We propose and discuss an efficient scheme for the in silico sampling for parts of the molecular low-energy chemical space by semiempirical tight-binding methods combined with a meta-dynamics driven search algorithm.

The application of quantum chemical, automatic multilevel modeling workflows for the determination of thermodynamic (e.g., conformation equilibria, partition coefficients, pK a values) and spectroscopic properties of relatively large, nonrigid molecules in solution is described. Key points are the computation of rather complete structure (conformer) ensembles with extremely fast but still reasonable GFN2-xTB or GFN-FF semiempirical methods in the CREST searching approach and subsequent refinement at a recently developed, accurate r 2 SCAN-3c DFT composite level. Solvation effects are included in all steps by accurate continuum solvation models (ALPB, (D)COSMO-RS). Consistent inclusion of thermostatistical contributions in the framework of the modified rigid-rotor-harmonic-oscillator approximation (mRRHO) based on xTB/FF computed PES is also recommended.

The calculation of redox potentials by semiempirical quantum mechanical (SQM) approaches is evaluated with a focus on the recently developed GFNn-xTB methods. The assessment is based on a data set comprising 313 experimental redox potentials of small to medium-sized organic and organometallic molecules in various solvents. This compilation is termed as ROP313 (reduction and oxidation potentials 313) and divided for analysis purposes into the organic subset OROP and the organometallic subset OMROP. Corresponding data for a few common density functional theory (DFT) functionals employing extended AO basis sets and small basis-set DFT composite schemes are computed for comparison. Continuum solvation models are used to calculate the important solvation free energy contribution. The results for ROP313 show that the GFNn-xTB methods provide a robust, efficient, and generally applicable workflow for the routine calculation of redox potentials. The GFNn-xTB methods outperform the PMx competitor for the OROP subset (mean absolute deviation from the experiment, MADGFN2‑xTB = 0.30 V, MADGFN1‑xTB = 0.31 V, PM6-D3H4 = 0.61 V, PM7 = 0.60 V), almost reaching low-cost DFT quality (MADB97‑3c = 0.25 V) at drastically reduced computational cost (2–3 orders of magnitude). All SQM methods perform considerably worse for the OMROP subset. Here, the GFN2-xTB still yields semiquantitative results slightly better and more robustly than with the PMx methods (MADGFN2‑xTB = 0.74 V, PM6-D3H4 = 0.78 V, PM7 = 0.82 V). The proposed workflow enables large-scale quantum chemical computations of organic and, to a lesser extent, organometallic molecule redox potentials on common laptop computers in seconds to minutes of computation time enabling, e.g., screening of extended compound libraries.

Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH–O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication.

This paper was selected as Featured ARTICLES YOU MAY BE INTERESTED INProbabilistic performance estimators for computational chemistry methods: Systematic improvement probability and ranking probability matrix. I. Theory

1,1,1,3,3,3-hexafluoro-propan-2-ol aggregates preferentially into an achiral dimer of achiral monomers,b ut the trimer is found to prefer three metastable chiral monomer units arranged into astrained OH···O hydrogen-bonded ring, which is reinforced by secondary CH···FC interactions.This is shown by ac ombination of infrared, microwave,a nd Raman spectroscopyi ns upersonic jet expansions and supported by high-level quantum chemical calculations.I ti nvolves an activation of the monomers by > 15 kJ mol À1 ,c learly driven by the muchs tronger hydrogen-bond interaction available to the gauche and even more to the cis monomer units.

Aromatic donor–acceptor interactions are of high importance in supramolecular chemistry, materials science and biology. Compared to other noncovalent interactions, such as hydrogen bonding, the binding is often weak. Here we show that strong donor–acceptor interactions between planar aromatics with binding free energies down to −10.1 kcal mol–1 and association constants of up to 2.34 × 107 L mol–1 for 1:1 complexes can be realized using cyclic trinuclear complexes of gold­(I) with pyridinate, imidazolate, or carbeniate ligands. Data were obtained through NMR and UV/vis absorption spectroscopic studies and supported by quantum chemical calculations for a variety of acceptors. By using a specifically designed bridged naphthalene diimide-based acceptor with only one binding site, we furthermore show that a 1:2 (donor:acceptor) binding model is best suited to quantify the donor and acceptor/complex equilibrium. Scanning electron microscopy on selected donor–acceptor pairs shows crystalline supramolecular assemblies. We anticipate this study to be relevant for the future design of supramolecular systems and chemical sensors and the determination of binding energies between planar donors and acceptors.

Aromatic stacking interactions of π-basic Au(i) complexes with π-acids were analyzed experimentally, theoretically and at the solid/liquid interface using STM.