Tanay Debnath

Hydrolysis of ammonia borane and metal amidoboranes: A comparative study

A gas phase mechanistic investigation has been carried out theoretically to explore the hydrolysis pathway of ammonia borane (NH3BH3) and metal amidoboranes (MNH2BH3, M = Li,Na). The Solvation Model based on Density (SMD) has been employed to show the effect of bulk water on the reaction mechanism. Gibbs free energy of solvation has also been computed to evaluate the stabilization of the participating systems in water medium which directly affects the barrier heights in the potential energy surface of hydrolysis reaction. To validate the experimentally observed kinetics studies, we have carried out transition state theory calculations on these hydrolysis reactions. Our result shows that the hydrolysis of both the metal amidoboranes exhibits greatly improved kinetics over the neat NH3BH3 hydrolysis which corroborates well with the experimental observation. Between the two amidoboranes, hydrolysis of LiNH2BH3 is found to be kinetically favored over that of NaNH2BH3, making it a better candidate for releasing molecular hydrogen.

Molecular hydrogen binding affinities of metal cation decorated substituted benzene systems: insight from computational exploration

The binding affinity of hydrogen molecules towards Li+ and Mg2+ decorated C6H5X (X = −CH3, −NH2, −CN, −COOH) systems has been investigated theoretically with special emphasis on the nature of the interaction between metal cations and H2 molecules. Our calculations show that binding of H2 over C6H5X−M (where M = Li+, Mg2+) is improved on moving from Li+ to Mg2+. For both C6H5X−M complexes the electron donating substituents weaken the H2 binding energy considerably whereas electron withdrawing substituents slightly strengthen the interaction relative to the C6H6−M complex. The interaction of H2 molecules with the metal centers in Li+ and Mg2+ decorated C6H5X systems has been explored in the light of AIM formalism, NBO analysis and LMOEDA analysis. The polarization and the charge transfer together stabilize the system whereas the pairwise steric exchange interaction renders destabilization of the system. In the case of Mg2+ decorated systems, the amount of charge transfer from the bonding orbital of the hydrogen molecule to the antibonding lone pair orbital of the metal cation and thereby the polarization factor is much higher than that found in corresponding Li+ decorated systems.

Exploration of Binding Interactions of Cu2+ with d-Penicillamine and its O- and Se- Analogues in Both Gas and Aqueous Phases: A Theoretical Approach

We have theoretically explored the entire binding phenomena of d-penicillamine and its O- and Se-analogues with Cu(2+) in both gas and aqueous phases. At first, a brief conformational analysis has been performed via -XH and -COOH rotations to investigate such conformers that are suitable for binding in both bidentate as well as tridentate fashions. The stability of each bidentate and tridentate complex is determined on the basis of relative energy (ΔE) and gas phase metal ion affinity (MIA) along with the bonding analysis by using atoms in molecule theory. The effect of conformational change on the stability of the complexes is also examined thoroughly. By analyzing the MIA values, we have shown that the side chain substitution makes an impact on the binding process. To delve into the binding phenomena in aqueous phase, we have introduced both the first and second hydration sphere models. In first hydration sphere model, to realize the precise effect of water molecules we have considered stable octahedral hexa-aqua copper complex, [Cu(H2O)6](+2) and accordingly substituted water molecules depending on the bidentate or tridentate nature of the chelating agents. The influence of bulk water molecules on the energetics and geometries of the first hydrated sphere complexes have also been investigated by employing second hydration sphere model assuming physiological pH through the implementation of implicit COSMO and polarizable continuum models, respectively. In the second hydration sphere model, the zwitterionic structures of the amino acids and their side chain deprotonated forms are also included to study the binding phenomena with Cu(2+). The complete work furnishes both the binding properties and the energetics of the copper-artificial amino acid complexes in both gas and aqueous phases that will reflect a realistic overview of the entire binding phenomena.

Efficient White-Light Generation from Ionically Self-Assembled Triply-Fluorescent Organic Nanoparticles.

