Dissociation Energy Research Articles

Terminal C(sp3)-H borylation through intermolecular radical sampling.

Hydrogen atom transfer (HAT) processes can overcome the strong bond dissociation energies (BDEs) of inert C(sp3)-H bonds and thereby convert feedstock alkanes into value-added fine chemicals. Nevertheless, the high reactivity of HAT reagents, coupled with the small differences among various C(sp3)-H bond strengths, renders site-selective transformations of straight-chain alkanes a great challenge. Here, we present a photocatalytic intermolecular radical sampling process for the iron-catalyzed borylation of terminal C(sp3)-H bonds in substrates with small steric hindrance, including unbranched alkanes. Mechanistic investigations have revealed that the reaction proceeds through a reversible HAT process, followed by a selective borylation of carbon radicals. A boron-sulfoxide complex may contribute to the high terminal regioselectivity observed.

Quantum chemical study on non-thermal plasma degradation tar in gasification syngas

The bond dissociation energies (BDEs) of benzene, toluene, and naphthalene which are the main components of tar in fluidized bed gasification syngas have been investigated by B3LYP method at 6-31G (d, p), 6-31G+ (d, p), 6-31G++ (d, p) and 6-311G++ (d, p) basis setsof density functional theory (DFT).The structures of benzene, toluene, naphthalene, and corresponding radicals were optimized, and their total energiesand zero-point energies (ZPE) were calculated.The frequency analysis was carried out, then, the transition state and the high order saddle were excluded, and the influence of zero point energy scaling factors was neglected.The results showed thatthe BDEs decreased with increasing computational basis sets. The calculated results obtained by B3LYP/6-31G (d, p) are much closer to the results of the documents than the other three basis sets. This indicates that the basis set of B3LYP/6-31G (d, p) is much more credible in reproducing the BDEs. The lowest electron energy values for the ring opening of benzene, toluene and naphthalene are 8.05 eV, 7.45 eV, and 7.35 eV, respectively, indicating that when the energy of high-energy electrons reaches 8.05 eV, the ring of aromatic hydrocarbon can be broken.

Superacidic Properties of Protonated PtFn (n = 1–6) and Their Ability to Form Supersalts: DFT Study

AbstractIn the present communication, this study has modeled protonated PtFn (n = 1–6), a new series of superacids. The calculated vertical de‐attachment energy (VDE) of PtFn (n = 1–6) reestablishes the superhalogenic behavior. The vibrational frequency, dissociation energy through the HF channel, and optimized geometries are utilized to discuss the stability of HPtFn (n = 1–6). The deprotonation energy of HPtFn is used to calculate the acidic strength of HPtFn (n = 1–6). The acidity of protonated PtFn (n = 1–6) is directly related to its counterpart superhalogen anions. The computed correlation factor (R2 = 0.9754) shows that VDE is directly associated with acidity. The mechanism of acidity of HPtFn (n = 1–6) is described by using natural bond orbital analysis charges on atoms. The electronic properties of HPtFn (n = 1–6) are calculated using the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy. The nature of chemical reactivity is also determined by the HOMO–LUMO plot of HPtFn (n = 1–6). It has formed the supersalts using superacids HPtFn (n = 1–6) and superbase (OLi3OH), and the nature of supersalts is compared with traditional salt LiF. The most stable conformers of supersalts PtFnOLi3 (n = 2–6) are analyzed for optoelectronic properties. It has computed the dissociation of supersalts through neutral and anions through superhalogns and superalkalis. The computed results show that PtF4OLi3 favors dissociation through anions as in traditional salts. The nonlinear optical parameters are calculated using dipole moment, mean polarizability, anisotropic polarizability, molar reflectivity (MR), order parameters, and hyperpolarizability of PtFnOLi3 (n = 2–4). The estimated nonlinear optical properties parameters are compared with corresponding parameters of traditional salt LiF by the same level theory.

Dissociation energies of labile C—H bonds in adducts of thiyl radicals with quinoids

Dissociation energies of labile C—H bonds in adducts of thiyl radicals with quinoids

C–H bond dissociation enthalpy prediction with machine learning reinforced semi-empirical quantum mechanical calculations

Abstract We introduce a combined fast semi-empirical quantum mechanical and machine learning (SQM/ML) approach capable of matching the C–H bond dissociation enthalpies (BDEs) computed with the highly accurate (RO)CBS-QB3 method. The usefulness of our proposed SQM/ML model is corroborated by the fact that a single C–H BDE of a molecule is calculated in seconds and the mean absolute error amounts to only 1 to 2 kcal/mol.

