Browsing by Author "Harmalkar, Sarvesh S."

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    C–H hydrogen bond and halogen bond directed self-assembly of ethereal podands and C–X⋯F−/HF2− halogen bonding in solution
    (Royal Society of Chemistry, 2023) Dutta, Dipjyoti; Gogoi, Anamika; Dutta, Rupjyoti; Harmalkar, Sarvesh S.; Lama, Prem; Dey, Sandeep Kumar
    A series of halogenated podands (P1–P8) have been synthesized from 1,3,5-tris(bromomethyl)mesitylene and halogen-substituted phenols to study the structure-directing roles of C–H hydrogen bonds and halogen bonds in the formation of self-assembled supramolecular frameworks. The ethereal podands are suitable for the study of C–H hydrogen bonds in the crystalline state due to the presence of three different types of C–H donors, such as methyl, methylene, and aromatic –CH groups, and three different types of acceptors such as ethereal oxygen, halogens, and aromatic rings. Single crystal X-ray structures of three halophenyl-functionalized podands (P2, P3 and P4) and a cyanophenyl-functionalized podand (P9) were determined at room temperature (298 K), and detailed Hirshfeld surface analysis of the crystal structures was performed to quantify the close contact contributions (in %) from different types of non-covalent interactions involved in the self-assembly of podands. The crystal structures of the halophenyl-functionalized podands (P2, P3, and P4) showed self-assembly primarily via intermolecular C–H⋯O, C–H⋯π, and halogen bonding interactions. Hirshfeld surface analysis of the crystal structures revealed significantly higher contributions from H⋯C and H⋯X (X = halogen) close contacts in comparison to H⋯O and X⋯C close contacts in 2D-fingerprint plots. The self-assembly of the cyanophenyl-functionalized podand (P9) was largely governed by intermolecular C–H⋯O and C–H⋯N interactions. The podand crystals showed relatively high thermal stability in thermogravimetry analysis (250–290 °C), which can be attributed to the hydrogen and halogen bond assisted formation of 3D supramolecular frameworks. 19F-NMR spectra of tetraethylammonium fluoride in the presence of an equivalent amount of tris(2-halophenoxymethyl)mesitylene podand (P5 or P6) showed a downfield shift of the fluoride signal (Δδ 3.2 ppm) indicating C–X⋯F− halogen bonding in solution. Further, 19F-NMR spectra of hydrogen bifluoride (HF2−) in the presence of P5 or P6 showed a large upfield shift of ≈21–22 ppm suggesting C–X⋯F−⋯H–F halogen bonding in solution.
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    Experimental and Theoretical Investigation on the Extractive Mass Transfer of Eu3+ Ions Using Novel Amide Ligands in 1-Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide
    (American Chemical Society, 2023) Ghosh, Ayan; Pandey, Amit; Sengupta, Arijit; Kathirvelu, Velavan; Harmalkar, Sarvesh S.; Dhuri, Sunder N.; Singh, Keisham S.; Ghanty, Tapan K.
    Novel amide ligands in the ionic liquid (1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) were utilized for the liquid–liquid biphasic mass transfer of Eu3+ ions from aqueous acidic waste solution. The cation exchange mechanism was found to be operative with the formation of [Eu(NO3)2L3]+ species (L = 4-chloro-N-(1-methyl-1H-pyrazol-3-yl)picolinamide). However, the presence of an inner-sphere water molecule was revealed by density functional theory (DFT) calculations. The viscosity-induced slower kinetics was evidenced during mass transfer, which was improved by increasing temperature. The process was exothermic in nature. The improvement in the kinetics of extractive mass transfer at higher temperatures is evinced by a reduction in the distribution ratio value. The spontaneity of the reaction was evidenced through the negative Gibbs free energy value, whereas the process enhances the entropy of the system, probably by releasing water molecules at least partially during complexation. The structures of bare ligands and complexes have been optimized by using DFT calculations. A high value of complexation energy, solvation energy, and associated enthalpy and free energy change reveal the efficacy in binding Eu with O and N donor atoms. In addition, natural population analysis, atoms-in-molecules analysis, and energy decomposition analysis have been employed to explore the nature of bonding existing in Eu–O and Eu–N bonds.