Catalysis enabled synthesis, structures, and reactivities of fluorinated S-corona[]arenes ( = 8-12).

Previously inaccessible large S-corona[]arene macrocycles ( = 8-12) with alternating aryl and 1,4-CF subunits are easily prepared on up to gram scales, without the need for chromatography (up to 45% yield, 10 different examples) through new high acceleration SAr substitution protocols (catalytic NRF in pyridine, R = H, Me, Bu). Macrocycle size and functionality are tunable by precursor and catalyst selection. Equivalent simple NRF catalysis allows facile late-stage SAr difunctionalisation of the ring CF units with thiols (8 derivatives, typically 95+% yields) providing two-step access to highly functionalised fluoromacrocycle libraries.

Static Electron Correlation in Anharmonic Molecular Vibrations: A Hybrid TAO-DFT Study.

Hybrid thermally-assisted-occupation density functional theory is used to examine the effects of static electron correlation on the prediction of a benchmark set of experimentally observed molecular vibrational frequencies. The B3LYP and B97-1 thermally-assisted-occupation measure of static electron correlation is important for describing the vibrations of many of the molecules that make up several popular test sets of experimental data. Shifts are seen for known multireference systems and for many molecules containing atoms from the second row of the periodic table of elements.

Wavelength dependent photoextrusion and tandem photo-extrusion reactions of ninhydrin bis-acetals for the synthesis of 8-ring lactones, benzocyclobutenes and orthoanhydrides.

Ninhydrin bis-acetals give access to 8-ring lactones, benzocyclo-butenes and spirocyclic orthoanhydrides through photoextrusion and tandem photoextrusion reactions. Syntheses of fimbricalyxlactone B, isoshihunine and numerous biologically-relevant heterocycles show the value of the methods, while TA-spectroscopy and TD-DFT studies provide mechanistic insights on their wavelength dependence.

Kernel Methods for Predicting Yields of Chemical Reactions.

The use of machine learning methods for the prediction of reaction yield is an emerging area. We demonstrate the applicability of support vector regression (SVR) for predicting reaction yields, using combinatorial data. Molecular descriptors used in regression tasks related to chemical reactivity have often been based on time-consuming, computationally demanding quantum chemical calculations, usually density functional theory.

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods.

Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO.

Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates.

Reduced Two-Electron Interactions in Anharmonic Molecular Vibrational Calculations Involving Localized Normal Coordinates.

Spatially localized vibrational normal mode coordinates are shown to reduce the importance of calculating the full set of two-electron terms in the molecular electronic Schrödinger equation. Electron correlation and dispersion interactions become less significant in (,)-1,3,5,7-octatetraene vibrational self-consistent field calculations when displacing remote atoms along multiple coordinates. Electron correlation interactions between spatially remote modes are also found to be less important compared to their corresponding uncorrelated interaction terms.

Calculating with Permanent Marker: How Blockchains Record Immutable Mistakes in Computational Chemistry.

Computational science experiments within an open blockchain environment have recently been demonstrated and can improve transparency, reproducibility, and censorship resistance in theoretical scientific work. However, the append-only nature of these records also means that historical calculation errors cannot be effectively removed or changed. This process preserves otherwise unavailable data on the scientific process of error correction and is shown here for simulations of carbon monoxide.

Vibrational Spectroscopic Map, Vibrational Spectroscopy, and Intermolecular Interaction.

Vibrational spectroscopy is an essential tool in chemical analyses, biological assays, and studies of functional materials. Over the past decade, various coherent nonlinear vibrational spectroscopic techniques have been developed and enabled researchers to study time-correlations of the fluctuating frequencies that are directly related to solute-solvent dynamics, dynamical changes in molecular conformations and local electrostatic environments, chemical and biochemical reactions, protein structural dynamics and functions, characteristic processes of functional materials, and so on. In order to gain incisive and quantitative information on the local electrostatic environment, molecular conformation, protein structure and interprotein contacts, ligand binding kinetics, and electric and optical properties of functional materials, a variety of vibrational probes have been developed and site-specifically incorporated into molecular, biological, and material systems for time-resolved vibrational spectroscopic investigation.

Möbius and Hückel Cyclacenes with Dewar and Ladenburg Defects.

