Pham Tony, Forrest Katherine A, Mostrom Matthew, Hunt Joseph R, Furukawa Hiroyasu, Eckert Juergen, Space Brian
Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, CHE205, Tampa, FL 33620-5250, USA.
Phys Chem Chem Phys. 2017 May 24;19(20):13075-13082. doi: 10.1039/c7cp00924k.
A combined inelastic neutron scattering (INS) and theoretical study was carried out on H adsorbed in two covalent organic framework (COF) materials: COF-1 and COF-102. These COFs are synthesized from self-condensation reactions of 1,4-benzenediboronic acid (BDBA) and tetra(4-(dihydroxy)borylphenyl)methane (TBPM) molecules, respectively. Molecular simulations of H adsorption in COF-1 revealed that the H molecules occupy the region between two eclipsed layers of the COF. The most favorable H binding site in COF-1 is located between two BO clusters of the eclipsed layers. Two distinct H binding sites were identified in COF-102 from the simulations: the BO clusters and the phenyl rings of the tetraphenylmethyl units. Two-dimensional quantum rotation calculations for H adsorbed at the considered sites in both COFs resulted in rotational transitions that are in good agreement with those that appear in the corresponding INS spectra. Such calculations were important for interpreting the INS spectra in these materials. Calculation of the rotational potential energy surface for H bound at the most favorable adsorption site in COF-1 and COF-102 revealed unusually high rotational barriers that are attributed to the nature of the BO rings. The values for these barriers to rotation are greater than or comparable to those observed in some metal-organic frameworks (MOFs) that possess open-metal sites. This study demonstrates the power of using INS experiments in conjunction with theoretical calculations to gain valuable insights into the nature of the binding sites and, for the first time, the rotational dynamics of H adsorbed in COFs.
对吸附在两种共价有机框架（COF）材料（COF-1和COF-102）中的氢进行了非弹性中子散射（INS）与理论相结合的研究。这些COF分别由1,4-苯二硼酸（BDBA）和四（4-（二羟基）硼苯基）甲烷（TBPM）分子的自缩合反应合成。对COF-1中氢吸附的分子模拟表明，氢分子占据了COF两个重叠层之间的区域。COF-1中最有利的氢结合位点位于重叠层的两个BO簇之间。模拟在COF-102中确定了两个不同的氢结合位点：BO簇和四苯基甲基单元的苯环。对吸附在两种COF中所考虑位点的氢进行二维量子旋转计算，得到的旋转跃迁与相应INS光谱中出现的跃迁非常吻合。此类计算对于解释这些材料中的INS光谱很重要。计算COF-1和COF-102中最有利吸附位点处结合的氢的旋转势能面，发现存在异常高的旋转势垒，这归因于BO环的性质。这些旋转势垒的值大于或与在一些具有开放金属位点的金属有机框架（MOF）中观察到的值相当。这项研究证明了结合使用INS实验和理论计算来深入了解结合位点的性质以及首次了解吸附在COF中的氢的旋转动力学的能力。
