VFe3S4 single and double cubane clusters: synthesis, structures, and dependence of redox potentials and electron distribution on ligation and heterometal.
VFe3S4 single and double cubane clusters: synthesis, structures, and dependence of redox potentials and electron distribution on ligation and heterometal.
复制标题
DOI：
10.1021/ic702372f
复制
发表时间：
2008-04
影响因子：
4.6
通讯作者：
T. Scott;R. H. Holm
中科院分区：
文献类型：
--
作者：
T. Scott;R. H. Holm
钒和钼辅因子簇都存在于固氮酶中。在仿生研究中，由于M = Mo与酶中钼配位单元的良好结构关系，M = V合成的杂金属MFe 3S 4立方烷型簇比M = Mo合成的少得多。本工作通过膦原子簇[（Tp）VFe 3S 4（PEt 3）3]1+和[（Tp）2 V2 Fe 6S 8（PEt 3）4]的配体取代，制备了一系列以[VFe 3（mu 3-S）4]2+和[V2 Fe 6（mu 3-S）6（mu 4-S）2]2+为核的单立方烷和边桥双立方烷原子簇.单立方烷[（Tp）VFe 3S 4L 3]2-和双立方烷[（Tp）2 V2 Fe 6S 8L 4]4-（L= F-，N3-，CN-，PhS-）分别具有三角对称性和中心对称性。单立方烷形成三元电子转移系列[（Tp）VFe_3S_4L_3]3-，2-，1-。已确定的氧化还原电位和电子分布在集群核心感测的57 Fe异构体位移（δ）的配体依赖性。将这些结果与先前针对类似钼簇确定的那些结果（Pesavento、Berlinguette和霍尔姆Inorg. Chem.2007，46，510）进行比较，允许检测杂金属M对性质的影响。在常数M和变量L，氧化还原电位是最低的π-供体配体和最大的氰化物，并与减少亚铁字符的集群与恒定电荷z = 2-。在L和z不变和M可变的情况下，EV > E（Mo）和Δ（av）V <Δ（av）Mo，表明M = Mo簇更容易被氧化，并表明较低的电位（更容易氧化）和亚铁特征之间的定性关系。
Both vanadium and molybdenum cofactor clusters are found in nitrogenase. In biomimetic research, many fewer heterometal MFe3S4 cubane-type clusters have been synthesized with M = V than with M = Mo because of the well-established structural relationship of the latter to the molybdenum coordination unit in the enzyme. In this work, a series of single cubane and edge-bridged double cubane clusters containing the cores [VFe3(mu3-S)4]2+ and [V2Fe6(mu3-S)6(mu4-S)2]2+ have been prepared by ligand substitution of the phosphine clusters [(Tp)VFe3S4(PEt3)3]1+ and [(Tp)2V2Fe6S8(PEt3)4]. The single cubanes [(Tp)VFe3S4L3]2- and double cubanes [(Tp)2V2Fe6S8L4]4- (L= F-, N3-, CN-, PhS-) are shown by X-ray structures to have trigonal symmetry and centrosymmetry, respectively. Single cubanes form the three-member electron transfer series [(Tp)VFe3S4L3]3-,2-,1-. The ligand dependence of redox potentials and electron distribution in cluster cores as sensed by 57Fe isomer shifts (delta) have been determined. Comparison of these results with those previously determined for the analogous molybdenum clusters (Pesavento, Berlinguette, and Holm Inorg. Chem. 2007, 46, 510) allows detection of the influence of heterometal M on the properties. At constant M and variable L, redox potentials are lowest for pi-donor ligands and largest for cyanide and relate approximately with decreasing ferrous character in clusters with constant charge z = 2-. At constant L and z and variable M, EV > E(Mo) and delta(av)V < delta(av)Mo, demonstrating that M = Mo clusters are more readily oxidized and suggesting a qualitative relation between lower potentials (greater ease of oxidation) and ferrous character.