Zavoisky Kazan Physical-Technical Institute, Russian Academy of Science, Sibirsky Tract 10/7, 420029 Kazan, Russia.
J Phys Chem B. 2013 Jun 27;117(25):7833-42. doi: 10.1021/jp403682p. Epub 2013 Jun 17.
The unusual magnetic behavior of the first dendritic Fe(3+) complex with general formula Fe(L)2Cl(-)·H2O based on a branched Schiff base has been investigated by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. EPR displays that complex consists of the three types of magnetically active iron centers: one S = 1/2 low-spin (LS) and two S = 5/2 high-spin (HS) centers with strong low-symmetry and weak distorted octahedral crystal fields. Analysis of the magnetic behavior reflected by I versus T (where I is the EPR lines integrated intensity of the spectrum) demonstrates that the dendritic Fe(3+) complex has sufficiently different behavior in three temperature intervals. The first (4.2-50 K) interval corresponds to the antiferromagnetic exchange interactions between LS-LS, LS-HS, and HS-HS centers. The appearance of a presumable magnetoelectric effect is registered in the second (50-200 K) temperature interval, whereas a spin transition process between LS and HS centers occurs in the third (200-330 K) one. The coexistence of the magnetic ordering, presumable magnetoelectric effect, and spin crossover in one and the same material has been detected for the first time. The Mössbauer spectroscopy data completely confirm the EPR results.
具有支化希夫碱的首个枝状 Fe(3+)配合物 Fe(L)2Cl(-)·H2O 的异常磁行为已通过电子顺磁共振 (EPR) 和穆斯堡尔光谱进行了研究。EPR 显示，该配合物由三种类型的磁性铁中心组成：一个 S = 1/2 低自旋 (LS) 和两个 S = 5/2 高自旋 (HS) 中心，具有强低对称性和弱扭曲八面体晶体场。对 I 与 T 之间的磁行为的分析（其中 I 是光谱的 EPR 线积分强度）表明，枝状 Fe(3+)配合物在三个温度区间具有足够不同的行为。第一个（4.2-50 K）区间对应于 LS-LS、LS-HS 和 HS-HS 中心之间的反铁磁交换相互作用。在第二个（50-200 K）温度区间中记录到了可能的磁电效应的出现，而在第三个（200-330 K）温度区间中则发生了 LS 和 HS 中心之间的自旋转变过程。首次在同一种材料中检测到磁有序、可能的磁电效应和自旋交叉的共存。穆斯堡尔光谱数据完全证实了 EPR 结果。
