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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 cm³ molecule-1 s-1 at 298.15 K. [ABSTRACT FROM AUTHOR]

The interaction between the metal cations and H2molecule has been investigated using dispersion-corrected and -uncorrected hybrid density functional and CCSD(T) methods in conjunction with the correlation consistent triple-ζ quality basis sets for the storage of the H2molecule. The molecular properties, potential energy surfaces, stability, binding energy and well-depth have been computed for the metal cation–dihydrogen (M+–H2, M = Mg, Ca, and Ag) complexes in the gas phase. The results obtained by the dispersion-corrected hybrid density functional B2PLYP-D method agree very well with the earlier experimental and theoretical results wherever available. Different components of the interaction energy have been estimated by the symmetry adapted perturbation theory (SAPT) to get physical insight into the interaction energy. Among the three complexes, only Ag+–H2is the most stable complex and it accumulates more H2molecules as the interaction between the metal cation Ag+and the H2molecule is the greatest. [ABSTRACT FROM PUBLISHER]

The electronic structure and the nature of Pb–S interaction in the [PbII(S2COEt)n]2−n (n = 1,2,3,4) complexes are investigated theoretically. The ELF analysis has been performed for qualitative assignment of position, shape and directionality of the valence basin V(Pb) of lead in these chelates. The Pb–S interaction is explored in the light of AIM formalism and NBO analysis. In all these complexes, lead mainly uses its 6p sub-shell to coordinate with the 3p sub-shells of S-atoms. In the [Pb(S2COEt)2] (n = 2) and [Pb(S2COEt)3]− (n = 3) complexes, significant participation of 6d and 7s orbitals of lead is also observed. As lead mainly uses the 6p orbitals in coordinating with the sulfur atoms of xanthate ligands, the structure becomes more holodirected when the three components of the 6p sub-shell of lead become equally populated. The ELF analysis reveals that the stereochemical activity of the valence lone pair of lead decreases as n increases, leading the lead xanthate structures from hemi to holodirected. The energetics of these chelates in the gas phase show that [Pb(S2COEt)3]− (n = 3) is the most stable one while [Pb(S2COEt)]+ (n = 1) is the least, when formation of these complexes are considered from Pb2+ and (S2COEt)− ligands. The complexation of these chelates is also investigated in water using the continuum SMD model which shows that Pb(S2COEt)2 is the most stable and the stability decreases successively as n changes from 2 to 4. Thus the reason behind the formation of Pb(S2COEt)2 in froth floatation is revealed. [ABSTRACT FROM AUTHOR]

The complexes of PbII(S2COR)2 [R = Me, Et, Ph] having three possible coordination patterns S,S/S,S or S,O/S,S or S,O/S,O are studied. The formation energy and relative energy of these isomers reveal that the order of stability is S,S/S,S > S,O/S,S > S,O/S,O. Complexation energy of the isomers decreases substantially from gas phase to water. The natural bond orbital (NBO) analysis has been performed to explore the metal–ligand coordination. Similar types of metal–ligand coordinations are observed for methyl and ethyl substituent. In S/S,S/S coordination, lead mainly uses its 6p sub-shells along with 6d and 7s orbitals to coordinate with 3p sub-shells of the surrounding sulfur atoms. Significant mixing of 6p and 6d orbitals of lead is also observed. In contrast, for phenyl substituent, lead uses only its 6p sub-shells to coordinate with sulfur atoms. In S,O/S,O or S,O/S,S coordination, oxygen uses its 2s and 2p sub-shells while sulfur uses its 3p sub-shells to coordinate with 7s and 6p sub-shells of lead. The binding energy and NBO analysis of these chelates indicate that lead–sulfur (soft–soft) coordination is preferred over lead–oxygen (soft–hard). In all these chelates, valence 6s orbital of lead shows inert pair effect with no participation in chelation. [ABSTRACT FROM PUBLISHER]

