Spectroscopic studies and molecular orbital calculations on the charge transfer reaction between DDQ and 2-aminopyridine

• CT-complex between DDQ and 2AP was studied spectrophotometrically.
• The studies included estimation of formation constant and molecular composition.
• Molecular orbital calculations have been carried out using GAMESS computations.
• The computations included Mulliken charges, molecular geometry and infrared spectra.
• Good correlation exists between theoretical and experimental results.

Charge transfer complex formation between 2-aminopyridine (donor, 2AP) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (acceptor, DDQ) has been studied spectrophotometrically in acetonitrile (CH3CN). The newly formed CT-complex has reddish brown color and is characterized by the appearance of new absorption bands in the 375–650 nm regions where acceptor and donor do not have any absorption. Maximum and constant absorbance of the complex was obtained after 10 min at 20 °C with 1 mL 5 × 10−3 M DDQ in CH3CN. Based on photometric titration method, the stoichiometry of the formed CT-complex was found to be 1:1 [(2AP)(DDQ)]. Minimum–maximum absorbances method has been applied to estimate the formation constant of the complex where it recorded large value confirming its high stability. Molecular orbital calculations utilizing GAMESS computations were carried out in order to record changes in the electronic structure and molecular geometry of the formed CT-complex. In addition, the infrared vibrational frequencies of the complex were computed and compared with experimental results.

Computed Infrared spectrum of 2AP-DDQ charge transfer complex.Figure optionsDownload as PowerPoint slide