Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, 790-784 Pohang, South Korea.
Phys Chem Chem Phys. 2011 Jan 21;13(3):991-1001. doi: 10.1039/c003008b. Epub 2010 Nov 9.
We have carried out extensive calculations for neutral, cationic protonated, anionic deprotonated phenol dimers. The structures and energetics of this system are determined by the delicate competition between H-bonding, H-π interaction and π-π interaction. Thus, the structures, binding energies and frequencies of the dimers are studied by using a variety of functionals of density functional theory (DFT) and Møller-Plesset second order perturbation theory (MP2) with medium and extended basis sets. The binding energies are compared with those of highly reliable coupled cluster theory with single, double, and perturbative triple excitations (CCSD(T)) at the complete basis set (CBS) limit. The neutral phenol dimer is unique in the sense that its experimental rotational constants have been measured. The geometry of the neutral phenol dimer is governed by the hydrogen bond formed by two hydroxyl groups and the H-π interaction between two aromatic rings, while the structure of the protonated/deprotonated phenol dimers is additionally governed by the electrostatic and induction effects due to the short strong hydrogen bond (SSHB) and the charges populated in the aromatic rings in the ionic systems. Our salient finding is the substantial differences in structure between neutral, protonated, and deprotonated phenol dimers. This is because the neutral dimer involves in both H(π)···O and H(π)···π interactions, the protonated dimer involves in H(π)···π interactions, and the deprotonated dimer involves in a strong H(π)···O interaction. It is important to compare the reliability of diverse computational approaches employed in quantum chemistry on the basis of the calculational results of this system. MP2 calculations using a small cc-pVDZ basis set give reasonable structures, but those using extended basis sets predict wrong π-stacked structures due to the overestimation of the dispersion energies of the π-π interactions. A few new DFT functionals with the empirical dispersion give reliable results consistent with the CCSD(T)/CBS results. The binding energies of the neutral, cationic protonated, and anionic deprotonated phenol dimers are estimated to be more than 28.5, 118.2, and 118.3 kJ mol(-1), respectively. The energy components of the intermolecular interactions for the neutral, protonated and deprotonated dimers are analyzed.
我们对中性、阳离子质子化、阴离子去质子化的苯酚二聚体进行了广泛的计算。该体系的结构和能量由氢键、H-π 相互作用和π-π 相互作用之间的微妙竞争决定。因此，通过使用各种密度泛函理论（DFT）和 Møller-Plesset 二级微扰理论（MP2）以及中扩展基组来研究二聚体的结构、结合能和频率。将结合能与完全基组（CBS）极限下具有单、双和微扰三重激发的高可靠性耦合簇理论（CCSD(T)）的结合能进行比较。中性苯酚二聚体是独一无二的，因为它的实验旋转常数已经被测量出来。中性苯酚二聚体的几何形状由两个羟基形成的氢键和两个芳环之间的 H-π 相互作用控制，而质子化/去质子化苯酚二聚体的结构则由静电和诱导效应决定，因为在离子体系中，芳香环中存在短强氢键（SSHB）和电荷。我们的主要发现是中性、质子化和去质子化的苯酚二聚体在结构上存在显著差异。这是因为中性二聚体同时涉及 H(π)···O 和 H(π)···π 相互作用，质子化二聚体涉及 H(π)···π 相互作用，而去质子化二聚体涉及强 H(π)···O 相互作用。基于该体系的计算结果，比较量子化学中不同计算方法的可靠性是很重要的。使用小 cc-pVDZ 基组的 MP2 计算给出了合理的结构，但使用扩展基组预测的π堆积结构是错误的，因为π-π 相互作用的色散能被高估了。几个具有经验色散的新 DFT 泛函给出了与 CCSD(T)/CBS 结果一致的可靠结果。中性、阳离子质子化和阴离子去质子化的苯酚二聚体的结合能分别估计为 28.5 以上、118.2 以上和 118.3 kJ mol(-1)。分析了中性、质子化和去质子化二聚体的分子间相互作用的能量组成。