The intermediates [Si,O,C,O] of the Si + CO reaction have been studied in detail using high level ab iniitio methods. Both singlet and triplet [Si,O,C,O] species are characterized structurally and energetically. On the singlet potential energy surface (PES), the vdw-OSi-CO isomer and in the triplet PES, the bent-SiOCO isomer is found to be thermodynamically as well as kinetically most stable species. All possible isomerization transition states (TS) are located on both singlet and triplet potential surfaces. On the triplet surface, the stability of the trans-OSiCO isomer is comparable with that of the bent-SiOCO isomer. A non-planar cis-SiOCO isomer is located on the triplet PES, which is predicted for the first time. Heats of formation at 0 K (Δ H°, 0 K) for all singlet and triplet species are computed using G3B3, G3MP2, and CBS-Q theories. The discrepancy between G3B3 and the other two methods for the heat of formation value for triplet trans-OSiCO is discussed. The PESs for singlet as well as triplet species with their dissociation asymptotes are explored at the CCSD(T)/6-311G(d,p)//MP2/6-311G(d,p) level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Stability, spectroscopic constants, and dissociation of CO2+ have been studied in detail using ab initio MP2, CCSD and CCSD(T) methods, and density functional B3LYP method. The stability and the ambiguity between the ground and metastable state of the molecular dication have been discussed. The spectroscopic constants of the molecular dication have been compared with the experimental and theoretical values wherever available. Various charge symmetric and charge asymmetric dissociation pathways of CO2+ have been investigated. After dissociation, the fragmented atoms and ions are considered to be either in their ground or in their metastable state. Interesting results have been obtained for the charge symmetric and charge asymmetric dissociation of the diatomic dication. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Reaction pathways for H2 release mediated by H2X (X = O, S, Se) and HY (Y = F, Cl, Br) set of reagents from ammonia-borane (NH3BH3) have been explored in gas phase using density functional theory (DFT). The optimized geometries of reactant complexes, transition states and product complexes have been obtained using M06-2X functional in conjunction with 6-311+G(d,p) basis set. The study of catalytic effect of these cheap and easily available, yet highly effective, assisting reagents has farther been extended to analyze the thermochemistry involved in H2 departure from two other ammonia-borane-related compounds: aziridine-borane [C2H5N.BH3] and 3-methyl-1,2-BN-cyclopentane. The mechanism of H2 release channel is identical for all three compounds considered. The free energy barrier falls significantly from H2O to H2S to H2Se for the H2X set of reagents and from HF to HCl to HBr for the HY analogs. Our study endorses the fact that the HY set of reagents serves as better assisting reagents kinetically compared to H2X, with HBr being the best of the lot. HBr reduces the free energy barrier to 41.9 kJ mol−1 for ammonia-borane [NH3BH3], 42.7 kJ mol−1 for aziridine-borane [C2H5N·BH3] and 30.2 kJ mol−1 for 3-methyl-1,2-BN-cyclopentane in H2 release at 1 atm. pressure and 298 K temperature. [ABSTRACT FROM AUTHOR]

Abstract: Mechanism and kinetics for the reaction of DMSO with O(3P) have been investigated by M06-2X/MG3S, CBS-QB3 and G4MP2 methods. Four possible reaction pathways are identified. Among them, the O(3P) addition to S-atom followed by CH3 elimination is almost exclusive. Four pre-reactive complexes have been located. AIM theory is used to determine the nature of interactions in these complexes. Considering the formation of pre-reactive complex, the rate constant for major pathway is calculated using transition state theory applied to a two-step mechanism. Enthalpies of formation at 298.15K (Δf H°298.15) have been calculated using the composite CBS-QB3, G4MP2 and G3B3 methods. [Copyright &y& Elsevier]

Abstract: The spectroscopic properties of I2–Rg (Rg=He, Ne, Ar) van der Waals complexes have been studied in detail using ab initio MP2 and CCSD(T) methods in conjunction with the correlation consistent quadruple-ζ quality basis sets. The dissociation energy and depth of the potential well have been calculated using potential method and supermolecular approach in order to remove the discrepancy among the existing theoretical and experimental values. Most of the spectroscopic properties are first reported and the rest agree very well with the theoretical and experimental values wherever available. [Copyright &y& Elsevier]

