Group 1 elements exhibit the lowest electronegativity values in the Periodic Table. The chemical reduction of Group 1 metal cations M + to M(0) is extremely challenging. Common tetraaryl borates demonstrate limited redox properties and are prone to decomposition upon oxidation. In this study, by employing simple yet versatile bipyridines as ligands, we synthesized a series of redox-active borate anions characterized by NMR and X-ray single-crystal diffraction. Notably, the borate anion can realize the reduction of Li + , generating elemental lithium metal and boron radical, thereby demonstrating its potent reducing ability. Furthermore, it can serve as a powerful two-electron-reducing reagent and be readily applied in various reductive homo-coupling reactions and Birch reduction of acridine. Additionally, this borate anion demonstrates its catalytic ability in the selective two-electron reduction of CO 2 into CO.

A single-layer of GaSe is widely regarded as one of the most promising photocatalysts for a solar-driven water-splitting reaction. However, its catalytic performance is limited by the high onset potential for the oxygen evolution reaction (OER). Achieving the ideal adsorption strength of each intermediate (HO*, O*, and HOO*) involved in the OER process simultaneously via the surface modification of two-dimensional (2D) materials is a significant challenge. In this study, the effects of partial replacement of Se atoms of GaSe with O atoms on the catalytic activity of the resulting 2D GaSe1-xOx surface toward OER have been systematically examined using density functional theory calculations. Our theoretical results revealed that manipulating the atomic configuration of O dopants largely improves the catalytic activity of GaSe1-xOx. When the O-dopants are separated by a -Ga-Se-Ga- unit, the OER is limited by the strong adsorption of the O* intermediate. On the contrary, when a -Ga- unit is bonded with three O-dopants, this O-saturated Ga atom serves as the best site to initiate the OER and exhibits high catalytic performance with a predicted overpotential of 0.38 V, which is comparable with the values of many state-of-the-art precise-metal-based catalysts.

Previous mass spectrometric (MS) studies demonstrated that singly charged hydration clusters of manganese ions [Mn(H2O)n]+ were, on one hand, highly reactive toward intracluster water insertion but, on the other hand, inert toward nitrous oxide activation. This contrast in reactivity has been rationalized by our present theoretical investigation for the interconversion between the pristine Mn(I) monovalent form as a monatomic ion in [MnI(H2O)n]+ and the oxidized Mn(III) trivalent form as a hydride-hydroxide in [HMnIIIOH(H2O)n-1], as well as their reactivity toward nitrous oxide activation. Our theoretical interpretations are supported with quantum chemical calculations based on density functional theory (DFT), performed systematically for the cluster-size range of n = 1 - 12. Our DFT results show that water insertion is kinetically and thermodynamically favorable for n ≥ 8, suggesting [HMnIIIOH(H2O)n-1]+ is the predominant form, as observed in previous MS experiments. While [MnI(H2O)n]+ is capable of N2O reduction, the process of which is highly exothermic, similar reactions are unfavorable with [HMnIIIOH(H2O)n-1]+, which can only form weakly bound adducts with N2O. This work demonstrates the masking effect of water molecules over the high reactivity of the hydrated Mn(I) center and sheds light on the potential roles of water in transition metal systems.

Molecular processes behind hydrogen evolution reactions can be quite complex. In macroscopic electrochemical cells, it is extremely difficult to elucidate and understand their mechanism. Gas phase models, consisting of a metal ion and a small number of water molecules, provide unique opportunities to understand the reaction pathways in great detail. Hydrogen evolution in clusters consisting of a singly charged metal ion and one to on the order of 50 water molecules has been studied extensively for magnesium, aluminum and vanadium. Such clusters with around 10-20 water molecules are known to eliminate atomic or molecular hydrogen upon mild activation by room temperature black-body radiation. Irradiation with ultraviolet light, by contrast, enables hydrogen evolution already with a single water molecule. Here, we analyze and compare the reaction mechanisms for hydrogen evolution on the ground state as well as excited state potential energy surfaces. Five distinct mechanisms for evolution of atomic or molecular hydrogen are identified and characterized.

