Pradip Kumar Mondal

Quantitative Investigation of the Structural, Thermal, and Mechanical Properties of Polymorphs of a Fluorinated Amide

The discovery of three polymorphs of N-(3,5-difluorophenyl)-2,4-difluorobenzamide, of which two exist as concomitant polymorphs, highlights the significance of short, linear C-H⋅⋅⋅F intermolecular interactions in the solid state. The formation of these polymorphs can be regulated by monitoring the scan rate in differential scanning calorimetry. The phases have been characterized structurally and the investigation of the mechanical properties depicts that Form 1 is stiffer and harder than Form 2 by 50 % and 33 %, respectively.

Quantitative characterization of new supramolecular synthons involving fluorine atoms in the crystal structures of di- and tetrafluorinated benzamides

Strong hydrogen bonds play a significant role in crystal packing. In particular, the involvement of interactions involving fluorine in controlling the crystal packing requires appropriate attention, especially in the presence of other strong hydrogen bonds. In the present study, a detailed quantitative assessment has been performed of the nature, energetics and topological properties derived from the electron density in model compounds based on fluorinated benzamides (a total of 46 fluorine-substituted benzamides containing multiple fluorine atoms) in the solid state. The primary motivation in the design of such molecules is to enhance the acidity of the interacting H atoms in the presence of an increasing number of F atoms on the molecular scaffold, resulting in increased propensity towards the formation of intermolecular interactions involving organic fluorine. This exercise has resulted in the identification of new and frequently occurring supramolecular synthons involving F atoms in the packing of molecules in the solid state. The energetics associated with short and directional intermolecular Csp2-H...F-Csp2 interactions with significantly high electrostatic contributions is noteworthy, and the topological analysis reveals the bonding character of these ubiquitous interactions in crystal packing in addition to the presence of Csp2-F...F-Csp2 contacts.

Metal-free Annulation at the Ortho- and Bay-Positions of Perylene Bisimide Leading to Lateral π-Extension with Strong NIR Absorption

A novel ortho/ bay annulation reaction of perylene bisimide (PBI) has been explored in a single step synthetic procedure using perylene bisimide 1 and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) in the absence of any metal catalyst. The single crystal solid-state X-ray diffraction structure showed a distorted framework of DBU-fused PBI 2. Compound 2 exhibited intense near-infrared absorption up to 950 nm. Reversible protonation and deprotonation accompany drastic changes in the photophysical characteristics. Further, the reaction of perylene biscarboxyanhydride with DBU offered a caprolactam ring-substituted perylene bisimide 3.

Capturing the metastable state in the spontaneous and reversible single-crystal-to-single-crystal phase transition of riluzolium oxalate

A spontaneous and reversible single-crystal-to-single-crystal (SCSC) polymorphic transition via a disordered state has been captured in a salt, riluzolium oxalate, with no categorical loss in the quality of the crystals. Variable-temperature powder X-ray diffraction (VTPXRD) experiments provide additional support for the observed SCSC transition. The conformational change, along with the more efficient packing at 100 K, is the driving force for the event.

Larvicidal study of tetrahydropyrimidine scaffolds against Anopheles arabiensis and structural insight by single crystal X-ray studies

A series of methyl or ethyl 4‐(substitutedphenyl/pyridyl)‐6‐methyl‐2‐oxo/thioxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylate (HPM) analogues 4a–g were synthesized and evaluated for larvicidal activity against Anopheles arabiensis. These newly synthesized compounds were characterized by spectral studies such as FT‐IR, NMR (1H and 13C), LC‐MS, and elemental analysis. The conformational features and supramolecular assembly of molecules 4a, 4b, and 4e were further analyzed from single crystal X‐ray study. The larvicidal activity of these tetrahydropyrimidine pharmacophore series was analyzed based on their relative substituents. Among the synthesized HPM analogous from the series, compounds 4d and 4e both having electron withdrawing chlorine group on phenyl ring at the fourth position of the tetrahydropyrimidine pharmacophore exhibited the most promising larvicidal activity.

Supramolecular synthons involving fluorine atoms in crystal structures of fluorobenzamides

The presence of both strong and weak intermolecular interactions has been observed to play a significant role in the crystal packing [1]. The systematic evaluation of the role of intermolecular interactions involving fluorine in crystal packing requires special mention, in particular, in the presence of other stronger intermolecular force(s) like strong hydrogen bonds [2]. In the present study, detailed crystallographic investigations (molecular conformation and crystal packing analysis) have been carried out on model compounds based on fluorinated benzamides. Herein we have synthesized a total of 46 benzamides containing multiple fluorine atoms, and these have been characterized using 1H NMR, IR, single crystal, and powder X-ray diffraction techniques. In addition, the melting points were determined by DSC. A plethora of weak interactions, namely C(sp2)-H•••FC(sp2), C(sp2)-F•••F-C(sp2) and C(sp2)-F•••π are involved in crystal packing in the presence of strong N-H•••O hydrogen bonds and π•••π contacts. The energetics associated with these intermolecular interactions are quantitatively assessed using PIXEL calculations. Complete topological analyses were used to characterize these interactions and identify the frequently occurring supramolecular synthons [Figure 1A and 1B], involving the fluorine atom (C-H•••F-C, C-F•••F-C, and C-H•••H-C). The deformation density and fingerprint analysis were performed to study the nature and evaluate the quantitative contribution of the interactions towards the crystal packing [3].

Structure analysis of hydroxy/non-hydroxy substituted dihydropyrimidine molecules

Keshab Mangal Bairagi1, Katharigatta N. Venugopala2, Pradip Kumar Mondal3, Deepak Chopra3, Bharti Odhav2, Susanta K. Nayak1 1Department Of Chemistry, Visvesvaraya National Institute Of Technology, Nagpur, Nagpur, India, 2Department of Biotechnology and Food Technology, Faculty of Applied Sciences, Durban University of Technology, Durban, South Africa, 3Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhauri, Bhopal, India E-mail: k100bairagi@gmail.com