Understanding the Reactivity of Supported Late Transition Metals on a Bare Anatase (101) Surface: A Periodic Conceptual DFT Investigation

The rapidly growing interest for new heterogeneous catalytic systems providing high atomic efficiency along with high stability and reactivity triggered an impressive progress in the field of single-atom catalysis. Nevertheless, unravelling the factors governing the interaction strength between the support and the adsorbed metal atoms remains a major challenge. Based on periodic density functional theory (DFT) calculations, this paper provides insight into the adsorption of single late transition metals on a defect-free anatase surface. The obtained adsorption energies fluctuate, with the exception of Pd, between -3.11 and -3.80 eV and are indicative of a strong interaction. Depending on the considered transition metal, we could attribute the strength of this interaction with the support to i) an electron transfer towards anatase (Ru, Rh, Ni), ii) s-d orbital hybridisation effects (Pt), or iii) a synergistic effect between both factors (Fe, Co, Os, Ir). The driving forces behind the adsorption were also found to be strongly related to Klechkowsky's rule for orbital filling. In contrast, the deviating behaviour of Pd is most likely associated with the lower dissociation enthalpy of the Pd-O bond. Additionally, the reactivity of these systems was evaluated using the Fermi weighted density of states approach. The resulting softness values can be clearly related to the electron configuration of the catalytic systems as well as with the net charge on the transition metal. Finally, these indices were used to construct a model that predicts the adsorption strength of CO on these anatase-supported d-metal atoms. The values obtained from this regression model show, within a 95 % probability interval, a correlation of 84 % with the explicitly calculated CO adsorption energies.

Synthesis, identification, density functional and Hirshfeld surface studies of 2,2'-disulfanediylbis(tetrahydro-4H-cyclopenta[d][1,3,2]dioxaphosphole-2-sulfide)

The new compound 2,2'-disulfanediylbis (tetrahydro-4H-cyclo penta[d][1,3,2]dioxaphosphole 2-sulfide), the dimeric form of 2-mercaptotetrahydro-4H-cyclopenta[d] [1,3,2] dioxaphosphole 2-sulfide, has been synthesized and characterized by elemental analysis, molecular weight determination and spectral data (¹ H-NMR, ¹³ C-NMR, ³¹ P-NMR, FTIR). The molecular geometry was confirmed by single X-Ray crystallography. The ground state property was examined by PBE0 and B3LYP density functionals using aug-cc-pV(Q+d)Z basis set in the gas phase and in DMSO solution. The preference of PBE0 functional was statistically established. Thermodynamic parameters and standard heat of dissociation reaction ( Δ H R 298 K o ) have been established. The calculated equilibrium constants at different temperatures reflect the stability of the dimer over the monomers at low temperatures and vice versa. Valency and Fukui indices calculations showed that the monomer is more reactive than the dimer. 2D-fingerprint revealed that, while the H…X; [X = H, O and S] nonbonding intermolecular interactions and reciprocals play a crucial role in strengthening of molecules packing in the crystal unit cell while the S…S ones contribute negatively on it.

Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation

The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8-10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO₂ support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from -1.40 to -1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between -2.20 and -2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.

The Nitrilimine-Alkene Cycloaddition Regioselectivity Rationalized by Density Functional Theory Reactivity Indices

Conventional frontier molecular orbital theory is not able to satisfactorily explain the regioselectivity outcome of the nitrilimine–alkene cycloaddition. We considered that conceptual density functional theory (DFT) could be an effective theoretical framework to rationalize the regioselectivity of the title reaction. Several nitrilimine–alkene cycloadditions were analyzed, for which we could find regioselectivity data in the literature. We computed DFT reactivity indices at the B3LYP/6-311G(2d,p)//B3LYP/6-31G(d,p) and employed the grand potential stabilization criterion to calculate the preferred regioisomer. Experimental and calculated regioselectivity agree in the vast majority of cases. It was concluded that predominance of a single regioisomer can be obtained by maximizing (i) the chemical potential difference between nitrilimine and alkene and (ii) the local softness difference between the reactive atomic sites within each reactant. Such maximization can be achieved by carefully selecting the substituents on both reactants.

A Computational Study of Structure and Reactivity of N-Substitued-4-Piperidones Curcumin Analogues and Their Radical Anions

In this work, a computational study of a series of N-substitued-4-piperidones curcumin analogues is presented. The molecular structure of the neutral molecules and their radical anions, as well as their reactivity, are investigated. N-substituents include methyl and benzyl groups, while substituents on the aromatic rings cover electron-donor and electron-acceptor groups. Substitutions at the nitrogen atom do not significantly affect the geometry and frontier molecular orbitals (FMO) energies of these molecules. On the other hand, substituents on the aromatic rings modify the distribution of FMO. In addition, they influence the capability of these molecules to attach an additional electron, which was studied through adiabatic (AEA) and vertical electron affinities (VEA), as well as vertical detachment energy (VDE). To study electrophilic properties of these structures, local reactivity indices, such as Fukui (f⁺) and Parr (P⁺) functions, were calculated, and show the influence of the aromatic rings substituents on the reactivity of α,β-unsaturated ketones towards nucleophilic attack. This study has potential implications for the design of curcumin analogues based on a 4-piperidone core with desired reactivity.

X-ray Single Crystal Structure, DFT Calculations and Biological Activity of 2-(3-Methyl-5-(pyridin-2'-yl)-1H-pyrazol-1-yl) Ethanol

A pyridylpyrazole bearing a hydroxyethyl substituent group has been synthesized by condensation of (Z)-4-hydroxy-4-(pyridin-2-yl)but-3-en-2-one with 2-hydroxyethylhydrazine. The compound was well characterized and its structure confirmed by single crystal X-ray diffraction. Density functional calculations have been performed using DFT method with 6-31G* basis set. The HOMO-LUMO energy gap, binding energies and electron deformation densities are calculated at the DFT (BLYP, PW91, PWC) level. The electrophilic f(-) and nucleophilic f(+) Fukui functions and also the electrophilic and nucleophilic Parr functions are well adapted to find the electrophile and nucleophile centers in the molecule. The title compound has been tested for its DPPH radical scavenging activity which is involved in aging processes, anti-inflammatory, anticancer and wound healing activity. Compound is also found with a significant antioxidant activity, probably due to the ability to donate a hydrogen atom to the DPPH radical.

Applications of the Conceptual Density Functional Theory Indices to Organic Chemistry Reactivity

Theoretical reactivity indices based on the conceptual Density Functional Theory (DFT) have become a powerful tool for the semiquantitative study of organic reactivity. A large number of reactivity indices have been proposed in the literature. Herein, global quantities like the electronic chemical potential μ, the electrophilicity ω and the nucleophilicity N indices, and local condensed indices like the electrophilic P k + and nucleophilic P k - Parr functions, as the most relevant indices for the study of organic reactivity, are discussed.