Cyclacene nanobelts have not been synthesized in over 60 years and remain one of the last unsynthesized building blocks of carbon nanotubes. Recent work has predicted that Hückel-cyclacenes containing Dewar benzenoid ring isomers are the most stable isomeric forms for several of the smaller sizes of cyclacene belts. Here, we give a more complete picture of the isomers that are possible within these nanobelt systems by simulating embedded Ladenburg (prismane) benzenoid rings in Hückel-[]cyclacenes ( = 5-14) and embedded Dewar benzenoid rings in twisted Möbius-[]cyclacenes ( = 9-14).

Dewar Benzenoids Discovered In Carbon Nanobelts.

The synthesis of cyclacene nanobelts remains an elusive goal dating back over 60 years. These molecules represent the last unsynthesized building block of carbon nanotubes and may be useful both as seed molecules for the preparation of structurally well-defined carbon nanotubes and for understanding the behavior and formation of zigzag nanotubes more broadly. Here we report the discovery that isomers containing two Dewar benzenoid rings are the preferred form for several sizes of cyclacene.

Computational chemistry experiments performed directly on a blockchain virtual computer.

Blockchain technology has had a substantial impact across multiple disciplines, creating new methods for storing and processing data with improved transparency, immutability, and reproducibility. These developments come at a time when the reproducibility of many scientific findings has been called into question, including computational studies. Here we present a computational chemistry simulation run directly on a blockchain virtual machine, using a harmonic potential to model the vibration of carbon monoxide.

Influence of molecular design on radical spin multiplicity: characterisation of BODIPY dyad and triad radical anions.

A strategy to create organic molecules with high degrees of radical spin multiplicity is reported in which molecular design is correlated with the behaviour of radical anions in a series of BODIPY dyads. Upon reduction of each BODIPY moiety radical anions are formed which are shown to have different spin multiplicities by electron paramagnetic resonance (EPR) spectroscopy and distinct profiles in their cyclic voltammograms and UV-visible spectra. The relationship between structure and multiplicity is demonstrated showing that the balance between singlet, biradical or triplet states in the dyads depends on relative orientation and connectivity of the BODIPY groups.

Benchmarking DFT-D Dispersion Corrections for Anharmonic Vibrational Frequencies and Harmonic Scaling Factors.

Improvements in the form of the DFT-D empirical dispersion corrections to hybrid density functional theory are shown to have made corrections sufficiently accurate to improve the calculation of both anharmonic frequencies and scaled harmonic vibrational frequencies across a wide range of commonly tested molecules. The Becke-Johnson damping function is noted as being particularly versatile across the molecules tested, and the B3LYP-D3M(BJ) and B3LYP-D3(CSO) methods are found to be the most widely applicable. Dispersion corrections are shown to be important for accurately describing carbon-hydrogen bond stretching vibrations, and standard triple-dipole based three-body terms are found to cause large errors in these anharmonic frequencies.

The effect of coordination of alkanes, Xe and CO (η-OCO) on changes in spin state and reactivity in organometallic chemistry: a combined experimental and theoretical study of the photochemistry of CpMn(CO).

A combined experimental and theoretical study is presented of several ligand addition reactions of the triplet fragment 3CpMn(CO)2 formed upon photolysis of CpMn(CO)3. Experimental data are provided for reactions in n-heptane and perfluoromethylcyclohexane (PFMCH), as well as in PFMCH doped with C2H6, Xe and CO2. In PFMCH we find that the conversion of 3CpMn(CO)2 to 1CpMn(CO)2(PFMCH) is much slower (τ = 18 (±3) ns) than the corresponding reactions in conventional alkanes (τ = 111 (±10) ps).

A scaled CIS(D) based method for the calculation of valence and core electron ionization energies.

The calculation of electron ionization energies is a key component for the simulation of photoelectron spectroscopy. CIS(D) is a perturbative doubles correction for the single excitation configuration interaction (CIS) method which provides a new approach for computing excitation energies. It is shown that by introducing a virtual orbital subspace that consists of a single "ghost" orbital, valence electron ionization energies can be computed using a scaled CIS(D) approach with an accuracy comparable with considerably more computationally intensive methods, such as ionization-potential equation of motion coupled cluster theory, and simulated spectra show a significant improvement relative to spectra based upon Koopmans' theorem.

Monitoring the Formation and Reactivity of Organometallic Alkane and Fluoroalkane Complexes with Silanes and Xe Using Time-Resolved X-ray Absorption Fine Structure Spectroscopy.

