Transition Metal Chelation Effect in MOF-253 Materials: Guest Molecule Adsorption Dynamics and Proposed Formic Acid Synthesis Investigated by Atomistic Simulations.

The dynamic characterization of guest molecules in the metal-organic frameworks (MOFs) can always provide the insightful and inspiring information to facilitate the synthetic design of MOF materials from the bottom-up design of perspective. Herein, we present a series of atomistic molecular dynamics simulation for investigating the bipyridine dicarboxylate (bpydc) linker rotation effect on guest molecule adsorption with and without considering the transition metal (TM) chelation in MOF-253 materials. The simulated PXRD patterns of the various linker orientations present the challenge of distinguishing these structural varieties by the conventional crystalline spectroscopic measurements. The observed short inter-TM stable structure may subsequently lead to the formation of a binuclear TM catalytic site, and a proposed formic acid generation mechanism from CO2 and H2 is derived based upon the density functional theory calculations for the application of CO2 reduction.

Enhanced Predictions for the Experimental Photophysical Data Using the Featurized Schnet-Bondstep Approach.

An assessment of modifying the SchNET model for the predictions of experimental molecular photophysical properties, including absorption energy (ΔEabs), emission energy (ΔEemi), and photoluminescence quantum yield (PLQY), was reported. The solution environment was properly introduced outside the interaction layers of SchNET for not overly amplifying the solute-solvent interactions, particularly being supported by the changes of prediction errors between the presence and absence of the solvent effect. Two featurization schemes under the framework of the Schnet-bondstep approach, with featuring the concepts of reduced-atomic-number and reduced-atomic-neighbor, were demonstrated. These featurized models can consequently provide fine predictions for ΔEabs and ΔEemi with errors less than 0.1 eV. The corresponding predictions of PLQY were shown to be comparable to the previous graph convolution network model.

Low-Temperature Observation of the Excited-State Decay of Ruthenium-(Mono-2,2':6',2″-Terpyridine) Ions with Innocent Ligands: DFT Modeling of an 3MLCT-3MC Intersystem Crossing Pathway.

The synthesis, electrochemistry, and photophysical characterization of five 2,2':6',2″-terpyridine ruthenium complexes (Ru-tpy complexes) is reported. The electrochemical and photophysical behavior varied depending on the ligands, i.e., amine (NH3), acetonitrile (AN), and bis(pyrazolyl)methane (bpm), for this series of Ru-tpy complexes. The target [Ru(tpy)(AN)3]2+ and [Ru(tpy)(bpm)(AN)]2+ complexes were found to have low-emission quantum yields in low-temperature observations. To better understand this phenomenon, density functional theory (DFT) calculations were performed to simulate the singlet ground state (S0), Te, and metal-centered excited states (3MC) of these complexes. The calculated energy barriers between Te and the low-lying 3MC state for [Ru(tpy)(AN)3]2+ and [Ru(tpy)(bpm)(AN)]2+ provided clear evidence in support of their emitting state decay behavior. Developing a knowledge of the underlying photophysics of these Ru-tpy complexes will allow new complexes to be designed for use in photophysical and photochemical applications in the future.

Operando time-resolved X-ray absorption spectroscopy reveals the chemical nature enabling highly selective CO2 reduction.

Copper electrocatalysts have been shown to selectively reduce carbon dioxide to hydrocarbons. Nevertheless, the absence of a systematic study based on time-resolved spectroscopy renders the functional agent-either metallic or oxidative Copper-for the selectivity still undecidable. Herein, we develop an operando seconds-resolved X-ray absorption spectroscopy to uncover the chemical state evolution of working catalysts. An oxide-derived Copper electrocatalyst is employed as a model catalyst to offer scientific insights into the roles metal states serve in carbon dioxide reduction reaction (CO2RR). Using a potential switching approach, the model catalyst can achieve a steady chemical state of half-Cu(0)-and-half-Cu(I) and selectively produce asymmetric C2 products - C2H5OH. Furthermore, a theoretical analysis reveals that a surface composed of Cu-Cu(I) ensembles can have dual carbon monoxide molecules coupled asymmetrically, which potentially enhances the catalyst's CO2RR product selectivity toward C2 products. Our results offer understandings of the fundamental chemical states and insights to the establishment of selective CO2RR.