The precise location of an ion or electron, whether it is internally solvated or residing on the surface of a water cluster, remains an intriguing question. Subtle differences in the hydrogen bonding network may lead to a preference for one or the other. Here we discuss spectroscopic probes of the structure of gas-phase hydrated ions in combination with quantum chemistry, as well as H/D exchange as a means of structure elucidation. With the help of nanocalorimetry, we look for thermochemical signatures of surface vs internal solvation. Examples of strongly size-dependent reactivity are reviewed which illustrate the influence of surface vs internal solvation on unimolecular rearrangements of the cluster, as well as on the rate and product distribution of ion-molecule reactions.

Introduction: A new series of organic liquid crystal tetramers containing two symmetrical mesogenic units of 4-(4’-phenoxylimino)methyl)phenol joined by methylene –(CH2)mspacer wherein m varied from 5 to 10 have been synthesized. Methods: The length for each of the mesogenic units was extended further via connection with two chiral entities of (S)-2- methylbutyl-4-(4’-bromobutyloxyphenyl)benzoate situated at both terminal ends. The structures of these tetramers were elucidated using elemental analysis and spectroscopic techniques (FT-IR and 1H-NMR) whilst the texture, and the phase transition temperatures were studied using polarizing optical microscopy (POM) along with differential scanning calorimetry (DSC). Results: All the homologues in this series are enantiotropic mesogens exhibiting oily streak texture or fan-shaped texture characteristic of the chiral nematic phase. The odd-even effect can be observed upon increasing the methylene spacer length. The structure-properties connectivity has demonstrated that the phase transition temperature for tetramers with even-numbered methylene units in the spacer is relatively higher in comparison with the odd-numbered members. Conclusion: The computational study via molecular constraint dynamics performed at the DFTB level of theory has further supported that more energy is required for the even-numbered tetramer than the odd-numbered member to undergo the structural transition from folded to extended geometries.

Developing metal-free electrocatalysts for direct nitrate-to-ammonia reduction is promising to remediate wastewater yet challenged by the poor ammonia selectivity. Amorphization has become an emerging strategy to afford conventional materials with exotic physical, chemical, and electronic properties. Transient laser heating of polymers produces graphene with an unusual polycrystalline lattice, yet the control of graphene amorphicity is difficult due to the extreme conditions and fast kinetics of the lasing process. Here, we report the synthesis of amorphous graphene with a tailorable heterophase, topologically disparate from crystalline graphene and amorphous carbon. Atomic-resolution imaging reveals the intermediate crystallinity comprising both six-membered rings and polygons, the ratio of which directly correlates with the aromatic structures of the precursors. These amorphous graphenes, as metal-free catalysts, show high performance in direct nitrate-to-ammonia electroreduction. The performance is associated with the amorphicity of graphene and reaches a maximum ammonia Faradaic efficiency of 83.7% at -0.94 V vs reversible hydrogen electrode. X-ray pair distribution functions and paramagnetism disclose the elongated carbon-carbon bonds and rich unpaired electrons in amorphous graphene, which exhibit more favorable adsorption of nitrate as suggested by theoretical calculations. Our findings shed light on the controllable synthesis of graphene with unusual topologies that could find broad applications in electronics, catalysis, and sensors.

