Synthesis, crystal structure, Hirshfeld surface investigation and comparative DFT studies of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate

Abstract

The ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1), a thiazole ester, was synthesized by refluxing 1-(2-nitrobenzylidene)thiosemicarbazide and ethyl bromopyruvate. The compound is characterized by spectrometric, spectroscopic and single crystal (SC-XRD) techniques. Non-covalent interactions that are responsible for crystal packing are explored by Hirshfeld surface analysis. All theoretical calculations were performed by DFT quantum chemical methods using 6-311G(d,p) and cc-pVTZ basis sets and compared. Theoretical harmonic frequencies of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1) were optimized. Confirmation of hydrogen bonding sites was analyzed by molecular electrostatic potential (MEP) and Mulliken population analysis. The vibrational frequencies of characteristic functional groups and chemical shifts were found in good agreement with experimental assignments. Frontier molecular orbital (FMO) revealed relatively small HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gape, which speaks off the nearly planar geometry and extended conjugation, as compared to the substituents with no conjugation possible. It has also been observed that -NO₂ substituent plays a vital role for this relatively small HOMO-LUMO gape and overall electronic properties when compared with similar thiazole carboxylates (2-6, Table 6). Ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1) was also evaluated for its anti-oxidant and anti-microbial activities.

Keywords: Anti-oxidant; DFT calculations; Spectroscopy; Thiazole; XRD.

Scheme 1

Synthesis of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate

Fig. 1

The ORTEP diagram drawn at probability level of 50% for (1). H-atoms are displayed by tiny circles of arbitrary radii

Fig. 2

Packing diagram showing 2D sheet formed by N–H…O, C–H…N and C–H…O bonding for (1)

Fig. 3

Graphical view of π–π stacking interaction for (1). Distance shown is measured in Å. H-atoms are omitted for clarity

Fig. 4

HS plotted over d_norm in the range − 0.5540 to 1.4207 a.u. for (1)

Fig. 5

HS plotted over shape index in the range − 1 to 1a.u. for (1)

Fig. 6

2D plots for (1), a for overall interaction, b–f for major contributor in crystal packing

Fig. 7

a–j 2D plots for minor contributor in crystal packing for (1)

Fig. 8

Percentage contribution of interaction of an atom located inside HS to atoms of molecules located in the surrounding of HS

Fig. 9

Optimized structure of compound (a) 6-311G(d,p) (b) ccPVTZ

Fig. 10

Overlay structure of compound optimized by 6-311G (d,p) and cc-pVTZ method

Fig. 11

Comparison of FT-IR spectra with experiment and calculated values (DFT/B3LYP method with the 6-311G(d,p) and cc-pVTZ basis sets)

Fig. 12

Correlation graphics of calculated and experimental chemical shifts of compound (a) ¹H–NMR (b) ¹³C–NMR by B3LYP/6-311G(d,p)

Fig. 13

Correlation graphics of calculated and experimental chemical shifts of compound (a) ¹H–NMR (b) ¹³C–NMR by B3LYP/cc-pVTZ

Fig. 14

FMOs at B3LYP/cc-pVTZ level

Fig. 15

MEP map of compound in gas phase usingB3LYP/cc-pVTZ

Fig. 16

The Mullikan charges diagram of compound (a) B3LYP/6-311G(d,p) (b) B3LYP/ccPVTZ

Fig. 17

Thermodynamic properties of compound (a) B3LYP/6-311G(d,p) (b) B3LYP/cc-pVTZ