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Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries. Herein, we report the first examp...

Transition metal-catalyzed reversible hydrogenation of CO2 to formate in aqueous solutions under ambient conditions is an attractive environmentally friendly strategy for the storage and transporta...

We report herein a series of Cp*Ir complexes containing a rigid 8-aminoquinolinesulfonamide moiety as highly efficient catalysts for the dehydrogenation of formic acid (FA). The complex [Cp*Ir(L)Cl] (HL = N-(quinolin-8-yl)benzenesulfonamide) displayed a high turnover frequency (TOF) of 2.97 × 104 h-1 and a good stability (>100 h) at 60 °C. Comparative studies of [Cp*Ir(L)Cl] with the rigid ligand and [Cp*Ir(L')Cl] (HL' = N-propylpypridine-2-sulfonamide) without the rigid aminoquinoline moiety demonstrated that the 8-aminoquinoline moiety could dramatically enhance the stability of the catalyst. The electron-donating ability of the N,N'-chelating ligand was tuned by functionalizing the phenyl group of the L ligand with OMe, Cl, and CF3 to have a systematical perturbation of the electronic structure of [Cp*Ir(L)Cl]. Experimental kinetic studies and density functional theory (DFT) calculations on this series of Cp*Ir complexes revealed that (i) the electron-donating groups enhance the hydrogen formation step while slowing down the β-hydride elimination and (ii) the electron-withdrawing groups display the opposite effect on these reaction steps, which in turn leads to lower optimum pH for catalytic activity compared to the electron-donating groups.

Alkali ion intercalation is fundamental to battery technologies for a wide spectrum of potential applications that permeate our modern lifestyle, including portable electronics, electric vehicles, and the electric grid. In spite of its importance, the Nernstian nature of the charge transfer process describing lithiation of carbon has not been described previously. Here we use the ultrathin few-layer graphene (FLG) with micron-sized grains as a powerful platform for exploring intercalation and co-intercalation mechanisms of alkali ions with high versatility. Using voltammetric and chronoamperometric methods and bolstered by density functional theory (DFT) calculations, we show the kinetically facile co-intercalation of Li+ and K+ within an ultrathin FLG electrode. While changes in the solution concentration of Li+ lead to a displacement of the staging voltammetric signature with characteristic slopes ca. 54–58 mV per decade, modification of the K+/Li+ ratio in the electrolyte leads to distinct shifts in the voltammetric peaks for (de)intercalation, with a changing slope as low as ca. 30 mV per decade. Bulk ion diffusion coefficients in the carbon host, as measured using the potentiometric intermittent titration technique (PITT) were similarly sensitive to solution composition. DFT results showed that co-intercalation of Li+ and K+ within the same layer in FLG can form thermodynamically favorable systems. Calculated binding energies for co-intercalation systems increased with respect to the area of Li+-only domains and decreased with respect to the concentration of –K–Li– phases. While previous studies of co-intercalation on a graphitic anode typically focus on co-intercalation of solvents and one particular alkali ion, this is to the best of our knowledge the first study elucidating the intercalation behavior of two monovalent alkali ions. This study establishes ultrathin graphitic electrodes as an enabling electroanalytical platform to uncover thermodynamic and kinetic processes of ion intercalation with high versatility., Nernstian signatures and swift voltammetry at graphene electrodes help elucidate alkali ion (co-)intercalation.

In a conventional lithium-ion battery (LIB), graphite forms the negative electrode or anode. Although Na is considered one of the most attractive alternatives to Li, achieving reversible Na intercalation within graphitic materials under ambient conditions remains a challenge. More efficient carbonaceous anode materials are desired for developing advanced LIBs and

