Sareeya Bureekaew

A Cryogenically Flexible Covalent Organic Framework for Efficient Hydrogen Isotope Separation by Quantum Sieving

Conventional molecular sieves are often utilized in industryfor the purification of gas mixtures consisting of differentmolecular sizes. However, separation of hydrogen isotopesrequires special efforts because of their identical size, shape,and thermodynamic properties. Separation of isotope mix-tures is only possible with limited techniques, such ascryogenic distillation, thermal diffusion, and the Girdlersulfide process, but these methods have a low separationfactor and are excessively time- and energy-intensive.

Hypothetical 3D-periodic covalent organic frameworks: exploring the possibilities by a first principles derived force field

A scheme to predict as yet unknown, hypothetical covalent organic frameworks (COFs) from scratch by screening the possible space of supramolecular isomers is presented. This is achieved by extending our currently developed first principles derived force field MOF-FF with a parametrization for the boroxin unit. We considered four non-tetrahedral monomers with four boronic acid groups inspired by the corresponding carboxylate linkers known from metal–organic frameworks, and investigated the potential 3,4-connected topologies with edge-transitivity (ctn, bor, pto and tbo) or transitivity 32 (ofp, tfj, fjh, iab and nju). Due to the partly lower symmetry of the building blocks with respect to the vertex, beyond topological isomerism also isoreticular isomers are formed. We have used our reverse topological approach to construct the fictitious structures and employed an automated genetic algorithm based global minimum search approach to screen the vast configurational space of isoreticular isomerism and predicted a series of hypothetical 3D-COFs. All structures are completely relaxed by including the lattice parameters. From the atomistic structures, the accessible surface areas were determined, and, because of the isomer screening procedure, the question of crystallographic disorder could also be answered. Beyond the examples of hypothetical 3D-COFs serving as a lead for future synthetic investigations, this work is intended in particular to introduce the efficient predictive modeling method which can be applied to any kind of hypothetical COF system.

Isoreticular isomerism in 4,4-connected paddle-wheel metal–organic frameworks: structural prediction by the reverse topological approach

The theoretical structure prediction for a series of 4,4-connected copper paddle-wheel metal–organic frameworks has been performed by using the reverse topological approach, starting from the nbo-b topology. Since the rectangular-shaped tetracarboxylate linkers have a lower symmetry than the square vertices in nbo-b, two alternative insertion modes are possible for each linker. This leads, in principle, to the formation of multiple isoreticular isomers, which have been screened by a genetic global minimum search algorithm, using the first principles parameterized force field MOF-FF for structure optimization and ranking. It is found that isoreticular isomerism does, in this case, not lead to disorder but to a number of well-defined but structurally distinct phases, which all share the same network topology but have substantially different pore shapes and properties. In all cases, the experimentally observed structure is correctly predicted, but in addition a number of other slightly less stable phases are observed. Only one of these phases has been synthesized yet. The theoretical analysis of the molecular model systems of the pore cages revealed the reasons for the trends in conformational energy. This proof-of-concept study demonstrates that screening of isoreticular isomerism using an efficient but accurate force field allows prediction of the atomistic structure of even complex and flexible frameworks.

Almost Enclosed Buckyball Joints: Synthesis, Complex Formation, and Computational Simulations of Pentypticene‐Extended Tribenzotriquinacene

We report the synthesis of a tribenzotriquinacene-based (TBTQ) receptor (3) for C60 fullerene, which is extended by pentiptycene moieties to provide an almost enclosed concave ball bearing. The system serves as a model for a self-assembling molecular rotor with a flexible and adapting stator. Unexpectedly, nuclear magnetic resonance spectroscopic investigations reveal a surprisingly low complex stability constant of K1 =213±37 M(-1) for [C60 ⊂3], seemingly inconsistent with the previously reported TBTQ systems. Molecular dynamics (MD) simulations have been conducted for three different [C60 ⊂TBTQ] complexes to resolve this. Because of the dominating dispersive interactions, the binding energies increase with the contact area between guest and host, however, only for rigid host structures. By means of free-energy calculations with an explicit solvent model it can be shown that the novel flexible TBTQ receptor 3 binds weakly because of hampering entropic contributions.