Ab initio simulation of the photoelectron spectra of HCO− and DCO−

Large scale, vibrational CI calculations using a global ab initio potential energy surface are used to calculate multidimensional Franck-Condon overlaps from the ground vibrational state of HCO⁻ and DCO⁻ to all final bound and several quasibound vibrational states of HCO and DCO. The resulting Franck-Condon spectra are compared with recent experimental photoelectron spectra of HCO⁻ and DCO⁻.     

Nonempirical calculations of the potential-energy fields of the nucleophilic addition of H− and F− to acetylene and methylacetylene molecules

By using the basis 3–21 + G, the minimum-energy routes for the nucleophilic addition to the F^– ion to methylacetylene have been calculated within the framework of the Hartree-Fock-Roothaan method according to and against the Markovnikov rule with the formation of the 1-fluoropropenyl and 2-fluoropropenyl anions. The results have been compared with data from previous calculations of the nucleophilic addition of H^– and F^– to acetylene with the formation of vinyl and fluorovinyl anions, as well as of the nucleophilic addition of H^– to methylacetylene according to and against the Markovnikov rule with the formation of the 1-propenyl and 2-propenyl anions. It has been established that the reaction with H^– is exothermic, while the reaction with F^– is endothermic. The activation energies of the reactions with F^– are lower than the activation energies of the corresponding reactions with H^–. It is shown that the reactions with H^– have a relatively early transition state, while the reactions with F^– are characterized by a later transition state.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 28, No. 1, pp. 5–11, January–February, 1992.     

Recent Advance in the Development of Singlet−Fission−Capable Polymeric Materials

Singlet fission (SF) is a spin–allowed process in which a higher–energy singlet exciton is converted into two lower-energy triplet excitons via a triplet pair intermediate state. Implementing SF in photovoltaic devices holds the potential to exceed the Shockley–Queisser limit of conventional single-junction solar cells. Although great progress has been made in exploiting the underlying mechanism of SF over the past decades, the scope of materials capable of SF, particularly polymeric materials, remains poor. SF–capable polymer is one of the most potential candidates in the implementation of SF into devices due to their distinct superiorities in flexibility, solution processability and self-assembly behavior. Notably, recent advancements have demonstrated high-performance SF in isolated donor-acceptor (D-A) copolymer chains. This review provides an overview of recent progress in the development of SF-capable polymeric materials, with a significant focus on elucidating the mechanisms of SF in polymers and optimizing the design strategies for SF-capable polymers. Additionally, the paper discusses the challenges encountered in this field and presents future perspectives. It is expected that this comprehensive review will offer valuable insights into the design of novel SF-capable polymeric materials, further advancing the potential for SF implementation in photovoltaic devices.     

DFT studies of the characteristics of Pd−Pt core-shell clusters

It is reported that Pd?Pt core-shell type nanoclusters in which the inner atoms of the Pd cluster are substituted by Pt significantly enhance the catalytic activity for cycloocatdiene hydrogenation. In order to discuss the electronic states of core-shell clusters, DFT calculations were carried out for Pd₁₃, Pt₁₃, Pt/Pd₁₂, Pd/Pt₁₂ Pd₃₈ and Pd₆/Pt₃₂ clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role for the modification of the electronic state of the surface atoms in them.     

Identifying the Types and Characterization of the Active Sites on M−X−C Single-Atom Catalysts

Single atom catalysts (SACs) have attracted much attention in recent years. As an essential group in SACs, M−X−C (X=nonmetallic element) materials have been demonstrated to be efficient in many reactions. However, identifying the active sites on M−X−C, especially under working conditions, is still challenging, which is crucial for chemists to further understand the mechanism underlying the reaction and better design proper SACs for specific reactions. Herein, the types and characterization of M−X−C are comprehensively summarized and discussed in this review. In addition to the basic information above, the challenges and opportunities remaining in this field will be also proposed to present a perspective to the research on the next step.     