Na-ion batteries (NIBs) are proposed as a promising candidate for beyond Li-ion chemistries, however, a key challenge associated with NIBs is the inability to achieve intercalation in graphite anodes. This phenomenon has been investigated and is believed to arise due to the thermodynamic instability of Na-intercalated graphite. We have recently demonstrated theoretical calculations showing it is possible to achieve thermodynamically stable Na-intercalated graphene structures with a fluorine surface modifier. Here, we present experimental evidence that Na+ intercalation is indeed possible in fluorinated few-layer graphene (F-FLG) structures using cyclic voltammetry (CV), ion-sensitive scanning electrochemical microscopy (SECM) and in situ Raman spectroscopy. SECM and Raman spectroscopy confirmed Na+ intercalation in F-FLG, while CV measurements allowed us to quantify Na-intercalated F-FLG stoichiometries around NaC14–18. These stoichiometries are higher than the previously reported values of NaC186 in graphite. Our experiments revealed that reversible Na+ ion intercalation also requires a pre-formed Li-based SEI in addition to the surface fluorination, thereby highlighting the critical role of SEI in controlling ion-transfer kinetics in alkali-ion batteries. In summary, our findings highlight the use of surface modification and careful study of electrode-electrolyte interfaces and interphases as an enabling strategy for NIBs.

Transition-metal-catalyzed cross-coupling reactions are central to many organic synthesis methodologies. Traditionally, Pd, Ni, Cu, and Fe catalysts are used to promote these reactions. Recently, many studies have showed that both homogeneous and heterogeneous Au catalysts can be used for activating selective cross-coupling reactions. Here, an overview of the past studies, current trends, and future directions in the field of gold-catalyzed coupling reactions is presented. Design strategies to accomplish selective homocoupling and cross-coupling reactions under both homogeneous and heterogeneous conditions, computational and experimental mechanistic studies, and their applications in diverse fields are critically reviewed. Specific topics covered are: oxidant-assisted and oxidant-free reactions; strain-assisted reactions; dual Au and photoredox catalysis; bimetallic synergistic reactions; mechanisms of reductive elimination processes; enzyme-mimicking Au chemistry; cluster and surface reactions; and plasmonic catalysis. In the relevant sections, theoretical and computational studies of AuI /AuIII chemistry are discussed and the predictions from the calculations are compared with the experimental observations to derive useful design strategies.

Titania metal-organic frameworks (MOFs) are attractive materials for noble-metal-free heterogeneous photocatalysis because of their tunable photoredox activity. In this work, we present the effect of decreased pore-steric interference in photocatalysis by creating a new series of MOFs via isoreticular expansion. These new UCFMOFs pack in a hex rod net, are composed of 1-dimensional titania secondary building units and organic links of increased metrics, exhibiting pore apertures with expanded sizes and increased photocatalytic kinetics. Powder based crystallography, in tandem with local structure, gas adsorption, and DFT studies, enabled elucidation of their crystal, steric, and electronic structures that explain their increased photocatalytic efficiency towards mild oxidation of organic probes.

In this study, we report a nonprecious metal catalyst for high-efficiency hydrogen evolution reaction (HER). A self-organized S-doped MoP nanoporous layer (S-MoP NPL) is achieved through a facile e...

The electronic structure and excited-state dynamics of heterojunctions composed of 2D silicane and germanane-based materials (SiR, GeR; R = H, Me) and anatase or rutile isomorphs of TiO2 are investigated. Our calculations reveal a high tunability of the band gaps of these heterostructures: 2.28 eV in SiH/a-TiO2 to 0.16 eV in GeMe/r-TiO2. Nonadiabatic molecular dynamic (NA-MD) simulations suggest that electron–hole recombination in SiH/a-TiO2, SiH/r-TiO2, and GeH/a-TiO2 occurs within 46.0, 3.6, and 1.2 ns, respectively, which is notably slower than in other analogous materials. The methylation of Si or Ge monolayers and the use of rutile polymorphs increase the nonadiabatic coupling and accelerate the recombination. A simple accelerated NA-MD method is devised in this work to evaluate the time scales for extremely slow dynamics of excited states. On the contrary to the electron–hole recombination, “hot” electrons are found to thermalize within a picosecond time scale, whereas some hot holes thermalize nota...

