Quantum effects in CH activation with [CuO] complexes.

We investigate the mechanism of primary alkane CH bond activation with dioxo-dicopper ([CuO]) complexes, which serve as model catalysts for enzymes capable of activating CH bonds under mild conditions. As large H/D kinetic isotope effects (KIEs) are observed in enzymes and their synthetic mimics, we employ density functional theory along with variational transition-state theory with multidimensional tunneling to estimate reaction rate coefficients. By systematically varying ligand electrophilicity and substrate chain length, we examine trends in rate coefficients and kinetic isotope effects for the two proposed CH activation pathways - one-step oxo-insertion and two-step radical recombination.

A configuration sampling study of reaction intermediates constituting catalytic cycles for CO oxidation with Pt1/TiO2.

We combine ab initio molecular dynamics (AIMD) simulations with an unsupervised machine learning approach to automate the search for possible configurations of CO oxidation reaction intermediates catalyzed by the atomically dispersed Pt1/TiO2 catalyst. Following the example of Roncoroni and co-workers [Phys. Chem.

Performance of Density Functionals for Excited-State Properties of Isolated Chromophores and Exciplexes: Emission Spectra, Solvatochromic Shifts, and Charge-Transfer Character.

This study assesses the performance of various meta-generalized gradient approximation (meta-GGA), global hybrid, and range-separated hybrid (RSH) density functionals in capturing the excited-state properties of organic chromophores and their excited-state complexes (exciplexes). Motivated by their uses in solar energy harvesting and photoredox CO reduction, we use oligo-(p-phenylenes) and their excited-state complexes with triethylamine as model systems. We focus on the fluorescence properties of these systems, specifically emission energies.

The Hydrogen Evolution Activity of BaZrS, BaTiS, and BaVS Chalcogenide Perovskites.

Chalcogenide perovskites are a class of materials with electronic and optoelectronic properties desirable for solar cells, infrared optics, and computing. The oxide counterparts of these chalcogenides have been studied extensively for their electrocatalytic and photoelectrochemical properties. As chalcogenide perovskites are more covalent, conductive, and stable, we hypothesize that they are more viable as electrocatalysts than oxide perovskites.

Simulating excited-state complex ensembles: Fluorescence and solvatochromism in amine-arene exciplexes.

Exciplexes are excited-state complexes formed as a result of partial charge transfer from the donor to the acceptor species when one moiety of the donor-acceptor pair is electronically excited. The arene-amine exciplex formed between oligo-(p-phenylene) (OPP) and triethylamine (TEA) is of interest in the catalytic photoreduction of CO2 because it can compete with complete electron transfer to the OPP catalyst. Therefore, formation of the exciplex can hinder the generation of a radical anion OPP·- necessary for subsequent CO2 reduction.

Inferring the Energetics of CO-Aniline Adduct Formation from Vibrational Spectroscopy.

Control of atmospheric CO is an important contemporary scientific and engineering challenge. Toward this goal, the reaction of CO with amines to form carbamate bonds is an established method for CO capture. However, controllable reversal of this reaction remains difficult and requires tuning the energetics of the carbamate bond.

Controlling selectivity for dechlorination of poly(vinyl chloride) with (xantphos)RhCl.

Reaction of poly(vinyl chloride) (PVC) with 5 equiv. of triethyl silane in THF, in the presence of generated (xantphos)RhCl catalyst, results in partial reduction of PVC hydrodechlorination to yield poly(vinyl chloride--ethylene). Increasing catalyst loading or using ,-dimethylacetamide (DMA) as a solvent both diminished selectivity for hydrodechlorination, promoting competitive dehydrochlorination reactions.

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi Fe O Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis.

Potential applications of the earth-abundant, low-cost, and non-critical perovskite CaTi Fe O in electrocatalysis, photocatalysis, and oxygen-transport membranes have motivated research to tune its chemical composition and morphology. However, investigations on the decomposition mechanism(s) of CaTi Fe O under thermochemically reducing conditions are limited, and direct evidence of the nano- and atomic-level decomposition process is not available in the literature. In this work, the phase evolution of CaTi Fe O ( = 0-0.