A new series of asymmetrical N,N'-disubstituted benzimidazolium derived N-heterocyclic carbene (NHC) ligands and their mononuclear silver(I)-NHC complexes are reported. The ligands were prepared from N- alkylation of 1-methylbenzimidazole with alkyl bromides (n = 10-18 in even parity), non-fluorinated or fluorinated benzyl bromides. In situ deprotonation of the ligands with silver oxide, followed by metathesis reaction with potassium hexafluorophosphate facilitated the formation of the mononuclear silver(I)-NHC complexes. Chemical structures of all the compounds were elucidated using Fourier transform infrared, H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy, and CHN elemental microanalysis. The coordination mode of the Ag(I)-NHC complexes was confirmed by single crystal XRD analysis. Single crystal analysis of ortho-fluorinated benzyl-containing complex showed that each complex consisted of one Ag(I) ion coordinated with two NHC ligands in a linear geometry in the presence of one PF6- anion in the lattice. Cytotoxic effects of the NHC ligands and their silver(I) complexes against human cervical cancer cells (HeLa) and normal human skin fibroblasts (Hs27) were investigated using the MTT assay. Cytotoxicity of these compounds was dependent on the N-substituents in the benzimidazolium moiety and the presence of silver ions. Benzylated ligands were non-active whilst their dialkylated analogues showed weak to excellent cytotoxic effects on HeLa cells. The incorporation of silver ions and elongation of alkyl chains significantly enhanced cytotoxicity. Density functional theory revealed that Ag-C bond strength was in-sensitive to the NHC ligand design, and about one-third of the overall complex binding enthalpy was con-tributed by the non-covalent interaction between the long alkyl chains. Long-chain ligands ( n = 16-18) and all silver(I)-NHC complexes exhibited superior cytotoxicity against HeLa cells (IC50 ranged between 1.18 mu M-9.38 mu M) as compared to that of the anticancer drug, Etoposide (IC50 = 25.67 mu M). (C) 2022 Elsevier B.V. All rights reserved.

Two-dimensional (2D) gallium selenide (GaSe) is known for its inert surface and wide bandgap, limiting its application as a photocatalytic material for the hydrogen evolution reaction (HER). Partial substitution of Se with O atoms can improve its catalytic efficiency. This work discovered that the surface activity of the substitutional O-doped single-layer GaSe surfaces (GaSe1-xOx, for x <= 22%) and their bandgap sizes are dependent on the detailed atomic configuration of the dopants, as revealed from density functional theory. For GaSe1-xOx at low O contents, where all O atoms are favorably separated by at least one-GaSe-Ga- unit, the surface activity for the HER is insignificantly improved by increasing dopant concentration. By contrast, when more O dopants are available and arranged in adjacent positions (O-Ga-O), the hydrogen adsorption efficiency of GaSe1-xOx increases and their bandgaps are reduced with increasing dopant concentration. These important features are attributed to weakening of the Ga-O covalent interaction in these more localized dopant arrangements, which in turn strengthens the O-H bonds. This weakened Ga-O covalent bond also descends the conduction band minimum toward the Fermi level, resulting in bandgap reduction and thus favoring visible-light absorption. Optimal atomic configurations (all having localized O-dopant arrangements) have been identified, and they exhibit almost thermoneutral hydrogen adsorption free energy Delta G(H) and small bandgaps (2.09-2.21 eV), making them promising materials to perform an efficient HER. Fine-tuning the Ga-O interaction by applying tensile strength T-s parallel to the 2D surface of up to 1% further reduces their bandgaps to 1.95-2.05 eV. Our theoretical predictions suggest that controlling the atomic configuration of dopants provides opportunities for engineering single-layered GaSe1-xOx materials with surface reactivity and bandgaps that suit photocatalytic water splitting.

Hydrated singly charged aluminum ions eliminate molecular hydrogen in a size regime from 11 to 24 water molecules. Here we probe the structure of HAlOH+ (H2 O)n-1 , n=9-14, by infrared multiple photon spectroscopy in the region of 1400-2250 cm-1 . Based on quantum chemical calculations, we assign the features at 1940 cm-1 and 1850 cm-1 to the Al-H stretch in five- and six-coordinate aluminum(III) complexes, respectively. Hydrogen bonding towards the hydride is observed, starting at n=12. The frequency of the Al-H stretch is very sensitive to the structure of the hydrogen bonding network, and the large number of isomers leads to significant broadening and red-shifting of the absorption of the hydrogen-bonded Al-H stretch. The hydride can even act as a double hydrogen bond acceptor, shifting the Al-H stretch to frequencies below those of the water bending mode. The onset of hydrogen bonding and disappearance of the free Al-H stretch coincides with the onset of hydrogen evolution.

