MOFGalaxyNet: a social network analysis for predicting guest accessibility in metal-organic frameworks utilizing graph convolutional networks.

Metal-organic frameworks (MOFs), are porous crystalline structures comprising of metal ions or clusters intricately linked with organic entities, displaying topological diversity and effortless chemical flexibility. These characteristics render them apt for multifarious applications such as adsorption, separation, sensing, and catalysis. Predominantly, the distinctive properties and prospective utility of MOFs are discerned post-manufacture or extrapolation from theoretically conceived models. For empirical researchers unfamiliar with hypothetical structure development, the meticulous crystal engineering of a high-performance MOF for a targeted application via a bottom-up approach resembles a gamble. For example, the precise pore limiting diameter (PLD), which determines the guest accessibility of any MOF cannot be easily inferred with mere knowledge of the metal ion and organic ligand. This limitation in bottom-up conceptual understanding of specific properties of the resultant MOF may contribute to the cautious industrial-scale adoption of MOFs.Consequently, in this study, we take a step towards circumventing this limitation by designing a new tool that predicts the guest accessibility-a MOF key performance indicator-of any given MOF from information on only the organic linkers and the metal ions. This new tool relies on clustering different MOFs in a galaxy-like social network, MOFGalaxyNet, combined with a Graphical Convolutional Network (GCN) to predict the guest accessibility of any new entry in the social network. The proposed network and GCN results provide a robust approach for screening MOFs for various host-guest interaction studies.

Covalent Organic Framework as a Metal-Free Photocatalyst for Dye Degradation and Radioactive Iodine Adsorption.

Exploring a covalent organic framework (COF) material as an efficient metal-free photocatalyst and as an adsorbent for the removal of pollutants from contaminated water is very challenging in the context of sustainable chemistry. Herein, we report a new porous crystalline COF, C6-TRZ-TPA COF, via segregation of donor-acceptor moieties through the extended Schiff base condensation between tris(4-formylphenyl)amine and 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline. This COF displayed a Brunauer-Emmett-Teller (BET) surface area of 1058 m2 g-1 with a pore volume of 0.73 cc g-1. Again, extended π-conjugation, the presence of heteroatoms throughout the framework, and a narrow band gap of 2.2 eV, all these features collectively work for the environmental remediation in two different perspectives: it could harness solar energy for environmental clean-up, where the COF has been explored as a robust metal-free photocatalyst for wastewater treatment and as an adsorbent for iodine capture. In our endeavor of wastewater treatment, we have conducted the photodegradation of rose bengal (RB) and methylene blue (MB) as model pollutants since these are extremely toxic, are health hazard, and bioaccumulative in nature. The catalyst C6-TRZ-TPA COF showed a very high catalytic efficiency of 99% towards the degradation of 250 parts per million (ppm) of RB solution in 80 min under visible light irradiation with the rate constant of 0.05 min-1. Further, C6-TRZ-TPA COF is found to be an excellent adsorbent as it efficiently adsorbed radioactive iodine from its solution as well as from the vapor phase. The material exhibits a very rapid iodine capturing tendency with an outstanding iodine vapor uptake capacity of 4832 mg g-1.

Effect of unwanted guest molecules on the stacking configuration of covalent organic frameworks: a periodic energy decomposition analysis.

Elucidating the precise stacking configuration of a covalent organic framework, COF, is critical to fully understand their various applications. Unfortunately, most COFs form powder crystals whose atomic characterisations are possible only through powder X-ray diffraction (PXRD) analysis. However, this analysis has to be coupled with computational simulations, wherein computed PXRD patterns for different stacking configurations are compared with experimental patterns to predict the precise stacking configuration. This task is often computationally challenging firstly because, computation of these systems mostly rely on the use of semi-empirical methods that need to be adequately parametrised for the system being studied and secondly because some of these compounds possess guest molecules, which are not often taken into account during computation. COF-1 is an extreme case in which the presence of the guest molecule plays a critical role in predicting the precise stacking configuration. Using this as a case study, we mapped out a full PES for the stacking configuration in the guest free and guest containing system using the GFN-xTB semi-empirical method followed by a periodic energy decomposition analysis using first-principles Density Functional Theory (DFT). Our results showed that the presence of the guest molecule leads to multiple low energy stacking configurations with significantly different lateral offsets. Also, the semi-empirical method does not precisely predict DFT low energy configurations, however, it accurately accounts for dispersion. Finally, our quantum-mechanical analysis demonstrates that electrostatic-dispersion model suggested Hunter and Sanders accurately describes the stacking in 2D COFs as opposed to the newly suggested Pauli-dispersion model.

