High Yield of L-Sorbose via D-Glucose Isomerization in Ethanol over a Bifunctional Titanium-Boron-Beta Zeolite.

D-Glucose-to-L-sorbose isomerization on Lewis acidic zeolite is a highly attractive avenue for sorbose production. But the L-sorbose yield is limited by the competing D-glucose-to-D-fructose isomerization and reaction equilibrium. In this work, it is suggested that ethanol directs the glucose conformation for selective D-glucose-to-L-sorbose isomerization.

Topological Transition in Aromatic and Quinonoid π-Conjugated Polymers Induced by Static Strain.

A topological quantum phase transition has been identified for the first time for 24 π-conjugated polymers as a function of external longitudinal strain due to a level crossing of the frontier orbitals at the topological phase transition. Topological phase is determined by the presence/absence of edge states. Out of the 24 polymers 15 are traditionally assigned an aromatic character, and 9 are traditionally assigned a quinonoid character.

A unique trimeric triphenylene radical cation: stacking aggregation, bonding, and stability.

A new and unique π-stacking triphenylene trimer cation radical unit appears in the crystal structure of a newly synthesized salt with an oligomeric gallium(iii) chloride, [(CH)]˙(GaCl), which is the first triphenylene aggregate observed. The structure is attributed to a shared electron distributed over the trimer displaying π-stacking pancake bonding. Computational modeling rationalizes the appearance of a "chain-shaped" rather than a "star-shaped" gallium chloride anion as well as the reasons why the trimer, rather than a radical cation aggregate of different size, is preferred in this system.

Structure and Bonding in π-Stacked Perylenes: The Impact of Charge on Pancake Bonding.

Perylene (PER) is a prototype of polycyclic aromatic hydrocarbons (PAHs), which play a pivotal role in various functional and electronic materials due to favorable molecule-to-molecule overlaps, which enhance electronic transport. This study provides guidelines regarding the impact of molecular charge on pancake bonding, a form of strong π-stacking interaction. Pancake bonding significantly boosts interaction energies within the monopositive dimer ([(CH)] or PER), crucial for stabilizing aggregation and crystal formation.

Continuous Topological Transition and Bandgap Tuning in Ethynylene-Linked Acene π-Conjugated Polymers through Mechanical Strain.

By variation of the chemical repeat units of conjugated polymers, only discrete tuning of essential physical parameters is possible. A unique property of a class of π-conjugated polymers, where polycyclic aromatic hydrocarbons are linked via ethynylene linkers, is their topological aromatic to quinoid phase transition discovered recently by Cirera et al. and González-Herrero et al.

Structure, Properties, and Reactivity of Polyoxocationic Zirconium and Hafnium Clusters: A Computational Investigation.

Tetravalent zirconium and hafnium molecular metal oxides clusters are key building blocks of many metal-organic frameworks; however, the chemical space to form all possible MOF nodes is vast, containing many potential new clusters. Our computational study provides a complete picture of the structure, properties, and reactivity of two tetrameric zirconium and hafnium [M(μ-η:η-O)(μ-OH)(HO)] polycationic clusters. The electronic structure of the studied species has characteristic polyoxometalate oxygen-based and metal-based bands in the valence region.

Aqueous Speciation of Tetravalent Actinides in the Presence of Chloride and Nitrate Ligands.

Speciation of hexachloride tetravalent uranium, neptunium, and plutonium species in aqueous media has been investigated using density functional theory in the presence of inner sphere ligands such as chloride, nitrate, and solvent molecules. All possible structures with the formula [An(Cl)(HO)(NO)] (An = U, Np, and Pu; = 0-6, = 0-8, and = 0-6) were considered to explore the speciation chemical space of each actinide. The nature of the mixed-ligand complexes present in solution is controlled by the concentration of free ligands in solution.

Stabilizing Porosity in Organic Cages through Coordination Chemistry.

The number of studies concerning the permanent porosity of molecular materials, especially porous organic cages (POCs) and porous coordination cages (PCCs), have increased substantially over the past decade. The work presented here outlines novel approaches to the preparation of porous molecular structures upon metalation of nonporous, amine-based organic cages. Reduction of the well-known CC3 and CC1 imine-based POCs affords nonporous, highly flexible amine cages.

Deoxygenation of nitrosoarene by N-heterocyclic carbene (NHC): an elusive Breslow-type intermediate bridging carbene and nitrene.

