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Density functional theory has been used for the systematic investigation of the mechanism involved in Ni(COD)2-catalyzed ipso-silylation of 2-methoxynaphthalene. The two fundamental mechanistic pathways, internal nucleophilic substitution and a nonclassical oxidative addition, have been studied. In both pathways, the first equivalent of K+OtBu directly reacts with the silyl boronate (Et3SiBpin) to generate the silyl anion surrogate Et3SiK+ or silylborate [Et3Si-Bpin(OtBu)]K+ (IN3), which further reacts with Ni(COD)2 to form a substrate-catalyst complex, [(η2-COD)2NiSiEt3]K+. The internal nucleophilic substitution reaction pathway proceeds through η2 complexation of nickel with the C(1)=C(2) bond of 2-methoxynaphthalene. Later, nickel connects to =C(1) through σ-bond formation and coordinates with oxygen of the -OMe group. Simultaneously, the -SiEt3 group approaches =C(2) possessing -OMe followed by rearomatization which is facilitated by coordination of K++ with nickel and methoxy oxygen. In a nonclassical oxidative addition, the chelation of K++ with -OMe as well as -SiEt3 from [(η2-COD)2NiSiEt3] is the key step which promotes the insertion of NiSiEt3 to the =C(2) carbon of 2-methoxynaphthalene. We also observed that the activation energy barrier in the non-π-extended aromatic systems is higher than that of the π-extended aromatic systems. The overall study manifests that Ni(COD)2-catalyzed ipso-silylation of 2-methoxynapthalene operates through an internal nucleophilic substitution pathway. [ABSTRACT FROM AUTHOR]

More than 47,000 articles have been published in the area of Metal-Organic Framework since its seminal discovery in 1995, exemplifying the intense research carried out in this short span of time. Among other applications, gas adsorption and storage are perceived as central to the MOFs research, and more than 10,000 MOFs structures are reported to date to utilize them for various gas storage/separation applications. Molecular modeling, particularly based on density functional theory, played a key role in (i) understanding the nature of interactions between the gas and the MOFs geometry (ii) establishing various binding pockets and relative binding energies, and (iii) offering design clues to improve the gas uptake capacity of existing MOF architectures. In this review, we have looked at various MOFs that are studied thoroughly using DFT/periodic DFT (pDFT) methods for CO2, H2, O2, and CH4 gases to provide a birds-eye-view on how various exchange-correlation functionals perform in estimating the binding energy for various gases and how factors such as nature of the (i) metal ion, (ii) linkers, (iii) ligand, (iv) spin state and (v) spin-couplings play a role in this process with selected examples. While there is still room for improvement, the rewards offered by the molecular modelling of MOFs were already substantial that we advocate experimental and theoretical studies to go hand-in-hand to undercut the trial-and-error approach that is often perceived in the selection of MOFs and gas partners in this area. The importance of density functional theory-based molecular modeling studies in offering design clues to improve the gas adsorption and storage capacity of existing MOF architectures is discussed here. The use of DFT-based investigation in conjunction with experimental synthesis is an imperative tool in designing new-generation MOFs with enhanced uptake capacity. [ABSTRACT FROM AUTHOR]

Metalclusters of silver have attracted recent interest of researchersas a result of their potential in different catalytic applicationsand low cost. However, due to the completely filled d orbital andvery high first ionization potential of the silver atom, the silver-basedcatalysts interact very weakly with the reacting molecules. In thecurrent work, density functional theory calculations were carriedout to investigate the effect of hydrogen atom chemisorption on thereactivity and catalytic properties of inert silver clusters. Ourresults affirm that the hydrogen atom chemisorption leads to enhancementin the binding energy of the adsorbed O2molecule on theinert silver clusters. The increase in the binding energy is alsocharacterized by the decrease in the Ag–O and increase in theO–O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O–Obond length, a significant red shift in the O–O stretchingfrequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbedsilver clusters show low reaction barriers and high heat of formationof the final products for the environmentally important CO oxidationreaction as compared to the parent catalytically inactive clusters.The obtained results were compared with those of the correspondinggold and hydrogen atom chemisorbed gold clusters obtained at the samelevel of theory. It is expected the current computational study willprovide key insights for future advances in the design of efficientnanosilver-based catalysts through the adsorption of a small atomor a ligand. [ABSTRACT FROM AUTHOR]

Aluminum clusters are now technologicallyimportant due to theirhigh catalytic activity. Our present study on the small-sized aluminumclusters applies density functional theory (DFT)-based reactivitydescriptors to identify potential sites for adsorption and eventualchemical reaction. Depending on symmetry, susceptibility of varioustype of reactive sites within a cluster toward an impending electrophilicand/or nucleophilic attack is predicted using the reactivity descriptors.In addition, the study devises general rules as to how the size, shape,and charge of the cluster influences the number of available sitesfor an electrophilic and/or nucleophilic attack. The predictions byreactivity descriptors are validated by performing an explicit adsorptionof water molecule on Al clusters with four atoms. The adsorption studiesdemonstrate that the most stable water–cluster complex is obtainedwhen the molecule is adsorbed through an oxygen atom on the site withthe highest relative electrophilicity. [ABSTRACT FROM AUTHOR]

