Cu and Ag as one‐valence‐electron atoms: Pseudopotential CI results for CuO and AgO

Explaining the High Catalytic Activity in Bis(indenyl)methyl Zirconium Cation Using Combined EDA-NOCV/QTAIM Approach

The main purpose of this study is to elucidate some discrepancies already observed in the catalytic activity values of some zirconocene methyl cations. The EDA-NOCV scheme was employed for a theoretical description of the interactions between an ethylene molecule and five catalysts of zirconocene methyl cation. The nature of the chemical interactions has been elucidated through the QTAIM topological analysis. The steric hindrance due to the ligands was evaluated qualitatively by means of an IRI-based analysis and quantitively through Fisher information. The findings prove that the indenyl ligand seems to favor the orbital interaction between the ethylene molecule and the metal centre of zirconocene methyl cation. Both electrostatic and orbital contributions play a crucial role in stabilising the studied complexes. Based on the NOCV deformation density contributions, the strongest orbital interaction is reached with the bis(indenyl)methyl zirconium cation, which is the only one exhibiting covalent interactions. Especially, the strong contribution of π-back donation (occurring from the occupied orbitals of the zirconium atom to the π* anti-bonding orbital of ethylene) may be a key to understand why this catalyst has a higher polymerisation yield than the other studied catalysts. This work suggests a perspective for predicting values of catalytic activity when theoretically designing novel catalysts of zirconocene type.

A combined QTAIM/IRI topological analysis of the effect of axial/equatorial positions of NH2 and CN substituents in the [(PY5Me2)MoO]+ complex

By means of the Interaction Region Indicator (IRI) and Quantum Theory of Atoms in Molecules (QTAIM), the influence exerted by NH₂ (amino) and CN (cyano) as electron donor and electron acceptor substituent groups, respectively, located at para-positions of axial and equatorial pyridine rings of derivatized complexes coming from the [(PY₅Me₂)MoO]⁺ complex during the hydrogen molecular release in the gas phase was analyzed. In any case, a H-H covalent bond is forming at the transition state, with a strengthening of the electron density of 5.5% when the substituent group involved is NH₂ at the para-position of the axial pyridine ring. However, there was no difference between NH₂ and CN when these substituent groups are located at the para-positions of the equatorial pyridine rings. The topological properties of electron densities from the QTAIM are not perturbed by the electron donor and electron acceptor nature of the substituents, even when these substituent groups are located at the axial or equatorial pyridine rings of the Mo-based complex.

The density polarization reveals directions of electron displacements due to the substituent effect: Analysis performed on a metal-organic Mo-Oxo catalyst

Some Mo-oxo complexes bearing pyridine rings have the capability for dihydrogen production from water. However, energy barrier and overall energy vary depending on the effect exerted by several substituent groups located at different positions around one or more pyridine rings which are ligands of these compounds. Based on the Karunadasa and coworkers investigation where the para-position was experimentally tested in compounds derivatised from the 2,6-bis[1,1-bis(2-pyridil)ethyl]-pyridine oxo-molybdenum complex synthesized (Karunadasa et al., Nature, 2010, 464, 1329), we tested the combined effect of electron-withdrawing and electron-donating groups simulated as perturbations represented by point-charges. Then, we used the density polarization concept, δρ(r), a local reactivity descriptor corresponding to the partially integrated linear response function, χ(r, r') (a non-local reactivity descriptor), which is able to reveal different displacements of π-electrons on molecular structures. We perturbed the para-positions in the pentadentate ligand 2,6-bis[1,1-bis(2-pyridil)ethyl]-pyridine in the Mo-based complex by means of point-charges. They were located in three different configurations of the organic ligand (trans, geminal, and cis) which could help to explain energy barriers and overall energy of reactions catalyzed by this type of Mo-complexes. Our results indicate that the trans configuration of point-charges induces the most amount of fraction of electron shifted on the complex. A Mo-based complex bearing the same trans configuration for electron-withdrawing and electron-donating substituent groups (cyano and amino, respectively), leads to a kinetically more favorable H₂ release than the cis or geminal configuration of the substituent groups aforementioned.

Scrutinizing the substituent effect on Mo-based electrocatalysts for molecular hydrogen release through axial–equatorial decomposition: a DFT study

The effect of electron-donating and -withdrawing groups is studied in terms of axial and equatorial locations at the p-pyridine rings in the [(PY₅Me₂)MoO]²⁺ for the H₂ release in aqueous media. It opens a way to modify its kinetics and thermodynamics.

Photoelectron spectra of copper oxide cluster anions from first principles methods

We present results and analyses for the photoelectron spectra of small copper oxide cluster anions (CuO^-, Cu O2- , Cu O3- , and Cu₂O^-). The spectra are computed using various techniques, including density functional theory (DFT) with semi-local, global hybrid, and optimally tuned range-separated hybrid functionals, as well as many-body perturbation theory within the GW approximation based on various DFT starting points. The results are compared with each other and with the available experimental data. We conclude that as in many metal-organic systems, self-interaction errors are a major issue that is mitigated by hybrid functionals. However, these need to be balanced against a strong role of non-dynamical correlation-especially in smaller, more symmetric systems-where errors are alleviated by semi-local functionals. The relative importance of the two phenomena, including practical ways of balancing the two constraints, is discussed in detail.

A 3D visualization of the substituent effect : A brief analysis of two components of the operational formula of dual descriptor for open-shell systems

Six organometallic compounds coming from a basic Mo-based complex were analyzed from the perspective of the dual descriptor in order to detect subtle influences that a substituent group could exert on the reactive core at a long range. Since the aforementioned complexes are open-shell systems, the used operational formula for the dual descriptor is that one defined for those aforementioned systems, which was then compared with spin density. In addition, dual descriptor was decomposed into two terms, each of which was also applied on every molecular system. The obtained results indicated that components of dual descriptor could become more useful than the operational formula of dual descriptor because differences exerted by the substituents at the para position were better detected by components of dual descriptor rather than the dual descriptor by itself.

Density functional calculation of the structure and electronic properties of Cu(n)O(n) (n = 1-8) clusters

Ab initio simulations and calculations were used to study the structures and stabilities of copper oxide clusters, Cu(n)O(n) (n = 1-8). The lowest energy structures of neutral and charged copper oxide clusters were determined using primarily the B3LYP/LANL2DZ model chemistry. For n ≥ 4, the clusters are nonplanar. Selected electronic properties including atomization energies, ionization energies, electron affinities, and Bader charges were calculated and examined as a function of n.