Begum Samiyara, Subramanian Ranga
Department of Chemistry, Indian Institute of Technology Patna, Bihta, 801118, India.
J Mol Model. 2016 Jan;22(1):6. doi: 10.1007/s00894-015-2866-z. Epub 2015 Dec 9.
The structural features, spectroscopic properties, and interaction energies of the linear proton-bound complexes of OCH(+) and its sulfur analog SCH(+) with N2 were investigated using the high-level ab initio methods MP2 and CCSD(T) as well as density functional theory with the aug-cc-pVXZ (X = D, T) basis sets. The rotational constants along with the vibrational frequencies of the cation-molecule complexes are reported here. A comparison of the interaction energies of the OCH(+)-N2 and SCH(+)-N2 complexes with those of the OCH(+)-CO and OCH(+)-OC complexes was also performed. The energies of all the complexes were determined at the complete basis set (CBS) limit. CS shows higher proton affinity at the C site than CO does, so the complex OCH(+)-N2 is relatively strongly bound and has a higher interaction energy than the SCH(+)-N2 complex. Symmetry-adapted perturbation theory (SAPT) was used to decompose the total interaction energies of the complexes into the attractive electrostatic interaction energy (E elst), induction energy (E ind), dispersion energy (E disp), and repulsive exchange energy (E exch). We found that the ratio of E ind to E disp is large for these linear proton-bound complexes, meaning that inductive effects are favored in these complexes. The bonding characteristics of the linear complexes were elucidated using natural bond orbital (NBO) theory. NBO analysis showed that the attractive interaction is caused by NBO charge transfer from the lone pair on N to the σ*(C-H) antibonding orbital in XCH(+)-N2 (X = O, S). The quantum theory of atoms in molecules (QTAIM) was used to analyze the strengths of the various bonds within and between the cation and molecule in each of these proton-bound complexes in terms of the electron density at bond critical points (BCP). Graphical Abstract Linear proton-bound complexes of OCH(+)-N2 and SCH(+)-N2. In these complexes, inductive effect is favored over dispersive effect. The attractive interaction is the NBO charge transfer from N-lone pair of N2 to CH σ* antibonding orbital of XCH(+) (X = O, S).
使用高水平从头算方法MP2和CCSD(T)以及采用aug-cc-pVXZ（X = D，T）基组的密度泛函理论，研究了OCH(+)及其硫类似物SCH(+)与N2形成的线性质子键合配合物的结构特征、光谱性质和相互作用能。本文报道了阳离子-分子配合物的转动常数以及振动频率。还对OCH(+)-N2和SCH(+)-N2配合物与OCH(+)-CO和OCH(+)-OC配合物的相互作用能进行了比较。所有配合物的能量均在完全基组（CBS）极限下确定。CS在C位点的质子亲和力高于CO，因此配合物OCH(+)-N2的结合相对较强，且相互作用能高于SCH(+)-N2配合物。采用对称适配微扰理论（SAPT）将配合物的总相互作用能分解为吸引性静电相互作用能（E elst）、诱导能（E ind）、色散能（E disp）和排斥性交换能（E exch）。我们发现，对于这些线性质子键合配合物，E ind与E disp的比值较大，这意味着在这些配合物中诱导效应占优。使用自然键轨道（NBO）理论阐明了线性配合物的键合特征。NBO分析表明，吸引相互作用是由N2上孤对电子的NBO电荷转移至XCH(+)-N2（X = O，S）中σ*(C-H)反键轨道引起的。采用分子中的原子量子理论（QTAIM），根据键临界点（BCP）处的电子密度，分析了这些质子键合配合物中阳离子与分子内部及之间各种键的强度。图形摘要：OCH(+)-N2和SCH(+)-N2的线性质子键合配合物。在这些配合物中，诱导效应优于色散效应。吸引相互作用是从N2的N孤对电子到XCH(+)（X = O，S）的CH σ*反键轨道的NBO电荷转移。
