Sparfloxacin charge transfer complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tetracyanoquinodimethane: Molecular structures, spectral, and DFT studies

•Quantitative analysis of sparfloxacin was done through CT formation.•Structural studies of CT complexes was done using spectral methods.•Sensitivity, reproducibility and accuracy of the reported complexes were recorded.•No interference from the studied excipients was found.•TD-DFT assigned perfectly the bands due to CT.

A simple, sensitive and rapid method was developed for the quantitative analysis of sparfloxacin in its pharmaceutical formulations through the formation of charge transfer complexes with π-acceptor systems. The Lambert–Beer’s law was obeyed in the concentration ranges of 7–70 and 10–50 μg/mL sparfloxacin for 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tetracyanoquinodimethane. Structural characterization of the isolated solid CT complexes was carried out by IR, 1H NMR, UV–Vis. and MS. The experimental studies were complemented by quantum chemical calculations at DFT level of theory. The electronic structures were investigated by TD-DFT calculations. Natural bond orbital analysis and molecular electrostatic potential maps were helpful in assigning the CT route. The formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy and ionization potential were calculated.

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