Spectroscopic characterization, crystallographic elucidation and DFT investigation of 5-fluoro-6-(4-methylpiperazin-1-yl)benzo[d]thiazol-2-amine

• Published in: Journal of molecular structure Vol. 1176; pp. 614 - 621
• Main Authors: Al-Harthy, Thuraya S., Shongwe, Musa S., Husband, John, Stoll, Raphael, Merz, Klaus, Abdel-Jalil, Raid J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2019
• Subjects: 2-aminobenzothiazole; Amino-imino tautomer; DFT calculations; H-bonding interactions; Single-crystal X-ray; H-bonding interactions; Amino-imino tautomer; Single-crystal X-ray; 2-aminobenzothiazole; DFT calculations
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2018.08.080

The spectroscopic features and molecular structure of 5-fluoro-6-(4-methylpiperazin-1-yl)benzo[d]thiazol-2-amine (2-ABT) have been determined. Single-crystal X-ray analysis and vibrational spectroscopy have revealed the existence of 2-ABT in the amino tautomeric form in the solid state. Properties of 2-ABT in solution have been investigated using 1H and 13C NMR spectroscopy along with electronic absorption spectroscopy. The experimental data are complemented by DFT and TD-DFT calculations at the B3LYP/6–311 + g(2d,p) level. TD-DTF-predicted spectroscopic and structural properties for both amino and imino tautomers of 2-ABT are compared with the measured data; no strong evidence for the presence of the imino tautomer is found within the experimental data. Calculated energy differences between the tautomers strongly favour the amino tautomer over the other. Indeed, X-ray crystallography has unequivocally shown the amino tautomer which co-crystallized with one water molecule in the orthorhombic space group Pnna. Analysis of the crystal packing reveals an interesting structural motif which comprises an assemblage of the 2-ABT molecules through π···π stacking interactions. Furthermore, there exist hydrogen-bonding interactions involving the lattice solvent and the amino group along with the benzothiazole nitrogen atom. [Display omitted] •Amino (CNH2)–imino (–CNH) tautomerism.•Spectroscopy and X-ray structure determination.•Density functional and time-dependent DFT calculations.