Synthesis and Characterization of Pyridine Amide Cation Radical Complexes of Iron: Stabilization Due to Coordination with Low-Spin Iron(III) Center
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- 作者：Apurba Kumar Patra ; Manabendra Ray ; and Rabindranath Mukherjee
- 刊名：Inorganic Chemistry
- 出版年：2000
- 出版时间：February 21, 2000
- 年：2000
- 卷：39
- 期：4
- 页码：652 - 657
- 全文大小：97K
- 年卷期：v.39,no.4(February 21, 2000)
- ISSN：1520-510X
文摘
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 iscoordinated to four nitrogen donors in the equatorial plane with two amide nitrogen anions and two pyridinenitrogen 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) [synthesizedfrom a new iron(III) complex [Fe(Me6bpb)(py)2][ClO4] (3) (S = 1/2)] [H2Me6bpb = 1,2-bis(3,5-dimethylpyridine-2-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 physicochemicaltechniques. 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) ligandcation radical complexes rather than iron(IV) complexes. Cyclic voltammetric studies on isolated oxidized complexes5 and 6 display identical behavior (a metal-centered reduction and a ligand-centered oxidation) to that observedfor complexes 2 and 4, respectively. The Mössbauer data for 6 are almost identical with those of the parentcompound 4, providing compelling evidence that oxidation has occurred at the ligand in a site remote from theiron atom. Strong antiferromagnetic coupling (
-2J 
450 cm-1) of the S = 1/2 iron atom with the S = 1/2 ligand
-cation radical leads to an effectively S = 0 ground state of 5 and 6. The oxidized complexes display 1H NMRspectra (in CDCl3 solution), characteristic of diamagnetic species.
-2J 450 cm-1) of the S = 1/2 iron atom with the S = 1/2 ligand-cation radical leads to an effectively S = 0 ground state of 5 and 6. The oxidized complexes display 1H NMRspectra (in CDCl3 solution), characteristic of diamagnetic species.