Mossbauer Spectroscopic Studies of Spin-Crossover Iron Complexes

制备了一系列具有中等配位场强度的不同配体的铁(II，III)配合物，用于研究温度或压力引起的自旋-交叉转变。根据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-邻菲咯啉(Phen)的混配对中心铁离子的影响。研究表明，[Fe(Bpy)(Phen)(NCS)2]中的混合配位使自旋交叉转变变得更加平缓。自旋-交叉转变温度受中心铁离子配位配体的电子性质和结构的影响。用穆斯堡尔谱、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，(高自旋态)氯化铁(III)的中心铁(III)离子被自动还原为亚铁低自旋态。热处理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淬灭到液氮温度，产生了新的混合价状态。更高压力下的穆斯堡尔谱实验正在进行中，以阐明压力增加引起的自旋-交叉跃迁的机制。

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.