СOMPOSITION AND THE CHEMICAL NATURE OF PRODUCTS OF INTERACTION IN SYSTEM CoSO4 – ZnSO4 – K4P2O7 – H2O

Abstract

Hydrated cobalt (II) and zinc diphosphates are used as a basis of of various modern materials: luminescent materials, catalysts of organic synthesis, pigments, heat-sensitive paints, corrosion-resistant coatings etc. Use for this solid solutions of cobalt (II) and zinc diphosphates, which contain both cations will create materials with a forecast complex of improved physicо-chemical and production characteristics. For practical implementation synthesis of solid solution of hydrated cobalt (II) and zinc diphosphates of given composition necessary to know the correlation between the conditions of its preparation, composition and properties. There are any data on the interaction of the system CoSO₄ – ZnSO₄ – K₄P₂O₇ – H₂O in literature. The purpose of this work - identify the chemical nature of the products of interaction in the system CoSO₄ – ZnSO₄ – K₄P₂O₇ – H₂O.

As parameters, providing a common deposition Co²⁺ and Zn²⁺ in the system CoSO₄ – ZnSO₄ – K₄P₂O₇ – H₂O, defined as follows: concentration of solutions - 0.1 mole/l; a ratio in composition of initial solutions n = P₂O₇^4-/åСо²⁺, Zn²⁺ = 0.2; 4.00 £ К= Со²⁺/Zn²⁺ £ 49.00; duration of contact of a solidphase with a mother solution – on achievement of equilibrium; temperature - 293-298 K.

The results of chemical analysis of the equilibrium solid phase obtained for all values K of field 4.00£К£49.00 including the case when Zn²⁺ as part of the initial solution is absent, indicate precipitation of diphosphates (atomic ratio n₁ = Р/ΣСо, Zn = 1.00). They anionic composition at 98.7-99.2 %. presented diphosphate anion. Diphosphates cationic composition is determined by the K consisting of the initial solution and it is proportional to the content of Co²⁺ and Zn²⁺. The water content of diphosphate obtained under conditions 9.00£К£49.00 virtually unchanged and corresponds to the value set Co₂P₂O₇·6H₂O (incl substitution proportion of Co(II) to Zn). In diphosphate, which are deposited at 4.00£К<9.00, H₂O content of 5 - 6% lower compared with the first group diphosphate.

As a result of X-ray diffraction analysis diphosphate, which formed in the absence of Zn²⁺, identified as cobalt(II) diphosphate hexahydrate. The diphosphates, which containing simultaneously two cations (4.00£К<9.00), are divided into two different groups for the phase composition. The first of them belong diphosphates that are deposited under conditions of 9.00£К≤49.0, the second - 4.00£К<9.00. X-ray characteristics of the first group diphosphates are similar to each other and corresponds to Со₂Р₂O₇·6H₂O. X-rays of diphosphate obtained at K = 5.67 and 4.00, clearly recorded the presence of a second crystalline phase of structure Zn₂P₂O₇·5H₂O. Any phase composition of the two groups diphosphates clearly reflected in their IR spectrums. Shapes of the curves, set the intensity maxima and absorption bands in the IR spectrums diphosphate obtained at 9.00£К≤49.0, identical to each other and correspond to a known individual Со₂Р₂O₇·6H₂O. IR spectrums of diphosphates of second group have certain features characteristic of a mechanical mixture of two phases with different structures - Со₂Р₂O₇·6H₂O and Zn₂P₂O₇·5H₂O. Most clearly, they are recorded in the vibrations of water molecules, where the absorption curve looks like a total envelope of vibrations ν(OH) belonging diphosphates of different hydrated.

Using complex physical and chemical methods revealed that during the interaction in the system CoSO₄ – ZnSO₄ – K₄P₂O₇ – H₂O formed limited solid solution substitution of general formula Со_2-хZn_хР₂O₇·6H₂O (0<x£0.39) The composition of the saturated solid solution corresponds diphosphate Co_1.61Zn_0.39P₂O₇·6H₂O. It is formed as a result of isomorphic substitution of Co(II) in the structure diphosphate-matrix - Со₂Р₂O₇·6H₂O in Zn. Attempts to replace Zn over 6.31 mas.% of Co(II) lead to the deposition of a mechanical mixture of two crystalline phases - saturated solid solution substitution Co_1.61Zn_0.39P₂O₇·6H₂O and phase structure Zn₂P₂O₇·5H₂O. Со_2-хZn_хР₂O₇·6H₂O (0<x£0.39) crystallize in the monoclinic system (sp. gr. Р2₁/n, Z=4). For saturated solid solution of composition Co_1.61Zn_0.39P₂O₇·6H₂O the unit cell parameters are, nm: a = 0.7199 (3), b = 1.8356 (4), c = 0.7680 (3), V = 1.0410 нм³, β = 92.25⁰ (5). In the IR spectrums of Со_2-хZn_хР₂O₇·6H₂O (0<х£0.39) presence of isomorphous cations (Zn²⁺) recorded a slight shift of the bands ν (OH) in the high-frequency region of the spectrum. Evaluation of H-bonds energy indicates the existence of a structure of diphosphates of solid solution the system rather strong H-bonds, which differ in energy (from 11.3 to 43.3 kJ/mole) and directivity. The three components of the band δ(Н₂О) indicate the presence in the diphosphate structure of three types of crystallographical non-identical molecules of crystalline hydrate water. Number of absorption bands in the fluctuations groups of P₂O₇^4- indicates low symmetry of diphosphate anion, which is characteristic curved bridge configuration Р–О–Р. POP angle is less than 160⁰ and in diphosphates of solid solution Со_2-хZn_хР₂O₇·6H₂O (0<х£0.39) of different composition does not change.