SYNTHESIS AND CHARACTERIZATION OF (MU-HYDROXO)BIS(MU-ACETATO)DIIRON(II) AND (MU-OXO)BIS(MU-ACETATO)DIIRON(III) 1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE COMPLEXES AS MODELS FOR BINUCLEAR IRON CENTERS IN BIOLOGY - PROPERTIES OF THE MIXED-VALENCE DIIRON(II,III) SPECIEST
SYNTHESIS AND CHARACTERIZATION OF (MU-HYDROXO)BIS(MU-ACETATO)DIIRON(II) AND (MU-OXO)BIS(MU-ACETATO)DIIRON(III) 1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE COMPLEXES AS MODELS FOR BINUCLEAR IRON CENTERS IN BIOLOGY - PROPERTIES OF THE MIXED-VALENCE DIIRON(II,III) SPECIEST
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DOI：
10.1021/ja00258a023
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发表时间：
1987-11-25
影响因子：
15
通讯作者：
LIPPARD, SJ
中科院分区：
文献类型：
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作者：
HARTMAN, JAR;RARDIN, RL;LIPPARD, SJ
合成了双核二铁（II）和二铁（III）化合物[Fe 2（OH）（OAc）2（Me 3 TACN）2]（ClO 4）2·H2O和[Fe 2 O-（OAc）2（Me 3 TACN）2]（ClO 4）2·H2O（Me 3 TACN = 1，4，7-三甲基-1，4，7-三氮杂环壬烷），并通过X射线晶体学确定了它们的结构。这两种配合物具有两个facially协调的Me 3 TACN配体与两个桥接乙酸酯配体封端的双八面体结构。剩余的桥连配体在亚铁络合物中是氢氧化物，在铁络合物中是氧化物。因此，其结构分别类似于脱氧血红蛋白和叠氮血红蛋白的桥接二铁核心。二铁（II）和二铁（III）结构之间的主要区别是较长的金属-配体键长和Fe原子数。cntdot.. cntdot. Fe距离，3.32（1）. vs. 3.12（1）. ANG.，在亚铁络合物中发现，几乎没有伴随的角变形（Fe-O-Fe角为113.2（1）°）。和119.7（1）°，分别）。这些络合物的穆斯堡尔谱和体磁性质与类似氧化态的大铁菊素的穆斯堡尔谱和体磁性质非常相似，= 1.16（3）mm/s，Δ EQ = 2.83（5）mm/s，对于二铁（II）络合物J = -13（1）cm-1，= 0.47（3）mm/s，Δ EQ = 1.50（5）mm/s，并且对于二铁（III）络合物J = -119（1）cm-1。用循环伏安法测定了这些二铁配合物的氧化还原行为。二铁（II）复合物的氧化产生一个阳极峰和两个紧密间隔的阴极峰上的返回扫描，暂时分配到氧代和羟基桥接二铁（II，III）物种的还原。在三乙胺存在下，于-0.29V（SCE）处出现一个准可逆波。二铁（III）络合物的CV研究揭示了在-0.37 V对SCE处的准可逆波。因此，与血红蛋白一样，混合价物质在结晶方面不稳定。控制电位库仑分析表明[Fe_2 O（OAc）_2（Me_3 TACN）_2]~（2+）只占据一个电子，电子自旋共振研究表明，在9.6K时，在g < 2.0的冻结玻璃中，该化合物的自旋积分值为一个未成对自旋的65%。这一结果，连同减少超精细领域的磁性穆斯堡尔谱，是一致的混合价二铁（II，III）配方。
The binuclear diiron(II) and diiron(III) compounds [Fe2(OH)(OAc)2(Me3TACN)2](ClO4).cntdot.H2O and [Fe2O-(OAc)2(Me3TACN)2](ClO4)2.cntdot.H2O (Me3TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane) were synthesized and their structures determined by X-ray crystallography. Both complexes have two facially coordinated Me3TACN ligands capping a bioctahedral structure with two bridging acetate ligands. The remaining bridging ligand is hydroxide in the ferrous complex and oxide in the ferric complex. The structures are thus analogous to the bridged diiron cores of deoxyhemerythrin and azidomethemerythrin, respectively. The major differences between the diiron(II) and diiron(III) structures are the longer metal-ligand bond lengths and Fe.cntdot..cntdot..cntdot. Fe distance, 3.32 (1) .ANG. vs. 3.12 (1) .ANG., found in the ferrous complex, with little accompanying angular distortion (the Fe-O-Fe angles are 113.2 (1).degree. and 119.7 (1).degree., respectively). The Mossbauer spectra and bulk magnetic properties of these complexes are very similar to those of hemerythrin in the analogous oxidation states, with .delta. = 1.16 (3) mm/s, .DELTA.EQ = 2.83 (5) mm/s, and J = -13 (1) cm-1 for the diiron(II) complex and .delta. = 0.47 (3) mm/s, .DELTA.EQ = 1.50 (5) mm/s, and J = -119 (1) cm-1 for the diiron(III) complex. The redox behavior of these diiron complexes has been measured by cyclic voltammetry. Oxidation of the diiron(II) complex yields one anodic peak and two closely spaced cathodic peaks on the return sweep, tentatively assigned to reduction of oxo- and hydroxo-bridged diiron(II,III) species. In the presence of triethylamine, only one, quasireversible wave appears at -0.29 V versus SCE. CV studies of the diiron(III) complex reveal a quasireversible wave at -0.37 V versus SCE. Thus, as in hemerythrin, the mixed-valence species is thermodynamically unstable with respect to disproportionation. Controlled potential coulometry revealed that [Fe2O(OAc)2(Me3TACN)2]2+ takes up one electron. Electron spin resonance studies of the resulting species reveal features at g < 2.0 in frozen glasses at 9.6 K which integrate to 65% of the value expected for one unpaired spin. This result, together with reduced hyperfine fields in the magnetic Mossbauer spectrum, is consistent with a mixed-valence diiron(II,III) formulation.