Antraptseva, N. M.

Koval, L. B.

Solod, N. V.

BSU Digital Library

 36 
On the participation of crystalline hydrate water  
in the solid phase Mn2P2O7 · 5H2O hydrolysis 
L. B. Koval1, N. M. Antraptseva2, N. V. Solod2 
1V.I. Vernadskii Institute of General and Inorganic Chemistry NAS of Ukraine, Kyiv, Ukraine, 
2National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine  
  e-mail: koval@ionc.kiev.ua 
Dehydration of hydrated salts is often accompanied by their solid-phase hydrolysis. It causes 
significant complications of thermal and structural transformations of crystalline hydrates, in 
particular the phenomenon of polycondensation of phosphate anion. However, it is not insuffi-
ciently studied. 
The purpose of this work is to establish the sequence of thermal and structural transfor-
mations accompanying thermolysis of Mn2P2O7 · 5H2O and the participation of crystalline hy-
drate water in its solid phase hydrolysis. 
Thermolysis of Mn2P2O7 · 5H2O was studied in the range of 298–1273 K under dynamic and 
quasi-isothermal heating conditions (derivatograph Q-1500D). Heat treatment products were ob-
tained at temperatures of thermal effects on DTA curves and identified using methods of analy-
sis: chemical, X-ray phase analysis, infrared spectroscopy. 
According to thermoanalytical experiment, the removal of 1.44 moles of H2O from Mn2P2O7 
· 5H2O (first stage of dehydration) occurs by the molecular mechanism. The main structural mo-
tif of the original crystalline hydrate is retained. Structural changes are recorded by removing 
3.96 moles of H2O (second stage of dehydration). Heating Mn2P2O7 · 5H2O to 463 K results in 
the formation of a mixture of two solid phases: Mn2P2O7 · 2H2O (38.2 wt. % in terms of P2O5) 
and X-ray amorphous monophosphate (8.7 wt.%). Its formation is due to the hydrolytic breaking 
of P–O–P bonds with the participation of crystalline hydrate water. 
The composition of the products of Mn2P2O7 · 5H2O heating to 573 K is the most complex. 
In addition to mono- (11.5 wt. %) and diphosphate anion (32.1 wt. %), they contain phosphate 
with higher degree of polycondensation that is triphosphate (4.3 wt.%). Interpretation of the re-
sults shows the realization of a dissociative mechanism of water removal, which leads to solid-
phase hydrolysis of the salt. The first step of this process is the formation of the groups of P–OH 
and M–OH type. They are capable to polycondensation at higher temperatures. 
Using the maximum degree of polycondensation (n) as a measure of the solid-phase hydrol-
ysis degree, it was found that in case of Mn2P2O7 · 5H2O  thermolysis n = 3 that is 2.0–2.5 times 
lower than in case of Co2P2O7 · 6H2O thermolysis when n = 7. The obtained data are correlating 
with the energy state of crystalline hydrate water in these diphosphates. The energy  of  H-bonds  
in the  structure  of  Mn2P2O7 · 5H2O  is  40 kJ/mol, and in that of Co2P2O7 · 6H2O it makes 45 
kJ/mol. This leads to a stronger phosphate anion polymerization. 
The removal of another portion of crystalline hydrate water from Mn2P2O7 · 5H2O in the 
range of 573–603 K leads to a simplification of the anionic composition of the thermolysis prod-
ucts. Owing to their solid-state interaction, the final product, anhydrous crystalline diphosphate 
Mn2P2O7, is formed. 
The formation of Mn2P2O7 takes place by two routes at the same time. The first route in-
volves the classical thermal dehydration of Mn2P2O7 · 5H2O (it is realized at 70 %). According to 
the second route, up to 30 % Mn2P2O7 is formed as a result of solid-phase hydrolysis of Mn2P2O7 
· 5H2O involving crystalline hydrate water.  


On the participation of crystalline hydrate water  in the solid phase Mn2P2O7 · 5H2O hydrolysis

http://elib.bsu.by/bitstream/123456789/115539/1/out022.pdf

On the participation of crystalline hydrate water in the solid phase Mn2P2O7 · 5H2O hydrolysis

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