Effect of pyridine on zinc phthalocyanine studied by density functional theory calculations and infrared absorption spectroscopy

In the present work, we have studied the effect of pyridine on the zinc phthalocyanine by recording the infrared absorption and X-ray diffraction spectra with and without pyridine. In the presence of pyridine phase of the crystalline zinc phthalocyanine changes from β to α. Some infrared bands show changes in their positions and/or intensities. These changes have been interpreted on the basis of coordination of the pyridine molecule with the central zinc ion. Coordinated pyridine transfers some of its charge to the π electron system of the phthalocyanine ring through zinc ion. Pyridine molecule also distorts the phthalocyanine molecule by pulling zinc ion out of the phthalocyanine plane. Density functional theory also confirms the ligation of pyridine molecule at the fifth coordination site of the central metal ion.