Normal-coordinate analysis of the TiO6−5 ion

Normal-coordinate analysis for the TiO⁶⁻₅ ion in M₂TiO₅ (M = rare earths) has been made on the basis of C_4ν-symmetry and using the Wilson's GF matrix method. The observed frequencies have been quantitatively assigned according to the obtained values of the potential-energy distributions. Force constants for the different bonds and angles have been calculated. The TiO′ (axial) and TiO (equatorial) stretching force constants were calculated to be 4.15 and 2.48 mdyn Å⁻¹, respectively.     

The thermodynamic stability of the LaBr 4 − ion

The thermodynamic stability of the LaBr ₄ ^? anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction $ LaBr_4^ - = Br^ - + LaBr_3 The thermodynamic stability of the LaBr₄⁻ anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction were Δ_r H°(298.15 K) = 302 ± 14 and 303 kJ/mol, respectively. The value Δ_f H° (LaBr₄⁻, g, 298.15 K) = −1105 ± 14 kJ/mol was recommended as the enthalpy of formation of the LaBr₄⁻ anion. Original Russian Text ? M.F. Butman, L.S. Kudin, V.B. Motalov, D.A. Ivanov, V.V. Sliznev, K.W. Kr?mer, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 5, pp. 885–890.     

A vibrational analysis of the MnO 4 − bands

Teltow'S [14,15] measurements of the permanganate bands are reanalyzed using the level scheme of Ballhausen and Liehr [2]. For KMnO ₄ dissolved in KClO ₄ the components of the first ¹ T ₂ state are found at 18050 cm^–1 18078 cm^–1 and 18043 cm^–1. The breathing frequency of the MnO _– ⁴ unit is in this state 768 ^–1. The electronic origin of the second ¹ T ₂ state is found at 30723 cm^–1 with a breathing frequency of 760 cm^–1.Evidence is further found for a ¹ T ₁ state with its split components located at 14446 cm^–1, 14526 cm^–1 and 14600 cm^–1. The breathing frequency is here found to be 800 cm^–1.Finally for KMnO ₄ dissolved in NaClO ₄ there are indications that one or two spin-triplets are located near 13200 cm^–1.

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Zusammenfassung TeltowS Messungen des Permanganatspektrums [14, 15] werden mit Hilfe des Termschemas von Ballhausen und Liehr [2] von neuem analysiert. Für KMn ₄ in KClO ₄ findet man die zum ersten ¹ T ₂-Zustand gehörenden Komponenten bei 18050, 18078 und 18043 cm^–1. Die Valenzschwingung des MnO _– ⁴ liegt hier bei 768 cm^–1. Der Ursprung des zweiten ¹ T ₂-Systems wird bei 30723 cm^–1 gefunden, die dazugehörige Valenzfrequenz ist 760 cm^–1.Bei 14446, 14526 und 14600 cm^–1 liegen offenbar die Komponenten eines ¹ T ₁-Terms, wozu eine Valenzfrequenz von 800 cm^–1 gehört.Schließlich findet man für KMnO ₄ in NaClO ₄ Anzeichen für ein oder zwei Spin-Tripletts um 13200 cm^–1.

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Résumé Les bandes d'absorption du permanganate, mesurées par Teltow [14,15], sont réanalysées à l'aide d'un système de termes proposé par Ballhausen et Liehr [2]. Pour KMnO ₄ dans KClO ₄, on trouve les composants du premier état ¹ T ₁ à 18050, 18078 et 18043 cm^–1. La vibration symétrique du MnO _– ⁴ dans cet état se situe à 768 cm^–1. L'origine électronique du second état ¹ T ₂ est trouvé à 30723 cm^–1, la fréquence oscillatrice correspondante est de 760 cm^–1.Un état ¹ T ₁ avec ses composants à 14446, 14526 et 14600 cm^–1 est mis en évidence, avec une vibration symétrique de 800 cm^–1.Finalement, au cas du KMnO ₄ dissous dans le NaClO ₄, il y a des indications pour un ou deux triplets de spin vers 13200 cm^–1.