Hydrolysis-Induced Cu2O Networks and the Triggered Peroxidase-Mimic Activity by Cr6+ under Neutral Conditions.

The current small-scale synthesis and relatively large size of Cu2O have limited its practical applications. Herein, we developed a hydrolysis strategy to prepare phase-pure Cu2O networks composed of small granules (ca. 25 nm) on a gram scale. The preparation involves in situ hydrolyzing the Hx[CuxCl2x] complexes prereduced in N,N'-dimethylformamide (DMF). The DMF-soluble Hx[CuxCl2x] complexes are critical for the homogeneous nucleation of CuCl seeds and subsequent hydrolysis, allowing for separate control over the nucleation and growth stages to regulate the formation of Cu2O networks. The novel Cu2O networks possess numerous exposed active sites and hierarchical porosities, conferring high catalytic activity and fast mass transfer capability. The inherent peroxidase-mimic activity of Cu2O is severely inhibited under neutral conditions but can be triggered by Cr6+, enabling the colorimetric assay of Cr6+ with the assistance of the oxidation-induced color change of 3,3',5,5'-tetramethylbenzidine. Through density functional theory calculation, we confirmed that the attachment of Cr6+ on the Cu2O surface reduced the dissociation energy of H2O2, enhancing the enzyme-mimic activity. The colorimetric detection method demonstrated a sensitive and specific assay capability for Cr6+ (LOD = 0.095 μM). Our work offers a straightforward protocol for novel design of metal or metal-based nanomaterials for nanozymes or other applications.

In Situ Creation of Surface Defects on Pd@NiPd with Core-shell Hierarchical Structure Toward Boosting Electrocatalytic Activity.

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure-activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core-shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm-2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm-2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.

Exploring Synergistic Effect on the Stability of Ni-, Pd-, Ir-Doped TiN (N = 1–15) Nanoparticles

Bimetallic nanoclusters have attracted great interest due to their ability to enhance the catalytic properties of nanoclusters through synergetic effects that emerge from the combination of the metal nanocluster with different transition metal (TM) species. However, their indefinite composition and broad distribution hinder the insightful understanding of the interaction between these invasive metals in bimetallic doped nanoalloys. In this study, we report a density functional theory calculation with the PBEsol exchange-correlation functional for 16-atom TiN−1TM (TM = Ni, Ir, Pd) nanoalloys, which provides new insights into the synergetic effect of these invasive metals. The probe into the effect of these metal impurities revealed that the replacement of a Ti atom with Ni, Ir and Pd enhances the relative stability of the nanoalloys, and the maximum stability for a lower bimetallic composition is reached for Ti4Ir, Ti5Pd and Ti7Ni. The most stable nanoalloy is reached for the Ti12Ir cluster in comparison with the Ti12Pd and Ti12Ni clusters and pure Ti13 monoatomic nanocluster. This stability trend is as revealed well by both the binding energy and the dissociation energy. The average HOMO-LUMO gap for the bigger clusters revealed that the valence electrons in the HOMO can absorb lower energy, which is indicatory of a higher reactivity and lower stability. The quantum confinement is higher for the smaller clusters, which illustrates a higher stability and lower reactivity for those systems.

Recent Advance in the C−F Bond Functionalization of Trifluoromethyl Aromatic and Carbonyl Compounds

AbstractThe selective C−F bonds functionalization in available trifluoromethyl compounds is an economic route for obtaining high‐value organic fluorine compounds. However, due to the high C−F bonds dissociation energy in trifluoromethyl group, the strength of the bond decreases continuously during defluorination, posing a challenge in modifying such molecules without over‐conversion. Over the past few years, there has been significant progress in developing efficient methods for constructing difluoromethylene unit, using approaches such as radical chemistry, photochemistry, electrochemistry, and organometallic chemistry. These methods involve difluorocarbon radicals, difluorocarbon cations, difluorocarbon anions, and trifluoromethyl carbenes as intermediates. In this review, we summarized the recent five years of research achievements in this field for selective single C−F bond cleavage in trifluoromethyl aromatic and carbonyl compounds to gain diverse difluoromethylene‐containing organic molecules via different intermediate strategies.