Enantioselective Rhodium-Catalyzed Allylation of Aliphatic Imines: Synthesis of Chiral C-Aliphatic Homoallylic Amines.

Reported herein is a method for the efficient syntheses of optically active 1-alkyl homoallylic amines in yields up to 95%, 13.5:1 dr, and 98% ee under mild, aqueous reaction conditions, via the Rh-catalyzed asymmetric allylation of aliphatic aldimines. This method provides a streamlined synthetic platform for the preparation of indolizidine and piperidine alkaloids, thus demonstrating its usefulness.

Superior Stability and Emission Quantum Yield (23% ± 3%) of Single-Layer 2D Tin Perovskite TEA2 SnI4 via Thiocyanate Passivation.

Tin-based perovskite, which exhibits narrower bandgap and comparable photophysical properties to its lead analogs, is one of the most forward-looking lead-free semiconductor materials. However, the poor oxidative stability of tin perovskite hinders the development toward practical application. In this work, the effect of pseudohalide anions on the stability and emission properties of single-layer 2D tin perovskite nanoplates with chemical formula TEA2 SnI4 (TEA = 2-thiophene-ethylammonium) is reported. The results reveal that ammonium thiocyanate (NH4 SCN) is the most effective additive in enhancing the stability and photoluminescence quantum yield of 2D TEA2 SnI4 (23 ± 3%). X-Ray photoelectron spectroscopic investigations on the thiocyanate passivated TEA2 SnI4 nanoplate show less than a 1% increase of Sn4+ signal upon 30 min exposure to air under ambient conditions (298 K, humidity ≈70%). Furthermore, no noticeable decrease in emission intensity of the nanoplate is observed after 20 h in air. The SCN- passivation during the growth stage of TEA2 SnI4 is proposed to play a crucial role in preventing the oxidation of Sn2+ and hence boosts both stability and photoluminescence yield of tin perovskite nanoplates.

PSb+P Ligand: Platform for a Stibenium to Transition-Metal Interaction.

The coordination chemistry of cationic divalent pnictogen ligands, such as nitrenium and phosphenium, has been well-explored in recent years. However, corresponding studies of a heavier congener, stibenium ion, are rare. To better facilitate a Sb+-metal interaction, a tridentate P-Sb+-P ligand with two phosphine buttresses was designed and synthesized, and its coordination chemistry toward late transition metals was investigated. The stibenium ligand was delivered as an activated P(SbCl)P-AgOTf complex (2) that releases AgCl and the P-Sb+-P ligand upon the treatment with transition metals. Reacting 2 with Rh(I) and Ir(I) metals yielded the anticipated stibenium-transition-metal complexes [(Rh(COD)Cl)2(µ-PSb+P)] OTf ([3][OTf]) and [(Ir(COD)Cl)2(µ-PSb+P)] OTf ([4][OTf]). The M-Sb+-M bridging structure was confirmed by single-crystal X-ray crystallography, and the bonding situation was examined computationally. Theoretical studies revealed the presence of three-center delocalized M-Sb+-M bonding interactions in [3][OTf] and [4][OTf].

Predicting the emission wavelength of organic molecules using a combinatorial QSAR and machine learning approach.

Organic fluorescent molecules play critical roles in fluorescence inspection, biological probes, and labeling indicators. More than ten thousand organic fluorescent molecules were imported in this study, followed by a machine learning based approach for extracting the intrinsic structural characteristics that were found to correlate with the fluorescence emission. A systematic informatics procedure was introduced, starting from descriptor cleaning, descriptor space reduction, and statistical-meaningful regression to build a broad and valid model for estimating the fluorescence emission wavelength. The least absolute shrinkage and selection operator (Lasso) regression coupling with the random forest model was finally reported as the numerical predictor as well as being fulfilled with the statistical criteria. Such an informatics model appeared to bring comparable predictive ability, being complementary to the conventional time-dependent density functional theory method in emission wavelength prediction, however, with a fractional computational expense.

