Reticular frameworks are crystalline porous materials that form via the self-assembly of molecular building blocks (i.e., nodes and linkers) in different topologies. Many of them have high internal surface areas and other desirable properties for gas storage, separation, and other applications. The notable variety of the possible building blocks and the diverse ways they can be assembled endow reticular frameworks with a near-infinite combinatorial design space, making reticular chemistry both promising and challenging for prospective materials design. Here, we propose an automated nanoporous materials discovery platform powered by a supramolecular variational autoencoder (SmVAE) for the generative design of reticular materials with desired functions. We demonstrate the automated design process with a class of metal-organic framework (MOF) structures and the goal of separating CO2 from natural gas or flue gas. Our model exhibits high fidelity in capturing structural features and reconstructing MOF structures. We show that the autoencoder has a promising optimization capability when jointly trained with multiple top adsorbent candidates identified for superior gas separation. MOFs discovered here are strongly competitive against some of the best-performing MOFs/zeolites ever reported. This platform lays the groundwork for the design of reticular frameworks for desired applications.

Postcombustion CO 2 capture and storage (CCS) is a key technological approach to reducing greenhouse gas emission while we transition to carbon-free energy production. However, current solvent-based CO 2 capture processes are considered too energetically expensive for widespread deployment. Vacuum swing adsorption (VSA) is a low-energy CCS that has the potential for industrial implementation if the right sorbents can be found. Metal−organic framework (MOF) materials are often promoted as sorbents for low-energy CCS by highlighting select adsorption properties without a clear understanding of how they perform in real-world VSA processes. In this work, atomistic simulations have been fully integrated with a detailed VSA simulator, validated at the pilot scale, to screen 1632 experimentally characterized MOFs. A total of 482 materials were found to meet the 95% CO 2 purity and 90% CO 2 recovery targets (95/90-PRTs) 365 of which have parasitic energies below that of solvent-based capture (∼290 kWh e / MT CO 2 ) with a low value of 217 kWh e /MT CO 2 . Machine learning models were developed using common adsorption metrics to predict a material's ability to meet the 95/90-PRT with an overall prediction accuracy of 91%. It was found that accurate parasitic energy and productivity estimates of a VSA process require full process simulations.

Incorporation of a solvent vapor-saturated nitrogen purge in an electrospray ionization source is demonstrated as a highly selective method for synthesizing clusters consisting of a transition-metal ion complex and organic solvent molecules for use in studies of the influence of local solvation on structure and reactivity. This new technique first uses collisions to completely remove the residual electrospray solvent from the gas-phase ions and then re-forms clusters by association of solvent molecules from the purge in an expansion as the ions pass through the first and second stages of differential pumping in the electrospray ionization source. The resolvation process is selective in that only clusters with the purge solvent are detected under the optimized conditions reported. Clusters of the tris(2,2‘-bipyridyl)iron(II) complex, [Fe(bpy)3]2+, with a variety of solvents (acetone, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, ethanol, and methanol) have been prepared by electrospraying a dilute methanolic solution and simply introducing the solvent of interest to the nitrogen purge. Dimethyl sulfoxide and N,N-dimethylformamide are unsuitable as electrospray solvents; nevertheless, clusters with these solvents can be formed using this purge technique. In addition, [Fe(bpy)3]2+ has been stabilized in clusters with dimethyl sulfoxide, a solvent which rapidly displaces the bipyridyl ligands of the complex in bulk solution.

The solvent dependence of metal-to-ligand charge transfer (MLCT) in the bis(2,2‘,2‘‘-terpyridyl)iron(II) complex, [Fe(terpy)2]2+, isolated in small gas-phase clusters with one or four molecules of the polar, organic solvents acetone, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, methanol, and pyridazine is reported. The shift in the maximum of the MLCT band, E op, for [Fe(terpy)2·(solvent)1]2+ clusters, measured using laser photofragmentation mass spectrometry, relative to the corresponding values in bulk solution ranges from +601 cm-1 for acetone to +764 cm-1 for pyridazine. The solvent dependence of the outer-sphere reorganization energy predicted by a dielectric continuum model provides a context for comparing E op values determined for MLCT in [Fe(terpy)2·(solvent) n ]2+ clusters (n = 1, 4) with those measured in solution. A model derived from Kirkwood's equation for the mutual electrostatic interaction energy of an ion and a polar medium predicts that the solvent reorganization energy associated with MLCT in [Fe(terpy)2]2+ is a linear function of (1 − D op)/(2D op + 1), where D op is the optical dielectric constant of the bulk solvent. A linear relationship between E op and (1 − D op)/(2D op + 1) is observed not only in the bulk solvents, as anticipated, but also in clusters containing as few as four solvent molecules.

This paper reports the first investigation of the energetics of charge transfer in a coordination complex containing a divalent transition-metal ion as a function of the extent of solvation and provides a detailed description of the first instrument designed for spectroscopic characterization of gas-phase ions and clusters produced by electrospray ionization. Metal-to-ligand charge transfer (MLCT) is probed by laser photofragmentation mass spectrometry in clusters of the complex tris(2,2‘-bipyridyl)iron(II), [Fe(bpy)3]2+, with methanol prepared by electrospray ionization. Excitation of the MLCT transition in [Fe(bpy)3]2+ triggers evaporation of methanol solvent molecules from these clusters, permitting indirect detection of absorption. Measurement of ion beam depletion and/or production of charged photofragments as a function of photon energy yields the red edge of the MLCT band for [Fe(bpy)3·(CH3OH) n ]2+ clusters, n = 2−6. Increasing the number of methanol molecules in the clusters shifts the onset of the MLCT band to lower energies, reflecting preferential solvation of the MLCT excited state of [Fe(bpy)3]2+ relative to its ground state. A measurable fraction of mass-selected [Fe(bpy)3·(CH3OH) n ]2+ clusters also lose methanol molecules through metastable decomposition between primary mass selection and secondary mass analysis. Application of the evaporative ensemble model with RRK rate constants for metastable decomposition permits estimation of sequential methanol binding energies and internal temperatures for [Fe(bpy)3·(CH3OH) n ]2+ clusters prepared by electrospray ionization.