Shaposhnyk A. Patterns of formation processes and structural features of oxalates MC2O4•nH2O (M=Mn,Co,Ni,Cd), formates M(HCO2)n (М=Ag,Ni) and products of their thermal decomposition

The thesis is devoted to the study of new structures as well as structural features of hydrates, anhydrous oxalates and transition metal formates already known from the literature using modern X-ray diffraction methods using data from scanning electron microscopy and thermogravimetric analysis. Structural data of three polymorphic α', α" and β-modifications of manganese(II) oxalate dihydrate were obtained, which were formed simultaneously during the spontaneous decomposition of manganese(II) oxalate trihydrate crystals. Study of powder samples of manganese(II), cobalt(II) and nickel(II) oxalate dihydrates showed that their structure is disordered. The model of disordering is proposed for calculations and can be used for similar compounds, whereas the existing model of OD-structures is unacceptable for use in the Rietveld method. A new polymorphic modification of anhydrous manganese(II) and cadmium(II) oxalate (γ-MnC2O4 and γ-CdC2O4) was obtained from powder X-ray diffraction data which was formed from thermal decomposition of hydrates and found to be metastable, not densely packed, and to have lower values of density than those of the known modifications. Structure of the β-modification of anhydrous nickel(II) and cobalt(II) oxalates was determined, which were obtained by thermal decomposition of corresponding hydrates. It was shown that the disordering of the structure was preserved during thermal decomposition, and therefore the β-modification can be disordered, contrary to the existing literature data. Crystal structure of the silver(I) formate has been determined whose feature is the formation of Ag–Ag = 2.919 Å clusters, which are also observed in other compounds of this metal. An analysis of this unstable compound structure has shown that its spontaneous decomposition at room temperature leads to the formation of layered metallic silver nanoparticles.