Department of Chemistry

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IIT Hyderabad

The role of the outer sphere ligand is reported to be very crucial for the hydrogenation of CO2. We have investigated a series of Fe complexes with flexible pendant amines and predicted their potentials for CO2 hydrogenation to formic acid using density functional theory calculations. Among the modeled Fe complexes, the Fe complex [CpC6F5Fe-(PtBu 2NtBu2)]+ containing the electron-withdrawing CpC6F5 ligand is the most active catalyst with a total free energy barrier of only 14.9 kcal/mol. Besides, we find that the ratedetermining steps (heterolytic cleavage and hydride transfer) of CO2 hydrogenation are improved significantly when catalyzed by the pendant amine based [CpC6F5Fe(PtBu2NtBu2)]+ complex. The roles of water and base have been found to be very crucial for the whole catalytic cycle. The ligand-assisted pathway is very favorable toward one of the rate-determining steps, and therefore such flexible outer sphere ligands are crucial for the design of catalyst for CO2 hydrogenation. © 2016 American Chemical Society.

World University root node

Journal of Physical Chemistry C

Catalytic hydrogenation of CO2 by Fe complexes containing pendant amines: Role of water and base

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru(tBu3tpy)(bpy)(NCCH3)]2+ (tBu3tpy=4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine; bpy=2,2′-bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO2 to CO. The methyl group enables CO2 binding already at the one-electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO2 reduction catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

Activating a Low Overpotential CO2 Reduction Mechanism by a Strategic Ligand Modification on a Ruthenium Polypyridyl Catalyst

Electronic spectra of C6H7 radicals, α-hydrofulvenyl and cis/trans-1-vinyl-3-methylpropargyl, have been measured in the gas phase. A resonant two-colour, two-photon ionisation scheme was used after the radicals were produced in a supersonically cooled discharge source. The origin bands in D1 (2A″) ← D0 (2A″) transitions are observed at 18,734, 21,278 and 21,698 cm−1, respectively. The assignment of the spectra is based on the calculated harmonic frequencies in the D1 states and the available literature data. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Molecular Physics

Electronic spectroscopy of resonance-stabilised C6H7 radicals

In the quest to engineer the nanofibrillar morphology of folic acid (F) gel, poly(4-vinylpyridine-co-styrene) (PVPS) is judiciously integrated as a polymeric additive because of its potential to form H-bonding and π-stacking with F. The hybrid gels are designated as F-PVPSx gels, where x denotes the amount of PVPS (mg) added in 2 mL of F gel (0.3%, w/v). The assistance of PVPS in the gelation of F is manifested from the drop in critical gelation concentration and increased fiber diameter and branching of F-PVPSx gels compared to that of F gel. PVPS induces a magnificent improvement of mechanical properties: a 500 times increase of storage modulus and ∼62 times increase of yield stress in the F-PVPS5 gel compared to the F gel. The complex modulus also increases with increasing PVPS concentration with a maximum in F-PVPS5 gel. Creep recovery experiments suggest PVPS induced elasticity in the otherwise viscous F gel. The fluorescence intensity of F-PVPSx gels at first increases with increasing PVPS concentration showing maxima at F-PVPS5 gel and then slowly decreases. Gelation is monitored by time-dependent fluorescence spectroscopy, and it is observed that F and F-PVPSx gels exhibit perfectly opposite trend; the former shows a sigmoidal decrease in fluorescence intensity during gelation, but the latter shows a sigmoidal increase. The gelation rate constants calculated from Avrami treatment on the time-dependent fluorescence data manifest that PVPS effectively enhances the gelation rate showing a maximum for F-PVPS5 gel. The hybrid gel exhibit 5 orders increase of dc conductivity than that of F-gel showing semiconducting nature in the current-voltage plot. The Nyquist plot in impedance spectra of F-PVPS5 xerogel exhibit a depressed semicircle with a spike at lower frequency region, and the equivalent circuit represents a complex combination of resistance-capacitance circuits attributed to the hybrid morphology of the gel fibers. © 2016 American Chemical Society.