Low cost, simple, and environmentally friendly strategies for white-light generation which do not require rare-earth phosphors or other toxic or elementally scare species remain an essentially unmet challenge. Progress in the area of all-organic approaches is highly sought, single molecular systems remaining a particular challenge. Taking inspiration from the designer nature of ionic-liquid chemistry, we now introduce a new strategy toward white-light emission based on the facile generation of nanoparticles comprising three different fluorophores assembled in a well-defined stoichiometry purely through electrostatic interactions. The building blocks consist of the fluorophores aminopyrene, fluorescein, and rhodamine 6G which represent blue, green, and red-emitting species, respectively. Spherical nanoparticles 16(±5) nm in size were prepared which display bright white-light emission with high fluorescence quantum efficiency (26 %) and color coordinate at (0.29, 0.38) which lie in close proximity to pure white light (0.33, 0.33). It is noteworthy that this same fluorophore mixture in free solution yields only blue emission. Density functional theory calculations reveal H-bond and ground-state proton transfer mediated absolute non-parallel orientation of the constituent units which result in frustrated energy transfer, giving rise to emission from the individual centers and concomitant white-light emission.

Exploration of Unimolecular Gas-Phase Detoxication Pathways of Sarin and Soman: A Computational Study from the Perspective of Reaction Energetics and Kinetics

A mechanistic investigation has been carried out to explore all possible gas phase unimolecular isomerization as well as decomposition pathways of toxic organophosphorus compounds (OPCs), namely, sarin (GB) and soman (GD), which are better known as nerve agents. We have identified a total of 13 detoxication pathways for sarin, where the α-H, β-H, and γ-H take part in the H-transfer process. However, for soman, due to the presence of ω-H, three additional detoxication pathways are obtained, where the ω-H is involved in the H-transfer process. Among all the pathways, the D3 decomposition pathway, where the phosphorus oxoacid derivative and alkene are generated via the formation of a six-membered ring in the transition state, is identified as the most feasible pathway from the perspective of both activation barrier and reaction enthalpy values. Moreover, we have studied the feasibility of the isomerization and decomposition pathways by performing the reaction kinetics in the temperature range of 300 K-1000 K using the one-dimensional Rice-Ramsperger-Kassel-Marcus (RRKM) master equation. From the RRKM calculation also, D3 pathway is confirmed as the most feasible pathway for both OPCs. The rate constant values associated with the D3 pathway within the temperature range of 600 K-700 K imply that the degradation of the OPCs is possible within this temperature range via the D3 pathway, which is in good agreement with the earlier reported experimental result. It is also observed that at higher temperature range (∼900 K), the increased rate constant values of other detoxication pathways indicate that along with D3, all other pathways become more or less equally feasible. Therefore, the entire work provides a widespread idea about the kinetic as well as thermodynamic feasibility of the explored detoxication pathways of the titled OPCs.

Cyclic amine-borane adducts [CnH2n+1N·BH3 (n = 2–6)] as chemical hydrogen storage systems: a computational analysis

A detailed theoretical analysis of the cyclic amine-borane adducts has been performed to explore their efficiency towards hydrogen storage. The proton affinities, gas phase basicities and heats of formation of cyclic amines, e.g., aziridine, azetidine, pyrrolidine, piperidine and azepane are calculated at the G4MP2 level. The thermodynamic properties of the borane adducts of these five cyclic aliphatic amines and their associated dehydrogenated products are also investigated. The potential energy surface (PES) associated with the dehydrogenation reaction of all these cyclic amine-borane systems has also been explored. The dehydrogenation reaction enthalpies being close to thermoneutral for all these five ring compounds indicate their potentiality as efficient hydrogen storage materials.

Towards a comprehensive understanding of the chemical vapor deposition of titanium nitride using Ti(NMe2)4: a density functional theory approach

A gas phase mechanistic investigation of the chemical vapor deposition (CVD) of titanium nitride (TiN) from the decomposition of Ti(NMe2)4, tetrakis(dimethylamido)titanium (TDMAT) as a single source precursor as well as from the reaction of Ti(NMe2)4 with NH3, i.e., the ammonia assisted mechanism is carried out and reported herein within the framework of density functional theory. Contrary to the theoretical result reported previously for a model TDMAT, metallacycle formation and β-H elimination pathways are found to be the major decomposition pathways responsible for the decomposition of TDMAT, and this finding is in accord with the experimental observation. Interestingly, agostic interaction is found to play a key role in promoting β-H elimination in the decomposition of TDMAT. A new additional pathway of decomposition of TDMAT has been identified theoretically in this present study. Exploration of the complex gas phase mechanism and thereby a detailed identification of the reaction intermediates enable us in realizing the origin of incorporation of carbon contamination in TiN films produced from TDMAT alone and then how the contamination is removed in the presence of ammonia. The ammonia assisted mechanism is found to proceed through the formation of a pre-equilibrium complex. The computed barrier height of 7.3 kcal mol(-1) for the initial transamination process associated with the Ti(NMe2)4 + NH3 reaction is found to be in very good agreement with the experimental activation energy. The total rate constant ktot for the ammonia assisted mechanism is calculated to be 1.28 × 10(-51) cm(3) molecule(-1) s(-1) at 298.15 K.

