Department of Chemistry
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Item Investigation of [CH2I2–R2S] complexes (R = –H, –CH3) in cryomatrix: Propensity towards C–I⋯S halogen bond and C–H⋯S hydrogen bond interaction(Elsevier, 2025-12) Chakraborty, Amrita; Chakraborty, ShamikThe volatile organic iodine compound (Image 1) and volatile bivalent sulphur compounds, such as, Image 2, Image 3, are trace gases present with high concentration in the coastal area and are important constituents for the chemical processes in the area of atmospheric science. The Image 4 is one of the iodine precursors in the atmosphere, and Image 5 and Image 6 play a major role in the sulphur cycle. Depending on the nature of the Lewis bases, the type of interactions between the constituents may alter, which would influence the final product in a chemical reaction, nucleation process, and radiative forcing. The key objective of this work is to understand the plausible interaction between Image 7 and sulphur-containing Lewis bases (Image 8, Image 9), and to identify the propensity towards the formation of hydrogen bond and halogen bond interaction at the molecular level using matrix-isolation FTIR spectroscopy. Electronic structure calculations have been performed in the ground electronic state to predict the possible structures and stability of the clusters. The thermodynamic properties of the dimers have been evaluated along with their higher-order clusters to understand the possibility of forming such complexes in the atmosphere.Item An Experimental Exploration of C−H⋅⋅⋅X Hydrogen Bond in [CHCl3−X(CH3)2] Complexes (X=O, S, and Se)(Wiley, 2023-05) Chakraborty, ShamikAmong the conglomeration of hydrogen bond donors, the C−H group is prevalent in chemistry and biology. In the present work, CHCl3 has been selected as the hydrogen bond donor and are X(CH3)2 are the hydrogen bond acceptors. Formation of C−H⋅⋅⋅X hydrogen bond under the matrix isolation condition is confirmed by the observation of red-shift in the C−H stretching frequency of CHCl3 and comparison with the simulated spectra. Stabilisation energy of all the three complexes is almost equal although the observed red-shift for the C−H⋅⋅⋅O complex is less compared to the C−H⋅⋅⋅S/Se complexes. The nature and origin of the hydrogen bond have been delineated using Natural Bond Orbital, Atoms in Molecules, Non-Covalent Interaction analyses, and Energy Decomposition Analysis. Charge transfer is found to be proportional to the observed red-shift. This work provides the first impression of C−H⋅⋅⋅Se hydrogen bond and its comparison with C−H⋅⋅⋅O/S hydrogen bond interaction under experimental condition.Item Matrix isolation infrared study of complexes between Image 1 and Image 2: Evidence of formation of hydrogen bond and chalcogen bond(Elsevier, 2023-11) Chakraborty, ShamikAmong the non-covalent interactions, the most well studied is the hydrogen bonding interaction. A new type of non-covalent interaction is the chalcogen bonding interaction. In the present work 1:1 complex of [Image 3] has been characterised using matrix isolation infrared spectroscopy and electronic structure calculations. Two minima have been obtained on the dimer potential energy surface at the MP2 level of calculations with 6-311++G(d,p) and 6-311++G(3df,2pd) basis sets. One of the minima is stabilised by Image 4 hydrogen bond and the other minima is stabilised by Image 5 chalcogen bond along with secondary Image 6 hydrogen bond. Vibrational spectra in the Image 7 stretching, Image 8 stretching, and Image 7 bending modes have been monitored to understand the complex formation. The formation of the hydrogen- and chalcogen-bonded complex in Image 9 and Image 10 matrices are confirmed by comparison of the experimental and simulated vibrational frequencies. Stabilisation energy, energy decomposition analysis, natural bond orbital analysis, and atoms in molecules analysis provide insight into the nature of the interactions. This work presents the first experimental report where both the hydrogen- and chalcogen-bonded complexes are formed simultaneously. This work also provides the first impression of the Image 4 hydrogen bonding and Image 5 chalcogen bonding interaction between Image 1 and Image 2.Item Investigation of [CHCl3-CH3OH] complex using matrix-isolation IR spectroscopy and quantum chemical calculation: Evidence of hydrogen- and halogen-bonding interaction(Elsevier, 2022-03) Chakraborty, Amrita; Chakraborty, ShamikMixture of CHCl3-CH3OH is a popular non-aqueous solvent mixture that exhibits strong synergistic solvation. The specific interaction between the CHCl3 and CH3OH is investigated using 1:1 complex in N2 matrix along with electronic structure calculation. Three different type of interactions are possible between CHCl3 and CH3OH at the molecular level: C-HO hydrogen bond, O-HCl hydrogen bond, and C-ClO halogen bond. One C-HO hydrogen bond minimum, two O-HCl hydrogen bond minima, and one C-ClO halogen bond minimum are obtained on the [CHCl3-CH3OH] dimer potential energy surface. Formation of