In this paper, we present linear and non-linear electric properties of BH, CO and H2O using a density functional response approach, which is a combination of numerical and analytical technique and is thus a simplification of fully analytic method. In the framework of an analytic response approach using Kohn–Sham (KS) density functional theory, the derivative of the KS operator with respect to external field is evaluated numerically, while the orbital derivatives and the subsequent energy derivatives are obtained fully analytically. The method is tested using three molecules BH, CO and H2O, which are marked by high degree of electron correlation and for which extensive ab initio benchmark results are available. Further, we have made a study of possible incorporation of non-dynamical electron correlation by studying BH at several inter-nuclear distances. [Copyright &y& Elsevier]

The article discusses a conference on "Recent Advances in Many-Electron Theory – 2017" held in Goa on February 9-12, 2017. Topics discussed includes dynamics of non-adiabatic effects and density functional theory, treatment of electron correlation effects in many-electron theory, and inclusion of relativistic effects in equation-of-motion coupled cluster based methods. It also mentions several events presented at the events includes Debashis Mukherjee, Hans-Joachim Werner, and B. K. Sahoo.

A series of Mn(I) complexes Mn(L1)(CO)3Br, Mn(L2)(CO)3Br, Mn(L1)(CO)3(OAc) and Mn(L3)(CO)3Br [L1=2‐(5‐tert‐butyl‐1H‐pyrazol‐3‐yl)‐1,8‐naphthyridine, L2=2‐(5‐tert‐butyl‐1H‐pyrazol‐3‐yl)pyridine, L3=2‐(5‐tert‐butyl‐1‐methyl‐1H‐pyrazol‐3‐yl)‐1,8‐naphthyridine] were synthesized and fully characterized. The acid‐base equilibrium between the pyrazole and the pyrazolato forms of Mn(L1)(CO)3Br was studied by 1H NMR and UV‐vis spectra. These complexes are screened as catalysts for acceptorless dehydrogenative coupling (ADC) of primary alcohols and aromatic diamines for the synthesis of benzimidazole and quinoline derivatives with the release of H2 and H2O as byproducts. The protic complex Mn(L1)(CO)3Br shows the highest catalytic activity for the synthesis of 2‐substituted benzimidazole derivatives with broad substrate scope, whereas a related complex [Mn(L3)(CO)3Br], which is devoid of the proton responsive β‐NH unit, shows significantly reduced catalytic efficiency validating the crucial role of the β‐NH functionality for the alcohol dehydrogenation reactions. Control experiments, kinetic and deuterated studies, and density functional theory (DFT) calculations reveal a synchronous hydride‐proton transfer by the metal‐ligand construct in the alcohol dehydrogenation step. [ABSTRACT FROM AUTHOR]

Primary H 2 adsorption sites in a zeolitic imidazolate framework, ZIF-7, are identified using ab-initio density functional theory (DFT) based molecular dynamics annealing simulations. The simulations suggest several low energy adsorption sites. The effect of light transition metal decoration on hydrogen storage properties was studied. Our ab-intio DFT calculations illustrate that decorating the ZIF with Sc increases both the number of H 2 molecules, as well as the H 2 binding energy. The binding energy (∼25 kJ/mol per H 2 ) at 8H 2 loading in the pore, suggests that Sc-ZIFs can be potential candidates for hydrogen storage. [ABSTRACT FROM AUTHOR]

A comparative study of dipole moments, polarizabilities and hyperpolarizabilities of 16 different molecules is performed employing two completely different theoretical approaches namely, density functional theory (DFT) and coupled cluster singles and doubles (CCSD). Both methods include electron correlation. The CCSD method is more accurate but highly expensive. DFT with auxiliary density allows non-iterative solutions which is computational advantage and useful for large molecules. Dipole moments and polarizability calculations from DFT are in very good agreement with CCSD calculations. However, negative hyperpolarizability values from DFT differ significantly from their CCSD counterparts, whereas positive hyperpolarizabilities show reasonable agreement between these methodologies. [ABSTRACT FROM AUTHOR]

