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‐bis1,1‐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‐bis1,1‐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.
The mesomeric effect is visualized by means of 3D pictures of the density polarization δρ(r) independently of the substituent group nature since it is represented as a perturbation on the external potential, δυ(r). When the linear response function χ(r, r′), a non‐local reactivity descriptor, is integrated with respect to r′ (coordinates of the perturbation), we obtain the δρ(r) a local reactivity descriptor that quantifies the fraction of electron shifted on the whole molecular structure.
In this paper, we assess the performance of 24 density functional theory (DFT) based methods classified into 5 categories (GGA, MGGA, HGGA, HMGGA and DHGGA) in predicting reaction energetics, ...transition state geometries, and the degree of synchronicity/nonsynchronicity in the formation of two new C-C single-bonds in three Diels-Alder reactions between symmetrically and unsymmetrically substituted cyanoethylenes and cyclopentadiene, which gradually proceed from fully synchronous to highly asynchronous concerted mechanisms. This important concept in reaction mechanisms is revealed by the fine structure of the reaction force constant
κ
(
ξ
) along the transition region. Some wave function theory (WFT) based methods are also assessed against the CCSD(T) and CCSD benchmarks for the energy and geometry, respectively. The results and the statistical analysis of the errors confirm the robustness of SCS-MP2 (a WFT-based method) as one of the most reliable computational approaches. Regarding DFT-based methods, hybrid exchange-correlation functionals combined with medium-range electron correlation effects or long-range corrected exchange appear as the best performing methods, highlighting both M11 and M06-2X, since a certain percentage of exact Hartree-Fock exchange could counterbalance the delocalization errors that affect pure functionals. Thus, they reliably describe energetics, geometries and the degree of synchronicity in the formation of new C-C single bonds in Diels-Alder reactions. Noticeably, moderate performance for double hybrid functionals and poor performance for the most popular B3LYP method were found as well.
The performance of 24 KS-DFT-based methods (GGA, MGGA, HGGA, HMGGA, and DHGGA) was assessed, finding that M11 and M06-2X (HMGGA) predicting reliable TS geometries, energetics, and (a)synchronicities in Diels-Alder reactions.
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.
The necessity of the human hippocampus for remote autobiographical recall remains fiercely debated. The standard model of consolidation predicts a time-limited role for the hippocampus, but the ...competing multiple trace/trace transformation theories posit indefinite involvement. Lesion evidence remains inconclusive, and the inferences one can draw from functional MRI (fMRI) have been limited by reliance on covert (silent) recall, which obscures dynamic, moment-to-moment content of retrieved memories. Here, we capitalized on advances in fMRI denoising to employ overtly spoken recall. Forty participants retrieved recent and remote memories, describing each for approximately 2 min. Details associated with each memory were identified and modeled in the fMRI time-series data using a variant of the Autobiographical Interview procedure, and activity associated with the recall of recent and remote memories was then compared. Posterior hippocampal regions exhibited temporally graded activity patterns (recent events > remote events), as did several regions of frontal and parietal cortex. Consistent with predictions of the standard model, recall-related hippocampal activity differed from a non-autobiographical control task only for recent, and not remote, events. Task-based connectivity between posterior hippocampal regions and others associated with mental scene construction also exhibited a temporal gradient, with greater connectivity accompanying the recall of recent events. These findings support predictions of the standard model of consolidation and demonstrate the potential benefits of overt recall in neuroimaging experiments.
In the current work, the authors analyzed and compared the chemical behavior of some (anti)aromatic compounds. The species selected are benzene and cyclobutadiene as the aromatic and antiaromatic ...classical examples, respectively. Next, the anion Al42−, which is the first all‐metal molecule catalogued as aromatic and its non‐metallic isoelectronic analog, B42− were also analyzed. The antiaromatic clusters Al44− and B44− were studied in form of lithium salts. And the end, the non‐planar B12 boron cluster and its isoelectronic analogs (B11Be− and B11C+) were considered for being analyzed under the same criterium. The analysis was realized employing the following descriptors: molecular electrostatic potential and local hyper‐softness to get insights concerning local reactivity when facing reagents leading to ionic or covalent interactions. The results show that all the molecules analyzed presented some specific variations in their respective local reactivity despite being labeled as aromatic compounds. This analysis provides a notion that the local reactivity is more based on the nature of the atoms and the molecular geometry than the aromatic character by itself.