C-HO hydrogen bonded and C-ClO halogen bonded 1:1 complex of [CHCl3-CH3OH] in N2 matrix is confirmed using experimental and simulated IR spectra. The outcome of the current work would help to explain the specific interactions present in CHCl3 and CH3OH binary solvent mixture and to estimate the responses of such non-aqueous solvent mixture.Item Atmospherically relevant halogen- and hydrogen- bond complex [CCl4 single bond(H2Y)n] with Y = O and S, n 4: A computational study on Rayleigh scattering properties(Elsevier, 2023-11) Chakraborty, Amrita; Chakraborty, ShamikIn troposphere, CCl4 may interact with volatile compounds that may finally contribute to the aerosol formation or atmospheric nucleation. Herein, first solvation shell of CCl4 with (H2O)n and (H2S)n is investigated. The Csingle bondClO and Csingle bondClS types of halogen bond and Osingle bondHCl and Ssingle bondHCl types of hydrogen bond have been considered. Molecular structure of the complexes have been optimised at the MP2/aug-cc-pVTZ level and the stabilisation energies are calculated at the CCSD(T)/aug-cc-pVTZ level. Halogen bond complexes of [CCl4 single bond(H2O)n] are more stable compared to the hydrogen bond complexes. Stability of halogen and hydrogen bond complexes of [CCl4 single bond(H2S)n] are comparable. The Rayleigh scattering intensity of these complexes have been investigated for the first time. Rayleigh scattering intensity increases with the number of H2O and H2S molecules in the complexes. The Rayleigh scattering intensity of the halogen bond complexes are higher compared to the hydrogen bond complexes.Item Matrix-isolation FTIR spectroscopic study and quantum chemical calculations of 1:1 adduct of CHCl3 and C2H5OH in N2 matrix(Elsevier, 2024-06) Chakraborty, Amrita; Chakraborty, Shamik[Image 1-Image 2] mixture is a common binary solvent used in industries, organic synthesis, lipid extraction, drug extraction, etc. The purpose of this study is to have a molecular level understanding of the interaction of Image 1 with Image 2. The experiments have been carried out in low temperature Image 3 matrix using Fourier Transform Infrared spectroscopy. Electronic structure calculations have been performed to identify the possible binding motifs between Image 1 and Image 2. Three minima have been obtained on the dimer potential energy surface stabilised by Image 4 and Image 5 hydrogen bond, and Image 6 halogen bond interactions. Formation of more than one complexes have been confirmed using the experimental and simulated IR spectra. Energy decomposition analysis and Natural bond orbital analysis have been performed to understand the nature of interaction and the driving force for complexation. This is one of the first reports where separate complexes have been identified between Image 1 and anti and gauche conformers of Image 2 in the low temperature matrix.Item Effect of ionic charge on O H⋯Se hydrogen bond: A computational study(Elsiever, 2017-02-15) Chakraborty, Shamik; Chakraborty, AmritaComplexes between para-substituted cationic phenol and SeH2 have been investigated in electronic ground state at the B3LYP, B3PW91, and ωB97xD levels of theory using 6-311++G(3df,3pd) basis set. Various electron-donating and withdrawing substituents (NH2, OH, CH3, H, F, Cl, CN, and NO2) are used to characterize electronic substituent effect on intermolecular +OH⋯Se hydrogen bond. Electron withdrawing substituent increases hydrogen bond stabilization energy and red shift in OH stretching frequency. Introduction of a positive charge transforms weak hydrogen bond of neutral OH⋯Se type into a strong hydrogen bond. Complexation induced changes on various hydrogen bond parameters, such as, stabilization energy, change in OH bond length, change in OH stretching frequency, extent of charge transfer from hydrogen bond acceptor to donor, hydrogen bond orders, electron density at the hydrogen bond critical point exhibit conventional electronic substitution effect. Stabilization energy of +OH⋯Y hydrogen bond are similar in the complexes between cationic phenol and SH2/SeH2, whereas it is almost twice with OH2 in case of +OH⋯Y hydrogen bond.Item Electronic substituent effect on Se-H⋯N hydrogen bond: A computational study of para-substituted pyridine-SeH2 complexes(Elsiever, 2019) Chakraborty, Shamik; Chakraborty, AmritaComplexes between para-substituted pyridine and SeH2 have been investigated at the MP2/aug-cc-pVTZ level. Various electron donating and withdrawing substituents (-NH2, -OH, -CH3, -H, -F, -Cl, -CN, and -NO2) are chosen in order to characterize their influence on Se-H⋯N intermolecular hydrogen-bonding interaction. The electron donating substituents lead to an increase of the stabilization energy along with elongation in the Se-H bond length and red-shift in Se-H stretching frequency. Conventional electronic substitution effect has been observed on various hydrogen-bond parameters, such as, stabilization energy, change in Se-H bond length and stretching frequency, charge transfer, bond order, electron density at hydrogen-bond critical point.