Applications of Time-Dependent and Time-Independent Density Functional Theory to Electronic Transitions in Tetrahedral d0 Metal Oxides

On the Origins of Some Spectroscopic Properties of "Purple Iron" (the Tetraoxoferrate(VI) Ion) and Its Pourbaix Safe-Space

In this work, the authors attempt to interpret the visible, infrared and Raman spectra of ferrate(VI) by means of theoretical physical-inorganic chemistry and historical highlights in this field of interest. In addition, the sacrificial decomposition of ferrate(VI) during water treatment will also be discussed together with a brief mention of how Rayleigh scattering caused by the decomposition of Fe^VIO₄²⁻ may render absorbance readings erroneous. This work is not a compendium of all the instrumental methods of analysis which have been deployed to identify ferrate(VI) or to study its plethora of reactions, but mention will be made of the relevant techniques (e.g., Mössbauer Spectroscopy amongst others) which support and advance this overall discourse at appropriate junctures, without undue elaboration on the foundational physics of these techniques.

Optical and nonlinear optical properties of Ln(Tp)2, where Ln = La,…,Lu and Tp = tris(pyrazolyl)borate: a DFT+TD-DFT study

DFT calculations of electronic, structural, thermodynamic properties, magnetic moment, static and dynamic polarizability and hyperpolarizability of Ln(Tp)₂ (Ln = rare earths, Tp = ring-unsubstituted tris(pyrazolyl)borate) complexes.

Mechanism of Permanganate-Promoted Dihydroxylation of Complex Diketopiperazines: Critical Roles of Counter-cation and Ion-Pairing

The mechanism of permanganate-mediated dual C-H oxidation of complex diketopiperazines has been examined with density functional theory computations. The products of these oxidations are enabling intermediates in the synthesis of structurally diverse ETP natural products. We evaluated, for the first time, the impact of ion-pairing and aggregation states of the permanganate ion and counter-cations, such as bis(pyridine)-silver(I) (Ag⁺) and tetra- n-butylammonium (TBA⁺), on the C-H oxidation mechanism. The C-H abstraction occurs through an open shell singlet species, as noted previously, followed by O-rebound and a competing OH-rebound pathway. The second C-H oxidation proceeds with a second equivalent of oxidant with lower free energy barriers than the first C-H oxidation due to directing effects and the generation of a more reactive oxidant species after the first C-H oxidation. The success and efficiency of the second C-H oxidation are found to be critically dependent on the presence of an ion-paired oxidant. We used the developed mechanistic knowledge to rationalize an experimentally observed oxidation pattern for C³-indole-substituted diketopiperazine (+)-5 under optimal oxidation conditions: namely, the formation of diol (-)-6 as a single diastereomer and lack of the ketone products. We proposed two factors that may impede the ketone formation: (i) the conformational flexibility of the diketopiperazine ring, and (ii) hindrance of this site, making it less accessible to the ion-paired oxidant species.

Ab Initio Computational Study of Chromate Molecular Anion Adsorption on the Surfaces of Pristine and B- or N-Doped Carbon Nanotubes and Graphene

Density functional theory (DFT) computations of the electronic structures of undoped, B- and N-doped CNT(3,3), CNT(5,5) carbon nanotubes, and graphene with adsorbed chromate anions CrO₄^2- were performed within molecular cluster approach. Relaxed geometries, binding energies, charge differences of the adsorbed CrO₄^2- anions, and electronic wave function contour plots were calculated using B3LYP hybrid exchange-correlation functional. Oscillator strengths of electronic transitions of CrO₄^2- anions adsorbed on the surfaces of studied carbon nanostructures were calculated by the TD-DFT method. Calculations reveal covalent bonding between the anion and the adsorbents in all studied adsorption configurations. For all studied types of adsorbent structures, doping with N strengthens chemical bonding with CrO₄^2- anions, providing a ~2-eV increase in binding energies comparatively to adsorption of the anion on undoped adsorbents. Additional electronic transitions of CrO₄^2- anions appear in the orange-green spectral region when the anions are adsorbed on the N-doped low-diameter carbon nanotubes CNT(3,3) and CNT(5,5).

Modeling the absorption spectrum of the permanganate ion in vacuum and in aqueous solution

The absorption spectrum of MnO₄⁻ in vacuum and aqueous solution is modeled using the range-separated complete active space short-range density functional theory method (CAS-srDFT) combined with either implicit (PCM) or explicit (PE) solvent models. The experimental vacuum-to-water solvent shift of the lowest intense transition is reproduced by PE-CAS-srDFT.