Department of Chemistry
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Item Matrix-isolation IR spectroscopy and quantum chemical characterisation of SOCl2 and [SOCl2 single bondHCl] clusters(Elsevier, 2025-11) Chakraborty, Amrita; Chakraborty, ShamikThe IR spectra of thionyl chloride (SOCl2) are reported for the first time under matrix-isolation conditions in argon and nitrogen matrices, focusing on symmetric and antisymmetric stretching, and stretching modes. Spontaneous hydrolysis of SOCl2 to SO2 and HCl is observed, as evidenced by distinct IR peaks. Two conformers of and three conformers of [ ] have been identified on their respective potential energy surfaces. The formation of two dimer conformers is confirmed by characteristic SOCl2 modes, while the formation of three [ ] clusters is confirmed by red-shifts in the HCl stretching frequency mode.Item Investigation of the molecular level interaction in [ch3oh−ch2x2] Complexes (x=I, br, and cl) using matrix-isolation ir spectroscopy(Wiley, 2025-01) Chakraborty, Amrita; Chakraborty, ShamikThe mathematical equation (X=Cl, Br, and I) complexes have been studied to understand the tendency towards the formation of hydrogen bonds and halogen bonds. Three different types of interactions viz., C–Xmathematical equation O, C-Hmathematical equation O, and O-Hmathematical equation X, are possible between the mathematical equation and mathematical equation . Experiments have been carried out in low temperature mathematical equation matrix using Fourier Transform Infrared spectroscopy. Electronic structure calculations have been performed to identify the possible binding motifs between mathematical equation and mathematical equation . Formation of more than one complex has been confirmed in mathematical equation (X=Br and I) mixture, using the experimental and simulated IR spectra, whereas only one type of complex is found in mathematical equation mixture. Energy decomposition analysis, quantum theory of atoms in molecules, and non-covalent interaction analysis have been performed to understand the nature of interaction and the driving force for complexation under experimental conditions.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 IR spectra of CH2I2 in Ar and N2 cryomatrices: Evidence of unusual band splitting in N2 matrix(Springer, 2022-08) Chakraborty, Amrita; Chakraborty, ShamikMatrix isolation IR spectra of in matrix are analysed using IR spectra obtained in the Ar matrix, quantum chemical calculations, and molecular point group symmetry to determine the origin of the unusual splitting observed in the antisymmetric stretching (), rocking (), wagging (), and antisymmetric stretching () modes of only in matrix and not in Ar matrix. The , , , and vibrational modes belong to either or irreducible representations under point group symmetry. IR spectra in matrix is reported for the first time. IR spectra recorded in Ar matrix are consistent with previous reports. Electronic structure calculations have been performed to obtain simulated IR spectra of with and point group symmetries, conformers, [-], and [-]. IR spectra obtained in Ar and matrices originate from , , and splitting of IR peaks in matrix. Splitting of the IR peaks of in solid state is described by Davydov splitting or factor group splitting. The observed splitting of IR peaks in matrix is due to the lowering of symmetry of from to one of its sub groups due to the perturbation of the rigid matrix that possess quadrupole moment.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 An Exploration of the Hydrogen Bond Donor Ability of Ammonia(Wiley, 2023-07) Chakraborty, ShamikAmmonia is an important molecule due to its wide use in the fertiliser industry. It is also used in aminolysis reactions. Theoretical studies of the reaction mechanism predict that in reactive complexes and transition states, ammonia acts as a hydrogen bond donor forming N−H⋅⋅⋅O hydrogen bond. Experimental reports of N−H⋅⋅⋅O hydrogen bond, where ammonia acts as a hydrogen bond donor are scarce. Herein, the hydrogen bond donor ability of ammonia is investigated with three chalcogen atoms i. e. O, S, and Se using matrix isolation infrared spectroscopy and electronic structure calculations. In addition, the chalcogen bond acceptor ability of ammonia has also been investigated. The hydrogen bond acceptor molecules used here are O(CH3)2, S(CH3)2, and Se(CH3)2. The formation of the 1 : 1 complex has been monitored in the N−H symmetric and anti-symmetric stretching modes of ammonia. The nature of the complex has been delineated using Atoms in Molecules analysis, Natural Bond Orbital analysis, and Energy Decomposition Analysis. This work presents the first comparison of the hydrogen bond donor ability of ammonia with O, S, and Se.Item Novel intermolecular