Chardon-Noblat Sylvie, Horner Olivier, Chabut Barbara, Avenier Frédéric, Debaecker Noëlle, Jones Peter, Pécaut Jacques, Dubois Lionel, Jeandey Claudine, Oddou Jean-Louis, Deronzier Alain, Latour Jean-Marc
Laboratoire d'Electrochimie Organique et de Photochimie Rédox, UMR CNRS 5630, ICMG FR CNRS 2607, Université Joseph Fourier Grenoble 1, BP 53, 38041 Grenoble Cédex 9, France.
Inorg Chem. 2004 Mar 8;43(5):1638-48. doi: 10.1021/ic030192+.
Reaction of the unsymmetrical phenol ligand 2-((bis(2-pyridylmethyl)amino)methyl)-6-(((2-pyridylmethyl)benzylamino)methyl)-4-methylphenol (HL-Bn) or its 2,6-dichlorobenzyl analogue (HL-BnCl(2)) with Fe(H(2)O)(6)(ClO(4))(2) in the presence of disodium m-phenylenedipropionate (Na(2)(mpdp)) followed by exposure to atmosphere affords the diiron(II,III) complexes Fe(2)(L-Bn)(mpdp)(H(2)O)(2) and Fe(2)(L-BnCl(2))(mpdp)(CH(3)OH)(2), respectively. The latter complex has been characterized by X-ray crystallography. It crystallizes in the monoclinic system, space group P2(1)/n, with a = 13.3095(14) A, b = 20.1073(19) A, c = 19.4997(19) A, alpha = 90 degrees, beta = 94.471(2) degrees, gamma = 90 degrees, V = 5202.6(9) A(3), and Z = 4. The structure of the compound is very similar to that of Fe(2)(L-Bn)(mpdp)(H(2)O)(2) determined earlier, except for the replacement of a water by a methanol on the ferrous site. Magnetic measurements of Fe(2)(L-Bn)(mpdp)(H(2)O)(2) reveal that the two high-spin Fe ions are moderately antiferromagnetically coupled (J = -3.2(2) cm(-)(1)). Upon dissolution in acetonitrile the terminal ligand on the ferrous site is replaced by a solvent molecule. The acetonitrile-water exchange has been investigated by various spectroscopic techniques (UV-visible, NMR, Mössbauer) and electrochemistry. The substitution of acetonitrile by water is clearly evidenced by Mössbauer spectroscopy by a reduction of the quadrupole splitting value from 3.14 to 2.41 mm/s. In addition, it causes a 210 mV downshift of the oxidation potential of the ferrous site and a similar reduction of the stability domain of the mixed-valence state. Exhaustive electrolysis of a solution of Fe(2)(L-Bn)(mpdp)(H(2)O) shows that the aqua diferric species is not stable and undergoes a chemical reaction which can be partly reversed by reduction to the mixed-valent state. This and other electrochemical observations suggest that upon oxidation of the diiron center to the diferric state the aqua ligand is deprotonated to a hydroxo. This hypothesis is supported by Mössbauer spectroscopy. Indeed, this species possesses a large quadrupole splitting value (DeltaE(Q) >or= 1.0 mm.s(-)(1)) similar to that of analogous complexes with a terminal phenolate ligand. This study illustrates the drastic effects of aqua ligand exchange and deprotonation on the electronic structure and redox potentials of diiron centers.
不对称酚配体2-((双(2-吡啶甲基)氨基)甲基)-6-(((2-吡啶甲基)苄基氨基)甲基)-4-甲基苯酚(HL-Bn)或其2,6-二氯苄基类似物(HL-BnCl₂)与六水合铁(II)(高氯酸根)₂(Fe(H₂O)₆(ClO₄)₂)在间苯二甲酸二钠(Na₂(mpdp))存在下反应，然后暴露于空气中，分别得到二铁(II,III)配合物Fe₂(L-Bn)(mpdp)(H₂O)₂和Fe₂(L-BnCl₂)(mpdp)(CH₃OH)₂。后一种配合物已通过X射线晶体学表征。它以单斜晶系结晶，空间群为P2₁/n，a = 13.3095(14) Å，b = 20.1073(19) Å，c = 19.4997(19) Å，α = 90°，β = 94.471(2)°，γ = 90°，V = 5202.6(9) ų，Z = 4。该化合物的结构与先前测定的Fe₂(L-Bn)(mpdp)(H₂O)₂非常相似，只是亚铁位点上的一个水被一个甲醇取代。对Fe₂(L-Bn)(mpdp)(H₂O)₂的磁性测量表明，两个高自旋铁离子存在适度的反铁磁耦合(J = -3.2(2) cm⁻¹)。溶解于乙腈中时，亚铁位点上的末端配体被一个溶剂分子取代。已通过各种光谱技术(紫外可见、核磁共振、穆斯堡尔)和电化学研究了乙腈 - 水交换。穆斯堡尔光谱清楚地证明了乙腈被水取代，四极分裂值从3.14降低到2.41 mm/s。此外，它导致亚铁位点的氧化电位下降210 mV，混合价态的稳定域也有类似程度的减小。对[Fe₂(L-Bn)(mpdp)(H₂O)]²⁺溶液进行彻底电解表明，水合二价铁物种不稳定，会发生化学反应，通过还原到混合价态可部分逆转该反应。这一以及其他电化学观察结果表明，二铁中心氧化为二价铁态时，水配体会去质子化为羟基。这一假设得到了穆斯堡尔光谱的支持。实际上，该物种具有较大的四极分裂值(ΔE(Q)≥1.0 mm·s⁻¹)，与具有末端酚盐配体的类似配合物相似。这项研究说明了水配体交换和去质子化对二铁中心电子结构和氧化还原电位的显著影响。