Mechanistic Insight into the Molecular TiO2-mediated Gas Phase Detoxication of DMMP: A Theoretical Approach

The detoxication of DMMP (dimethyl methylphosphonate) mediated by molecular TiO2 has been investigated computationally using density functional theory (DFT). From our previous studies, it is evident that the unimolecular detoxication of OPCs (organophosphorus compounds) is kinetically unfeasible at room temperature due to the significantly high activation barrier. Thus, the aim of our work is to find out whether molecular TiO2 can make any significant impact on the kinetic feasibility of the detoxication processes or not. Here, we have identified a total of three detoxication pathways, where in the first step the detoxication occurs through H-abstraction with the assistance of TiO2, and in the second step, the titanium complex is separated from the respective phospho-titanium complexes. The outcomes reveal that the TiO2-mediated detoxication pathways are at least 20.0 kcal/mol more favorable than their respective unimolecular pathways and that among them, the α-H-mediated isomerization is found to be the most feasible pathway. When the separation of a titanium complex is under consideration, the double H2O-assisted mechanism is found to be the favored pathway. Overall, the entire work provides a widespread idea about the efficiency of molecular TiO2-assisted detoxication of DMMP, which can be well applicable to other OPCs also.

Investigation of agostic interaction through NBO analysis and its impact on β-hydride elimination and dehydrogenation: a DFT approach

Agostic interactions have been investigated through NBO analysis tuning each part of H2LMMZCHR2 by varying metal centre and intramolecular groups in different positions of the molecule. We have calculated the energy transfer phenomena between donor and acceptor orbitals associated with the agostic bond by second-order perturbation analysis and characterized the acceptor orbitals for whether it is a vacant metal lone pair or molecular orbital associated with both metal and ligand. The investigation of agostic phenomenon by altering the orientation of the metal-associated ligand is another aspect of this work to reveal the orientation effect as one of the controlling factors of the agostic interaction. We have further studied the impact of agostic interaction on the two well-recognized reaction processes, namely β-hydride elimination and dehydrogenation for all the d0 systems under investigation. Both the reactions are found to be facilitated by agostic interaction, where the nature of agostic hydrogen varies from reaction to reaction. The complete work furnishes both characterization and reaction pathways to portray agostic phenomena by interconnecting the molecular geometry with the reaction processes.

Interactions between metal cations with H2 in the M+- H2 complexes: Performance of DFT and DFT-D methods

AbstractThe interactions between metal cations (Ni+, Cu+, Zn+) and H2 molecule have been investigated in detail using dispersion-corrected and -uncorrected double hybrid density functional (DHDF), gradient corrected density functional, ordinary density functional and CCSD(T) methods in conjunction with the correlation consistent triple- ζ quality basis sets. Structural properties, depth of the potential well and dissociation energies are calculated using DFT, DFT-D and CCSD(T) methods and are compared with experimental results. A comparative analysis has been made among DFT, DFT-D and CCSD(T) methods with respect to experiments. The energy components of the interaction energy have been estimated by the symmetry-adapted perturbation theory (SAPT) to analyze the effect of various components on the interaction of the complexes. The dispersion-corrected DHDF, mPW2PLYP-D method shows the best agreement with the experimental values. An NBO analysis has been performed to understand the orbital participation in metal ligand interaction and charge transfer process in these complexes. Graphical AbstractInteractions between metal cations (Ni+, Cu+, Zn+) and H2 molecule were investigated using double hybrid density functional (DHDF), gradient corrected density functional, ordinary density functional and CCSD(T) methods in conjunction with cc-pVTZ basis set. NBO analysis was performed to understand the orbital participation in metal ligand interaction and charge transfer process.