C–H Se hydrogen bond interaction: a matrix isolation infrared spectroscopic study(Springer, 2024-02) Chakraborty, ShamikUnderstanding the nature of selenium centred hydrogen bond is a growing field of research. Intermolecular hydrogen bond has not yet been investigated experimentally in aromatic molecules. The current work aims at understanding the nature and origin of hydrogen bond interaction between phenylacetylene () and dimethyl selenide (). The 1:1 complex of [] is formed in nitrogen matrix at 14 K and probed using infrared spectroscopy. The experimentally obtained infrared spectra have been corroborated with simulated spectra. The nature of the complex has been delineated using Atoms in Molecules (AIM) theory, Natural Bond Orbital (NBO) analysis, and energy decomposition analysis by Symmetry Adapted Perturbation Theory (SAPT).Item Presenting a new fluorescent probe, methyl(10-phenylphenanthren-9-yl)sulfane sensitive to the polarity and rigidity of the microenvironment: applications toward microheterogeneous systems(RSC, 2024) Murugesan, Sankaranarayanan; Chakraborty, ShamikA molecule, methyl(10-phenylphenanthren-9-yl)sulfane (MPPS), with a straightforward structure, has been synthesized, characterized, and explored as a new fluorescent probe for microheterogeneous systems. The photophysical properties of MPPS have been studied through experimental and theoretical calculations using the range-separated hybrid functional CAM-B3LYP in conjunction with a 6-311++g(d,p) basis set. Theoretical calculations show that the freely rotating phenyl ring forms a 94° dihedral angle with the phenanthrene ring in the ground state. Experimentally found two absorption bands correspond to the n → π* and π → π* transitions supported by the frontier molecular orbital calculations. Two excited singlet states, E-1 and E-2 (the former being more stable than the latter in the gas phase), exist with dihedral angles between the phenyl and phenanthrene rings as 142° and 133°, respectively, in the gas phase. Two emitting states in a condensed medium of varying polarities are supported by the steady-state fluorescence and fluorescence intensity decay data. Emission energies, fluorescence intensities, and excited singlet state lifetimes change with the polarity of the solvents. To support that the free rotation in the molecule is responsible for these changes, the fluorescence properties of another molecule, methyl(10-(o-tolyl)phenanthren-9-yl)sulfane (MTPS), with restricted rotation of the substituted benzene, i.e., o-tolyl ring have been studied. The fast-intensity decay component of MPPS is ascribed to the conformer in the E-1 state. The molecule has proved to be an excellent polarity probe explored to determine the critical micelle concentrations (cmc) values of different surfactants, which agree well with the literature reports. Different regions of binding isotherm (specific, non-cooperative, cooperative, and massive binding) of a gemini surfactant, 12-6-12,2Br− with bovine serum albumin (BSA) have been successfully demonstrated by the steady-state and time-resolved fluorescence and fluorescence anisotropic properties of MPPS. Docking results show that MPPS resides in the hydrophobic pocket of BSA. The fluorescence quenching of BSA by MPPS reveals the location of Trp residues of BSA. Thus, a polarity and molecular rigidity-sensitive fluorescent molecule, MPPS has been presented here that can potentially be used to monitor the changes in the microenvironment of biomolecules in different processes.Item IR spectra of in Ar and cryomatrices: Evidence of unusual band splitting in matrix(Elsevier, 2022-08) Chakraborty, Amrita; Chakraborty, ShamikMatrix isolation IR spectra of in matrix are analysed using IR spectra obtained in the Ar matrix, quantum chemical calculations, and molecular point group symmetry to determine the origin of the unusual splitting observed in the antisymmetric stretching (), rocking (), wagging (), and antisymmetric stretching () modes of only in matrix and not in Ar matrix. The , , , and vibrational modes belong to either or irreducible representations under point group symmetry. IR spectra in matrix is reported for the first time. IR spectra recorded in Ar matrix are consistent with previous reports. Electronic structure calculations have been performed to obtain simulated IR spectra of with and point group symmetries, conformers, [-], and [-]. IR spectra obtained in Ar and matrices originate from , , and splitting of IR peaks in matrix. Splitting of the IR peaks of in solid state is described by Davydov splitting or factor group splitting. The observed splitting of IR peaks in matrix is due to the lowering of symmetry of from to one of its sub groups due to the perturbation of the rigid matrix that possess quadrupole moment.