Theoretical study of the anion exchange properties and the thermal decomposition of Zn5(OH)8(NO3)2•2H2O and Zn5(OH)8(NO3)2•2NH3

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)(NO3)(2)center dot 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)(NO3)(2)center dot 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)(NO3)(2)center dot 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. (C) 2015 Elsevier B.V. All rights reserved.