Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK.
Phys Chem Chem Phys. 2018 May 3;20(17):12200-12209. doi: 10.1039/c7cp08220g.
The solvation structures of two systems rich in hydrogen and dihydrogen bonding interactions have been studied in detail experimentally through neutron diffraction with hydrogen/deuterium isotopic substitution. The results were analysed by an atomistic Monte Carlo simulation employing refinement to the experimental scattering data. The systems studied were the hydrogen storage material ammonia borane (NH3BH3, AB) dissolved in tetrahydrofuran (THF), and liquid ammonia (NH3), the latter in which AB shows unusually high solubility (260 g AB per 100 g NH3) and potential regeneration properties. The full orientational and positional manner in which AB-AB, AB-THF and AB-NH3 pairs interact with each other were successfully deciphered from the wide Q-range total neutron scattering data. This provided an unprecedented level of detail into such highly (di)hydrogen bonding solute-solvent interactions. In particular this allowed insight into the way in which H-B acts as a hydrogen bond acceptor. The (di)hydrogen bonding was naturally determined to dictate the intermolecular interactions, at times negating the otherwise expected tendency for polar molecules to align themselves with anti-parallel dipole moments. Several causes for the extreme solubility of AB in ammonia were determined, including the ability of ammonia to (di)hydrogen bond to both ends of the AB molecule and the small size of the ammonia molecule relative to AB and THF. The AB B-H to ammonia H dihydrogen bond was found to dominate the intermolecular interactions, occurring almost three times more often than any other hydrogen or dihydrogen bond in the system. The favourability of this interaction was seen on the bulk scale by a large decrease in AB clustering in ammonia compared to in the dihydrogen bond-less THF.
两个富含氢键和双氢键相互作用的系统的溶剂化结构已通过含有氢/氘同位素取代的中子衍射实验进行了详细的实验研究。结果通过采用对实验散射数据进行细化的原子蒙特卡罗模拟进行了分析。研究的系统是储氢材料氨硼烷（NH3BH3，AB）在四氢呋喃（THF）中的溶解，以及液态氨（NH3），后者中 AB 表现出异常高的溶解度（每 100g NH3 中溶解 260g AB）和潜在的再生性能。通过全向和全位置方式，成功地从宽 Q 范围的全中子散射数据中破译了 AB-AB、AB-THF 和 AB-NH3 对之间相互作用的方式。这为这种高度（双）氢键溶质-溶剂相互作用提供了前所未有的细节水平。特别是，这使得人们能够深入了解 H-B 作为氢键受体的作用方式。（双）氢键自然决定了分子间相互作用，有时会否定极性分子与反平行偶极子对齐的预期趋势。确定了 AB 在氨中具有极高溶解度的几个原因，包括氨能够与 AB 分子的两端形成（双）氢键以及氨分子相对于 AB 和 THF 的尺寸较小。AB 的 B-H 与氨的 H 二氢键被发现支配着分子间相互作用，其发生的频率几乎是该体系中任何其他氢键或双氢键的三倍。这种相互作用的有利性在较大范围内得到了证实，与没有双氢键的 THF 相比，AB 在氨中的聚集程度大大降低。
