Articles written in Journal of Chemical Sciences

    • A philicity based analysis of adsorption of small molecules in zeolites

      Angeles Cuán Marcelo Galván Pratim Kumar Chattaraj

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      Adsorption of small molecules like CH4, CO and NH3 into the acid sites of zeolites is analysed as an interaction between an electrophile and a nucleophile. Global reactivity descriptors like softness and electrophilicity, and local reactivity descriptors like the Fukui function, local softness and local philicity are calculated within density functional as well as Hartree-Fock frameworks using both Mulliken and Hirshfeld population analysis schemes. The HSAB principle and the best electrophile-nucleophile combination suggest that the reaction between the NH3 and Brönsted acid site of the zeolite is the strongest. Interaction between the zeolite and a small probe molecule takes place through the most electrophilic atom of one with the most nucleophilic atom of the other. This result is in conformity with those provided by the frontier orbital theory and the local HSAB principle.

    • Fitness landscapes in natural rocks system evolution: A conceptual DFT treatment

      Soma Duley Jean-Louis Vigneresse Pratim Kumar Chattaraj

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      The chemical reactivity descriptors, such as electronegativity, hardness and electrophilicity of major oxides computed from density functional theory are reported in this paper. These parameters are plotted within a fitness landscape diagram, showing that the principles of minimum electrophilicity (MEP) and maximum hardness (MHP) act as guides towards the region of higher stability. The diagrams indicate the trends and the parameters that control the evolution of natural rocks. Application of the principle S-bearing copper compounds shows the possible and preferred combinations of elements, that give rise to compounds observed during ore formation.

    • A computational study on structure, stability and bonding in Noble Gas bound metal Nitrates, Sulfates and Carbonates (Metal = Cu, Ag, Au)


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      A density functional theory based study is performed to investigate the noble gas (Ng = Ar-Rn) binding ability of nitrates, sulfates and carbonates of noble metal (M). Their ability to bind Ng atoms is assessed through bond dissociation energy and thermochemical parameters like dissociation enthalpy and dissociation free energy change corresponding to the dissociation of Ng bound compound producing Ngand the respective salt. The zero-point energy corrected dissociation energy values per Ng atom for the dissociation process producing Ng atom(s) and the corresponding salts range within 6.0–13.1 kcal/mol in NgCuNO₃, 3.1–9.8 kcal/mol in NgAgNO₃, 6.0–13.2 kcal/mol in NgCuSO₄, 3.2–10.1 kcal/mol in NgAgSO₄, 5.1–11.7 kcal/mol in Ng₂Cu₂SO₄, 2.5–8.6 kcal/mol in Ng₂Ag₂SO₂, 8.1–19.9 kcal/mol in Ng₂Au2SO₂, 5.7–12.4 kcal/mol in NgCuCO₃, 2.3–8.0 kcal/mol in Ng₂Ag₂CO₃ and 7.3–18.2 kcal/mol in Ng₂Au₂CO₃, with a gradual increase in moving from Ar to Rn. For a given type of system, the stability of Ng bound analogues follows the order as Au > Cu > Ag. All dissociation processes are endothermic in nature whereas they become endergonic as well in most of the cases of Kr-Rn bound analogues at 298 K. Natural population analysis along with the computation of Wiberg bond indices, and electron density analyses provide insights into the nature of the Ng-M bonds. The Ng-M bonds can be represented as partial covalent bonds as supported by the different electron density descriptors.

    • Can a chemical bond be exclusively covalent or ionic?


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      The important aspects of bonding are discussed in this perspective article, focusing on commonmisconceptions regarding ‘covalent’ and ‘ionic’ bonds. Special attention is given to the calculation ofpercentage covalent and ionic characters in a bond. In a course on chemical bonding, the graduate studentswere given an assignment: ‘‘Covalent versus ionic bonding in molecules.’’ The outcome shows the majorityof the students are unaware of the fact that no bond is purely ionic or covalent. To that end, a set ofcompounds are considered that are commonly used as examples of ‘covalent’ and ‘ionic’ compounds instandard textbooks, along with some ‘partially covalent’ noble gas (Ng) compounds containing noble coinagemetals (M = Cu and Ag). State-of-the-art quantum chemical tools are utilized to analyze the bonding nature.The set contains alkali and alkaline earth metal halides, hydrogen halides, and main-group molecules likedihydrogen, dinitrogen, fluorine, chlorine, carbon monoxide, ammonia, and water, simple hydrocarbons, andnoble gas- noble metal complexes.

      A perspective towards utilizing the most popular techniques in understanding the nature of bonding to eliminate certain common misconceptions among students including researchers, and a caution against the impetuous usage of the terms ‘ionic’ and ‘covalent’ to describe a bond.