Kinetic and thermodynamic preferences for the reductive elimination of Caryl-CF3, Caryl-X, Caryl-P, and CF3-X bonds and competitive phosphine dissociation from a series of Au(III) complexes, (Ph3P)Au(Ar)(CF3)(X), (1X, Ar = 4-Me-C6H4, X = F, Cl, Br, I) are studied computationally. Kinetically, most favorable pathways consist of an initial phosphine dissociation from 1X, furnishing respective three coordinate Au(III) complexes Au(Ar)(CF3)(X), 2X. The computed barriers for various reductive elimination reactions from 2X via a direct (or uncatalyzed) mechanism showed Caryl-CF3 bond formation as the most favorable fate for any X. When the direct elimination is compared with an autocatalytic mechanism that proceed through the formation of a mixed valent binuclear AuIII-AuI intermediate, the preference for the formation of Caryl-CF3 bond follows the order, F > Cl > Br > I. Concomitantly, selectivity for the formation of Caryl-X bonds for various X follow opposite trends. The preference for the direct and autocatalytic processes is controlled entirely by the nature of the halide ligand. The predicted mechanisms and product selectivity trends for various halides show excellent agreement with recent experimental observation. Selectivity of various reductive elimination pathways are rationalized using molecular orbital theory and distortion interaction model analyses. Attractive interactions between the AuI-complex and the 2X reduces the activation barrier for Caryl-X elimination.

The recently synthesized all-cis 1,2,3,4,5,6-hexafluorocyclohexane (1) has a large dipole moment (6.2 D) and uniaxial facial polarization. Based on density functional theory (DFT) calculations, it is shown that both the “positive” and “negative” surfaces of 1 can recognize flat aromatic molecules (X, X = benzene, pyrene, and coronene), 2D materials (graphene), and their fully hydrogenated analogues through attractive noncovalent interactions. 1 can be sandwiched between graphene and graphane layers, where the enhanced polarity of the axial C—H and C—F bonds leads to the formation of an unusual “triple-decker” complex. Upon adsorption with 1, the band gap of graphane reduces from 3.40 to 2.05 eV, which might be useful for visible-light energy-conversion applications. We demonstrate the controlled tuning of the structural and electronic properties in 1-benzene, 1-cyclohexane, and benzene-1-cyclohexane complexes by the application of an external electric field along the polarization axis. The extended analog...

In a conventional lithium ion battery (LIB), graphite forms the negative electrode or anode. Although Na is considered one of the most attractive alternatives to Li, achieving reversible Na intercalation within graphitic materials under ambient conditions remains a challenge. More efficient carbonaceous anode materials are desired for developing advanced LIBs and beyond Li-ion battery technologies. We hypothesized that two-dimensional materials with distinct surface electronic properties create conditions for ion insertion into few-layer graphene (FLG) anodes. This is because modification of the electrode/electrolyte interface potentially modifies the energetics and mechanisms of ion intercalation in the thin bulk of FLG. Through a first principles calculations; we show that the electronic, structural, and thermodynamic properties of FLG anodes can be fine-tuned by a covalent heteroatom substitution at the uppermost layer of the FLG electrode, or by interfacing FLG with a single-side fluorinated graphene or a Janus-type hydrofluorographene monolayer. When suitably interfaced with the 2D surface modifier, the FLG exhibits favorable thermodynamics for the Li+, Na+, and K+ intercalation. Remarkably, the reversible binding of Na within carbon layers becomes thermodynamically allowed and a large storage capacity can be achieved for the Na intercalated modified FLG anodes. The origin of charge-transfer promoted electronic tunability of modified FLGs are rationalized by various theoretical methods.

Recently synthesized all-cis-1,2,3,4,5,6-hexafluorocyclohexane is the least stable among all possible configurational isomers of 1,2,3,4,5,6-hexafluorocyclohexane. This molecule has a remarkably large dipole moment (6.2 D) as well as high facial polarization. Solid-state, dispersion-corrected DFT (DFT-D3) calculations are performed on the crystalline phase of all-cis-1,2,3,4,5,6- hexafluorocyclohexane, which reveal that dispersion interactions play a crucial role in its stabilization. A number of thermodynamically favorable orientations of dimers, trimers and tetramers are demonstrated for this molecule. Parallel-stacked aggregates, from dimers to higher-order aggregates, which are absent in the crystal, are found to be thermodynamically most favorable due to the presence of strong short-range C-H⋅⋅⋅F-C intermolecular hydrogen-bonding networks. Because of their cooperative nature, binding energies, dipole moments, and polarizations per molecule increase from monomer to tetramer, whereas the HOMO-LUMO gaps follow the opposite trend. Based on the DFT-D3 calculations, it is proposed that this parallel-stacked arrangement can be further extended to prepare stable a 1D crystal such that a large dipole moment and macroscopic polarizations can arise, which might be useful in designing electronic and nonlinear optical devices. Because the molecule has conformational flexibility, the potential energy surface is investigated for ring flipping and the effects of fluorine substitution are studied by comparing the barrier with respect to cyclohexane and all-cis-1,2,3-trifluorocyclohexane.