Enhancing C-C bond formation by surface strain: a computational investigation for C2 and C3 intermediate formation on strained Cu surfaces.

In this study, 121 copper(100) models with surface strain are used for simulating C-C bond formation by CO2 electrochemical reduction. Its catalytic properties have been characterized by considering the formation energies of various C1 and C2 intermediates, and critical reaction steps along the CO2/CO reduction reaction paths. It turns out that the surface strain with one compressed axis and one elongated axis is geometrically beneficial for C2 product formation. The surface strain stabilizes the CO binding on the bridge sites (*CObridge) and the C2 intermediates - *OCCOH and *OCCO, and maintains a low activation energy of CO-CO coupling at around 0.57 to 0.69 eV. The surface strain also suppresses *H formation, which would allow more *CO formation leading to a higher CO2/CO reduction efficiency. Furthermore, the displaced copper models only exist under high compressing strain and were found to have great potential to activate CO2/CO into C3 products under a mild condition during the electrochemical reduction process. The activation energies for the third carbon atom coupling with C2 intermediates are 0.45-0.63 eV subject to the condition of the surface strain. The atomic arrangement with an adjacent rectangle and parallelogram is found to play an important role in producing C3 products. The selectivity of C-C bond formation induced by surface strain is demonstrated by this computational study.

Harnessing Dielectric Confinement on Tin Perovskites to Achieve Emission Quantum Yield up to 21.

Tin perovskite nanomaterial is one of the promising candidates to replace organic lead halide perovskites in lighting applications. Unfortunately, the performance of tin-based systems is markedly inferior to those featuring toxic Pb salts. In an effort to improve the emission quantum efficiency of nanoscale 2D layered tin iodide perovskites through fine-tuning the electronic property of organic ammonium salts, we came to unveil the relationship between dielectric confinement and the photoluminescent properties of tin iodide perovskite nanodisks. Our results show that increasing the dielectric contrast for organic versus inorganic layers leads to a bathochromic shift in emission peak wavelength, a decrease of exciton recombination time, and importantly a significant boost in the emission efficiency. Under optimized conditions, a leap in emission quantum yield to a record high 21% was accomplished for the nanoscale thienylethylammonium tin iodide perovskite (TEA2SnI4). The as-prepared TEA2SnI4 also possessed superior photostability, showing no sign of degradation under continuous irradiation (10 mW/cm2) over a period of 120 h.

Asymmetric Synthesis of ß-Aryl ß-Imido Sulfones Using Rhodium Catalysts with Chiral Diene Ligands: Synthesis of Apremilast.

A chiral rhodium(I)-diene catalyst enabled the one-step synthesis of ß-aryl ß-imido sulfones under mild reaction conditions. By selection of the chiral diene ligand L1a or L2, each enantiomer of the chiral ß-aryl ß-imido sulfone target can be accessed with high stereoselectivity. Demonstration of the scope of the reaction, which includes the synthesis of an N-protected chiral ß-amino ß-phenyl sulfone, culminated with the efficient synthesis of the heteroatom-rich active pharmaceutical ingredient apremilast.

Identification of Stabilizing High-Valent Active Sites by Operando High-Energy Resolution Fluorescence-Detected X-ray Absorption Spectroscopy for High-Efficiency Water Oxidation.

Composite electrocatalysts have exhibited high activities toward water electrolysis, but the catalytically active sites really in charge of the reaction are still debatable while the conventional in situ X-ray spectroscopies are not capable of conclusively identifying the interaction of these materials with the electrolyte because of the complexity of catalysis. In this work, by utilization of operando Kß1,3 high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) with a small incident angle, the operando quadrupole transition obviously showed that oxygen directly interacted with 3d orbitals of Co ions rather than that of Fe ions. Most importantly, Fe ions can promote the stabilization of the Co ions under a higher valent state during water oxidation, which may lead to a stable intermediate of reactant and its superior intrinsic activity. Accompanied by the first-principle calculations, the intermediates between 3d orbitals for surface Co ions and O 2p orbitals for the attaching hydroxide ions were ascribed to this orbital hybridization. Because of the unvaried structural features in conventional in situ techniques, operando HERFD-XAS revealed the remarkable change of chemical status to correlate with the orbital interaction rather than with the structural variation. This operando HERFD-XAS approach corresponding to the local orbital interaction in reactant/catalyst interface can potentially offer synergetic strategies toward realizing the chemical reactions or reaction pathways in various fields.