Langmuir

Nanoengineering of a Supramolecular Gel by Copolymer Incorporation: Enhancement of Gelation Rate, Mechanical Property, Fluorescence, and Conductivity

Conducting dihybrid(GP), trihybrid(GPPS) hydrogels have been constructed using 5,5'-(1,3,5,7-tetraoxopyrrolo[3,4-f]isoindole-2,6-diyl) diisophthalic acid (P), graphene oxide(GO,G) and PEDOT:PSS(PS). These gels are well characterised by SEM, TEM, rheology, FTIR and Raman Spectroscopy. GP hybrid gels display higher mechanical stability, compared to the P gel. GPPS trihybrid gels shows dc-conductivity up to 0.011 Scm−1. In gel state it shows rectification property with a highest rectification ratio of 61; however, the xerogels exhibit semiconducting nature. Dye sensitized solar cells (DSSCs) are engineered using the GPPS gels as active materials and exhibit a maximum power conversion efficiency of 4.46%. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Macromolecular Symposia

Mechanically Robust Hybrid Hydrogels for Photovoltaic Applications

Macromolecular Chemistry and Physics

Macromol. Chem. Phys. 12/2016

Eight new compounds with a general formula Ca14–xRExMnSb11(RE = La–Nd, Sm, Gd–Dy; x ≈ 1) were synthesized by the molten flux method and their structures were established via single-crystal X-ray diffraction. The overarching goal of this study was to investigate the effect of electron doping, via substitution of RE3+at Ca2+sites, on the crystal structure and physical properties of Ca14MnSb11, which is a candidate for thermoelectric applications. All studied phases are isostructural, and crystallize in the tetragonal body-centered space group I41/acd (Ca14AlSb11structure type, Pearson index tI208). The structure is made up of MnSb410–tetrahedra, randomly mixed Ca2+and RE3+cations, Sb3–anions, and linear Sb37–polyanions. Comprehensive structural work confirms high rare-earth metal content with Ca2+/RE3+randomly mixed on all four cation sites, with the caveat that the larger RE atoms (La–Nd) prefer to occupy the Ca2 site, while the smaller RE atoms (Sm, Gd, Tb, and Dy) preferably occupy the Ca1 site. Nearly phase-pure polycrystalline samples have been synthesized using solid-state reactions, and have been used for physical property measurements. The resistivities of the bulk Ca14–xRExMnSb11(RE = La–Nd, Sm, Gd; x ≈ 1) samples reveal semiconducting behavior, consistent with the notion of electron doping in the parent p-type Ca14MnSb11material. Magnetic susceptibilities suggest complex magnetic ordering at temperatures below ca. 50 K, likely originating from coupling between two or more magnetic sub-lattices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

European Journal of Inorganic Chemistry

On the Extended Series of Quaternary Zintl Phases Ca13REMnSb11 (RE = La–Nd, Sm, Gd–Dy)

The syntheses, characterisation and utilisation of the calcium complexes [{Lx}CaN(SiMe3)2·(THF)] supported by monoanionic, tridentate imino-phosphinanilido chalcogenide ligands {Ph2P(E)-N-C6H4-CHN(Dipp)}- (E = S, {L2}-; E = Se, {L3}-; Dipp = 2,6-diisopropylphenyl) as molecular precatalysts for the heterofunctionalisation of styrene are reported. The protio-ligand {L1}H (for E = O) was obtained upon reaction of the aniline-iminophosphane {Ph2PHN-C6H4-CHN(Dipp)} ({L0}H) and hydrogen peroxide at room temperature. The related sulphide and selenide compounds {L2}H and {L3}H were prepared by treatment of {L0}H with elemental sulphur and selenium. Beside, reaction of {L0}H with Me2S·BH3 yielded the corresponding imino-phosphinanilido borane protio-ligand {Ph2P(BH3)N-C6H4-CHN(Dipp)}H ({L4}H). The heteroleptic calcium complexes [{Lx}CaN(SiMe3)2·(THF)] (E = S, 2; E = Se, 3) were synthesised by one-pot reaction of {L2}H and {L3}H with 2 equiv of [KN(SiMe3)2] and CaI2 at room temperature. The reaction of {L2}H with [KN(SiMe3)2] and CaI2 in 2:2:1 proportions yielded the homoleptic complex [Ca{L2}2] (5). The molecular structures of the protio-ligand {L3}H and complexes 3 and 5 were established by single crystal X-ray analysis. The heteroleptic complexes 2 and 3 constitute moderately efficient precatalysts for the intermolecular hydrophosphination and hydroamination of styrene with diphenylphosphine or pyrrolidine, respectively, to mediate the formation of C-P and C-N σ-bonds. © 2016 The Royal Society of Chemistry.

