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首页> 外文期刊>RSC Advances >Theoretical view on a linear end-on manganese-dioxygen complex bearing a calix[4]arene ligand
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Theoretical view on a linear end-on manganese-dioxygen complex bearing a calix[4]arene ligand

机译：带有杯[4]芳烃配体的线性端基锰-二氧配合物的理论视图

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By taking a Mn-dioxygen complex supported by a zwitterionic calix[4]arene ligand ([MnL(O-2)(H2O)](PF6)(2); H4L = [5,11,17,23-tetrakis(trimethylammonium)-25,26,27,28-tetrahydroxycalix[4]arene], CSD refcode: CAGVAJ) as a model system, we investigated the geometric and electronic structures of [MnL(O-2)(H2O)](2+) through density functional theory (DFT) calculations without and with the presence of additional waters. It was found that the ground-state structure of [MnL(O-2)(H2O)](2+) possesses a typical bent end-on binding mode (Mn-O-O angle at around 130 degrees and dioxygen bond length at similar to 1.32 angstrom) within a sextet state (S = 5/2) irrespective of calculated methodologies. The experimently proposed linear end-on structure (Mn-O-O angle at similar to 180 degrees) and the side-on structure (Mn-O-O angle similar to 75 degrees) are shown to be transition-state structures in the process of dioxygen flipping from one bent-end-on structure to another. By the inclusion of water solvation effect via both the explicit water-cluster model ([MnL(O-2)(H2O)](2+)-nH(2)O, n = 1, 4, 6, 8) and implicit CPCM solvation model, a good correlation was concluded: the more additional waters and the more contracted Oe square benefit the larger Mn-O-O angle, indicating a water solvation effect and a ligand size effect. Inspired by the relationship of linear end-on mode with bent end-on mode and the consistence of the projected dioxygen bond length of [MnL(O-2)(H2O)](2+)-8H(2)O in the CPCM model along the Mn-O bond direction (d(O1-O2)(p) = 1.240 angstrom) with the experimental dioxygen bond length (1.249 angstrom), we concluded that the linear Mn-O-O arrangement fitted by experimentalists should be a result of the flipping motion of dioxygen rotating about the Mn-O bond in solid-state structures of the [MnL(O-2)(H2O)](PF6)(2) complex based on analyses of the crystallographic data. Natural bond orbital (NBO) analyses show the sextet [MnL(O-2)(H2O)](2+)-nH(2)O (n = 0, 1, 4, 6, 8) have a Mn(III)-superoxo nature, consistent with experimental observations. The differences in the bonding structures of the three binding modes were discussed by the second-order perturbation energies Delta E-i -> j from the superoxo lone pair (LP) orbitals to Mn(III) 3d orbitals in beta electron space. It can also give clues about the instability of the linear end-on binding mode and the increased Mn-O-O angle in the presence of water solvents.
机译：通过获取两性离子杯[4]芳烃配体（[MnL（O-2）（H2O）]（PF6）（2）; H4L = [5,11,17,23-四（三甲基铵） ）-25,26,27,28-四羟基杯[4]芳烃]，CSD参考代码：CAGVAJ）作为模型系统，我们研究了[MnL（O-2）（H2O）]（2+）的几何和电子结构通过密度泛函理论（DFT）的计算，无需添加附加水。发现[MnL（O-2）（H2O）]（2+）的基态结构具有典型的弯曲末端键合模式（Mn-OO角约为130度，双氧键长度与六重态（S = 5/2）内的1.32埃），与计算方法无关。实验提出的线性末端结构（Mn-OO角与180度相似）和侧面结构（Mn-OO角与75度相似）在双氧翻转过程中显示为过渡态结构。一个弯曲的末端结构。通过显式水团模型（[MnL（O-2）（H2O）]（2 +）-nH（2）O，n = 1、4、6、8）都包含水溶剂化作用CPCM溶剂化模型得出了很好的相关性：更多的水和Oe平方越收缩，受益的Mn-OO角越大，表明存在水溶作用和配体尺寸效应。受线性末端模式与弯曲末端模式的关系以及CPCM中[MnL（O-2）（H2O）]（2 +）-8H（2）O的投影双氧键长度的一致性的启发沿Mn-O键方向（d（O1-O2）（p）= 1.240埃）的模型，实验中的双氧键长度（1.249埃），我们得出结论，实验学家拟合的线性Mn-OO排列应该是根据晶体学数据分析，[MnL（O-2）（H2O）]（PF6）（2）配合物固态结构中围绕Mn-O键旋转的双氧的翻转运动。自然键轨道（NBO）分析显示六重键[MnL（O-2）（H2O）]（2 +）-nH（2）O（n = 0、1、4、6、8）具有Mn（III） -superoxo性质，与实验观察结果一致。通过β电子空间中从超氧代孤对（LP）轨道到Mn（III）3d轨道的二阶摄动能Delta E-i-> j讨论了三种键合模式的键合结构的差异。在存在水溶剂的情况下，它也可以提供关于线性端基结合模式的不稳定性和增加的Mn-O-O角的线索。

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