Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
J Biol Inorg Chem. 2013 Aug;18(6):609-22. doi: 10.1007/s00775-013-1005-5. Epub 2013 May 23.
Mössbauer studies of [{μ-S(CH2C(CH3)2CH2S}(μ-CO)Fe(II)Fe(I)(PMe3)2(CO)3]PF6 (1 OX ), a model complex for the oxidized state of the [FeFe] hydrogenases, and the parent Fe(I)Fe(I) derivative are reported. The paramagnetic 1 OX is part of a series featuring a dimethylpropanedithiolate bridge, introducing steric hindrance with profound impact on the electronic structure of the diiron complex. Well-resolved spectra of 1 OX allow determination of the magnetic hyperfine couplings for the low-spin distal Fe(I) ([Formula: see text]) site, A x,y,z = [-24 (6), -12 (2), 20 (2)] MHz, and the detection of significant internal fields (approximately 2.3 T) at the low-spin ferrous site, confirmed by density functional theory (DFT) calculations. Mössbauer spectra of 1 OX show nonequivalent sites and no evidence of delocalization up to 200 K. Insight from the experimental hyperfine tensors of the Fe(I) site is used in correlation with DFT to reveal the spatial distribution of metal orbitals. The Fe-Fe bond in [Fe2{μ-S(CH2C(CH3)2CH2S}(PMe3)2(CO)4] (1) involving two [Formula: see text]-type orbitals is crucial in keeping the structure intact in the presence of strain. On oxidation, the distal iron site is not restricted by the Fe-Fe bond, and thus the more stable isomer results from inversion of the square pyramid, rotating the [Formula: see text] orbital of [Formula: see text]. DFT calculations imply that the Mössbauer properties can be traced to this [Formula: see text] orbital. The structure of the magnetic hyperfine coupling tensor, A, of the low-spin Fe(I) in 1 OX is discussed in the context of the known A tensors for the oxidized states of the [FeFe] hydrogenases.
[{μ-S(CH2C(CH3)2CH2S}(μ-CO)Fe(II)Fe(I)(PMe3)2(CO)3]PF6 (1 OX )，一种模拟 [FeFe] 氢化酶氧化态的模型配合物，以及其母体 Fe(I)Fe(I) 衍生物的穆斯堡尔研究报告。顺磁 1 OX 是一系列具有二甲基丙二硫醇桥的配合物的一部分，该桥引入了空间位阻，对二铁配合物的电子结构产生了深远的影响。1 OX 的高分辨率谱图允许确定低自旋远端 Fe(I) ([Formula: see text]) 位点的磁超精细耦合，A x,y,z = [-24 (6), -12 (2), 20 (2)] MHz，并且在低自旋亚铁位点检测到显著的内场（约 2.3 T），这通过密度泛函理论（DFT）计算得到证实。1 OX 的穆斯堡尔谱图显示出不等价的位点，并且在 200 K 以下没有离域的证据。从 Fe(I) 位点的实验超精细张量中获得的见解与 DFT 相关联，以揭示金属轨道的空间分布。在应变存在的情况下，涉及两个 [Formula: see text]-type 轨道的 [Fe2{μ-S(CH2C(CH3)2CH2S}(PMe3)2(CO)4] (1) 中的 Fe-Fe 键对于保持结构完整至关重要。在氧化过程中，远端铁位点不受 Fe-Fe 键的限制，因此更稳定的异构体是由于四方锥的反转，旋转 [Formula: see text] 轨道。DFT 计算表明，穆斯堡尔性质可以追溯到这个 [Formula: see text] 轨道。在已知的 [FeFe] 氢化酶氧化态的 A 张量的背景下，讨论了 1 OX 中低自旋 Fe(I) 的磁超精细耦合张量 A 的结构。
