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M. Head-Gordon

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Open access Sep 2026

Using energy decomposition analysis from correlated wavefunction theory to characterize a range of hydrogen, halogen, and tetrel bonds: the relative importance of electrostatics, charge-transfer and polarization.

Second-order Møller-Plesset theory (MP2) is the simplest wavefunction-based treatment of electron correlation and is a good compromise between accuracy and efficiency for evaluating the strength of many non-covalent intermolecular interactions. It has also been improved in accuracy and robustness by regularized methods, such as the size-consistent second order Brillouin-Wigner perturbation theory (BWs2) and κ-MP2. This work presents a non-technical summary of the recently developed second-generation absolutely localized molecular orbital (ALMO) energy decomposition analysis (EDA) method at the post-SCF level of MP2 and regularized MP2. The so-called frozen term is redefined to ensure that long range correlation contributions to electrostatics are correctly captured. The resulting EDA provides useful basis set limits to the correlation corrections for all physical contributions: donor-acceptor charge transfer, electrical polarization, dispersion, and Pauli repulsions and electrostatic interactions associated with frozen monomer orbitals. EDA calculations using MP2 are reported on several classes of systems: model systems to assess correlation effects on permanent and induced electrostatics, hydrogen bonds between water and model carbohydrate molecules, tetrel bonds ranging from 15 to 90 kJ mol-1 in strength, two halogen bonds - one of which is known to be solvent resistant, and a pair of "anti-electrostatic" halogen bonds. Several general conclusions emerge. First, to obtain physically reasonable conclusions, it is essential that the correlation contribution is not identified with dispersion alone: large corrections to the frozen term corresponding to changes in electrostatics are observed due to correlation. Second, the fingerprint of intermolecular interactions provided by the EDA reveals a range of interesting trends in the character of intermolecular interactions as a function of their type and strength. For example, the solvent-stable halogen bond is confirmed to be dominated by charge-transfer stabilization. On the other hand, the strongest tetrel bonds studied here are dominated by contributions from polarization, while more conventional hydrogen bonds between water and model carbohydrates represent a synergy between electrostatics, dispersion, and charge transfer. The metastability (or stability) of nominally antielectrostatic interactions depends strongly on the differing distance dependence of attractive and repulsive terms, and we demonstrated tuning based on changes in permanent electrostatics by increasing charge-separation through use of phenyl linkers.

Heng-Yuan Shen, Zhen-Ling Wang, Kevin Ikeda et al. · Physical Chemistry, Chemical... · 0 citations

Aug 2026

Molecular Approaches to the Mechanism of CO2 Reduction to Methanol by Cobalt Phthalocyanine.

The electrochemical reduction of CO2 has received significant scientific interest over the past two decades as a key step in the synthesis of CO2 into combustible fuels. Cobalt phthalocyanine (CoPc) adsorbed on carbon nanotubes has risen as a rare electrocatalyst that reduces CO2 beyond two electrons, specifically to methanol. Recent efforts have improved the efficiency of this process and established that methanol production proceeds by reduction of a free CO intermediate, however, many aspects of the catalytic pathway remain unclear, which may underpin persistent issues of stability and selectivity. Here we employ electrochemistry, spectroelectrochemistry, X-ray adsorption spectroscopy (XAS), synthesis of catalytic intermediates, and density functional theory (DFT) calculations to understand the catalytic mechanism and identify distinguishing molecular features. We find that CoPc undergoes three sequential reductions between 0 and -2.5 vs NHE; the first reduction occurring at the Co center, and the second two reductions populating the Pc ring. XAS and theory show the Pc ligand to be noninnocent, interacting with the electronic structure of the Co center and causing Co to adopt a Co(II) state as the complex undergoes the second and third reductions. Consistent with previous studies, [CoPc]2- is found to be active for CO2 reduction, however, we find that the catalyst must be reduced further to [CoPc]3- to bind CO at the Co site. Carbonylation of [CoPc]3- under aprotic conditions leads to fast decomposition, forming [Co(CO)4]-. However, we show that [CoPc]3-, if ring protonated by weak acid to form [CoPc-H]2-, reacts with CO to generate a formyl without decomposition, the first step in methanol synthesis. DFT calculations of the mechanism indicate that the reaction of [CoPc-H]2- with CO to generate the formyl in solution proceeds by an intermolecular proton transfer between the Pc ring of [CoPc-H]2- and the Co-CO of [Co-COPc-H]2-. Overall, this study points to the importance of the Pc ligand in determining the catalytic behavior of CoPc and provides the first examples of several isolated reduced CoPc complexes and catalytic intermediates that we hope will guide future work.

Emile E. DeLuca, Cheolwoo Park, Pooja Basera et al. · Journal of the American Chem... · 0 citations