Complexes with FeIII2(μ-O)(μ-OH), FeIII2(μ-O)2, and [FeIII3(μ2-O)3] cores:: Structures, spectroscopy, and core interconversions
Complexes with FeIII2(μ-O)(μ-OH), FeIII2(μ-O)2, and [FeIII3(μ2-O)3] cores:: Structures, spectroscopy, and core interconversions
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DOI：
10.1021/ja983615t
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发表时间：
1999-03-17
影响因子：
15
通讯作者：
Que, L
中科院分区：
文献类型：
--
作者：
Zheng, H;Zang, Y;Que, L
我们已经合成了第一批具有双（μ-氧代）二铁（III）和（μ-氧代）（μ-羟基）二铁（III）核的配合物（1和2，L = TPA（a），5-Et-3-TPA（B），6-Me-3-TPA（c），4，6-Me-6-TPA（d），BQPA（e），BPEEN（f）和BPMEN（g）），并发现它们具有新颖的结构性质。特别地，在这些配合物中存在两个单原子桥将Fe-Fe距离限制为2.7 - 3.0埃，并且将Fe-mu-O-Fe角度限制为小100度dr。由于Fe_2 O_2（H）核所形成的明显的Fe-O-Fe夹角（如1c为92.5（2）度，2f为100.2（2）度），使这些配合物具有与其它（μ-氧代）二铁（III）配合物截然不同的紫外-可见、拉曼和磁性。配合物Ic在470（λ = 560 M-1 cm（-1））和760 nm（λ = 80 M-1 cm（-1））处显示出可见吸收带，而配合物2在约100 nm处显示出可见吸收带。550（大约800 M-1 cm（-1））和约。800 nm（λ =约70 M-1 cm（-1）），与其他（μ-氧代）-二铁（III）配合物相比，所有这些都发生了红移。这些配合物也表现出明显的nu（Fe-O-Fe）振动在约。600和CA。670 cm（-1）分别归属于Fe-O-Fe单元的nu（sym）和nu（asym）。nu（对称）和nu（不对称）带的相对强度受Fe-O-Fe单元的对称性的影响;不对称的核增强了nu（不对称）的强度。配合物2在Ca. 500 cm（-1），由于其对（H2O）-O-18和（H2O）-H-2的敏感性，其被指定为Fe-（OH）-Fe伸缩模式。磁化率研究表明，对于Ic和ca，J = 54 cm（-1）。110 cm（-1）的2（H = JS（1）.S-2），值小于（μ-氧代）二铁（III）配合物中发现的反铁磁相互作用。这种弱化是由于Fe 2 O2（H）金刚石核结构中较长的Fe-mu-O键和较小的Fe-mu-O-Fe角引起的。因此，这些光谱特征可以作为有用的工具，以确定金属酶活性位点的核心结构的存在。这两种核心结构Fe-2（mu-O）（2）（1）和Fe-2（mu-O）（mu-OH）（2）也可以通过质子化平衡相互转化，在CH 3CN中pK（a）为16-18。此外，Fe-2（mu-O）（2）核（1）异构化为Fe-3（mu（2）-O）（3）核（7），而Fe-2（mu-O）（mu-OH）核（2）表现出与Fe-2（mu-O）（mu-H3 O2）核（5）的水合平衡，除了L = 6-Me 3-TPA和4，6-Me-6-TPA。从这些研究中可以清楚地看出，配体的电子和空间性质显着影响各种平衡，证明了仅涉及水衍生配体的丰富化学。
We have synthesized the first complexes with bis(mu-oxo)diiron(III) and (mu-oxo)(mu-hydroxo)diiron-(III) cores (1 and 2, L = TPA (a), 5-Et-3-TPA (b), 6-Me-3-TPA (c), 4,6-Me-6-TPA (d), BQPA (e), BPEEN (f), and BPMEN (g)) and found them to have novel structural properties. In particular, the presence of two single-atom bridges in these complexes constrains the Fe-Fe distances to 2.7 - 3.0 Angstrom and the Fe-mu-O-Fe angles to 100 degrees dr smaller. The significantly acute Fe-O-Fe angles (e.g, 92.5(2)degrees for 1c and 100.2(2)degrees for 2f) enforced by the Fe2O2(H) core endow these complexes with UV-vis, Raman, and magnetic properties quite distinct from those of other (mu-oxo)diiron(III) complexes. Complex Ic exhibits visible absorption bands at 470 (epsilon = 560 M-1 cm(-1)) and 760 nm (epsilon approximate to 80 M-1 cm(-1)), while complexes 2 show features at ca. 550 (epsilon approximate to 800 M-1 cm(-1)) and ca. 800 nm (epsilon approximate to 70 M-1 cm(-1)), all of which are red shifted compared to those of other (mu-oxo)-diiron(III) complexes. These complexes also exhibit distinct nu(Fe-O-Fe) vibrations at ca. 600 and ca. 670 cm(-1) assigned to the nu(sym) and the nu(asym) of the Fe-O-Fe units, respectively. The relative intensities of the nu(sym) and nu(asym) bands are affected by the symmetry of the Fe-O-Fe units; an unsymmetric core enhances the intensity of the nu(asym). Complexes 2 exhibit another band at ca. 500 cm(-1), which is assigned to the Fe-(OH)-Fe stretching mode due to its sensitivity to both (H2O)-O-18 and (H2O)-H-2. Magnetic susceptibility studies reveal J = 54 cm(-1) for Ic and ca. 110 cm(-1) for 2 (H = JS(1).S-2), values smaller than those for the antiferromagnetic interactions found in (mu-oxo)diiron(III) complexes. This weakening arises from the longer Fe-mu-O bonds and the smaller Fe-mu-O-Fe angles in the Fe2O2(H) diamond core structure. These spectroscopic signatures can thus serve as useful tools to ascertain the presence of such core structures in metalloenzyme active sites. These two core structures, Fe-2(mu-O)(2) (1) and Fe-2(mu-O)(mu-OH) (2), can also be interconverted by protonation equilibria with pK(a)'s of 16-18 in CH3CN. Furthermore, the Fe-2(mu-O)(2) core (1) isomerizes to the Fe-3(mu(2)-O)(3) core (7), while the Fe-2(mu-O)(mu-OH) core (2) exhibits aquation equilibria to the Fe-2(mu-O)(mu-H3O2) core (5), except for L = 6-Me3-TPA and 4,6-Me-6-TPA. It is clear from these studies that electronic and steric properties of the ligands significantly affect the various equilibria, demonstrating a rich chemistry involving water-derived ligands alone.