Horner Olivier, Anxolabéhère-Mallart Elodie, Charlot Marie-France, Tchertanov Lyuba, Guilhem Jean, Mattioli Tony A., Boussac Alain, Girerd Jean-Jacques
Laboratoire de Chimie Inorganique, URA CNRS 420, Université de Paris-Sud, 91405 Orsay, France, Laboratoire de Cristallochimie, Institut de Chimie des Substances Naturelles, 91198 Gif-sur-Yvette, France, Section de Bioenergétique, URA CNRS 2096, DBCM, CEA Saclay, 91191 Gif-sur-Yvette, France, and Section de Biophysique des Protéines et des Membranes, URA CNRS 2096, DBCM, CEA Saclay, 91191 Gif-sur-Yvette, France.
Inorg Chem. 1999 Mar 22;38(6):1222-1232. doi: 10.1021/ic980832m.
The compound Mn(III)(2)OL(2)(2).2.23CHCl(3).0.65CH(2)Cl(2) where L(-) is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicyliden-1,2-diaminoethane ligand, has been synthesized. The complex dication Mn(III)(2)OL(2) contains a linear Mn(III)-O-Mn(III) unit with a Mn-Mn distance of 3.516 Å. The pentadentate ligand L(-) wraps around the Mn(III) ion. Electrochemically, it is possible to prepare the one electron oxidized trication Mn(2)OL(2) which crystallizes as Mn(2)OL(2)(2.37)(PF(6))(0.63).1.5CH(3)CN. The complex trication Mn(2)OL(2) contains a Mn(III)-O-Mn(IV) unit with a Mn-Mn distance of 3.524 Å and a Mn-O-Mn angle of 178.7(2) degrees. The contraction of the coordination sphere around the Mn(IV) is clearly observed. The Mn(2)OL(2) dication possesses a S = 0 electronic ground state with J = -216 cm(-)(1) (H = -JS(1)().S(2)()), whereas the Mn(2)OL(2) trication shows a S = (1)/(2) ground state with J = -353 cm(-)(1). The UV-visible spectrum of Mn(2)OL(2) exhibits an intense absorption band (epsilon = 3040 M(-)(1) cm(-)(1)) centered at 570 nm assigned to a phenolate --> Mn(IV) charge-transfer transition. The potentials of the redox couples determined by cyclic voltammetry are E degrees (Mn(2)OL(2)/Mn(2)OL(2)) = 0.54 V/saturated calomel electrode (SCE) and E degrees (Mn(2)OL(2)/Mn(2)OL(2)) = 0.99 V/SCE. Upon oxidation at 1.3 V/SCE, the band at 570 nm shifts to 710 nm (epsilon = 2500 M(-)(1) cm(-)(1)) and a well-defined band appears at 400 nm which suggests the formation of a phenoxyl radical. The Mn(2)OL(2)( )()complex exhibits a 18-line X-band electron paramagnetic resonance (EPR) spectrum which has been simulated with rhombic tensors |A(1)(x)()| = 160 x 10(-)(4) cm(-)(1); |A(1)(y)()| = 130 x 10(-)(4) cm(-)(1); |A(1)(z)()| = 91 x 10(-)(4) cm(-)(1); |A(2)(x)()| = 62 x 10(-)(4) cm(-)(1); |A(2)(y)()| = 59 x 10(-)(4) cm(-)(1); |A(2)(z)()| = 62 x 10(-)(4) cm(-)(1) and g(x)() = 2.006; g(y)() = 1.997; g(z)() = 1.982. This EPR spectrum( )()shows that the 16-line paradigm related to a large antiferromagnetic exchange coupling and a low anisotropy can be overcome by a large rhombic anisotropy. Molecular orbital calculations relate this rhombicity to the nature of the orbital describing the extra electron on Mn(III). This orbital has a majority but not pure d(z)()2 contribution (with the z axis perpendicular to the Mn-Mn axis). Low-temperature resonance Raman spectroscopy on an acetonitrile solution of Mn(2)OL(2) prepared at -35 degrees C indicated the formation of a phenoxyl radical. This suggests that the ligand was oxidized rather than the Mn(III)Mn(IV) pair to Mn(IV)Mn(IV), which illustrates the difficulty to store a second positive charge in a short range of potential in a manganese mono-&mgr;-oxo pair. The relevance of these results to the study of the photosynthetic oxygen evolving complex is discussed.