    • Possible C-F bond activation by B(C6F5)3/lutidine and Al(C6F5)3/lutidine frustrated Lewis pair: an in silico study


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      The activation of the C-F bond in 1-fluorobutane, 1, 1-difluorobutane and 1, 1, 1-trifluorobutaneby some frustrated Lewis pair (FLP) has been assessed by DFT based computational study. The FLPs areconstructed from lutidine Lewis base in association with either B(C6F5)3 or Al(C6F5)3. Thermodynamics andkinetics of the reactions are studied, which reveals the concerning bond activation mediated by the Al(C6-F5)3/lutidine FLP is more favourable than the analogous reactions mediated by the B(C6F5)3/lutidine pair.Therefore, the Al(C6F5)3 acid is superior to the B(C6F5)3 acid to construct an effective FLP for some unusualbond activation. The EDA-NOCV study together with the WBI calculation reveals the C-F bond activation inthe studied systems takes place by the cooperative action of the FLP partners. The activation strain modelreveals the strain energy of the reactants to reach the transition state (TS) rather than the interaction energy atthe TS is the decisive factor to the TS barrier height of the concerned reactions.

      The activation of C-F bond in 1-fluorobutane, 1, 1-difluorobutane and 1, 1, 1-trifluorobutane by B(C6F5)3/lutidine and Al(C6F5)3/lutidine pairs has been assessed computationally. The Al(C6F5)3/lutidine pair is superior to the B(C6F5)3/lutidine pairs for such unusual bond activation as revealed by this study.

    • Unveiling novel reactivity of P/Al frustrated Lewis pair: ring sizedependent activation of cyclic ethers/thioethers and CO2 insertion therein


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      Rational design strategies for the Lewis acid and Lewis base functionalities have been probed using a series of ‘‘frustrated Lewis pairs’’ (FLPs) through density functional theory (DFT) based calculations.Generally, FLPs are designed by manipulating Lewis base and Lewis acid centers with group 15 and group 13 elements, respectively. These modeled FLPs are used to tune the rate-limiting step for ring-opening reactionsin cyclic ethers and thioethers. Detailed computational investigation reveals that the free energy of activationis ring-size sensitive and increases with the ring size in homologous series. For P/Al FLP catalyzed pathways,the P–C bond gets strengthened at the TS with increased ring size due to favorable bonding alignment in theopen form of the ring. Herein, utilizing CO2 as a C1 feedstock, we also take advantage of P/Al FLP’sreactivity to form cyclic carbonates from epoxide derivatives. Weak non-covalent interactions (NCI), namelypi stacking (π - π stacking) and interaction of C - H with π system (C-H - π interactions) play crucial roles instabilizing various species along the reaction pathway. Such factors are essential to modulate the FLP catalysts for well-balanced catalytic activity, which is critical for the further design of a novel catalytic process.

      A series of intra-molecular frustrated Lewis pairs (FLPs) are designed by changing the base centers (group 15) and acid centers (group 13). These FLPs are considered to study the ring opening reactions of cyclic ethers and thioethers. It is concluded that the P/Al FLP is the best choice.

    • BSinGe4-n + (n =0-2): prospective systems containing planar tetracoordinate boron (ptB)


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      The potential energy surface (PES) has been explored for BSinGe4−n+ (n = 0-2) systems using density functional theory (DFT). The global minima (1a, 1b, and 1c) of the considered systems contain a planar tetracoordinate boron (ptB) center. The neutral states of the systems do not have a ptB in the global minimum structures. The designed BGe4+, BSiGe3+, and BSi2Ge2+ systems have 18 valence electrons. TheCCSD(T)/aug-cc-pVTZ level of theory has been applied to compute the relative energies of the low-lying isomers with respect to the global minima. The dynamical stability of BSinGe4−n+ (n = 0-2) systems is confirmed from the atom-centered density matrix propagation (ADMP) simulation over 20 ps of time at temperatures of 300 K and 500 K. The natural charge computations show that the charges on the ptB are highly negative, indicating strong r-acceptance from the peripheral atoms. The 1a, 1b, and 1c structures of BGe4+, BSiGe3+, and BSi2Ge2+ systems, respectively, have r/p-dual aromaticity as predicted from the nucleus-independent chemical shift (NICS) values.

      Density functional theory (DFT) based computation predicts the presence of a planar tetracoordinate boron (ptB) in the global minimum energy structures of BSinGe4−n+ (n = 0−2) systems. The systems are kinetically stable and show σ- and π- electronic delocalization.

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