ИСТИНА

This work is dedicated to the synthesis of metal trifluoroacetate hydrates of several 3d-metals (NiII, CoII, MnII, CrIII and FeIII) and the investigation of their thermal decomposition in order to obtain corresponding complex fluorides with the composition Na2MIIMIIIF7. Trifluoroacetate hydrates of manganese, cobalt and nickel were obtained by the interaction of basic carbonates of corresponding metals with trifluoroacetic acid; and trifluoroacetate hydrates of chromium and iron – by the reaction of their hydroxides (precipitated by ammonia from the nitrate solution) with trifluoroacetic acid. Chemical composition of the obtained hydrates was confirmed by the titrimetric method. XRD analysis revealed the identity of their structures to the corresponding ones described by other authors [1]. The process of thermal decomposition of the metal trifluoroacetate hydrates was investigated in air and in argon flow by means of thermogravimetric and differential thermal analysis. According to these data, a decomposition process consists of two main stages. The first one is connected with the loss of crystallohydrate water while the second one – with the decomposition of trifluoroacetic group to fluoride one. It is interesting to note that the influence of decomposition atmosphere is negligible for the nickel compound only. However, even in this case, the difference appeared at T > 500C. This can be attributed to the process of pyrohydrolysis of obtained products. According to TG-MS analysis of evolved gases, the main gaseous products of these thermal decomposition processes are water vapor, carbon dioxide and various fluorocarbons. The relative amount of these gases gave additional information about the processes occurred during the decomposition. Along with individual metal trifluoracetate hydrates, a thermal decomposition of their mixtures with and without β-cyclodextrin was also studied. XRD analysis of thermolysis products and intermediates demonstrated the absence of oxide phases among thermolysis products at T = 400 and 700C in all cases. Along with Na2MIIMIIIF7, these products usually contained Na3M(III)F6, NaM(II)F3, M(II)F2 and M(III)F3. The smallest amount of secondary phases was observed at 400 °C for MIII = Fe and MII = Ni, Co. According to previous studies [2,3], a synthesis of Na2NiFeF7 and Na2CoFeF7 by the solid state method in noble metal ampoules demands a continuous reaction time (4 days at T = 800C) and is also accompanied by the formation of secondary phases. The present study demonstrated a possibility to obtain these complex fluorides within 4 hours due to the application of the modern soft chemistry synthesis techniques.