In this paper, we study the reactivity of diimines like 2, 2-bipyridine, 1, l0-phenanthroline and 1, 2, 4-triazines using density-based reactivity descriptors. We discuss the enhancement or diminution in the reactivity of these ligands as a function of two substituent groups, namely methyl (-CH) group and phenyl (-CH) group. The global reactivity descriptors explain the global affinity and philicity of these ligands, whereas the local softness depicts the particular site selectivity. The inter-molecular reactivity trends for the same systems are analysed through the philicity and group philicity indices. The σ-donor character of these ligands is quantified with the help of electron density profile. In addition, the possible strength of interaction of these ligands with metal ions is supported with actual reaction energies of Ru-L complexes. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Structural and electronic properties of Au32 cluster are analyzed using relativistic density functional theory (DFT) based methods. Further, DFT based molecular dynamical (MD) simulations are performed on Au32 golden fullerene with an aim of understanding its thermal stability at various working temperatures. Various conformations being populated at different temperatures of a cluster are analyzed. The study shows that the ground state icosahedral conformation is stable only up to 300K and structure remains in a hollow conformation only up to 400K. This clearly explains the reasons for failure by experimentalists in trapping the unique fullerene conformation in spite of the theoretical predictions of it being a very stable one. The above MD study also indicates that the bare fullerene Au32 cluster (without any stabilizing ligands) can be used for potential catalytic applications only around room temperatures. [Copyright &y& Elsevier]

Abstract: The effect of light metal (M=Li, Be, Mg, and Al) decoration on the stability of metal organic framework MOF-5 and its hydrogen adsorption is investigated by ab initio and periodic density functional theory (DFT) calculations by employing models of the form BDC:M2:nH2 and MOF-5:M2:nH2, where BDC stands for the benzenedicarboxylate organic linker and MOF-5 represents the primitive unit cell. The suitability of the periodic DFT method employing the GGA-PBE functional is tested against MP2/6-311+G* and MP2/cc-pVTZ molecular calculations. A correlation between the charge transfer and interaction energies is revealed. The metal-MOF-5 interactions are analyzed using the frontier molecular orbital approach. Difference charge density plots show that H2 molecules get polarized due to the charge generated on the metal atom adsorbed over the BDC linker, resulting in electrostatic guest-host interactions. Our solid state results show that amongst the four metal atoms, Mg and Be decoration does not stabilize the MOF-5 to any significant extent. Li and Al decoration strengthened the H2-MOF-5 interactions relative to the pure MOF-5 exhibited by the enhanced binding energies. The hydrogen binding energies for the Li- and Al-decorated MOF-5 were found to be sensible for allowing reversible hydrogen storage at ambient temperatures. A high hydrogen uptake of 4.3wt.% and 3.9wt.% is also predicted for the Li- and Al-decorated MOF-5, respectively. [Copyright &y& Elsevier]

The C–X [X = Cl, Br] bond dissociation is a challenging problem due to its high activation barrier. Many transition metal-based clusters, acting as catalysts, are known to dissociate this bond. We have carried out DFT-based calculation and found that small-sized aluminum clusters can break these bonds quite effectively with a high rate constant. Our analysis gives a detailed description of thermodynamics and kinetics of the reaction. Fukui functions and NBO calculation provide an insight into the reactivity and mechanism. Hence nanoaluminum clusters can dissociate C–X bond with a lower activation barrier compared to the known gold or platinum catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Photoelectrochemical splitting of water with nanocrystalline Zn1−x Mn x O thin films was investigated. ZnO thin films with 1, 3, 5 and 7% at. Mn incorporation were synthesized by sol–gel method and characterized by X-Ray Diffraction (XRD) analysis, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Photoelectron spectroscopy (XPS), High Resolution Transmission Electron Microscopy (HR-TEM) and UV–Vis spectroscopy. Mn incorporation coupled with variation in sintering temperature led to significant microstructural changes, which tentatively influenced the magnitude of optical absorption and charge carrier mobility, thereby impacting the performance of such systems towards photoelectrochemical splitting of water. Electronic structure computations based on first principle density functional theory (DFT) revealed electronic states of Mn being responsible for the marginally recorded red shift in bandgap energy. Photoelectrochemical measurements using thin films of 1% at. Mn:ZnO sintered at 600 °C yielded 3 times enhanced photocurrent at zero bias due to improved optical absorption. Plausible explanations for the effect have also been offered. [Copyright &y& Elsevier]

The adsorption of water molecules around a polar region (in particular around the phosphate moiety) in the phospholipid molecules is studied in this work. Phospholipid molecules with different functional groups are known to respond differently to the water molecules. Hence, we attempt to study the adsorption of water molecules around the phosphate group as a consequence of the change of functional group attached to the phosphate group, viz. phosphatidyl ethanolamine (PE), phosphatidyl choline (PC) and phosphatidyl glycerol (PG). As the latter is anionic in nature, the charge is compensated by Na+counterion. Up to seven water molecules are adsorbed around the phosphate groups in model systems mimicking phospholipid molecule. The corresponding changes in the structural and electronic aspects are analysed. The significant difference between the PE and PC model systems is the formation of clathrate-like structure in the latter. It is noticed that as the number of water molecules increases to seven, both the hydrogen atoms in the water molecule participate in hydrogen bonding. However, in the PG model system, the charge-compensating counterion prevents the water molecule to form clathrate-like structures. The adsorption sites for water molecules are validated by density functional theory-based reactivity descriptors, viz. Fukui functions in the PE model system. [ABSTRACT FROM PUBLISHER]