Complexes with weakly coordinating ligands are often formed in chemical reactions and can play key roles in determining the reactivity, particularly in catalytic reactions. Using time-resolved X-ray absorption fine structure (XAFS) spectroscopy in combination with time-resolved IR (TRIR) spectroscopy and tungsten hexacarbonyl, W(CO), we are able to structurally characterize the formation of an organometallic alkane complex, determine the W-C distances, and monitor the reactivity with silane to form an organometallic silane complex. Experiments in perfluorosolvents doped with xenon afford initially the corresponding solvated complex, which is sufficiently reactive in the presence of Xe that we can then observe the coordination of Xe to the metal center, providing a unique insight into the metal-xenon bonding.

Excited-State Vibrational Frequencies: Restricted Virtual Space Time-Dependent Density Functional Theory.

Calculating accurate vibrational frequencies for molecules with electronically excited states has an important function in many areas of photochemistry. However, calculations are often limited to smaller molecules due to the rapid growth in the degrees of freedom that must be taken into account to accurately describe larger systems. The applicability of the restricted virtual space (RVS) approximation has been studied within adiabatic linear response time-dependent density functional theory when calculating excited-state nuclear vibrational frequencies.

Dimers of acetic acid in helium nanodroplets.

The structural arrangement of small carboxylic acid molecules in the liquid phase remains a controversial topic. Some studies indicate a dominance of the cyclic dimer that prevails in the gas phase, whilst other studies favor short fragments of the infinite catemer chains that are found in the crystalline phase. Furthermore, difficulties in preparing and probing size-selected catemer segments have resulted in a lack of benchmark data upon which theoretical models of the condensed phases can be built.

The impact of sulfur functionalisation on nitrogen-based ionic liquid cations.

It has been demonstrated that bonding and interactions within ionic liquids (ILs) can be elegantly tuned by manipulation of structure and the introduction of functional groups. Here we use XPS to investigate the impact of sulfur containing substituents on the electronic structure of a series of N-based cations, all with a common anion, [NTf2]-. The experiments reveal complexity and perturbation of delocalised systems which cannot be easily interpreted by NMR and XPS alone, DFT provides critical insight into bonding and underpins the assignment of spectra and development of deconstruction models for each system studied.

Reduced Basis Set Dependence in Anharmonic Frequency Calculations Involving Localized Coordinates.

Localized normal coordinates are known to be effective in speeding up anharmonic frequency calculations by reducing the complexity of the nuclear Hamiltonian and wave function. Displacing atoms in localized coordinates can also cause relatively small changes in the electronic structure, which can be exploited for further computational efficiency improvements during ab initio electronic structure calculations of the potential energy surface by reducing the electronic basis set dependence. Three different schemes for reducing the basis set dependence have been investigated in this work.

Photoaquation Mechanism of Hexacyanoferrate(II) Ions: Ultrafast 2D UV and Transient Visible and IR Spectroscopies.

Ferrous iron(II) hexacyanide in aqueous solutions is known to undergo photoionization and photoaquation reactions depending on the excitation wavelength. To investigate this wavelength dependence, we implemented ultrafast two-dimensional UV transient absorption spectroscopy, covering a range from 280 to 370 nm in both excitation and probing, along with UV pump/visible probe or time-resolved infrared (TRIR) transient absorption spectroscopy and density functional theory (DFT) calculations. As far as photoaquation is concerned, we find that excitation of the molecule leads to ultrafast intramolecular relaxation to the lowest triplet state of the [Fe(CN)] complex, followed by its dissociation into CN and [Fe(CN)] fragments and partial geminate recombination, all within <0.

Infrared Spectroscopy of NaCl(CHOH) Complexes in Helium Nanodroplets.

Infrared (IR) spectra of complexes between NaCl and methanol have been recorded for the first time. These complexes were formed in liquid helium nanodroplets by consecutive pick-up of NaCl and CHOH molecules. For the smallest NaCl(CHOH), complexes where n = 1-3, the IR data suggest that the lowest-energy isomer is the primary product in each case.

Intermediate vibrational coordinate localization with harmonic coupling constraints.

Optimized normal coordinates can significantly improve the speed and accuracy of vibrational frequency calculations. However, over-localization can occur when using unconstrained spatial localization techniques. The unintuitive mixtures of stretching and bending coordinates that result can make interpreting spectra more difficult and also cause artificial increases in mode-coupling during anharmonic calculations.