Singh Ankit, Sahoo Dipak Kumar, Sethi Srikant Kumar, Jena Subhrakant, Biswal Himansu S
School of Chemical Sciences, National Institute of Science Education and Research (NISER), PO- Bhimpur-Padanpur, Via-Jatni, District- Khurda, PIN, 752050, Bhubaneswar, India.
Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, 400094, India.
Chemphyschem. 2017 Dec 15;18(24):3625-3633. doi: 10.1002/cphc.201700742. Epub 2017 Nov 6.
Several recent publications have illustrated that electrostatic attraction is not solely responsible for strong hydrogen bonds. Even electropositive and less electronegative atoms such as Te and Se are capable of forming strong H-bonds. Herein, we provide evidence for intramolecular homopolar dihydrogen bonds [HOMO-DHBs; X-N(C)-H ⋅⋅⋅ H-N(C)-Y] in porphyrins and related compounds for the first time; these bonds are revealed by careful Cambridge Structural Database (CSD) exploration, quantum theory of atoms in molecules, compliance constant calculations, and natural bond orbital and noncovalent interaction (NCI) analysis. A search of the CSD showed that the inner-core hydrogen atom distances were less than 2.5 Å (sum of the van der Waals radii of two hydrogen atoms is 2.4 Å) in porphyrinoids, i.e. about 75 % of the cases. This suggested an attractive interaction between hydrogen atoms carrying a positive charge, which was further supported by quantum-chemical calculations. The HOMO-DHB energy in some cases was found to be as much as around 20 kJ mol , which is comparable to that of any conventional H-bond energy such as for the NH dimer. The interplay between hyperconjugative attraction and steric constraint favorably decided the strength of the HOMO-DHBs. We expect that HOMO-DHBs could be revealed in many more systems, such as corroles, phlorins, crown ethers, and constrained systems having hydrogen atoms in close contact, and could be an important noncovalent interaction to consider in supramolecular chemistry.
最近的几篇出版物表明，静电吸引并非强氢键形成的唯一原因。即使是电正性且电负性较小的原子，如碲（Te）和硒（Se），也能够形成强氢键。在此，我们首次提供了卟啉及相关化合物中分子内同极双氢键[HOMO-DHBs；X-N(C)-H ⋅⋅⋅ H-N(C)-Y]的证据；这些键通过仔细的剑桥晶体结构数据库（CSD）探索、分子中的原子量子理论、柔顺常数计算以及自然键轨道和非共价相互作用（NCI）分析得以揭示。对CSD的搜索表明，在类卟啉中，内核氢原子间距小于2.5 Å（两个氢原子的范德华半径之和为2.4 Å），即约75%的情况如此。这表明带正电荷的氢原子之间存在吸引相互作用，量子化学计算进一步支持了这一点。在某些情况下，发现HOMO-DHB能量高达约20 kJ·mol⁻¹，这与任何传统氢键能量（如NH二聚体的氢键能量）相当。超共轭吸引和空间位阻之间的相互作用有利地决定了HOMO-DHBs的强度。我们预计，在更多的体系中，如咕啉、卟吩、冠醚以及氢原子紧密接触的受限体系中，都能揭示出HOMO-DHBs，并且它可能是超分子化学中需要考虑的一种重要非共价相互作用。
