Synthesis and characterization of pyridine amide cation radical complexes of iron: stabilization due to coordination with low-spin iron(III) center.
Synthesis and characterization of pyridine amide cation radical complexes of iron: stabilization due to coordination with low-spin iron(III) center.
复制标题
铁的吡啶酰胺阳离子自由基配合物的合成和表征：由于与低自旋铁（III）中心的配位而稳定。
作者：
A. Patra;M. Ray;R. Mukherjee
报道了低自旋铁（III） [Fe(bpb)(py)2][ClO4](1)和Na[Fe(bpb)(CN)2] (2) [H2bpb = 1,2-二（吡啶-2-羧胺）苯肽配合物的合成和表征；（Ray， M.; Mukherjee， R.; Richardson， J. F.; Buchanan， R. M. J. Chem）。Soc。，道尔顿译，1993,2451)。2的化学氧化和一种新的低自旋铁（III）配合物Na[Fe(Me6bpb)(CN)2]。H2O(4)[由新的铁（III）配合物[Fe(Me6bpb)(py)2][ClO4] (3) (S = 1/2)] [H2Me6bpb = 1,2-二（3,5-二甲基吡啶-羧胺）-4,5-二甲苯]由（NH4）2Ce(NO3)6合成]分离出两个新的配合物[Fe(bpb)-(CN)2](5)和[Fe(Me6bpb)(CN)2]。水(6)。所有的配合物都用物理化学技术进行了表征。1-4号是棕色/绿色，5号和6号是紫色/蓝紫色。来自红外、电子、Mössbauer和1H NMR光谱、温度相关磁化率数据和循环伏安研究的集体证据提供了明确的证据，表明5和6是低自旋铁（III）配体阳离子自由基配合物，而不是铁（IV）配合物。对分离的氧化配合物5和6的循环伏安研究分别显示了与配合物2和4相同的行为（以金属为中心的还原和以配体为中心的氧化）。6的Mössbauer数据与母体化合物4的数据几乎相同，提供了令人信服的证据，证明在远离铁原子的位置上的配体发生了氧化。S = 1/2铁原子与S = 1/2配体阳离子自由基的强反铁磁耦合（-2J >或= 450 cm(-1)）导致有效的S = 0基态为5和6。氧化后的配合物（在CDCl3溶液中）具有抗磁性的1H NMR谱。
We reported the synthesis and characterization of peptide complexes of low-spin iron(III) [Fe(bpb)(py)2][ClO4] (1) and Na[Fe(bpb)(CN)2] (2) [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; py = pyridine], where iron is coordinated to four nitrogen donors in the equatorial plane with two amide nitrogen anions and two pyridine nitrogen donors (Ray, M.; Mukherjee, R.; Richardson, J. F.; Buchanan, R. M. J. Chem. Soc., Dalton Trans. 1993, 2451). Chemical oxidation of 2 and a new low-spin iron(III) complex Na[Fe(Me6bpb)(CN)2].H2O (4) [synthesized from a new iron(III) complex [Fe(Me6bpb)(py)2][ClO4] (3) (S = 1/2)] [H2Me6bpb = 1,2-bis(3,5-dimethylpyridine2-carboxamido)-4,5-dimethylbenzene) by (NH4)2Ce(NO3)6 afforded isolation of two novel complexes [Fe(bpb)-(CN)2] (5) and [Fe(Me6bpb)(CN)2].H2O (6). All the complexes have been characterized by physicochemical techniques. While 1-4 are brown/green, 5 and 6 are violet/bluish violet. The collective evidence from infrared, electronic, Mössbauer, and 1H NMR spectroscopies, from temperature-dependent magnetic susceptibility data, and from cyclic voltammetric studies provides unambiguous evidence that 5 and 6 are low-spin iron(III) ligand cation radical complexes rather than iron(IV) complexes. Cyclic voltammetric studies on isolated oxidized complexes 5 and 6 display identical behavior (a metal-centered reduction and a ligand-centered oxidation) to that observed for complexes 2 and 4, respectively. The Mössbauer data for 6 are almost identical with those of the parent compound 4, providing compelling evidence that oxidation has occurred at the ligand in a site remote from the iron atom. Strong antiferromagnetic coupling (-2J > or = 450 cm(-1)) of the S = 1/2 iron atom with the S = 1/2 ligand pi-cation radical leads to an effectively S = 0 ground state of 5 and 6. The oxidized complexes display 1H NMR spectra (in CDCl3 solution), characteristic of diamagnetic species.