Combined XRD and infrared studies of pyridinium species in (PyH)(3)[PW12O40] single crystals
Résumé
The pyridinium salts of 12-tungstophosphoric acid (PyH)(3)[PW12O40]center dot 2CH(3)CN (1) and (PyH)(3)[PW12O40] (2) have been prepared and studied by single crystal and powder X-ray diffraction (XRD) in order to characterize the crystallographic sites occupied by the pyridinium species. The three PyH+ species are located on two unequivalent sites. Two species are linearly H-bonded to the oxygen atoms of the Keggins unit (alpha species), whereas the third one (beta) forms a bent H-bond. In order to determine the infrared bands characterizing each type of pyridinium species in the 1650-1300 cm(-1) range, infrared spectra have been recorded from room temperature to 100 K. They reveal that only a pyridinium species give rise to the unusual splitting of the PyH+ nu 8b and nu 19b modes, whereas beta pyridinium species lead to a classical pyridinium spectrum.