Activation of C–H, B–H as well N–H sigma bonds has been a subject of fundamental interest due to potential feedstock in chemical industry. The co-operative effect of the metal centers in a di-nuclear carbide cluster Ta 2 C 4 − for methane C–H activation and dissociation has recently been revealed, in which a molecule of hydrogen is evolved. Based on that, we have explored reaction pathways for 'E−H' sigma bond activation and dissociation processes of gaseous Ammonia (E: N) and Borane (E: B) using the stable form of the aforesaid complex at DFT levels. The geometries and energetics associated with the reactions are found to be method insensitive. The course of the reaction is initiated by a 1:1 precursor complex formed between the cluster and N (/B)H 3. This complex formation is found to be more exothermic than that of its methane counterpart. In case of BH 3 , considerable lengthening of two B–H bonds in the first step is observed which implies that the two B–H bonds are activated simultaneously under the influence of Ta 2 C 4 −. But for NH 3 , N–H bond lengthening as well as activation is observed to be insignificant in this precursor complex. The chemical nature of the participating hydrogen atoms is inspected by NPA analysis (' protic ' type in NH 3 and 'hydride ' type in BH 3).The overall dehydrogenation procedures for both the molecules are found to be multi-step with high exothermicity. Highly negative net energy change in terms of Gibbs Free Energy (−31.03 kcal/mol for ammonia and −31.36 kcal/mol for borane) as well as Enthalpy (−33.68 kcal/mol for ammonia and −34.13 kcal/mol for borane), in forming a H 2 molecule with stable Ta 2 C 4 N(/B)H− complex, with respect to the reactant pair govern the thermodynamic feasibility of the overall process. In a nutshell, this computational study provides a detail understanding of the activation and dissociation processes of the concerned gaseous molecules, which will be beneficial for further experimental studies. Image 1 • Dehydrogenation of gaseous NH 3 and BH 3 by Tantalum carbide cluster anion (Ta 2 C 4 -). • The participating hydrogen atoms are ' protic ' type in NH 3 and 'hydride ' type in BH 3. • The multi-step reaction is initiated by a 1:1 precursor complex (Exothermic). • Primarily, significant activation of two B-H sigma bonds is noted though N-H sigma bond activation is inconsequential. • Overall H 2 release process, for both the molecules is highly exothermic making the procedure to be thermodynamically facile. [ABSTRACT FROM AUTHOR]

• Doping with Al and Ga substituting one of the B atoms of the B 12 N 12 and B 12 P 12 nanocages increases the reactivity of the cage. • THF/F adsorbed complexes show the highest adsorption energy for Al-doped nanocages. • For a given nanocage, THF molecule is adsorbed strongly than F. • B 12 P 12 complexes show higher optical responses compared to its B 12 N 12 counterparts. Removing pollutants like furan (F) and tetrahydrofuran (THF) from the environment is challenging, and adsorption can efficiently remove pollutants. Fullerene like inorganic nanocages B 12 N 12 and B 12 P 12 are known for their efficient adsorption capability. To address these concerns, we report here the adsorption of the F and THF on the pristine and Al and Ga-doped B 12 N 12 and B 12 P 12 nanocages and consequently the change in the electronic structure, property and optical responses. Doping Al and Ga at the nanocage diminishes the HOMO-LUMO energy gap by 2.9 to 0.4 eV compared to the pristine cage, making the doped cage surface more reactive. The doped surface of nanocage adsorbs F (F@AlB 11 N 12 (-130.1 kJ/mole) and THF (THF@AlB 11 N 12 (-202.3 kJ/mole) more effectively compared to pristine ones (F@B 12 N 12 -28.7 kJ/mole, THF@B 12 N 12 (-98.3 kJ/mole) at ωB97XD/6–31+ G (d,p) level. For a given cage, THF is more strongly adsorbed (THF@B 12 N 12 (-98.3 kJ/mole)) on the cage surface than F (F@B 12 N 12 -28.7 kJ/mole). Interestingly, Al-doped cages exhibit the highest adsorption energy value ranging from -68.5 kJ/mole to -202.3 kJ/mole. Natural bonding orbital analysis, global reactivity descriptor, molecular electrostatic potential, frontier molecular orbital, etc. have been employed to comprehend the distinctive patterns of adsorption. The optical response properties of the studied complexes show that the complexes of B 12 P 12 nanocages exhibit higher polarizability and second hyperpolarizability value (1.51 × 105 to 1.62 × 105 au) compared to its analogous B 12 N 12 complex (3.62 × 104 to 4.15 × 104 au) at ωB97XD/6–311+ G (d,p) level. Our theoretical results further demonstrate the capability of AlB 11 N 12 and AlB 11 P 12 as promising adsorbents of the toxic organic pollutants F and THF, and the computed higher second hyperpolarizability value of the B 12 P 12 complexes indicates these nanomaterials could be used as potential optoelectronic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Reaction pathways for dehydrogenation and hence cyclization of diamine-monoborane and amine-borane alcohol have been explored theoretically using Density Functional Theory (DFT). The diamine-monoborane and amine-borane alcohol chosen for investigation in the present venture are N -(tert -butyl)(BH 3)– N′ - tert -butyl-ethylenediamine and α,α -Diphenyl-2-pyrrolidinemethanol-borane. Alkali metal catalysts, viz., 1-lithio-2- tert -butyl-1,2-dihydropyridine and its sodium and potassium analogues have been employed for the removal of two equivalents of H 2. The optimized geometries of all the reactant complexes, intermediates, transition states and product complexes have been obtained using ωB97xd functional in conjunction with 6–31++G(d,p) basis set. The whole assisting phenomena in solvent medium has been investigated through the implementation of conductor-like screening solvation model (COSMO) primarily considering benzene as the bulk solvent medium. The investigation has further been extended to solvents tetrahydrofuran and pyridine to examine the participation of solvent molecules in bringing any change in reaction mechanism and catalytic cycle of the lithium catalyst over diamine-borane. The intramolecular and all possible intermolecular (catalytic) pathways have been studied in detail. Our study supports previous experimental studies and elucidates key role in the catalytic regime of 1,2-dihydropyridine, which is able to store and deliver Li–H on demand. Image 1 • Dehydrocyclization of diamine-borane and amine-borane alcohol. • Catalysts considered are 1-lithio-2-alkyl-1,2-dihydropyridine and its Na & K analogues. • Implementation of solvent medium (benzene, THF, pyridine) on reaction mechanism through COSMO. • Investigation of all possible pathways involved in H 2 -release. • Activation barriers and Turnover frequencies suggest effective catalytic activity. [ABSTRACT FROM AUTHOR]

