The chemistry of complex compounds has always raised great interest among scientists as a result of the variety of structure, properties and uses of substances in this class. The close relationship between the composition, structure and properties of the secompounds, the mutual influence of ligands and complexing agents makes them interesting objects of scientific research, allowing them to predict and synthesize new coordination substances with pre-planned properties.
We synthesized complex compounds of the composition [M(Thio)n][Fe(CN)5NO]·mH2O, M-Co2 +, Ni2 +, n = 2Cu2 +, Zn2 +, Mn2 +, n = 2,4, m = 1-6. The process of the thermal decomposition of these compounds in an atmosphere of an inert gas (argon) and in air and processes of their thermal transformations is studied by the method of differential thermal analysis. It was established that the thermal stability and character of the thermolysis of the complexes [M(Thio)n][Fe(CN)5NO]·mH2O, M-Co2 +, Ni2 +, n = 2Cu2 +, Zn2 +, Mn2 +, n = 1-3, m = 5 depends on the coordination and reciprocal placement of ligands in the coordination field.
It is shown that the thermolysis of synthesized compounds can proceed in several stages. The first stage is the process of dehydration. The crystallization water is relatively weak with the complex and is isolated during heating. Dehydration of complex compounds is accompanied for all studied substances with a clear endeavor on the DTA curve and the loss of sample mass in the range of temperatures 40-170 ° C, due to the splitting of molecules of crystallization water. The exception is the complexes [Ni(Thio)4][Fe(CN)5NO]·6H2O where thetemperature interval increases slightly in the range 40-180 ° C and [Mn(Thio)2][Fe(CN)5NO]·2H2O, where the temperature intervalis 40-190°C. The second stage is the decomposition of a complex cation. On the curves of DTA synthesized complexes, endo-effects wererecorded in the region 150-200oC, which correspond to the expansion of thiourea. For complexes [Ni(Thio)4][Fe(CN)5NO]·6H2O and [Mn(Thio)2][Fe(CN)5NO]·2H2O, an overlay of endoeffects of dehydration and expansion of thiourea in this region is observed. Deep endoeffects, which are noticeable on the differential-thermal curves of the complexes [M(Thio)n][Fe(CN)5NO]·mH2O in the region of high temperatures (200-500oC), are associated with the complicated decay process of the external spheric thioester-containing cation. Schedule of the anion [Fe (CN) 5NO]2-passes at 320-420°C and ends with the formation of iron and iron carbide at the nitrogen temperature of 800°C. and a partial release of the metal of the complexing agent into the external sphere of the compound. The mathematical treatment of the DTA results by the non-isothermal integral method of the Horowitz-Metzger method allowed us to obtain some kinetic parameters of the dehydration reactions of the synthesized complexes.With the help of calculations, the activation energy, the reciprocal factor and enthalpy are obtained. The process of dehydration for the obtained binuclear complex compounds occurs in a slightly lower temperature range than for the initial cationic complexes. Reducing the activation energy can reduce energy costs for the formation of the activated complex and increase the rate of dehydration. This pattern is related with the replacement of simple anionsCl-, Br- on the complex anion [Fe (CN) 5NO]2-. The complex anion creates a weaker electrostatic field, since it is less polarized. This leads to less water retention and facilitates the process of dehydration.
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