Recent Advances toward Efficient Calculation of Higher Nuclear Derivatives in Quantum Chemistry.

In this paper, we provide an overview of state-of-the-art techniques that are being developed for efficient calculation of second and higher nuclear derivatives of quantum mechanical (QM) energy. Calculations of nuclear Hessians and anharmonic terms incur high costs and memory and scale poorly with system size. Three emerging classes of methods─machine learning (ML), automatic differentiation (AD), and matrix completion (MC)─have demonstrated promise in overcoming these challenges.

Toward Efficient Direct Dynamics Studies of Chemical Reactions: A Novel Matrix Completion Algorithm.

This paper describes the development and testing of a polynomial variety-based matrix completion (PVMC) algorithm. Our goal is to reduce computational effort associated with reaction rate coefficient calculations using variational transition state theory with multidimensional tunneling (VTST-MT). The algorithm recovers eigenvalues of quantum mechanical Hessians constituting the minimum energy path (MEP) of a reaction using only a small sample of the information, by leveraging underlying properties of these eigenvalues.

A matrix completion algorithm for efficient calculation of quantum and variational effects in chemical reactions.

This work examines the viability of matrix completion methods as cost-effective alternatives to full nuclear Hessians for calculating quantum and variational effects in chemical reactions. The harmonic variety-based matrix completion (HVMC) algorithm, developed in a previous study [S. J.

Organic photoredox catalysts for CO reduction: Driving discovery with genetic algorithms.

This work implements a genetic algorithm (GA) to discover organic catalysts for photoredox CO reduction that are both highly active and resistant to degradation. The lowest unoccupied molecular orbital energy of the ground state catalyst is chosen as the activity descriptor and the average Mulliken charge on all ring carbons is chosen as the descriptor for resistance to degradation via carboxylation (both obtained using density functional theory) to construct the fitness function of the GA. We combine the results of multiple GA runs, each based on different relative weighting of the two descriptors, and rigorously assess GA performance by calculating electron transfer barriers to CO reduction.

Kinetics and mechanistic details of bulk ZnO dissolution using a thiol-imidazole system.

Oxide dissolution is important for metal extraction from ores and has become an attractive route for the preparation of inks for thin film solution deposition; however, oxide dissolution is often kinetically challenging. While binary "alkahest" systems comprised of thiols and -donor species, such as amines, are known to dissolve a wide range of oxides, the mechanism of dissolution and identity of the resulting solute(s) remain unstudied. Here, we demonstrate facile dissolution of both bulk synthetic and natural mineral ZnO samples using an "alkahest" that operates reaction with thiophenol and 1-methylimidazole (MeIm) to give a single, pseudotetrahedral Zn(SPh)(MeIm) molecular solute identified by X-ray crystallography.

A computational study of the mechanism of chloroalkane dechlorination with Rh(I) complexes.

This work utilizes density functional theory and the energetic span model to determine steps constituting the catalytic cycle and turnover frequencies, respectively, for C(sp)-Cl activation and dechlorination by model Rh(I) complexes containing POP-Pincer ligands with the aid of Na salts. The steps in the catalytic cycle with NaHCO as the hydrogen carrier are (i) rotation of the Rh-Cl bond out of the ligand plane, (ii) metal insertion into the C-Cl bond, (iii) formate binding and removal of one Cl as NaCl, (iv) formation and removal of CO from formate-bound Rh, and (v) hydrogenation of the alkyl bound to Rh to form an alkane, followed by Rh-Cl rotation to restore the catalyst resting state. We find that the the turnover-determining states and TOFs for monochloropropane (MCP) dechlorination depend strongly on the hydrogen carrier, with significantly higher TOF for NaH than NaHCO.

Photoredox Chemistry with Organic Catalysts: Role of Computational Methods.