Role of Host-Guest Interaction in Understanding Polymerisation in Metal-Organic Frameworks.

Metal-organic frameworks, MOFs, offer an effective template for polymerisation of polymers with precisely controlled structures within the sub-nanometre scales. However, synthetic difficulties such as monomer infiltration, detailed understanding of polymerisation mechanisms within the MOF nanochannels and the mechanism for removing the MOF template post polymerisation have prevented wide scale implementation of polymerisation in MOFs. This is partly due to the significant lack in understanding of the energetic and atomic-scale intermolecular interactions between the monomers and the MOFs. Consequently in this study, we explore the interaction of varied concentration of styrene, and 3,4-ethylenedioxythiophene (EDOT), at the surface and in the nanochannel of Zn2(1,4-ndc)2 (dabco), where 1,4-ndc = 1,4-naphthalenedicarboxylate and dabco = 1,4-diazabicyclo[2.2.2]octane. Our results showed that the interactions between monomers are stronger in the nanochannels than at the surfaces of the MOF. Moreover, the MOF-monomer interactions are strongest in the nanochannels and increase with the number of monomers. However, as the number of monomers increases, the monomers turn to bind more strongly at the surface leading to a potential agglomeration of the monomers at the surface.

Supramolecular Chromatographic Separation of C60 and C70 Fullerenes: Flash Column Chromatography vs. High Pressure Liquid Chromatography.

A silica-bound C-butylpyrogallol[4]arene chromatographic stationary phase was prepared and characterised by thermogravimetric analysis, scanning electron microscopy, NMR and mass spectrometry. The chromatographic performance was investigated by using C60 and C70 fullerenes in reverse phase mode via flash column and high-pressure liquid chromatography (HPLC). The resulting new stationary phase was observed to demonstrate size-selective molecular recognition as postulated from our in-silico studies. The silica-bound C-butylpyrogallol[4]arene flash and HPLC stationary phases were able to separate a C60- and C70-fullerene mixture more effectively than an RP-C18 stationary phase. The presence of toluene in the mobile phase plays a significant role in achieving symmetrical peaks in flash column chromatography.

Pore engineering of ultrathin covalent organic framework membranes for organic solvent nanofiltration and molecular sieving.

The advantages of two dimensional covalent organic framework membranes to achieve high flux have been demonstrated, but the capability of easy structural modification to manipulate the pore size has not been fully explored yet. Here we report the use of the Langmuir-Blodgett method to synthesize two ultrathin covalent organic framework membranes (TFP-DPF and TFP-DNF) that have a similar framework structure to our previously reported covalent organic framework membrane (TFP-DHF) but different lengths of carbon chains aiming to rationally control the pore size. The membrane permeation results in the applications of organic solvent nanofiltration and molecular sieving of organic dyes showed a systematic shift of the membrane flux and molecular weight cut-off correlated to the pore size change. These results enhanced our fundamental understanding of transport through uniform channels at nanometer scales. Pore engineering of the covalent organic framework membranes was demonstrated for the first time.

Predicting the Outcome of Photocyclisation Reactions: A Joint Experimental and Computational Investigation.

Photochemical oxidative cyclodehydrogenation reactions are a versatile class of aromatic ring-forming reactions. They are tolerant to functional group substitution and heteroatom inclusion, so can be used to form a diverse range of extended polyaromatic systems by fusing existing ring substituents. However, despite their undoubted synthetic utility, there are no existing models-computational or heuristic-that predict the outcome of photocyclisation reactions across all possible classes of reactants. This can be traced back to the fact that "negative" results are rarely published in the synthetic literature and the lack of a general conceptual framework for understanding how photoexcitation affects reactivity. In this work, we address both of these issues. We present experimental data for a series of aromatically substituted pyrroles and indoles, and show that quantifying induced atomic forces upon photoexcitation provides a powerful predictive model for determining whether a given reactant will photoplanarise and hence proceed to photocyclised product under appropriate reaction conditions. The propensity of a molecule to photoplanarise is related to localised changes in charge distribution around the putative forming ring upon photoexcitation. This is promoted by asymmetry in molecular structures and/or charge distributions, inclusion of heteroatoms and ethylene bridging and well-separated or isolated photocyclisation sites.