N-Heterocyclic carbene (NHC) activates and deoxygenates nitrosoarene (ArNO) to afford arylnitrene (ArN), thereby portraying a fundamental route connecting two 6e- species. A combination of spectroscopic and computational studies suggests that the interaction of ArNO with NHC affords a transient 2,2'-diamino imine-N-oxide as a key intermediate in ArNO deoxygenation.

Design and synthesis of aryl-functionalized carbazole-based porous coordination cages.

A subset of coordination cages have garnered considerable recent attention for their potential permanent porosity in the solid state. Herein, we report a series of functionalized carbazole-based cages of the structure type M(R-cdc) (M = Cr, Cu, Mo) where the functional groups include a range of aromatic substituents. Single-crystal X-ray structure determinations reveal a variety of intercage interactions in these materials, largely governed by pi-pi stacking.

Design and synthesis of capped-paddlewheel-based porous coordination cages.

To leverage the structural diversity of metal-organic frameworks, the ability to controllably terminate them for the isolation of porous coordination cages is advantageous. However, the strategy has largely been limited to ligand termination methods, particularly for paddlewheel-based materials. Here, we show a paddlewheel-capping strategy can be employed to afford previously unattainable coordination cage structures that are mimetic of metal-organic framework pores.

Analysis of pseudo jahn-teller distortion based on natural bond orbital theory: Case study for silicene.

Ground state (GS) instability of nondegenerate molecules in high symmetric structures is understood through Pseudo Jahn-Teller mixing of the electronic states through the vibronic coupling. The general approach involves setting up of a Pseudo Jahn-Teller (PJT) problem wherein one or more symmetry allowed excited states couple to the GS to create vibrational instability along a normal mode. This faces two major complications namely (1) estimating the adiabatic potential energy surfaces for the excited states which are often difficult to describe in case the excited states have charge-transfer or multi-excitonic (ME) character and (2) finding out how many such excited states (all satisfying the symmetry requirements for vibronic coupling) of increasing energies need to be coupled with the GS for a particular PJT problem.

Transforming atmospheric CO into alternative fuels: a metal-free approach under ambient conditions.

This work demonstrates the first-ever completely metal-free approach to the capture of CO from air followed by reduction to methoxyborane (which produces methanol on hydrolysis) or sodium formate (which produces formic acid on hydrolysis) under ambient conditions. This was accomplished using an abnormal N-heterocyclic carbene (NHC)-borane adduct. The intermediate involved in CO capture (NHC-H, HCOO, B(OH)) was structurally characterized by single-crystal X-ray diffraction.

Effects of Ancillary Ligands on Redox and Chemical Properties of Ruthenium Coordinated Azoaromatic Pincer.

In this work, the effect of the electronically different ancillary ligands on the overall properties of the RuL moiety (L = 2,6-bis(phenylazo)pyridine) in heteroleptic complexes of general formula [RuLQCl] was investigated. Four different ancillary ligands (Q) with different electronic effects were used to prepare the heteroleptic compounds from the precursor complex, [RuL(CHCN)Cl] (1); Q = pcp: 2-(4-chloro-phenylazo)pyridine (strong π-acceptor), [2]; bpy: 2,2'-bipyridyl (moderate π-acceptor), [3]; acac: acetylacetonate (strong σ-donor), 4; and DTBCat: 3,5-di- tert-butyl catecholate (strong π-donor), 5. The complexes [2], [3], 4, and 5 were fully characterized and structurally identified.

Understanding Thermal and Photochemical Aryl-Aryl Cross-Coupling by the Au /Au Redox Couple.

Systematic mechanistic investigations of the gold(I)/gold(III) redox-controlled aryl-aryl cross-coupling reaction have been performed by using both a thermal and photochemical approach. Electron-deficient and electron-rich arenes were considered as the coupling partners of the reaction. Based on transition-state modeling and distortion/interaction analyses, it is shown that Au prefers to react with electron-deficient arenes whereas Au likes to activate electron-rich arenes.

An Azoaromatic Ligand as Four Electron Four Proton Reservoir: Catalytic Dehydrogenation of Alcohols by Its Zinc(II) Complex.

Electroprotic storage materials, though invaluable in energy-related research, are scanty among non-natural compounds. Herein, we report a zinc(II) complex of the ligand 2,6-bis(phenylazo)pyridine (L), which acts as a multiple electron and proton reservoir during catalytic dehydrogenation of alcohols to aldehydes/ketones. The redox-inactive metal ion Zn(II) serves as an oxophilic Lewis acid, while the ligand behaves as efficient storage of electron and proton.