已合成化合物Mn(III)₂OL₂₂·2.23CHCl₃·0.65CH₂Cl₂，其中L⁻为单阴离子N,N - 双(2 - 吡啶甲基)-N'-水杨醛基 - 1,2 - 二氨基乙烷配体。配合物二价阳离子[Mn(III)₂OL₂]²⁺包含一个线性Mn(III) - O - Mn(III)单元，Mn - Mn距离为3.516 Å。五齿配体L⁻环绕在Mn(III)离子周围。在电化学方面，可以制备单电子氧化的三价阳离子[Mn₂OL₂]³⁺，其结晶为Mn₂OL₂₂.₃₇(PF₆)₀.₆₃·1.5CH₃CN。配合物三价阳离子[Mn₂OL₂]³⁺包含一个Mn(III) - O - Mn(IV)单元，Mn - Mn距离为3.524 Å，Mn - O - Mn角度为178.7(2)°。可以清楚地观察到Mn(IV)周围配位球的收缩。[Mn₂OL₂]²⁺二价阳离子具有S = 0的电子基态，J = - 216 cm⁻¹(H = - JS₁·S₂)，而[Mn₂OL₂]³⁺三价阳离子显示S = (1)/(2)的基态，J = - 353 cm⁻¹。[Mn₂OL₂]³⁺的紫外 - 可见光谱在570 nm处呈现一个强吸收带(ε = 3040 M⁻¹ cm⁻¹)，归属于酚盐→Mn(IV)电荷转移跃迁。通过循环伏安法测定的氧化还原对的电位为E°([Mn₂OL₂]³⁺/[Mn₂OL₂]²⁺)=0.54 V/饱和甘汞电极(SCE)和E°([Mn₂OL₂]⁴⁺/[Mn₂OL₂]³⁺)=0.99 V/SCE。在1.3 V/SCE下氧化时，570 nm处的吸收带移至710 nm(ε = 2500 M⁻¹ cm⁻¹)，并且在400 nm处出现一个明确的吸收带，这表明形成了苯氧基自由基。[Mn₂OL₂]³⁺配合物呈现出一个18线的X波段电子顺磁共振(EPR)谱，已用菱形张量模拟：|A₁(x)| = 160×10⁻⁴ cm⁻¹；|A₁(y)| = 130×10⁻⁴ cm⁻¹；|A₁(z)| = 91×10⁻⁴ cm⁻¹；|A₂(x)| = 62×10⁻⁴ cm⁻¹；|A₂(y)| = 59×10⁻⁴ cm⁻¹；|A₂(z)| = 62×10⁻⁴ cm⁻¹以及g(x)=2.006；g(y)=1.997；g(z)=1.982。该EPR谱表明与大反铁磁交换耦合和低各向异性相关的16线模式可以被大的菱形各向异性克服。分子轨道计算将这种菱形度与描述Mn(III)上额外电子的轨道性质相关联。该轨道主要但并非纯粹是d(z)²贡献(其中z轴垂直于Mn - Mn轴)。在 - 35℃制备的[Mn₂OL₂]⁴⁺乙腈溶液的低温共振拉曼光谱表明形成了苯氧基自由基。这表明被氧化的是配体而非Mn(III)Mn(IV)对变成Mn(IV)Mn(IV)，这说明了在锰单 - μ - 氧对的短电位范围内存储第二个正电荷的困难。讨论了这些结果与光合放氧复合物研究的相关性。