The possibility of ionization of six moderately reactive molecules (Y), namely silicon dioxide (SiO2), ammonia (NH3), water (H2O), carbon dioxide (CO2), chloroform (CHCl3) and dichlorodifluoromethane (CCl2F2) by two properly chosen superhalogens (SHs), gold tetrafluoride (AuF4), and gold hexafluoride (AuF6) denoted as AuXn (n = 4 and 6) has been explored at density functional theory (DFT) level. With increasing electron affinity (EA) of superhalogen, its capability to oxidize molecules with higher ionization potential also increases. We have demonstrated that this competition between the electron-binding energy of the superhalogen system and the ionization potential (IP) of the molecule with which the superhalogen combines is a key factor to predict the stability and nature of the formed complex. Binding energies have been evaluated to predict the stability of the formed complexes. The charge flow between Y and AuXn and localization of spin density distribution on the Y molecules have been estimated to verify the nature of interaction between the two. Atom in molecule (AIM) analysis has been performed to predict the nature of the bonds formed between the two interacting species. Overall, our study gives a comprehensive idea about the nature and stability of the complexes formed when moderately reactive (or inert) molecules interact with superhalogens containing coinage metal. [ABSTRACT FROM AUTHOR]

• Ester synthesis from primary alcohol. • (PNP)Ru pincer complex acts as effective catalyst. • Investigation of thermal and kinetic feasibility by DFT. • Involves release of two equivalent of hydrogen. • Comparative study with isoelectronic (PNP)Os and (PNP)Rh+pincer complex. Mechanistic pathway of (PNP)Ru {PNP = bis[(2- dimethylphosphino)- ethyl ]amine} mediated synthesis of an ester (2-methoxyethyl-2-methoxyacetate) from two equivalent of a primary alcohol (3-oxabutanol) is investigated using density functional theory. A ten-stage catalytic cycle is proposed. The key steps of this process is broadly described as the oxidation of first equivalent of primary alcohol into aldehyde with the elimination of H 2 molecule, coupling of the aldehyde with second equivalent of alcohol to form an ester followed by the regeneration of the pincer catalyst with the liberation of second H 2 molecule. Two isoelectronic pincer complexes (PNP)Os and (PNP)Rh+ are also considered to shed light on the variation of the energetics. Prior to H 2 elimination, a η2-bonded metal-dihydride complex is obtained for (PNP)Ru and (PNP)Rh+, whereas pure Os-H bonds are observed in case of (PNP)Os. Theoretical catalytic efficiency and TOF values infer that (PNP)Ru is the best amongst the three pincer complexes considered here. [Display omitted] [ABSTRACT FROM AUTHOR]