Access to ß2-Amino Acids via Enantioselective 1,4-Arylation of ß-Nitroacrylates Catalyzed by Chiral Rhodium Catalysts.

The highly enantioselective conjugate addition of a variety of arylboronic acids to ß-nitroacrylates is reported to provide optically active α-aryl ß-nitropropionates in up to 70% yields and >99.5% ee's, which are useful building blocks for preparing chiral ß2-amino acids. The applicability of this transformation is demonstrated by converting 3aa into the ß2-amino acid 5 and transforming 3ap to ß-amino ester 7 via reduction and reductive N-alkylation. The latter compound is a precursor for preparing ent-ipatasertib.

Interplay between Polarizability and Hydrogen Bond Network of Water: Reparametrizing the Flexible Single-Point-Charge Water Model by the Nonlinear Adaptive Force Matching Approach.

An adaptive force matching (AFM) scheme using the nonlinear optimization to reparametrize the three-site, flexible, and polarizable single-point-charge (SPC) water model is reported. We compare the radial distribution functions of the intermolecular oxygen-oxygen, oxygen-hydrogen, and hydrogen-hydrogen distances with the recent scattering experiments, the previous AFM-fitting water model (MP2f), and the atomic multipole expanded AMOEBA model. Our nonpolarizable SPC-3f(0) model captures the feature of the first solvation shell of bulk water. With the ad hoc inclusion of the isotropic polarizability, the polarizable SPC-3f(0.6) water model recovers the many-body effect of the second solvation shell. In the n-body decomposition analysis, the SPC-3f(0) model predicts the best agreement with MP2/aug-cc-pVTZ calculations with the use of the low-dimensional (H2O)4-ring and (H2O)6-ring clusters. For the comparison using the three-dimensional (H2O)6-prism and (H2O)16-4444a clusters, SPC-3f(0.6) predicts the results consistent with those of AMOEBA and MP2 levels. For simulating a water-cluster-dominant system such as supercritical water, SPC-3f(0) well characterizes the combination mode of bending and stretching at 5300 cm-1.

A computational exploration of CO2 reduction via CO dimerization on mixed-valence copper oxide surface.

The catalytic role of Cu ions in CO2 reduction on oxide-derived Cu has been elusive. In the presence of oxygen vacancy, COCO dimerization is predicted to be thermodynamically favorable with an accessible barrier on Cu4O3(202). The material's mixed valency is responsible for stabilizing the charge-separated (OC)δ+(CO)δ- intermediate.

Dual-Hole Excitons Activated Photoelectrolysis in Neutral Solution.

II-VI semiconductors exhibit unique behaviors that can generate dual-holes ("heavy and light"), but the application in photocatalysis is still missing. Herein, an empirical utilization of light/heavy holes in a hybrid metal cluster-2D semiconductor nanoplatelets is reported. This hybrid material can boost the hole-transfer at the surface and suppress the recombination. Different roles are enacted by light-holes and heavy-holes, in which the light-holes with higher energy and mobility can facilitate the slow kinetics of water oxidation and further reduce the onset voltage, while the massive heavy-holes can increase the resulting photocurrent by about five times, achieving a photocurrent of 2 mA cm-2 at 1.23 V versus RHE under AM 1.5 G illumination in nonsacrificial neutral solution. These strategies can be the solutions for photoelectrolysis and be beneficial for sustainable development in solar conversion.

CO2 reduction catalysis by tunable square-planar transition-metal complexes: a theoretical investigation using nitrogen-substituted carbon nanotube models.