Hydrated cobalt(i) cluster ions, [Co(H2O)n]+, can decompose the inert nitrous oxide molecule, N2O. Density functional theory suggests that N2O can anchor to Co+ of [Co(N2O)(H2O)n]+ through either O end-on (η1-OL) or N end-on (η1-NL) coordinate mode. The latter is thermodynamically more favorable resulting from a subtle π backdonation from Co+ to N2O. N2O decomposition involves two major processes: (1) redox reaction and (2) N-O bond dissociation. The initial activation of N2O through an electron transfer from Co+ to N2O yields anionic N2O-, which binds to the metal center of [Co2+(N2O-)(H2O)n] also through either O end-on (η1-O) or N end-on (η1-N) mode and is stabilized by water molecules through hydrogen bonding. From η1-O, subsequent N-O bond dissociation to liberate N2, producing [CoO(H2O)n]+, is straightforward via a mechanism that is commonplace for typical metal-catalyzed N2O decompositions. Unexpectedly, the N-O bond dissociation directly from η1-N is also possible and eliminates both N2 and OH, explaining the formation of [CoOH(H2O)n]+ as observed in a previous experimental study. Interestingly, formation of [CoO(H2O)n]+ is kinetically controlled by the initial redox process between Co+ and the O-bound N2O, the activation barriers of which in large water clusters (n ≥ 14) are higher than that of the unexpected N-O bond dissociation from the N-bound structure forming [CoOH(H2O)n]+. This theoretical discovery implies that in the present of water molecules, the metal-catalyzed N2O decomposition starting from an O-bound metal complex is not mandatory.

AbstractHydratisierte Al+‐Ionen eliminieren H2 in einem Bereich von 11 bis 24 Wassermolekülen. Wir untersuchten die Struktur von HAlOH+(H2O)n−1, n=9–14, durch IR‐Mehrfachphotonendissoziationsspektroskopie bei 1400–2250 cm−1. Aufgrund quantenchemischer Rechnungen ordnen wir die Merkmale bei 1940 und 1850 cm−1 der Al‐H‐Streckschwingung in fünf‐ bzw. sechsfach koordinierten AlIII‐Komplexen zu. Es werden Wasserstoffbrücken in Richtung des Hydrids beobachtet, beginnend bei n=12. Die Frequenz der Al‐H‐Streckschwingung ist sehr empfindlich gegenüber der Struktur des Netzwerks aus Wasserstoffbrücken, und die große Anzahl von Isomeren führt zu einer deutlichen Verbreiterung und Rotverschiebung der Absorptionen der wasserstoffbrückengebundenen Al‐H‐Streckschwingung. Das Hydrid kann sogar als doppelter Wasserstoffbrücken‐Akzeptor wirken und die Al‐H‐Streckschwingung zu Frequenzen verschieben, die unter denen der Wasser‐Biegemoden liegen. Das Einsetzen der Wasserstoffbrückenbindung und das Verschwinden der freien Al‐H‐Streckschwingung fallen mit dem Einsetzen der Wasserstoffentwicklung zusammen.

The hydrolytic stability of Pt(iv) complexes is determined by all the six ligands that coordinate to the Pt(iv) center. By appropriately choosing all the ligands during the design of Pt(iv) prodrugs, the stability of Pt(iv) prodrugs can be improved.

