Mossbauer Spectroscopic Studies of Spin-Crossover Iron Complexes

制备了一系列具有中等配体场强度的不同配体的铁（II， III）配合物，以研究温度或压力诱导的自旋交叉转变。根据^<57>Fe穆斯堡尔谱和磁矩的温度变化，讨论了2,2′-联吡啶（bpy）和1,10 -菲罗啉（phen）的混合配体配位对中心铁离子的影响。[Fe(bpy)(phen)(NCS)_2]中的混合配位使自旋交叉转变更加缓慢。自旋交叉转变温度受电子性质以及与中心铁离子配位的配体结构的影响。用^<57>Fe穆斯堡尔、核磁共振和x射线光电子能谱研究了金属叶绿素和普鲁士蓝类似物中的自旋交叉现象或自旋平衡。在吡啶及其衍生物的轴向配位作用下，（叶绿素）氯化铁（III）的中心铁（III）离子在高自旋状态下自动还原为亚铁低自旋状态。加热普鲁士蓝的光谱测量表明，通过热翻转氰基配体并将翻转的氰基配体猝灭到液氮温度，可以产生新的混合价态。高压下的姆斯堡尔谱实验正在进行，以阐明压力增加引起的自旋交叉跃迁的机理。

A series of iron (II, III) complexes of various ligands with an intermediate ligand-field strength have been prepared to investigate the spin-crossover transition induced by temperature or pressure. The influence of the mixed ligand coordination of 2, 2'-bipyridine (bpy) and 1, 10-phenanthroline (phen) to a central iron (II) ion is discussed on the basis of the temperature variation of ^<57>Fe Mossbauer spectra and magnetic moments. The mixed coordination in [Fe(bpy)(phen)(NCS)_2] has been demonstrated to make the spincrossover transition more gradual. The spin-crossover transition temperature is affected by the electronic property as well as the stracture of the ligands coordinated to the central iron (II) ion. The spin-crossover phenomenon or the spin-equilibrium in metallochlorophylls and Prussian blue analogs has been also studied by ^<57>Fe Mossbauer, NMR and X-ray photoelectron spectroscopy. The central iron (III) ion of (pheophytinato) iron (III) chloride in the high-spin state is autoreduced to the ferrous low-spin state upon the axial coordination of pyridine and its derivatives. The spectral measurements of heattrated Prussian blue have revealed that a new mixed-valence state is produced by thermally flipping the cyano ligand and quenching the flipped cyano ligand to liquid nitrogen temperature. Mbssbauer spectral experiments under higher pressure are in progress to elucidate the mechanism of the spin-crossover transition induced by increasing pressure.