Organic catalysts have the potential to carry out a wide range of otherwise thermally inaccessible reactions via photoredox routes. Early demonstrated successes of organic photoredox catalysts include one-electron CO reduction and H generation via water splitting. Photoredox systems are challenging to study and design owing to the sheer number and diversity of phenomena involved, including light absorption, emission, intersystem crossing, partial or complete charge transfer, and bond breaking or formation.

Perspective and challenges in electrochemical approaches for reactive CO separations.

The desire toward decarbonization and renewable energy has sparked research interests in reactive CO separations, such as direct air capture that utilize electricity as opposed to conventional thermal and pressure swing processes, which are energy-intensive, cost-prohibitive, and fossil-fuel dependent. Although the electrochemical approaches in CO capture that support negative emissions technologies are promising in terms of modularity, smaller footprint, mild reaction conditions, and possibility to integrate into conversion processes, their practice depends on the wider availability of renewable electricity. This perspective discusses key advances made in electrolytes and electrodes with redox-active moieties that reversibly capture CO or facilitate its transport from a CO-rich side to a CO-lean side within the last decade.

Probing the Ligand Exchange of N-Heterocyclic Carbene-Capped AgS Nanocrystals with Amines and Carboxylic Acids.

N-Heterocyclic carbenes (NHCs) are versatile L-type ligands that have been shown to stabilize coinage metal chalcogenide nanocrystals, such as AgS, remarkably well. However, very little research has been done on the interaction between NHC ligands and coinage metal chalcogenide nanocrystal surfaces and subsequent ligand exchange reactions. Herein, solution H nuclear magnetic resonance methods were used to monitor ligand exchange reactions on stoichiometric AgS nanocrystal platforms with various primary amine and carboxylic acid ligands.

A framework for constructing linear free energy relationships to design molecular transition metal catalysts.

A computational framework for ligand-driven design of transition metal complexes is presented in this work. We propose a general procedure for the construction of active site-specific linear free energy relationships (LFERs), which are inspired from Hammett and Taft correlations in organic chemistry and grounded in the activation strain model (ASM). Ligand effects are isolated and quantified in terms of their contribution to interaction and strain energy components of ASM.

Adsorbate-assisted migration of the metal atom in atomically dispersed catalysts: An ab initio molecular dynamics study.

We present a phenomenological study of dynamical evolution of the active site in atomically dispersed catalysts in the presence of reaction intermediates associated with CO oxidation and low-temperature water-gas shift reaction. Using picosecond ab initio molecular dynamics, we probe the initiation of adsorbate-induced diffusion of atomically dispersed platinum on rutile TiO(110). NVT trajectories spanning 5 ps at 500 K reveal that the dynamical stability of the metal atom is governed by its local coordination to the support and adsorbate.

Consistent inclusion of continuum solvation in energy decomposition analysis: theory and application to molecular CO reduction catalysts.

To facilitate computational investigation of intermolecular interactions in the solution phase, we report the development of ALMO-EDA(solv), a scheme that allows the application of continuum solvent models within the framework of energy decomposition analysis (EDA) based on absolutely localized molecular orbitals (ALMOs). In this scheme, all the quantum mechanical states involved in the variational EDA procedure are computed with the presence of solvent environment so that solvation effects are incorporated in the evaluation of its energy components. After validation on several model complexes, we employ ALMO-EDA(solv) to investigate substituent effects on two classes of complexes that are related to molecular CO reduction catalysis.

A matrix completion algorithm to recover modes orthogonal to the minimum energy path in chemical reactions.

Structured statistical methods are promising for recovering or completing information from noisy and incomplete data with high fidelity. In particular, matrix completion exploits underlying structural properties such as rank or sparsity. Our objective is to employ matrix completion to reduce computational effort associated with the calculation of multiple quantum chemical Hessians, which are necessary for identification of temperature-dependent free energy maxima under canonical variational transition state theory (VTST).