Control of oxo-molybdenum reduction and ionization potentials by dithiolate donors
Control of oxo-molybdenum reduction and ionization potentials by dithiolate donors
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DOI：
10.1021/ic9912878
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发表时间：
2000-05-29
影响因子：
4.6
通讯作者：
Kirk, ML
中科院分区：
文献类型：
--
作者：
Helton, ME;Gruhn, NE;Kirk, ML
化合物（L-N-3）MoO（qdt）和（L-N-3）MoO(tdt) [(L-N-3) =（3,5-二甲基-1-吡唑基）硼酸盐；TDT =甲苯-3,4-二硫醚；通过循环伏安法、光电子、磁圆二色性和电子吸收光谱对QDT =喹诺啉-2,3-二硫酸盐进行了研究，并在各种二硫酸盐配体的从头算分子轨道计算的背景下对实验数据进行了解释。PES数据显示（L-N-3）MoO（qdt）和（L-N-3）MoO（tdt）之间存在很大差异，（L-N-3）MoO（qdt）的第一电离（源自Mo d（xy）轨道）比（L-N-3）MoO（tdt）的结合能高0.8 eV左右。这种稳定作用也体现在溶液还原电位上，其中（L-N-3）MoO（qdt）与220 mV相近，比（L-N-3）MoO（tdt）更容易还原。观察到给定二硫代酸配体的相对给体能力与（L-N-3）MoO（二硫代酸）配合物的还原电位之间存在直接的相关关系，二硫代酸离子S原子上计算的Mulliken电荷与Mo还原电位之间存在线性关系。该研究证实了先前的沟通工作（Helton, m.e.; Kirk, m.l. Inorg）。Chern. 1999, 38, 4384-4385)的研究表明，各向异性共价的贡献仅涉及二硫酯的面外S轨道，通过调节金属的有效核电负荷来控制Mo还原电位，这与理解铁氰化物抑制亚硫酸盐氧化酶的机制直接相关。此外，这些结果表明，部分氧化的吡蝶呤可能在某些吡蝶呤钨酶中起促进电子和/或原子转移的作用，这些酶在相当低的电位下催化正式的氧原子转移反应。
The compounds (L-N-3)MoO(qdt) and (L-N-3)MoO(tdt) [(L-N-3) = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; tdt = toluene-3,4-dithiolate; qdt = quinoxaline-2,3-dithiolate] have been studied by cyclic voltammetry and photoelectron, magnetic circular dichroism, and electronic absorption spectroscopies, and the experimental data have been interpreted in the context of ab initio molecular orbital calculations on a variety of dithiolate dianion ligands. The PES data reveal very substantial differences between (L-N-3)MoO(qdt) and (L-N-3)MoO(tdt) in that the first ionization (originating from the Mo d(xy) orbital) for (L-N-3)MoO(qdt) is about 0.8 eV to deeper binding energy than that of (L-N-3)MoO(tdt). This stabilizing effect is also reflected in the solution reduction potentials, where (L-N-3)MoO(qdt) is similar to 220 mV easier to reduce than (L-N-3)MoO(tdt). A direct correlation between the relative donating ability of a given dithiolate ligand and the reduction potential of the (L-N-3)MoO(dithiolate) complex has been observed, and a linear relationship exists between the calculated Mulliken charge on the S atoms of the dithiolate dianion and the Mo reduction potential. The study confirms previously communicated work (Helton, M. E.; Kirk, M. L. Inorg. Chern. 1999, 38, 4384-4385) that suggests that anisotropic covalency contributions involving only the out-of-plane S orbitals of the coordinated dithiolate control the Mo reduction potential by modulating the effective nuclear charge of the metal, and this has direct relevance to understanding the mechanism of ferricyanide inhibition in sulfite oxidase. Furthermore, these results indicate that partially oxidized pyranopterins may play a role in facilitating electron and/or atom transfer in certain pyranopterin tungsten enzymes which catalyze formal oxygen atom transfer reactions at considerably lower potentials.