Theory and X-ray Absorption Spectroscopy for Aluminum Coordination Complexes - Al K-Edge Studies of Charge and Bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 Complexes
Theory and X-ray Absorption Spectroscopy for Aluminum Coordination Complexes - Al K-Edge Studies of Charge and Bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 Complexes
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DOI：
10.1021/jacs.5b05854
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发表时间：
2015-08-19
影响因子：
15
通讯作者：
Tyliszczak, Tolek
中科院分区：
文献类型：
--
作者：
Altman, Alison B.;Pemmaraju, C. D.;Tyliszczak, Tolek
利用极化铝K边X射线吸收近边结构（XANES）光谱和第一性原理计算研究了一系列（BDI）Al、（BDI）AlX 2和（BDI）AlR 2（X = F，Cl，I; R = H，Me; BDI = 2，6-二异丙基苯基-β-二酮亚胺）配合物的电子结构.光谱解释的指导下，检查计算的跃迁能量和偏振相关的振子强度，同意与XANES光谱测量。前边缘功能被分配到与参与metalligand键合的Al 3 p轨道的过渡。定性趋势Al 1 s的核心能量和价轨道占领建立了通过系统的比较来自Al 3 p轨道的分子轨道框架中具有相似的对称性的激发态。这些趋势表明，较高的跃迁能观察到的（BDI）AlX 2系统与更多的电负性的X-1配体可以归因于周围的铝原子的电子密度的减少，这导致增加的吸引力的潜力的Al核和随之而来的Al 1 s核心轨道的结合能的增加。对于（BDI）Al和（BDI）AlH 2，实验Al K边XANES谱和使用激发电子和芯空穴（XCH）方法计算的谱具有几乎相同的能量，用于跃迁到具有相似组成和对称性的终态轨道。这些结果表明，（BDI）Al和（BDI）AlH 2中铝原子的电荷分布与（BDI）AlX 2和（BDI）AlMe 2化合物相似，尽管分别具有不同的+1和+3形式氧化态。然而，（BDI）Al的独特之处在于，它表现出低能量特征，这归因于跃迁到位于Al上并与（BDI）Al平面正交的B（1）对称的低位p轨道。这种低能未占分子轨道在富电子（BDI）Al上的存在将其价电子结构与形式上的三价化合物（BDI）AlX 2和（BDI）AlR 2的价电子结构区分开来。这项工作表明，铝K边XANES光谱可以用来提供有价值的洞察主族配位化合物的电子结构和反应性关系。
Polarized aluminum K-edge X-ray absorption near edge structure (XANES) spectroscopy and first-principles calculations were used to probe electronic structure in a series of (BDI)Al, (BDI)AlX2, and (BDI)AlR2 coordination compounds (X = F, Cl, I; R = H, Me; BDI = 2,6-diisopropylphenyl-beta-diketiminate). Spectral interpretations were guided by examination of the calculated transition energies and polarization-dependent oscillator strengths, which agreed well with the XANES spectroscopy measurements. Pre-edge features were assigned to transitions associated with the Al 3p orbitals involved in metalligand bonding. Qualitative trends in Al 1s core energy and valence orbital occupation were established through a systematic comparison of excited states derived from Al 3p orbitals with similar symmetries in a molecular orbital framework. These trends suggested that the higher transition energies observed for (BDI)AlX2 systems with more electronegative X-1 ligands could be ascribed to a decrease in electron density around the aluminum atom, which causes an increase in the attractive potential of the Al nucleus and concomitant increase in the binding energy of the Al 1s core orbitals. For (BDI)Al and (BDI)AlH2 the experimental Al K-edge XANES spectra and spectra calculated using the eXcited electron and CoreHole (XCH) approach had nearly identical energies for transitions to final state orbitals of similar composition and symmetry. These results implied that the charge distributions about the aluminum atoms in (BDI)Al and (BDI)AlH2 are similar relative to the (BDI)AlX2 and (BDI)AlMe2 compounds, despite having different formal oxidation states of +1 and +3, respectively. However, (BDI)Al was unique in that it exhibited a low-energy feature that was attributed to transitions into a low-lying p-orbital of b(1) symmetry that is localized on Al and orthogonal to the (BDI)Al plane. The presence of this low-energy unoccupied molecular orbital on electron-rich (BDI)Al distinguishes its valence electronic structure from that of the formally trivalent compounds (BDI)AlX2 and (BDI)AlR2. The work shows that Al K-edge XANES spectroscopy can be used to provide valuable insight into electronic structure and reactivity relationships for main-group coordination compounds.