Through the use of the local hyper‐softness, s2r, we found that, despite being B12, B11C+, and B11Be+ isoelectronic aromatic molecules, C+ distorts the local reactivity more than Be− does, thus revealing the capability of s2r to distinguish effects caused by the different nature of the substituent atomic ions aforementioned. Consequently, the two resulting species, B11C+ and B11Be−, are still aromatic molecules like B12, but differ in their local reactivities.
Based on the experimental precedent discovered by Kuranadasa and coworkers H. I. Karunadasa
et al.
,
Nature
, 2010,
464
, 1329 to produce dihydrogen from water electrocatalyzed by ...2,6-bis1,1-bis(2-pyridyl)ethyl-pyridine oxo-molybdenum complexes, we performed an extensive analysis to study the substituent group effect of derivatised compounds coming from the before mentioned Mo-based metal-organic cations in terms of two kinds of substitutions: axial and equatorial at the
para
-position of pyridine rings; several conceptual tools were used to back up our conclusions. We found that each type of substituent group (electron-withdrawing and electron-donating ones) exerts an independent influence on energetic parameters (energy barrier and overall energy). This opens the chance to search for a synergistic effect by combining these opposite behaviours of these substituents located in the equatorial and axial
para
-positions of pyridine rings to computationally modulate the aforementioned energetic parameters. This procedure will make easier the proposal of new catalysts to favour either kinetically or thermodynamically or in both ways the production of dihydrogen from water. Additionally, we encompassed a key point: the number of solvent molecules, so that including their presence in further investigations is mandatory.
The effect of electron-donating and -withdrawing groups is studied in terms of axial and equatorial locations at the p-pyridine rings in the (PY
5
Me
2
)MoO
2+
for the H
2
release in aqueous media. It opens a way to modify its kinetics and thermodynamics.
A fundamental link between conceptual density functional theory and statistical thermodynamics is herein drawn, showing that intermolecular electrostatic interactions can be understood in terms of ...effective work and heat exchange. From a more detailed analysis of the heat exchange in a perturbation theory framework, an associated entropy can be subsequently derived, which appears to be a suitable descriptor for the local polarisability of the electron density. A general rule of thumb is evidenced: the more the perturbation can be spread, both through space and among the excited states, the larger the heat exchange and entropy.
A fundamental link between conceptual density functional theory and statistical thermodynamics is herein drawn, showing that intermolecular electrostatic interactions can be understood in terms of effective work and heat exchange.
The reason why the local softness (LS) and the local hyper-softness (LHS) allow comparisons of local reactivities among molecular systems of similar or different sizes is analyzed. We evidenced this ...scaling behavior on these functions by means of their working formulae. This feature bases on the scaling capacity of LS and LHS according to the molecular size. The Fukui function (FF), and the dual descriptor (DD) do not satisfy that property.
The dual descriptor potential Martínez-Araya, Jorge I.
Journal of mathematical chemistry,
05/2024, Letnik:
62, Številka:
5
Journal Article
Recenzirano
The dual descriptor potential (DDP) has appeared in several papers, It is proposed as a local reactivity descriptor within the framework of the Conceptual Density Functional Theory and as a ...complementary tool of the molecular electrostatic potential (MEP) rather than the dual descriptor (DD). DDP provides information concerning the most energetically favorable sites to undergo nucleophilic and electrophilic attacks. Unlike the dual descriptor, DDP is directly related with energy. Furthermore, the DDP seems to depure the scalar field, allowing us to unveil the predominance of nucleophilic and electrophilic regions on a molecule. This is in stark contrast to the dual descriptor, which tends to scatter around the molecule, hindering the interpretation of the local reactivity on regions that exceed the atomic volume. To the best of our knowledge, this is the first time that DDP is represented as a 3D picture. To assess its capability to describe interaction among molecules, DDP was tested on some molecular systems, along with MEP. Results show that the joint use of these tools helps in the understanding of certain experimental evidences, serving as an alternative to the molecular orbital theory.
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