Relationship between infrared spectra and stoichiometry of pyridine-H3PW12O40 salts using a new TGA-infrared coupling

A new thermogravimetric–infrared coupled apparatus was used to determine the stoichiometry of the pyridinium salts resulting from absorption of pyridine on H3PW12O40 (HPW). Gravimetric measurements showed that two pyridinium salts with definite stoichiometry—(Py2H+)3PW12O40 (bis-pyridinium salt) and (PyH+)3PW12O40 (mono-pyridinium salt)—are formed. Their infrared spectra closely correspond to those reported for pyridinium salts in strong acid solutions. The splitting of the ν8b and ν19b bands of absorbed pyridine (1610–1603 cm−1 and 1540–1532 cm−1, respectively) is characteristic of mono-pyridinium formation in the HPW structure.