Ligand-mediated exciton dissociation and interparticle energy transfer on CsPbBr3 perovskite quantum dots for efficient CO2-to-CO photoreduction

Perovskite quantum dots (PQDs) hold immense potential as photocatalysts for CO2 reduction due to their remarkable quantum properties, which facilitates the generation of multiple excitons, providing the necessary high-energy electrons for CO2 photoreduction. However, harnessing multi-excitons in PQDs for superior photocatalysis remains challenging, as achieving the concurrent dissociation of excitons and interparticle energy transfer proves elusive. This study introduces a ligand density-controlled strategy to enhance both exciton dissociation and interparticle energy transfer in CsPbBr3 PQDs. Optimized CsPbBr3 PQDs with the regulated ligand density exhibit efficient photocatalytic conversion of CO2 to CO, achieving a 2.26-fold improvement over unoptimized counterparts while maintaining chemical integrity. Multiple analytical techniques, including Kelvin probe force microscopy, temperature-dependent photoluminescence, femtosecond transient absorption spectroscopy, and density functional theory calculations, collectively affirm that the proper ligand termination promotes the charge separation and the interparticle transfer through ligand-mediated interfacial electron coupling and electronic interactions. This work reveals ligand density-dependent variations in the gas-solid photocatalytic CO2 reduction performance of CsPbBr3 PQDs, underscoring the importance of ligand engineering for enhancing quantum dot photocatalysis.

Two‐dimensional β‐ketoenamine linked azo covalent organic frameworks as heterogeneous catalysts for photo‐induced RCMP

AbstractPhoto‐induced reversible complexation‐mediated polymerization (RCMP) is a green and economical method to prepare polymers with precise molecular weights, narrow molecular weight distributions and functionally active chain ends. Covalent organic frameworks (COFs) are a promising heterogeneous photocatalyst for mediating RCMP due to their adjustable structure, band gap, and porosity. In this work, 1,3,5‐triformylphloroglucinol (Tp) and p‐azoaniline (Azo) were selected to construct 2D β‐ketoenamine linked Tp‐Azo‐COF as a heterogeneous photocatalyst to trigger RCMP under white light irradiation. A series of polymers with controllable molecular weight and narrow molecular weight distribution were successfully prepared by using Tp‐Azo‐COF as photocatalysis. On/off light experiments confirmed the good spatiotemporal control feature, and chain expansion experiments demonstrated the high “activity” of polymer chain ends. Furthermore, the mechanistic research elucidated that electron transfer between Tp‐Azo‐COF and initiator occurred, allowing the formation of reactive radicals to mediate RCMP. Density functional theory calculations revealed that the coordination of iodine on the initiator to catalyst obviously reduced the bond dissociation energy, leading to enhance in the polymerization rate. This work provides a platform for constructing heterogeneous photocatalysts with more efficient and stable to mediate RCMP.

Bond Strength and Interaction Energies in Togni Reagents: Insights from Molecular Electrostatic Potential-Based Parameters.

Togni reagents and their analogs, classified as hypervalent iodine(III) complexes, serve as potent trifluoromethylation agents. The interplay of cis and trans factors plays a pivotal role in shaping their performance, affecting aspects such as bond strength, interaction energies, stability, and subsequent nucleophilic reactions. In this context, we propose the utilization of the molecular electrostatic potential (MESP) at the carbon atom (VC) of the I-CF3 moiety as a sensitive parameter to quantify the cis and trans influences in Togni-type reagents. Our study has shown that VC serves as a convenient probe for determining the heterolytic bond dissociation energy (BDE) and, consequently, assessing the reactivity of these reagents. Moreover, these parameters have been successfully applied to evaluate the strength of the σ-hole interactions with nucleophiles (Cl- and NMe3). Additionally, we provide insights into interactions of Togni reagents with Brønsted acids such as HCl and HSO3F, elucidating them in terms of MESP topological parameters. These findings yield valuable information about the electronic properties of hypervalent iodine reagents, particularly Togni-type reagents, offering the potential for optimizing structurally modified reagents with enhanced activity and stability.