Fulltext

RSC Advances

Calcium complexes with imino-phosphinanilido chalcogenide ligands for heterofunctionalisation catalysis

Herein, we explored the photophysical properties of the antimalarial, anticancer drug cryptolepine (CRYP) in the presence of the macrocyclic host cucurbit[7]uril (CB7) and DNA with the help of steady-state and time-resolved fluorescence techniques. Ground-state and excited-state calculations based on density functional theory were also performed to obtain insight into the shape, electron density distribution, and energetics of the molecular orbitals of CRYP. CRYP exists in two forms depending on the pH of the medium, namely, a cationic (charge transfer) form and a neutral form, which emit at λ=540 and 420 nm, respectively. In a buffer solution of pH 7, the drug exists in the cationic form, and upon encapsulation with CB7, it exhibits a huge enhancement in fluorescence intensity due to a decrement in nonradiative decay pathways of the emitting cryptolepine species. Furthermore, docking and quantum chemical calculations were employed to decipher the molecular orientation of the drug in the inclusion complex. Studies with natural DNA indicate that CRYP molecules intercalate into DNA, which leads to a huge quenching of the fluorescence of CRYP. Keeping this in mind, we studied the DNA-assisted release of CRYP molecules from the nanocavity of CB7. Strikingly, DNA alone could not remove the drug from the nanocavity of CB7. However, an external stimulus such as acetylcholine chloride was able to displace CRYP from the nanocavity, and subsequently, the displaced drug could bind to DNA. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

ChemPhysChem

Spectroscopy and Dynamics of Cryptolepine in the Nanocavity of Cucurbit[7]uril and DNA

Reclaimed asphalt pavement (RAP) is a milled material obtained from the distressed pavement sections, containing a thin coating of aged bitumen on the aggregate surface. In spite of their inferior properties, RAP has been promoted to use in new pavement layers after blending with virgin aggregates (VA) and/or chemical stabilizers such as fly ash. Due to thin amorphous asphalt coating present on RAP aggregates, expected level of improvement is not witnessed. Hence, the non-reactive type fly ashes can be activated in an alkali environment, such as lime, sodium hydroxide, potassium hydroxide or a combination of sodium hydroxide and sodium silicate to further improve the reactivity to participate in the pozzolanic reactions. The present study investigates the degree of chemical and micro-mechanical interactions between the alkali (sodium hydroxide) activated fly ash mortar and RAP:VA base course mixes on strength development. To accomplish this task, specimens were prepared at various proportions of RAP and VA materials; stabilized with fly ash at 20% and 30% by dry weight with and without alkali activation at 2% and 4% sodium hydroxide (NaOH) solution. These mixes were cured for 1, 7 and 28 days and then tested for their unconfined compressive strength (UCS). Mineralogical studies such as X-ray fluorescence (XRF), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were then conducted on the powdered samples to identify and quantify the formation of possible hydration products. Since the RAP aggregates are coated with an amorphous asphalt coating, the amount of exposed aggregate surface of RAP particles plays a major role in the formation of pozzolanic compounds with fly ash. To verify the amount of exposed surface of RAP particles, surface area analysis was performed through high definition image processing. The interaction mechanism of RAP with other constituents of the mix is also studied. It is observed that a random RAP sample has exposed aggregate surface area between 15 and 70%, which is responsible for high pozzolanic reactions between the alkali activated fly ash mortar and RAP aggregates. The data are presented in terms of the exposed surface area and the strength characteristics of the mixes. © 2016 Elsevier Ltd