Topochemical transformations of layered materials CaX2 (X=Si, Ge) are the method of choice for the high-yield synthesis of pristine, defect-free two-dimensional systems silicane and germanane, which have advanced electronic properties. Based on solid-state dispersion-corrected calculations, mechanisms for such transformations are elucidated that provide an in-depth understanding of phase transition in these layered materials. While formation of such layered materials is highly favorable for silicane and germanane, a barrier of 1.2 eV in the case of graphane precludes its synthesis from CaC2 topochemically. The energy penalty required for distorting linear acetylene into a trans-bent geometry accounts for this barrier. In contrast it is highly favorable in the heavier analogues, resulting in barrierless topochemical generation of silicane and germanane. Photochemical generation of the trans-bent structure of acetylene in its first excited state (S1 ) can directly generate graphane through a barrierless condensation. Unlike the buckled structure of silicene, the phase-h of CaSi2 with perfectly planar silicene layers exhibits the Dirac cones at the high symmetry points K and H. Interestingly, topochemical acidification of the cubic phase of calcium carbide is predicted to generate the previously elusive platonic hydrocarbon, tetrahedrane.

The heavier analogues of graphene, namely silicene and germanene, are known to be buckled. Such buckling leads to interesting properties like direct band gap in hydrogenated germanene, known as germanane. This article shows that the sequential replacement of C by Ge in benzene leads to increasing buckling with the maximal buckling distance (d = 0.61 A) in Ge6H6. The origin of such buckling induced lowering of symmetry (D6h → D3d) is traced to pseudo Jahn–Teller (PJT) distortion along the b2g normal mode arising out of mixing of the nondegenerate (A1g) ground state with low lying (Δ0 = 4.36 eV) excited state of B2g symmetry. Buckling also leads to enhanced chemical reactivity of germanene toward hydrogen to form germanane. The large affinity of germanene toward hydrogenation explains the experimental synthesis of exfoliated layers of germanane by Goldberger and co-workers [ACS Nano 2013, 7, 4414−4421]. Germanene → germanane formation leads to the opening up of a large band gap making hydrogenation a chemic...

The reactions of [RuCl2(η6-C6H6)]2 with chiral aroylthiourea ligands yielded pseudo-octahedral half-sandwich “piano-stool” complexes. All the Ru(II) complexes were characterized by analytical and spectral (UV-visible, FT-IR, 1H NMR and 13C NMR) studies. The molecular structures of the ligands (L2 and L4) and the complexes (2, 4 and 5) were confirmed by single crystal XRD. All the complexes were successfully screened as catalysts for the asymmetric transfer hydrogenation (ATH) of ketones using 2-propanol as the hydrogen source in the presence of KOH. The ATH reactions proceeded with excellent yields (up to 99%) and very good enantioselectivity (up to 99% ee). The scope of the present catalytic system was extended to substituted aromatic ketones and few hetero-aromatic ketones. Density functional theory (DFT) calculations predicted non-classical, concerted transition states for the ATH reactions. The catalytic activity of Ru–benzene complexes toward asymmetric reduction of ketones was significantly higher compared to that of p-cymene complex analogues. Such enhanced efficiency and product selectivity of Ru–benzene complexes compared to those of Ru–p-cymene complexes were rationalized by the computational study.

Chalcogenide perovskites constitute an emerging class of promising photovoltaic materials that are stable and less toxic than popular lead-halide perovskites. Transition-metal and chalcogenide doping are the possible strategies for improving the photovoltaic properties of these materials via the band gap engineering. At the same time, doping can facilitate nonradiative charge-carrier recombination in these materials, adversely affecting their photovoltaic properties. We report a systematic study of electronic structure and nonadiabatic dynamics in transition-metal- and chalcogenide-doped barium-zirconium-sulfide-based perovskites. The potential of these doping strategies to modulate the performance of photovoltaic materials is explored. Through the detailed analysis of the factors affecting the dynamics, we illustrate how symmetry (both structural and orbital) and decoherence can be critical to furnishing the most favorable properties. The noted factors of symmetry and decoherence may provide new rational design principles for efficient photovoltaics.

