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 (ν^as POP and ν^s 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.