THERMAL TRANSFORMATIONS AND INFRARED STUDIES OF Mn2P2O7 · 2H2O

The thermal dehydration of Mn2P2O7·2H2O was studied, in the range 25–600°C by thermogravimetric analysis (TG-DTG and DSC), x-ray diffraction, and infrared spectroscopy. According to the (TG-DTG and DSC) curves, the dehydration of this salt takes place in two stages. The results of thermal analysis, x-ray patterns, and infrared spectra of this compound heated at different temperatures showed that after dehydration, Mn2P2O7·2H2O decomposes to an amorphous product which crystallizes at 544°C to give anhydrous diphosphate MN2P2O7. The free enthalpy of the dehydration of Mn2P2O7·2H2O and of the formation of Mn2P2O7 have been calculated from thermogravimetric data. The infrared spectroscopic study of Mn2P2O7· 2H2O and of its heated products reveals the existence of the characteristic bands of the P2O7 group (νas POP and νs POP) and showed that the POP angle is bent for the initial product and a linear POP bridge is observed in the diphosphate Mn2P2O7. The infrared spectrum of Mn2P2O7· 2H2O has been interpreted using factor group analysis.

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