In this study, dissociative one-electron transfer dissociation of[Cu-II(dien)Y(G/A)W](center dot 2+)[dien = diethylenetriamine; Y(G/A)W = tyrosyl (glycyl/alanyl)tryptophan] was used to generate the tripeptide radical cations[Y(G/A)W](center dot+); subsequent loss of the Tyr side chain formed[G(alpha)(center dot)(G/A)W](+). The pi-centered species[YGW(pi)(center dot)](+)generated the alpha-centered species[G(alpha)(center dot)GW](+)through C-alpha-C(beta)bond cleavage, as revealed using infrared multiple photon dissociation (IRMPD) measurements and density functional theory (DFT) calculations. Comparisons of experimental and theoretical IR spectra confirmed that both the charge and spin densities of[Y(G/A)W-pi(center dot)](+)were delocalized initially at the tryptophan indolyl ring; subsequent formation of the final[G(alpha)(center dot)(G/A)W](+)structure gave the highest spin density at the alpha-carbon atom of the N-terminal glycine residue, with a proton solvated by the first amide oxygen atom. The IRMPD mass spectra and action spectra of the[G(alpha)(center dot)(G/A)W](+)species were all distinctly different from those of their isomeric[G(G/A)W-pi(center dot)](+)species. The mechanism of formation of the captodative[G(alpha)(center dot)(G/A)W](+)species-with the charge site separated from the radical site-from[Y(G/A)W-pi(center dot)](+)has been elucidated. DFT calculations suggested that the C-alpha-C(beta)bond cleavage of the tyrosine residue in the radical cationic[Y(G/A)W-pi(center dot)](+)precursor involves (a) through-space electron transfer between the indolyl and phenolic groups; (b) formation of proton-bound dimers through C-alpha-C(beta)cleavage of the tyrosine residue; and (c) a concerted proton rearrangement from the phenolic OH group to the carboxyl group and formation of the alpha-carbon-centered product[G(alpha)(center dot)(G/A)W](+)through hydrogen bond cleavage. The barriers for the electron transfer (a), the C-alpha-C(beta)cleavage (b), and the protonation rearrangement (c) were 12.8, 26.5, and 10.3 kcal mol(-1), respectively.

IRMPD suggests existence of π-radicals of [FYGG]˙+ featuring the n → π+ interaction, which are reactive intermediates toward dissociative electron transfer.

Treatment of the amidinato amidosilylene [L{(Me3Si)2N}Si:] [1, L = PhC(NtBu)2] with a slight excess of borane-tetrahydrofuran complex [BH3·THF] in toluene at room temperature afforded the silylene-borane adduct [L{(Me3Si)2N}Si:→BH3] (2). A triflate substituent was introduced on the boron center by reacting 2 with methyl triflate [MeOTf] (OTf = OSO2CF3) in toluene at room temperature to form [L{(Me3Si)2N}Si:→BH2OTf] (3), with the elimination of CH4 gas. The intramolecular C(sp3)-H borylation and H2 elimination occurred by reacting complex 3 with 1 in refluxing toluene to form a C-B bond in the resulting silylene-boronium ion 5. Complex 5 activated H2 gas or NH3BH3 at room temperature to form silylene-borane adduct 2 and [L{(Me3Si)2N}Si-H]OTf. Additionally, the reaction of 5 with H2 was studied through density functional theory calculations.

We report herein the first detailed study of the mechanism of redox reactions occurring during the gas-phase dissociative electron transfer of prototypical ternary [CuII(dien)M]˙2+ complexes (M, peptide). The two final products are (i) the oxidized non-zwitterionic π-centered [M]˙+ species with both the charge and spin densities delocalized over the indole ring of the tryptophan residue and with a C-terminal COOH group intact, and (ii) the complementary ion [CuI(dien)]+. Infrared multiple photon dissociation (IRMPD) action spectroscopy and low-energy collision-induced dissociation (CID) experiments, in conjunction with density functional theory (DFT) calculations, revealed the structural details of the mass-isolated precursor and product cations. Our experimental and theoretical results indicate that the doubly positively charged precursor [CuII(dien)M]˙2+ features electrostatic coordination through the anionic carboxylate end of the zwitterionic M moiety. An additional interaction exists between the indole ring of the tryptophan residue and one of the primary amino groups of the dien ligand; the DFT calculations provided the structures of the precursor ion, intermediates, and products, and enabled us to keep track of the locations of the charge and unpaired electron. The dissociative one-electron transfer reaction is initiated by a gradual transition of the M tripeptide from the zwitterionic form in [CuII(dien)M]˙2+ to the non-zwitterionic M intermediate, through a cascade of conformational changes and proton transfers. In the next step, the highest energy intermediate is formed; here, the copper center is 5-coordinate with coordination from both the carboxylic acid group and the indole ring. A subsequent switch back to 4-coordination to an intermediate IM1, where attachment to GGW occurs through the indole ring only, creates the structure that ultimately undergoes dissociation.