Photo-isomerization of cis -cycloheptenone fused to a ring with a defined stereochemistry at the ring fusion to its trans-stereoisomer and in situ Diels–Alder reaction with cyclic and acyclic dienes have been investigated. The reaction was found to proceed through one of the two possible isomerized trans -enones that produce the thermodynamically more stable adduct with a trans-fused seven-membered ring system. This protocol has been employed to construct a tetracycle with trans-fused 6-7 ring system, the core structure present in several terpenes. The observed selectivity has been supported by computational method.

We have demonstrated that the nonbonding molecular orbital (NBMO) of the phenalenyl (PLY) cation can be used as a Lewis acid catalyst for different organic transformations. Detailed computational and spectroscopic studies for the aminolysis reaction of epoxide reveal that this catalysis works through a different mechanism, and the phenalenyl cation activates the amine moiety using its empty NBMO, which triggers the epoxide ring-opening reaction. It has been shown that the energy of the NBMO of PLY cation plays a key role in modulating the catalytic activity. This study establishes that the cationic state of phenalenyl unit is useful not only for construction of the spin memory device by external spin injection using its NBMO, but in addition, the same NBMO can act as an organic Lewis acceptor unit to influence the catalytic outcome of a homogeneous reaction.

We report herein the synthesis and photophysical studies on a new multicomponent chemosensor dyad comprising two fluorescing units, dansylamide (DANS) and nitrobenzoxadiazole (NBD). The system has been developed to investigate receptor-analyte binding interactions in the presence of both cations and anions in a single molecular system. A dimethyl amino (in the DANS unit) group is used as a receptor for cations, and acidic hydrogens of sulfonamide and the NBD group are used as receptors for anions. The system is characterized by conventional analytical techniques. The photophysical properties of this supramolecular system in the absence and presence of various metal ions and nonmetal ions as additives are investigated in an acetonitrile medium. Utility of this system in an aqueous medium has also been demonstrated. The absorption and fluorescence spectrum of the molecular system consists of a broad band typical of an intramolecular charge-transfer (ICT) transition. A low quantum yield and lifetime of the NBD moiety in the present dyad indicates photoinduced electron transfer (PET) between DANS and the NBD moiety. The fluorescence intensity of the system is found to decrease in the presence of fluoride and acetate anions; however, the quenching is found to be much higher for fluoride. This quenching behavior is attributed to the enhanced PET from the anion receptor to the fluorophore moiety. The mechanistic aspect of the fluoride ion signaling behavior has also been studied by infrared (IR) and (1)H NMR experiments. The hydrogen bonding interaction between the acidic NH protons of the DPN moiety and F(-) is found to be primarily responsible for the fluoride selective signaling behavior. While investigating the cation signaling behavior, contrary to anions, significant fluorescence enhancement has been observed only in the presence of transition-metal ions. This behavior is rationalized by considering the disruption of PET communication between DANS and the NBD moiety due to transition-metal ion binding. Theoretical (density functional theory) studies are also performed for the better understanding of the receptor-analyte interaction. Interestingly, negative cooperativity in binding is observed when the interaction of this system is studied in the presence of both Zn(2+) and F(-). Fluorescence microscopy studies also revealed that the newly developed fluorescent sensor system can be employed as an imaging probe in live cells.

The ground-state structures, HOMO–LUMO gaps, singlet–triplet splitting, and the UV–vis absorption spectra for Si, Ge-substituted analogues of the recently synthesized disk-like π-conjugated molecules, like octathio[8]circulene, popularly termed “sulflower”, and 2H-benzo[cd]pyrene, popularly termed “olympicene”, are studied using density functional theory. Unlike their pure organic counterparts, these molecules are found to be nonplanar with substantial puckering from the high symmetric structures. The origin of puckering is traced to pseudo Jahn–Teller (PJT) distortions due to favorable mixing of the occupied molecular orbitals (OMO) and unoccupied molecular orbitals (UMO). Even though the HOMO–LUMO and singlet–triplet gaps for these molecules are smaller than their organic counterparts, the reorganization energies (both hole, λh, and electron, λe) for the Si, Ge analogues of sulflower and olympicene are much higher. Therefore, these molecules are expected to be rather inefficient for field effect transis...