the ferromagnetic exchange has been related to the energy of this ILCT transition, the magnitude of the NN single site exchange integral, and the magnitude of the electronic coupling matrix element that connects the SQ SOMO with the NN LUMO. (c) 2005 Elsevier Ltd. All rights reserved.