Tautomerizations of biologically and medicinally important heterocyclic compound, 2,5-pyrrolidinedione, commonly known as succinimide and two of its analogous compounds, 2,4-pyrrolidinedione and 3,4-pyrrolidinedione have been investigated at the density functional theory (DFT)/M06-2X level in aqueous medium, implementing polarizable continuum model (PCM). We have extended our investigation of tautomerism to the sulfur analogues of the aforementioned compounds also, i.e., 2,5-pyrrolidinedithione, 2,4-pyrrolidinedithione, and 3,4-pyrrolidinedithione. Tautomerism observed in these compounds are mainly keto-enol, thio-thiol and amine-imine, but we have detected two new kind of tautomerization shown by some of the abovementioned compounds, named as keto-epoxy (for the oxygen analogue) and thio-thioepoxy (for the sulfur analogue) which have not yet been reported in the literature. Relative energies (Er) and activation energies (Ea) have been calculated for all the tautomers and tautomerization processes. The potential energy surfaces (PESs) have been constructed using the M06-2X energy values. It has been observed that the energy difference found in the tautomers of sulfur analogues is relatively lower than that of the corresponding oxygen analogues, so does the activation energy barrier. As one-electron redox properties play an important role in biological systems, we have also explored the effect of conformational changes on the overall redox properties of the said compounds by calculating the adiabatic and vertical ionization potentials (AIPs and VIPs, respectively) and adiabatic electron affinities (AEAs). [ABSTRACT FROM AUTHOR]

The stabilization of non-IPR fullerenes for their isolation and characterization is an area of recent interest. In the present study, we have explored the stabilization techniques of C 72 isomers via endo and exo-modifications and finally approached dual modification. A total of four isomers of C 72 have been considered in this study; among them, one is IPR derivative (1), and the rest are non-IPR derivatives with one (2) and two (3 and 4) fused pentagon rings. First, we have studied the endohedral modification by encapsulating one and two La atoms in the C 72 cavity. Secondly, we have exohedrally modified the C 72 isomers via chlorination by adding four and eight chlorides, respectively. Our final approach is to study the dual modification, where we have implemented both endo exo-modifications together. This dual modification can be achieved in two ways: exo followed by endo and endo followed by exo. For each modification, the relative stability of every modified C 72 derivative has been checked by calculating the relative energy with respect to the most stable modified analogue. To find out whether these modifications are energetically feasible or not, we have calculated the binding energy of each modified C 72 isomer. The binding energy calculation reveals that the encapsulation and exo-modification techniques are good enough to stabilize the non-IPR C 72 derivatives. Moreover, the effectiveness of dual modification has also been established from the enhanced binding energy compared to either endo- or exo-modification. We have also studied the NPA charges on the encapsulated La atoms for each endo- and dual-modified C 72 derivative. Furthermore, the AIM study has also been perceived to find out the interaction between the La atom and the fullerene cages for both mono- and di-encapsulated fullerene derivatives and also between La–La centres for di-encapsulated derivatives. Overall, the present theoretical study will provide an idea about the stability of the modified C 72 derivatives, which will help the experimentalists to design new strategies for synthesizing modified non-IPR fullerene derivatives that have vast applications in the medicinal and industrial fields. [Display omitted] • The stabilization techniques of Non-IPR C 72 isomers have been discussed in the light of DFT. • Both endo- and exo-modifications have been considered separately before going into the dual modification approach. • The thermodynamic feasibility of these modifications has been checked by binding energy calculations. • Enhanced binding energy has predicted effectiveness of dual modification compared to each modification in separation. • The present study will be helpful for experimentalists to design modified non-IPR fullerene derivatives. [ABSTRACT FROM AUTHOR]

Abstract: Molecular properties of the OCS–C2H2 van der Waals complex are studied in detail in order to explore the possibility of formation of three isomers of the complex and to verify the experimental findings. Both dispersion-corrected and -uncorrected double hybrid density functional theories with correlation consistent triple zeta basis set are used to investigate the complex. The results obtained by the dispersion corrected density functional method, mPW2PLYP-D, agree very well with the experimental values. The Symmetry Adapted Perturbation Theory (SAPT) is applied to study the interaction. [Copyright &y& Elsevier]