     

Thermodynamic study of the LaNi5−xCux system

The enthalpies of formation of LaNi_5−xCu_x compounds (x = 0, 1, 2, 3, 4, 5) were measured using a calorimetric method and were found to increase linearly from LaNi₅to LaCu₅. A relation taking the substitution of copper for nickel into account is proposed to explain this behaviour. The enthalpies of hydrogenation are calculated from these values for the enthalpies of formation using relations established previously and are compared with experimental data.     

Topology of the electron density of multicenter bonding in the anion TCNE2 2−

For TCNE₂ ^2? the role of bond paths in the electron density is emphasized to show that the anion contains multicenter bonding interactions across 4 central carbon atoms conferring inherent stability to it, consistent with experimental, and theoretical studies of other authors.     

Elucidating the N−N and C−N Bond-breaking Mechanism in the Photoinduced Formation of Nitrile Imine

In this study, we revealed the significance of chemical bonding for the photochemically induced mechanism of 2-phenyl tetrazole derivatives generating nitrile imines. The correlated electron localization function shows that the formation of imine nitrile involves two key bond events: (i) the heterolytic C−N breakage taking place in the T₁ state and (ii) the homolytic N−N rupture occurring in the T₂ excited state. In particular, a cation-radical specie results from the C−N cleavage, whereas the N−N rupture creates a biradical resonant form of imine nitrile. Additionally, we noticed that the substantial pair delocalization of the C−C-N bonded structure could play a significant role in the conversion of the biradical imine nitrile into both the propargylic and allenic forms via the T₁→S₀ deactivation.     

C−F Transformations of Benzotrifluorides by the Activation of Ortho-Hydrosilyl Group

Single C−F transformations of aromatic trifluoromethyl compounds are challenging issues due to the strong C−F bond. We have recently developed selective methods for single C−F transformations such as allylation of o-hydrosilyl-substituted benzotrifluorides through the hydride abstraction with trityl cations. Single C−F thiolation and azidation of o-(hydrosilyl)benzotrifluorides were achieved using trityl sulfides and trityl azide catalyzed by Yb(OTf)₃. Treatment of o-(hydrosilyl)benzotrifluorides with trityl chloride resulted in single C−F chlorination. The resulting fluorosilyl group served in further transformations including protonation, halogenation, and Hiyama cross-coupling with C−Si cleavage. We also synthesized benzyl fluorides by LiAlH₄-reduction of the resulting fluorosilanes and further C−F transformations. These methods enabled us to prepare a broad range of organofluorines from simple benzotrifluorides through C−F and C−Si transformations.     

Calculated vibrational structure of the first band of the photoelectron spectrum of HO 2 − and the electron affinity of HO2

The vibrational structure of the first band of the photoelectron (PE) spectrum of HO ₂ ^? and DO ₂ ^? has been calculated on the basis of (slightly modified) ab initio potentials. The best agreement with the experimental spectrum of HO ₂ ^? is obtained for a vibrational temperature of ca. 600 K. “Peak D”, which has been under debate in earlier work, is composed of two transitions, with the “hot” transition 3 ₁ ¹ being more intense than the adiabatic transition. Since thev ₂ bending mode of DO₂ has significant OO stretching character, the vibrational structure of the PE spectrum of DO ₂ ^? is more complex than that of HO ₂ ^? . Large-scale RCCSD(T) calculations of the equilibrium electron affinity of HO₂ yield 1.058 eV which agrees with the experimental value of 1.044 ± 0.020 eV.     

Spin-adduct of the P4 ·− radical anion during the electrochemical reduction of white phosphorus

The radical anion P₄·⁻ was detected and identified by the ESR method as a spin-adduct with nitrone during the electrochemical reduction of white phosphorus in the presence of a spin trap, viz., α-phenyl-N-tert-butylnitrone, in a special electrolysis cell with a helical platinum working electrode in the potentiostatic mode. The character of the behavior of P₄·⁻ and the spin trap during electrochemical reduction was monitored by cyclic voltammetry directly in the electrolysis cell, and the spin-adduct formed was detected by ESR.     

The Influence of Weakly Coordinating Cations on the O−H⋅⋅⋅O− Hydrogen Bond of Silanol-Silanolate Anions

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state.     

A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.