Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
Inorg Chem. 2010 Feb 15;49(4):1647-50. doi: 10.1021/ic902050k.
Two all-ferrous, edge-bridged 8Fe-8S clusters, one capped with carbenes (2) and the other with phosphenes (3), have been characterized by (57)Fe Mossbauer spectroscopy. The clusters have diamagnetic ground states that yield spectra consisting of one quadrupole doublet with a large splitting (25% of absorption) and one (3) or two (2) doublets with much smaller splittings (75% of absorption). These patterns closely resemble those observed for all-ferrous 4Fe-4S clusters. Structurally, the 4Fe-4S fragments of 2 and 3 are remarkably similar to all-ferrous 4Fe-4S clusters, sharing with them the characteristic 3:1 pattern of the iron sites, a differentiation that has been shown previously to reflect spontaneous distortions of the cluster core. These spectroscopic and geometric similarities suggest that the diamagnetic ground state of the 8Fe-8S cluster results from antiferromagnetic exchange coupling of two identical 4Fe-4S modules, each carrying spin S(4Fe) = 4. The iron atoms with the largest quadrupole splittings are located at the opposite ends of the body diagonal containing the bridging sulfides.
两段全铁、边缘桥连的 8Fe-8S 簇，一个被碳化物（2）封端，另一个被膦（3）封端，已通过 (57)Fe Mossbauer 光谱进行了表征。这些簇具有抗磁性基态，产生的光谱由一个具有较大分裂（吸收的 25%）的四极子双峰和一个（3）或两个（2）具有较小分裂（吸收的 75%）的双峰组成。这些模式与观察到的所有亚铁 4Fe-4S 簇非常相似。在结构上，2 和 3 的 4Fe-4S 片段与所有亚铁 4Fe-4S 簇非常相似，它们具有铁位的特征 3:1 模式，这种差异以前已经表明反映了簇核的自发变形。这些光谱和几何相似性表明，8Fe-8S 簇的抗磁性基态是由两个相同的 4Fe-4S 模块的反铁磁交换耦合产生的，每个模块都带有自旋 S(4Fe) = 4。具有最大四极分裂的铁原子位于包含桥接硫原子的体对角线的相对两端。
