No abstract

Raman spectroscopy was used to establish direct evidence of heterometallic metal centers in a metal–organic framework (MOF). The Cu3(BTC)2 MOF HKUST-1 (BTC3– = benzenetricarboxylate) was transmetalated by heating it in a solution of RhCl3 to substitute Rh2+ ions for Cu2+ ions in the dinuclear paddlewheel nodes of the framework. In addition to the Cu–Cu and Rh–Rh stretching modes, Raman spectra of (Cu x Rh1–x )3(BTC)2 show the Cu–Rh stretching mode, indicating that mixed-metal Cu–Rh nodes are formed after transmetalation. Density functional theory studies confirmed the assignment of a Raman peak at 285 cm–1 to the Cu–Rh stretching vibration. Electron paramagnetic resonance spectroscopy experiments further supported the conclusion that Rh2+ ions are substituted into the paddlewheel nodes of Cu3(BTC)2 to form an isostructural heterometallic MOF, and electron microscopy studies showed that Rh and Cu are homogeneously distributed in (Cu x Rh1–x )3(BTC)2 on the nanoscale.

The remediation of organohalides from water is a challenging process in environment protection and water treatment. Herein, we report a molecular copper(I) complex with two triazole units, CuT2, in a heterogeneous aqueous system that is capable of dechlorinating dichloromethane (CH 2 Cl 2 ) to afford hydrocarbons (methane, ethane, and ethylene). The catalytic performance is evaluated in water and presented high Faradaic efficiency (average 70% CH 4 ) across a range of potentials (−1.1 to −1.6 V vs Ag/AgCl) and high activity (maximum −25.1 mA/cm 2 at −1.6 V vs Ag/AgCl) with a turnover number of 2.0 × 10 7 . The CuT2 catalyst also showed excellent stability for 14 h of constant exposure to CH 2 Cl 2 and 10 h of CH 2 Cl 2 exposure cycling. The control compound, a copper-free triazole unit (T1), was also investigated under the same condition and showed inferior catalytic activity, indicating the importance of the copper center. Plausible catalytic mechanisms are proposed for the formation of C 1 and C 2 products via radical intermediates. Computational studies provided additional insight into the reaction mechanism and the selectivity toward the CH 4 formation. The findings in this study demonstrate that complex CuT2 is an efficient and stable catalyst for the dehalogenation of CH 2 Cl 2 and could potentially be used for the exploration of the removal of halogenated species from aqueous systems.

An analysis of how different density functionals, basis sets, and relativistic approximations affect the computed properties of lanthanide-containing molecules allows one to determine which method provides the highest accuracy. Historically, many different density functional methods have been employed to perform calculations on lanthanide complexes and so herein is a detailed analysis of how different methodological combinations change the computed properties of three different families of lanthanide-bearing species: lanthanide diatomic molecules (fluorides and oxides) and their dissociation energies; larger, molecular complexes and their geometries; and lanthanide bis(2-ethylhexyl)phosphate structures and their separation free energies among the lanthanide series. The B3LYP/Sapporo/Douglas−Kroll−Hess (DKH) method was shown to most accurately reproduce dissociation energies calculated at the CCSDT(Q) level of theory with a mean absolute deviation of 1.3 kcal/mol. For the calculations of larger, molecular complexes, the TPSSh/Sapporo/DKH method led to the smallest deviation from experimentally refined crystal structures. Finally, this same method led to calculated separation factors for lanthanide bis(2ethylhexyl)phosphate structures that matched very closely with experimental values.

Electrocatalytic proton reduction to form dihydrogen (H 2 ) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main-group-element-based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (À 4.6 mA cm À 2 at À 1.7 V vs. Fc/Fc + ) and high selectivity (H 2 Faradaic efficiency of 94 % at À 1.7 V vs. Fc/Fc + ) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOF max ) for H 2 production was obtained as 1099 s À 1 . Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron-chemical-electron-chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction.

The prediction of a variety of polymer properties from their monomer composition has been a challenge for material informatics, and their development can lead to a more effective exploration of the material space. In this work, PolymerGNN, a multitask machine learning architecture that relies on polymeric features and graph neural networks has been developed towards this goal. PolymerGNN provides accurate estimates for polymer properties based on a database of complex and heterogeneous polyesters (linear/branched, homopolymers/copolymers) with experimentally refined properties. In PolymerGNN, each polyester is represented as a set of monomer units, which are introduced as molecular graphs. A virtual screening of a large, computationally generated database with materials of variable composition was performed, a task that demonstrates the applicability of the PolymerGNN on future studies that target the exploration of the polymer space. Finally, a discussion on the explainability of the models is provided.

Step-shaped adsorption–desorption of gaseous payloads by flexible metal–organic frameworks can facilitate the delivery of large usable capacities with significantly reduced energetic penalties. This is desirable for the storage, transport, and delivery of H2, as prototypical adsorbents require large swings in pressure and temperature to achieve usable capacities approaching their total capacities. However, the weak physisorption of H2 typically necessitates undesirably high pressures to induce the framework phase change. As de novo design of flexible frameworks is exceedingly challenging, the ability to intuitively adapt known frameworks is required. We demonstrate that the multivariate linker approach is a powerful tool for tuning the phase change behavior of flexible frameworks. In this work, 2-methyl-5,6-difluorobenzimidazolate was solvothermally incorporated into the known framework CdIF-13 (sod-Cd(benzimidazolate)2), resulting in the multivariate framework sod-Cd(benzimidazolate)1.87(2-methyl-5,6-difluorobenzimidazolate)0.13 (ratio = 14:1), which exhibited a considerably reduced stepped adsorption threshold pressure while maintaining the desirable adsorption–desorption profile and capacity of CdIF-13. At 77 K, the multivariate framework exhibits stepped H2 adsorption with saturation below 50 bar and minimal desorption hysteresis at 5 bar. At 87 K, saturation of step-shaped adsorption occurs by 90 bar, with hysteresis closing at 30 bar. These adsorption–desorption profiles enable usable capacities in a mild pressure swing process above 1 mass %, representing 85–92% of the total capacities. This work demonstrates that the desirable performance of flexible frameworks can be readily adapted through the multivariate approach to enable efficient storage and delivery of weakly physisorbing species.

Electrocatalytic hydrogen gas production is considered a potential pathway towards carbon-neutral energy sources. However, the development of this technology is hindered by the lack of efficient, cost-effective, and environmentally benign catalysts. In this study, a main-groupelement-based electrocatalyst, SbSalen, is reported to catalyze the hydrogen evolution reaction (HER) in an aqueous medium. The heterogenized molecular system achieved a Faradaic efficiency of 100 % at À 1.4 V vs. NHE with a maximum current density of À 30.7 mA/cm 2 . X-ray photoelectron spectroscopy of the catalyst-bound working electrode before and after electrolysis confirmed the molecular stability during catalysis. The turnover frequency was calculated as 43.4 s À 1 using redox-peak integration. The kinetic and mechanistic aspects of the electrocatalytic reaction were further examined by computational methods. This study provides mechanistic insights into main-group-element electrocatalysts for heterogeneous small-molecule conversion.