Antraptseva, N. M.

Solod, N. V.

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Particular features of crystallization and chemical nature of diphosphates in the system MnSO4 – СоSO4 – K4P2O7 – H2O

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Particular features of crystallization and chemical nature of diphosphates in 
the system MnSO4 – СоSO4 – K4P2O7 – H2O 
N. V. Solod, N. M. Antraptseva  
Department of General Chemistry, National University of Life and Environmental Sciences of 
Ukraine, Kiev, Ukraine, e-mail: Tkachova_Nadya@ukr.net 
Individual cobalt(ІІ) and manganese(ІІ) diphosphates are used as a basis of various modern ma-
terials such as catalysts in organic synthesis, corrosion-resistant coatings, components of lubricating 
fluids etc. It is perspective to synthesize solid solution based on Co(ІІ) and Mn(ІІ) diphosphates with 
a variable Co : Mn ratio on purpose to improve physicо-chemical and production characteristics of 
the materials. The aim of this work was to find out the conditions of synthesis of solid solutions 
based on hydrated manganese(ІІ) and cobalt(ІІ) diphosphates and to determine their chemical nature. 
Мn2-xСоxP2O7·5H2O and Со2-xМnxP2O7·6H2O diphosphates were synthesized by interaction of 
the mixture of manganese(ІІ) and cobalt(ІІ) sulfates in the water solutions with  potassium diphos-
phate solution, taken in a certain ratio. The most significant parameters of their synthesis has been 
established that appeared to be the atomic ratio of components in initial solutions n = Р2О74-: ΣМe2+  
= 0.25; К = Мn : Со = 9,000,02; concentration of solutions equal to 0.1 mole/l; duration of contact 
between a solid phase and a parent solution enough to achieve the equilibrium; temperature of 
293─298 K. Using a complex of chemical and physicо-chemical methods of research it was estab-
lished that Мn2-xСоxP2O7·5H2O and Со2-xМnxP2O7·6H2O present solid solutions of substitution with 
limited solubility on the basis of diphosphate-matrixes of Мn2P2O7·5H2O and Со2P2O7·6H2O, which 
have different structure. The limits of homogeneity of solid solutions was defined as 0 < х  0,83 and 
0 х  0,23, respectively.  
By X-ray diffraction method it was established that Мn2-xСоxP2O7·5H2O solid solutions crystal-
lize  in  orthorhombic  system  and  they  were  structural  analogs  of  Мn2P2O7·5H2O. Со2-
xМnxP2O7·6H2O solid solutions crystallize in monoclinic system and they are structural analogs of 
Со2P2O7·6H2O. Parameters and the volume of primary cell of the synthesized diphosphates crystal-
line lattice together with correlation between their values and cationic composition of diphosphates 
were determined.  
Detailed analysis of the IR spectra of synthesized diphosphates allowed us to estimate the cation 
nature effect on the energy of hydrogen bonds which is realized in the structure of diphosphates. For 
example, the values of H-bonds energy in Мn2-xСоxP2O7·5H2O vary depending on the composition 
of diphosphates within 9.5─40.8 kJ/mole. With the increase in cobalt(II) content in diphosphates the 
energy of H-bonds increases, causing an increase in the strength of the whole system of H-bonds at 
the transition from Мn2P2O7·5H2O to Мn1,17Co0,83P2O7·5H2O. The influence of the cation nature on 
diphosphate anion was appreciated. It was displayed in the change in the angle of Р–O–Р bridge 
bond. For example, the ∆ values (where ∆ = [νas ─ νs (POP)] : [νas + νs (POP)]) for Со2P2O7·6H2O,   
Co1,80Mn0,20P2O7·6H2O  and  Co1,77Mn0,23P2O7·6H2O are 10.94, 11.02 and 11.08 %. These changes 
in the ∆ value characterize the gradual increase in the Р–O–Р bond angle and in the symmetry of un-
symmetrical Р2О74─ anions. 
Thus, for the first time the hydrated diphosphates of Мn2-xСоxP2O7·5H2O (0<х0,83) and Co2-
хМnхP2O7·6H2O (0х0,23) composition were synthesized by the interaction in the system СоSO4 – 
MnSO4 – K4P2O7 – H2O. They present solid solutions of substitution with the limited solubility, 
which are formed owing to substitutability of isomorphic Mn(II) and Co(II) cations in the structures 
of Мn2P2O7·5H2O and Со2P2O7·6H2О diphosphate-matrixes. Peculiarities of diphosphates crystal-
line structure and their possible effect on physical and chemical properties of substituted diphos-
phates are discussed in the report.  


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Particular features of crystallization and chemical nature of diphosphates in the system MnSO4 – СоSO4 – K4P2O7 – H2O

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