Vijayalakshmi Kunduchi P, Suresh Cherumuttathu H
Analytical and Spectroscopy Division, Analytical, Spectroscopy and Ceramics Group, Propellants, Polymers, Chemicals and Materials Entity, Vikram Sarabhai Space Centre , Thiruvananthapuram- 695022, India.
Chemical Sciences and Technology Division, CSIR- National Institute for Interdisciplinary Science and Technology , Thiruvananthapuram, 695 019, India.
J Phys Chem A. 2017 Apr 6;121(13):2704-2714. doi: 10.1021/acs.jpca.7b01527. Epub 2017 Mar 24.
Cluster formation of ammonia borane (NHBH) driven by noncovalent H···H dihydrogen interaction is investigated at the M06L/6-311+G(d,p) level of density functional theory. For clusters containing up to six monomers, ladder, cyclic, stacked, cross-stacked, end-on, mixed and hexagonal configurations have been screened for their energetic stability. In the dimer, 7.94 kcal/mol stabilization energy per monomer (E) is observed. Compared to ladder and cyclic configurations, a tetramer consisting of stacked dimer units is more stable by 3.0 kcal/mol whereas a hexamer composed of hexagonally arranged monomers promoting side-on H···H interaction is more stable than a stacked configuration by 2.5 kcal/mol. The hexagonal packing of cluster is repeated to obtain (NHBH), (NHBH), (NHBH), (NHBH), and (NHBH) clusters. The E 17.81 kcal/mol observed for (NHBH) is 2.24 fold higher than the dimer, suggesting strong cooperativity in cluster growth mechanism. The zwitterionic features of NHBH is characterized in terms of molecular electrostatic potential (MESP) features. During cluster formation, donation of electron density from negatively charged BH unit of a monomer to the positively charged NH unit of other interacting monomers occurs through H···H dihydrogen bonding. The extent of electron donation is revealed through the value of MESP minium (V) in every monomer. A strong linear correlation between the total value of V for a cluster (ΣV) and the total stabilization energy of the cluster (E) is established. Further, MESP at the nuclei of N (V) and B (V) are found to be very sensitive to the strength of H···H bonding. With respect to free NHBH, the total change in V (ΣΔV) as well as the total change in V (ΣΔV) in a cluster shows near-perfect linear correlation with E. Further, the magnitude of the three quantities, viz. ΣΔV, ΣΔV, and E is nearly same and indicates that the cluster formation of NHBH is almost effectively controlled by electrostatics of dihydrogen interactions. The extended network of dihydrogen interactions observed in large clusters and the significant positive cooperativity effect of such interactions support the use of ammonia borane as a potential hydrogen storage material.
在密度泛函理论的M06L/6 - 311 + G(d,p)水平下，研究了由非共价H···H双氢键驱动的氨硼烷（NHBH）团簇的形成。对于包含多达六个单体的团簇，筛选了阶梯状、环状、堆叠状、交叉堆叠状、端对端、混合状和六边形构型的能量稳定性。在二聚体中，观察到每个单体的稳定化能量（E）为7.94 kcal/mol。与阶梯状和环状构型相比，由堆叠二聚体单元组成的四聚体更稳定，稳定化能量高3.0 kcal/mol，而由促进侧向H···H相互作用的六边形排列单体组成的六聚体比堆叠构型更稳定，稳定化能量高2.5 kcal/mol。将团簇的六边形堆积重复以获得(NHBH)、(NHBH)、(NHBH)、(NHBH)和(NHBH)团簇。(NHBH)的E为17.81 kcal/mol，比二聚体高2.24倍，表明团簇生长机制中存在强协同作用。氨硼烷的两性离子特征通过分子静电势（MESP）特征来表征。在团簇形成过程中，一个单体带负电的BH单元向其他相互作用单体带正电的NH单元的电子密度转移通过H···H双氢键发生。电子转移程度通过每个单体的MESP最小值（V）的值来揭示。建立了团簇的V总值（ΣV）与团簇的总稳定化能量（E）之间的强线性相关性。此外，发现N原子核处的MESP（V）和B原子核处的MESP（V）对H···H键的强度非常敏感。相对于游离的氨硼烷，团簇中V的总变化（ΣΔV）以及V的总变化（ΣΔV）与E呈现近乎完美的线性相关性。此外，ΣΔV、ΣΔV和E这三个量的大小几乎相同，表明氨硼烷团簇的形成几乎有效地由双氢键的静电作用控制。在大团簇中观察到的双氢键扩展网络以及这种相互作用的显著正协同效应支持了将氨硼烷用作潜在储氢材料。
