Thermally induced two-step, two-site incomplete 6A12T2 crossover in a mononuclear iron(III) phenolate-pyridyl Schiff-base complex: a rare crystallographic observation of the coexistence of pure S=5/2 and 1/2 metal centers in the asymmetric unit.
Thermally induced two-step, two-site incomplete 6A12T2 crossover in a mononuclear iron(III) phenolate-pyridyl Schiff-base complex: a rare crystallographic observation of the coexistence of pure S=5/2 and 1/2 metal centers in the asymmetric unit.
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DOI：
10.1021/ic700397u
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发表时间：
2007-10
影响因子：
4.6
通讯作者：
M. Shongwe;Badria A Al-Rashdi;H. Adams;M. J. Morris;M. Mikuriya;G. Hearne
中科院分区：
文献类型：
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作者：
M. Shongwe;Badria A Al-Rashdi;H. Adams;M. J. Morris;M. Mikuriya;G. Hearne
合成了六配位单核铁配合物[Fe（salpm）2]ClO（4）.0.5EtOH，[Fe（salpm）2]Cl，[（3，5-tBu2）-salpm}2]X（X= ClO 4-或Cl-）和[Fe{（3，5-tBu2）-salpm}2]NO（3）.2H2O [Hsalpm=N-（吡啶-2-基甲基）水杨醛胺（3，5-tBu2）-salpm=N-（吡啶-2-基甲基）-3，5-二叔丁基亚水杨基胺]的合成和分离;通过元素分析、FAB质谱和红外光谱确定了它们的化学特性。这些配合物的室温有效磁矩[（8 chiMT）1/2约5.85-5.90 microB]与高自旋（S=5/2）基态一致。这些复合物由于强烈的λ->dpi* LMCT可见吸收而颜色很深。[Fe（salpm）_2]ClO（4）·0.5EtOH和[Fe{（3，5-tBu_2）-salpm}_2]NO（3）·2H_2O的结构由单晶X射线晶体学提供了有力的证据。两种化合物中的单体络合物阳离子包括两个单负性酚盐-吡啶基三齿席夫碱配体，其与铁（III）配位，以提供具有反式，顺式，顺式-[FeO 2N 4]核心的扭曲八面体几何形状。而[Fe（salpm）2]ClO（4）.0.5EtOH经历热诱导的6A 12 T2交叉，[Fe{（3，5-tBu 2）-salpm}2]NO（3）.2H2O在低至5 K的固态中保持其自旋状态。然而，EPR光谱显示，后者的复杂的溶液中表现出自旋变换，虽然在很小的程度上比前者。[Fe（salpm）2]ClO（4）.0.5EtOH中的自旋交叉导致了在100 K附近以相等比例共存的高自旋和低自旋铁（III）络合物阳离子的前所未有的晶体学观察。在室温下，两个晶体学上不同的铁中心都是高自旋的，然而，一个[Fe（salpm）2]+络合物阳离子在大约200-100 K的温度范围内经历了完全的自旋转变，而另一个在100 - 65 K之间几乎完全转变;[Fe（salpm）2]ClO（4）.0.5EtOH中约10%的络合物阳离子在低至5 K时保持高自旋状态。
The six-coordinate mononuclear iron(III) complexes [Fe(salpm)2]ClO(4).0.5EtOH, [Fe(salpm)2]Cl, [Fe{(3,5-tBu2)-salpm}2]X (X=ClO4- or Cl-), and [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O [Hsalpm=N-(pyridin-2-ylmethyl)salicylideneamine; H(3,5-tBu2)-salpm=N-(pyridin-2-ylmethyl)-3,5-di-tert-butylsalicylideneamine] have been synthesized and isolated in crystalline form; their chemical identities have been ascertained by elemental analyses, FAB mass spectrometry, and infrared spectroscopy. The room-temperature effective magnetic moments [(8chiMT)1/2 approximately 5.85-5.90 microB] of these complexes are consistent with the high-spin (S=5/2) ground state. These complexes are intensely colored on account of the strong ppi-->dpi* LMCT visible absorptions. Definitive evidence for the structures of [Fe(salpm)2]ClO(4).0.5EtOH and [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O has been provided by single-crystal X-ray crystallography. The monomeric complex cations in both compounds comprise two uninegative phenolate-pyridyl tridentate Schiff-base ligands coordinated meridionally to the iron(III) to afford a distorted octahedral geometry with a trans,cis,cis-[FeO2N4] core. Whereas [Fe(salpm)2]ClO(4).0.5EtOH undergoes a thermally induced 6A12T2 crossover, [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O retains its spin state in the solid state down to 5 K. However, EPR spectroscopy reveals that the latter complex does exhibit a spin transformation in solution, albeit to a much lesser extent than does the former. The spin crossover in [Fe(salpm)2]ClO(4).0.5EtOH has resulted in an unprecedented crystallographic observation of the coexistence of high-spin and low-spin iron(III) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct ferric centers are both high spin; however, one [Fe(salpm)2]+ complex cation undergoes a complete spin transition over the temperature range approximately 200-100 K, whereas the other converts very nearly completely between 100 and 65 K; approximately 10% of the complex cations in [Fe(salpm)2]ClO(4).0.5EtOH remain in the high-spin state down to 5 K.