Electronic configuration assignment and the importance of low-lying excited states in high-spin imidazole-ligated iron(II) porphyrinates
Electronic configuration assignment and the importance of low-lying excited states in high-spin imidazole-ligated iron(II) porphyrinates
复制标题
DOI：
10.1021/ja044077p
复制
发表时间：
2005-04-20
影响因子：
15
通讯作者：
Scheidt, WR
中科院分区：
文献类型：
--
作者：
Hu, CJ;Roth, A;Scheidt, WR
本文报道了六种新的高自旋脱氧肌红蛋白模型(咪唑(四芳基卟啉)铁(II))的合成和表征。在295~4.2K温度范围内，用随温度变化的穆斯堡尔谱对它们进行了深入的研究。所有的配合物都表现出强烈的温度依赖性，其四极分裂与相同或更低重数的低激发态相一致。通过对外加磁场数据的分析，确定了四极分裂的符号。所有的模型化合物，以及之前研究过的脱氧肌球蛋白和脱氧血红蛋白的模型化合物，都有四极分裂的负号。尽管之前没有预测，但这一实验观察导致了所有高自旋咪唑连接的铁(11)的基态电子构型被指定为(d(xz))(2)(d(yz))(1)(d(xy))(1)(d(z)(2))(1)(d(z)(2))(1).这是一个明显不同于其他高自旋铁(II)卟啉的基态电子组态；还讨论了这两类高自旋络合物在结构细节上的差异。解决了以前研究的模型络合物和血红素蛋白之间零场分裂常数符号不同的明显异常；这种差异似乎是由于应用于这些络合物的自旋哈密顿方法中使用的假设没有得到充分满足。确定了其中四个新的五配位物种的结构。这些衍生物的核心构象表现出多样性，但这些化合物和以前研究的化合物揭示了有限数量的构象模式。键长和其他几何参数，如卟啉核大小和铁的离面位移，支持铁(II)的高自旋态分配。
The synthesis and characterization of six new high-spin deoxymyoglobin models (imidazole(tetraarylporphyrinato)iron(II)) are described. These have been intensively studied by temperature-dependent Mossbauer spectroscopy from 295 to 4.2 K. All complexes show a strong temperature dependence for the quadrupole splitting consistent with low-lying excited states of the same or lower multiplicity. An analysis of the data obtained in applied magnetic fields leads to the assignment of the sign of the quadrupole splitting. All model compounds as well as those of deoxymyoglobin and deoxyhemoglobin, previously studied, have a negative sign for the quadrupole splitting. Although not previously predicted, this experimental observation leads to the assignment of the ground-state electronic configuration for all high-spin imidazole-ligated iron(11) porphyrinates as (d(xz))(2)(d(yz))(1)(d(xy))(1)(d(z)(2))(1)(d(z)(2))(1). This is a distinctly different ground-state electronic configuration from other high-spin iron(II) porphyrinates; differences in structural details for the two classes of high-spin complexes are also discussed. The apparent anomaly of differing signs for the zero-field splitting constant between previously studied model complexes and the heme proteins is addressed; the difference appears to result from the fact that the assumptions used in the spin Hamiltonian approach that has been applied to these complexes are not adequately satisfied. Structures of four of the new five-coordinate species have been determined. Core conformations in these derivatives show variation, but these and previously studied compounds reveal a limited number of conformational patterns. The bond lengths and other geometrical parameters such as porphyrin core size and iron out-of-plane displacement support a high-spin state assignment for the iron(II).