Direct and Autocatalytic Reductive Elimination from Gold Complexes ([(Ph P)Au(Ar)(CF )(X)], X=F, Cl, Br, I): The Key Role of Halide Ligands.

Kinetic and thermodynamic preferences for the reductive elimination of C -CF , C -X, C -P, and CF -X bonds and competitive phosphine dissociation from a series of Au complexes [(Ph P)Au(Ar)(CF )(X)] (1  ; Ar=4-Me-C H ; X=F, Cl, Br, I) are studied computationally. Kinetically, the most favorable pathways were found to consist of an initial phosphine dissociation from complex 1  , which furnished the respective three-coordinate Au complexes [Au(Ar)(CF )(X)] (2  ). The computed enthalpy barriers for various reductive elimination reactions from complex 2  by a direct (or uncatalyzed) mechanism showed that C -CF bond formation was the most favorable fate for any X group.

Metal-Free Reduction of CO to Methoxyborane under Ambient Conditions through Borondiformate Formation.

An abnormal N-heterocyclic carbene (aNHC) based homogeneous catalyst has been used for the reduction of carbon dioxide to methoxyborane in the presence of a range of hydroboranes under ambient conditions and resulted in the highest turnover number of 6000. A catalytically active reaction intermediate, [aNHC-H⋅9BBN(OCOH) ] was structurally characterized and authenticated by NMR spectroscopy. A detailed mechanistic cycle of this catalytic process via borondiformate formation has been proposed from tandem experimental and computational experiments.

Exclusively Ligand-Mediated Catalytic Dehydrogenation of Alcohols.

Design of an efficient new catalyst that can mimic the enzymatic pathway for catalytic dehydrogenation of liquid fuels like alcohols is described in this report. The catalyst is a nickel(II) complex of 2,6-bis(phenylazo)pyridine ligand (L), which possesses the above requisite with excellent catalytic efficiencies for controlled dehydrogenation of alcohols using ligand-based redox couple. Mechanistic studies supported by density functional theory calculations revealed that the catalytic cycle involves hydrogen atom transfer via quantum mechanical tunneling with significant k/k isotope effect of 12.

Complete Transmetalation in a Metal-Organic Framework by Metal Ion Metathesis in a Single Crystal for Selective Sensing of Phosphate Ions in Aqueous Media.

A complete transmetalation has been achieved on a barium metal-organic framework (MOF), leading to the isolation of a new Tb-MOF in a single-crystal (SC) to single-crystal (SC) fashion. It leads to the transformation of an anionic framework with cations in the pore to one that is neutral. The mechanistic studies proposed a core-shell metal exchange through dissociation of metal-ligand bonds.

Strain Control: Reversible H2 Activation and H2/D2 Exchange in Pt Complexes.

Experiments have indicated that bulky ligands are required for efficient H2 activation by Pt-Sn complexes. Herein, we unravel the mechanisms for a Pt-Sn complex, Pt(Sn(t)Bu3)2(CN(t)Bu)2 (1a), catalyzed reversible H2 activation. Among a number of Pt-Sn catalysts used to model H2 activation and H2/D2 exchange reactions, only 1a with large strain was found to be suitable because the addition of H2 to 1a requires lowest distortion energy, minimal structural changes, and smallest entropy of activation.

Mechanistic insights into the synergistic catalysis by Au(I), Ga(III), and counterions in the Nakamura reaction.

A computational study based on density functional theory (DFT) establishes the mechanisms for synergistic Au/Ga catalyzed addition of unactivated terminal alkynes to dicarbonyls, the Nakamura reaction. The role played by each of the metal catalysts and the counterion in the reaction has been elucidated. It has been shown that the triazole (TA) ligand could specifically activate the formation of a particular regioisomer through strong non-covalent interactions.

Preparation of multi-coloured different sized fluorescent gold clusters from blue to NIR, structural analysis of the blue emitting Au7 cluster, and cell-imaging by the NIR gold cluster.

Blue, green, orange-red, red and NIR emitting gold quantum clusters have been prepared in aqueous media by using a bioactive peptide glutathione (reduced) at physiological pH. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) analyses show that the core structure sizes of the five different gold clusters are Au7 (blue), Au16 (green), Au19 (orange-red), Au21 (red) and Au22 (NIR). The photo-stability and pH-stability of these quantum clusters have been measured, and these are photo-stable against continuous UV irradiation for a few hours.