Anomalous difference in magnetic behavior between highly saddled iron(III) porphyrin complexes in the solid state
Anomalous difference in magnetic behavior between highly saddled iron(III) porphyrin complexes in the solid state
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DOI：
10.1002/ejic.200300566
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发表时间：
2004-02-20
影响因子：
2.3
通讯作者：
Nakamura, M
中科院分区：
文献类型：
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作者：
Ohgo, Y;Ikeue, T;Nakamura, M
本文用穆斯堡尔谱、SQUID磁强计和X射线晶体学方法研究了[Fe（OMTPP）L-2]（+）（L = DMAP或Py）微晶样品的自旋态。[Fe（OMTPP）（DMAP）（2）]（+）和[Fe（OMTPP）Py-2]（+）的穆斯堡尔谱表明，这两种配合物在77-300 K温度范围内均保持低自旋（S = 1/2）态。这些配合物的自旋态进一步证实了SQUID磁。因此，[Fe（OMTPP）Py-2]（+）的磁性行为与结构相关物种[Fe（OETPP）Py-2]（+）的磁性行为完全不同。后者表现出一种新的自旋交叉之间的S = 3/2和S = 1/2状态所揭示的光谱和磁性测量。为了理解[Fe（OMTPP）Py-2]（+）中没有自旋交叉过程的原因，我们比较了[Fe（OMTPP）Py-2]（+）和最近报道的[Fe（OETPP）Py-2]（+）的晶体和分子结构.在[Fe（OMTPP）Py-2]（+）的情况下，Fe-N-轴向键长几乎不随温度变化，在298和80 K时分别为2.058（6）和2.024（4）埃。这些结果与自旋交叉配合物[Fe（OETPP）Py-2]（+）的结果形成鲜明对比，在该配合物中，Fe-N轴键从298 K的2.201（3）埃收缩到80 K的1.993（3）埃。我们将[Fe（OMTPP）Py-2]（+）和[Fe（OETPP）Py-2]（+）的磁行为差异归因于分子堆积的差异;前者采用密集堆积的立方晶系，而后者显示出较少凝聚的单斜晶系。空腔计算进一步证实了上述假设。[Fe（OETPP）Py-2]（+）中吡啶配体周围的空穴尺寸在298 K时分别为32.08和28.88埃（3），而[Fe（OMTPP）Py-2]（+）中的空穴尺寸仅为19.81埃（3）。当温度从298 K降低到80 K时，[Fe（OETPP）Py-2]+的空穴收缩率为17.7%，而[Fe（OMTPP）Py-2]（+）的空穴收缩率仅为5.3%。在此基础上，我们得出结论：轴向配体周围的松散堆积的晶体系统和宽腔是固态自旋交叉过程发生的重要条件。(C)Wiley-VCH Verlag GmbH & Co. KGaA，69451魏因海姆，德国，2004.
The spin states of microcrystalline samples of [Fe(OMTPP)L-2](+) (L = DMAP or Py) have been examined and interpreted using Mossbauer spectroscopy, SQUID magnetometry and X-ray crystallography. The Mossbauer spectra of [Fe(OMTPP)(DMAP)(2)](+) and [Fe(OMTPP)Py-2](+) showed that both of these complexes maintain the low-spin (S = 1/2) state over the 77-300 K temperature range. The spin states of these complexes were further confirmed by SQUID magnetometry. Thus, the magnetic behavior of [Fe(OMTPP)Py-2](+) is quite different from that of the structurally related species [Fe(OETPP)Py-2](+). The latter complex exhibits a novel spin crossover between the S = 3/2 and S = 1/2 states as revealed by the spectroscopic and magnetic measurements. In order to understand the reasons for the absence of the spin crossover process in [Fe(OMTPP)Py-2](+), we have compared the crystal and molecular structures of [Fe(OMTPP)Py-2](+) with those of the recently reported species [Fe(OETPP)Py-2](+). In the case of [Fe(OMTPP)Py-2](+), the Fe-N-axial bond lengths hardly change with temperature and are 2.058(6) and 2.024(4) Angstrom at 298 and 80 K, respectively. These results are in sharp contrast to those of the spin crossover complex [Fe(OETPP)Py-2](+), in which the Fe-N-axial bonds contract from 2.201(3) Angstrom at 298 K to 1.993(3) Angstrom at 80 K. We have ascribed the difference in magnetic behavior between [Fe(OMTPP)Py-2](+) and [Fe(OETPP)Py-2](+) to the difference in molecular packing; the former adopts a densely packed cubic crystal system while the latter shows a less condensed monoclinic system. A cavity calculation has further confirmed the above mentioned assumption. While the cavity sizes around the pyridine ligands in [Fe(OETPP)Py-2](+) are 32.08 and 28.88 Angstrom(3) at 298 K, that in [Fe(OMTPP)Py-2](+) is only 19.81 Angstrom(3). Furthermore, the cavities contract by 17.7% in [Fe(OETPP)Py-2]+ when the temperature is lowered from 298 to 80 K whereas the contraction is only 5.3% in the case of [Fe(OMTPP)Py-2](+). On the basis of these results, we have concluded that the loosely packed crystal system and the wide cavities around the axial ligands are the important requirements for the occurrence of the spin crossover process in the solid state. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.