Wang Feng, Islam Shawkat, Vasilyev Vladislav
Molecular Model Discovery Laboratory, Department of Chemistry and Biotechnology, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Melbourne 3122, Australia.
National Computational Infrastructure, Australian National University, Canberra 0200, Australia.
Materials (Basel). 2015 Nov 16;8(11):7723-7737. doi: 10.3390/ma8115419.
Two very different quantum mechanically based energy decomposition analyses (EDA) schemes are employed to study the dominant energy differences between the eclipsed and staggered ferrocene conformers. One is the extended transition state (ETS) based on the Amsterdam Density Functional (ADF) package and the other is natural EDA (NEDA) based in the General Atomic and Molecular Electronic Structure System (GAMESS) package. It reveals that in addition to the model (theory and basis set), the fragmentation channels more significantly affect the interaction energy terms (Δ) between the conformers. It is discovered that such an interaction energy can be absorbed into the pre-partitioned fragment channels so that to affect the interaction energies in a particular conformer of Fc. To avoid this, the present study employs a complete fragment channel-the fragments of ferrocene are individual neutral atoms. It therefore discovers that the major difference between the ferrocene conformers is due to the quantum mechanical Pauli repulsive energy and orbital attractive energy, leading to the eclipsed ferrocene the energy preferred structure. The NEDA scheme further indicates that the sum of attractive (negative) polarization (POL) and charge transfer (CL) energies prefers the eclipsed ferrocene. The repulsive (positive) deformation (DEF) energy, which is dominated by the cyclopentadienyle (Cp) rings, prefers the staggered ferrocene. Again, the cancellation results in a small energy residue in favour of the eclipsed ferrocene, in agreement with the ETS scheme. Further Natural Bond Orbital (NBO) analysis indicates that all NBO energies, total Lewis (no Fe) and lone pair (LP) deletion all prefer the eclipsed Fc conformer. The most significant energy preferring the eclipsed ferrocene without cancellation is the interactions between the donor lone pairs (LP) of the Fe atom and the acceptor antibond (BD*) NBOs of all C-C and C-H bonds in the ligand, LP(Fe)-BD*(C-C & C-H), which strongly stabilizes the eclipsed (D) conformation by -457.6 kcal·mol.
采用两种基于量子力学的截然不同的能量分解分析（EDA）方案，来研究重叠式和交叉式二茂铁构象异构体之间的主要能量差异。一种是基于阿姆斯特丹密度泛函（ADF）软件包的扩展过渡态（ETS）方案，另一种是基于通用原子和分子电子结构系统（GAMESS）软件包的自然EDA（NEDA）方案。结果表明，除了模型（理论和基组）外，碎片通道对构象异构体之间的相互作用能项（Δ）影响更大。研究发现，这种相互作用能可被吸收到预先划分的碎片通道中，从而影响二茂铁特定构象异构体中的相互作用能。为避免这种情况，本研究采用了完整的碎片通道——二茂铁的碎片为单个中性原子。因此发现，二茂铁构象异构体之间的主要差异源于量子力学泡利排斥能和轨道吸引能，这使得重叠式二茂铁成为能量更优的结构。NEDA方案进一步表明，吸引性（负）极化（POL）能和电荷转移（CL）能之和更倾向于重叠式二茂铁。由环戊二烯基（Cp）环主导的排斥性（正）变形（DEF）能更倾向于交叉式二茂铁。同样，两者相互抵消后，会产生一个有利于重叠式二茂铁的小能量残余，这与ETS方案一致。进一步的自然键轨道（NBO）分析表明，所有NBO能量、总的路易斯（不含铁）能量和孤对（LP）消除都更倾向于重叠式二茂铁构象异构体。在没有抵消的情况下，最显著地倾向于重叠式二茂铁的能量是铁原子的供体孤对（LP）与配体中所有碳 - 碳和碳 - 氢键的受体反键（BD*）NBO之间的相互作用，即LP(Fe)-BD*(C-C & C-H)，它通过-457.6 kcal·mol的能量强烈稳定了重叠式（D）构象。