Metal-Free Visible-Light Induced Oxidative Cleavage of C(sp3 )-C, and C(sp3 )-N Bonds of Nitriles, Alcohols, and Amines.

Selective cleavage of unstrained (sp3 ) C-C/ C-N bonds under mild conditions is highly challenging due to the higher bond dissociation energy. A visible light mediated metal-free oxidative dehomologation of aryl acetonitriles, primary alcohols and diols to carboxylic acids via organophotocatalyzed C(sp3 )-CN, C(sp3 )-C(OH) bond cleavage is reported. Notably, this methodology was further extended towards selective synthesis of aldehydes via deamination of both primary as well as secondary amines. This mild protocol features wide array of substrate variation with excellent functional group tolerance, preparative-scale synthesis, and operational simplicity. Possible mechanisms for these transformations were demonstrated through a series of control experiments.

Deficient Tin oxide nanofibers with regulated valence for efficient nitrate reduction to ammonia

Electrocatalytic nitrate reduction emerges as a promising process for removal of nitrate and simultaneous production of value-added ammonia, but robust electrocatalysts with high selectivity are required due to the large dissociation energy of N≡O in nitrate. Herein, we propose oxygen deficient Tin oxide nanofibers with regulated bivalence (SnO) and tetravalency (SnO2-δ) as efficient catalysts for nitrate reduction reaction (NitRR). Such quadrivalent catalyst achieves a large NH3 yield of 17.27 mg h−1 mgcat.−1 and an extremely high Faradaic Efficiency (FE) of 95.67 % in 0.1 M PBS with 0.1 M NO3−, which also exhibits excellent electrochemical stability. Material calculations reveal that SnO2-δ exhibits a direct band gap of 0.79 eV, smaller than 1.17 eV for SnO with an indirect band gap, and the potential determining step (*NO2 → *NO) hits a free energy change of only 0.1 eV.

Rational design of blue TADF host of various polarity according to cyano- group applicable to blue thermally activated delayed fluorescence emitter

Although remarkable progress has been made in the field of blue organic light-emitting diodes (OLEDs), many challenges persist. In particular, the emitting material layer of an OLED is composed of a host and a dopant, and the host material has a significant influence on the device efficiency and lifetime along with the dopant. Therefore, in this study, 9-(2′-(dibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole, 3′-(9H-carbazol-9-yl)-2-(dibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-3-carbonitrile, and 3′-(9H-carbazol-9-yl)-2-(dibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-4-carbonitrile were synthesised to investigate the changes in the device efficiency and lifetime through various properties such as the polarity of the host molecule and anionic bond dissociation energies (BDEs) according to the substitution position of the CN group. In addition, 2,4,6-tris(2-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-1,3,5-triazine, a blue thermally activated delayed fluorescence dopant, was synthesised and evaluated. The roll-off at 5000 nit decreased from 30.2% to 21.9% depending on the polarity of the host molecule, whereas the lifetime increased from 7.95 to 15.5 h according to the anionic BDE of blue thermally activated delayed fluorescence hosts.

Exploring a Fused Triazole-Tetrazine Binary CN Material for a Promising Initiating Substance.

The pursuit of binary carbon-nitrogen (CN) materials with high density and good thermal stability presents a significant challenge due to the inherent trade-off between high-energy storage and low bond dissociation energy. In this study, we designed and synthesized (S)-1,2-bis(3-azido-1H-1,2,4-triazol-1-yl)diazene (BAzTD) and 2,9-diazidobis([1,2,4]-triazolo)[1,5-d:5',1'-f][1,2,3,4]tetrazine (DAzTT) through a straightforward reaction. Remarkably, DAzTT demonstrated a high density of 1.816 g·cm-3 (at 298 K) and a considerable thermal decomposition temperature of 216.86 °C. These properties outperform those of previously reported binary heterocyclic CN compounds and polyazido heterocyclic compounds. The quantum-chemical methods further substantiated the integral role of aromaticity as the driving force behind this difference. Additionally, the initiation capability of DAzTT was evaluated by a notably low minimum primary charge (MPC = 40 mg), surpassing conventional organic primary explosives, such as commercial 2-diazo-4,6-dinitrophenol (DDNP, MPC = 70 mg). The exceptional priming ability highlights the potential as an environmentally friendly replacement for toxic lead azide. DAzTT sets a new standard for binary CN compounds and provides a valuable precursor for high-nitrogen carbon nitride materials.

