Theoretical study of the anion exchange properties and the thermal decomposition of Zn5(OH)8(NO3)22H2O and Zn5(OH)8(NO3)22NH3

Abstract The structures of the hydrated, ammoniated and anhydrous zinc hydroxide nitrate were studied by ab initio density-functional calculations so that some of their properties could be analyzed. The dehydrated structure is not yet refined from x-ray diffraction data and, therefore, several optimization calculations were conducted in order to test different sites to coordinated nitrate anions. Charge difference plots and projected density of states calculations (PDOS) were carried out to solve the interactions between the layers, which occur through the coordinated molecules and the nitrate anions. This result also validated our simulated dehydrated structure. Thermodynamical potentials and entropy of the dehydration and ammonia removal processes were also computed and it could be concluded that the water molecules leave the structure at different temperatures. In the case of Zn 5 (OH) 8 (NO 3 ) 2 2NH 3 , the dehydrated structure cannot be obtained by thermal treatment before the formation of zinc oxide, that was also studied for Zn 5 (OH) 8 (NO 3 ) 2 2H 2 O and its formation temperature corroborated the experimental works. We proposed and studied a chemical equation for the nitrate anion exchange reactions of the Zn 5 (OH) 8 (NO 3 ) 2 2H 2 O using fluoride, chloride, bromide and iodide and it could be concluded that all of the exchanges at 298.15 K are thermodynamically spontaneous.