Chlorination of Pr2O3 and Pr6O11. Crystal structure, magnetic and spectroscopic properties of praseodymium oxychloride

The reactions of Pr₂O₃ and Pr₆O₁₁ with Cl₂(g) were studied thermodynamically and experimentally, and proposed in the systems Pr₂O₃/Cl₂(g) and Pr₆O₁₁/Cl₂(g). A kinetic analysis was performed on Pr₆O₁₁ chlorination, which differs from with other light rare earth oxide chlorinations. The praseodymium oxychlorides obtained by full chlorination of Pr₆O₁₁ at 425 °C and 800 °C are different, being well characterized by X-ray diffraction, scanning electron microscopy, magnetic susceptibility measurements and X-ray photoelectron spectroscopy. The crystal structures of the oxychlorides were refined with the Rietveld method. The comparison between the theoretical magnetic moment of Pr³⁺ and the estimated magnetic moment in the praseodymium oxychloride obtained at 425 °C revealed the presence of Pr³⁺ and Pr⁴⁺, whereas no significant difference was observed between the theoretical and the experimental values of Pr³⁺ obtained for the praseodymium oxychloride prepared at 800 °C. These observations are consistent with the analyses in the X-ray photoelectron spectra for both oxychlorides. Finally, a general formula of PrO_1+xCl is proposed for the oxychlorides synthesized at T < 800 °C.