Graphene/Hexagonal Boron Nitride Heterostructures for O2 Activation and CO Oxidation: Metal-Free Catalysts by Design.

Pristine graphene and h-BN monolayers are chemically inert to oxygen and thus exhibit very limited catalytic activity toward O2 activation. Herein, we show that graphene/h-BN heterostructures exhibit a surprising O2 activation capability. We theoretically designed ten graphene/h-BN heterostructures with three types of interfaces and investigated their catalytic activities toward O2 activation and CO-oxidation. In general, O2 can be molecularly chemisorbed and activated on electron-rich graphene/h-BN heterostructures. Electron-deficient graphene/h-BN heterostructures can lead to dissociative O2 adsorption with relatively low dissociation energy barriers (<0.4 eV). For CO-oxidation, the computed energy barrier can be as low as 0.67 eV. The high catalytic activities toward O2 stem from either electron-deficient heterostructures' accumulated electrons or electron richness and low work function for the electron-rich heterostructures. Although the catalytic activities of graphene/h-BN heterostructures depend strongly on the interface type, they are insensitive to the patterns of BN-substitutes, hence benefiting applicability of a wide range of heterostructures.

Bond dissociation energy of FeCr+ determined through threshold photodissociation in a cryogenic ion trap.

The bond dissociation energy of FeCr+ is measured using resonance enhanced photodissociation spectroscopy in a cryogenic ion trap. The onset for FeCr+ → Fe + Cr+ photodissociation occurs well above the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit. In contrast, the higher energy FeCr+ → Fe+ + Cr photodissociation process exhibits an abrupt onset at the energy of the Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) limit, enabling accurate dissociation energies to be extracted: D(Fe-Cr+) = 1.655 ± 0.006eV and D(Fe+-Cr) = 2.791 ± 0.006eV. The measured D(Fe-Cr+) bond energy is 10%-20% larger than predictions from accompanying CAM (Coulomb Attenuated Method)-B3LYP and NEVPT2 and coupled cluster singles, doubles, and perturbative triples electronic structure calculations, which give D(Fe-Cr+) = 1.48, 1.40, and 1.35eV, respectively. The study emphasizes that an abrupt increase in the photodissociation yield at threshold requires that the molecule possesses a dense manifold of optically accessible, coupled electronic states adjacent to the dissociation asymptote. This condition is not met for the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit of FeCr+ but is satisfied for the higher energy Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) dissociation limit.

CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi‐Hydrogenation/Reduction Strategy

AbstractDue to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi‐hydrogenation/reduction strategy utilizing CsPbBr3 quantum dots (CPB‐QDs) and Hantzsch ester (HEH2) as a synergistic catalytic system was introduced to reduce the BDE of Cβ−O−Ar, achieving effective cleavage of the Cβ−O−Ar bond. This strategy offers a wide substrate scope encompassing various β‐O‐4 model lignin dimers, preoxidized β‐O‐4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir‐catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH2 can be activated by CPB‐QDs via single electron transfer (SET), generating HEH2⋅+ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH2⋅+ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton‐coupled electron transfer (PCET) from HEH2⋅+ to the carbonyl group of the substrate generates a Cα⋅ intermediate.

CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi-Hydrogenation/Reduction Strategy.

Due to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi-hydrogenation/reduction strategy utilizing CsPbBr3 quantum dots (CPB-QDs) and Hantzsch ester (HEH2 ) as a synergistic catalytic system was introduced to reduce the BDE of Cβ -O-Ar, achieving effective cleavage of the Cβ -O-Ar bond. This strategy offers a wide substrate scope encompassing various β-O-4 model lignin dimers, preoxidized β-O-4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir-catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH2 can be activated by CPB-QDs via single electron transfer (SET), generating HEH2 ⋅+ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH2 ⋅+ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton-coupled electron transfer (PCET) from HEH2 ⋅+ to the carbonyl group of the substrate generates a Cα ⋅ intermediate.