In this work, using density functional theory, we have characterized the CO2 reduction capabilities of a series of nine transition-metal-chelated nitrogen-substituted carbon nanotube models (TM-4N2v-CNT). Each of the chelated models consists of a four-N-substituted and one vacancy framework to mimic square planar homogeneous catalysts, and is coordinated to Fe, Ru, Os, Co, Rh, Ir, Ni, Pt or Cu. The results are further investigated to search for the possible electrochemical intermediates along the CO2 reduction pathway. We've found that all of the tested elements are predicted to favor the hydrogen evolution reaction over CO2 reduction energetically (with the exception of Cu), and that only Group 8 elements are predicted to bind CO effectively and other cases prefer HCOOH formation. The observed CO binding preference could be rationalized via ligand field theory based on the molecular orbitals of the square planar complexes. With a suitable applied voltage to stabilize all of the adsorbed CO intermediates, Ru and Os are predicted to produce CH4, whereas Fe is predicted to produce CH3OH. Increasing the curvature of the CNT could reduce the required potential in the potential-determining step substantially. However, the predicted catalytic sequence is subject to only the selection of a metal center.

Adsorption and dehydrogenation of ethane, propane and butane on Rh13 clusters supported on unzipped graphene oxide and TiO2(110) - a DFT study.

The catalytic activity for the adsorption and dehydrogenation of alkanes (CnH2n+2, n = 2, 3, 4) on a low-symmetry Rh13 cluster (Rh13-Ls) is compared with a system consisting of the same cluster (Rh13-Ls) supported on either an unzipped graphene-oxide (UGO) sheet (Rh13-Ls/UGO) or a TiO2(110) surface (Rh13-Ls/TiO2). The adsorption energies of these alkanes, calculated using density-functional theory, follow the order Rh13-Ls/TiO2 ≈ Rh13-Ls/UGO > Rh13-Ls. Our proposed reaction path for the dehydrogenation of ethane, propane and butane on Rh13-Ls/UGO has first barrier heights of 0.21, 0.22 and 0.16 eV for the dissociation of a terminal C-H bond to form -C2H5, -C3H7 and -C4H9, respectively. Compared with the barriers on Rh13-Ls and Rh13-Ls/TiO2, the barrier on Rh13-Ls/UGO is the lowest for all alkanes. The calculated data, including the electronic distribution and the density of states of alkanes adsorbed on Rh13-Ls/UGO, Rh13-Ls and Rh13-Ls/TiO2, to support our results are presented.

Solvation Dynamics of CO2(g) by Monoethanolamine at the Gas-Liquid Interface: A Molecular Mechanics Approach.

A classical force field approach was used to characterize the solvation dynamics of high-density CO2(g) by monoethanolamine (MEA) at the air-liquid interface. Intra- and intermolecular CO2 and MEA potentials were parameterized according to the energetics calculated at the MP2 and BLYP-D2 levels of theory. The thermodynamic properties of CO2 and MEA, such as heat capacity and melting point, were consistently predicted using this classical potential. An approximate interfacial simulation for CO2(g)/MEA(l) was performed to monitor the depletion of the CO2(g) phase, which was influenced by amino and hydroxyl groups of MEA. There are more intramolecular hydrogen bond interactions notably identified in the interfacial simulation than the case of bulk MEA(l) simulation. The hydroxyl group of MEA was found to more actively approach CO2 and overpower the amino group to interact with CO2 at the air-liquid interface. With artificially reducing the dipole moment of the hydroxyl group, CO2-amino group interaction was enhanced and suppressed CO2(g) depletion. The hydroxyl group of MEA was concluded to play dual but contradictory roles for CO2 capture.

Dihydrooxazine N-Oxide Intermediates as Resting States in Organocatalytic Kinetic Resolution of Functionalized Nitroallylic Amines with Aldehydes.

Kinetic resolution of nitroallylic amines was established using chiral α,α-l-diphenylprolinol silyl ether auxiliary through isolation of the dihydrooxazine N-oxide intermediates. Further hydrolyzing the resting states provided tetrahydropyridines in high chemical yields and high to excellent stereoselectivities (up to >20:1 dr and 98% ee). A detailed mechanistic explanation for stereoselective protonation in the dihydrooxazine was probed computationally. In addition, the probable intermediates in α-halogenation of aldehydes (masked with enamines) were isolated to provide crystallographic evidence.