Crystal structure and solid-state transformations of Zn–triethanolamine–acetate complexes to ZnO

Abstract

The rapid and massive formation of a foamy precipitate while reacting zinc acetate (Zn(Ac)₂) and triethanolamine (TEA) in proper conditions led to an unravelled complex and a molecular tetra-metallic zinc cluster: their synthesis was optimised and they were characterised by single crystal X-ray diffraction. The structure shows the direct link of the acetate anion to the Zn cation, a feature not observed in parent compounds. The structural and chemical evolution of these materials upon heating have been studied, targeting the production of zinc oxide thin films or particles with particular properties. The phase transitions occurring during thermal treatments and the conversion to ZnO were studied by in situ X-ray powder diffraction, thermo-gravimetry and Raman spectroscopy. The cluster structure can be considered an even more interesting precursor for zinc oxide as nano-aggregates of four ZnO moieties are already present and the formation of ZnO particles requires a smaller number of broken and newly formed bonds. A third metastable hydrated phase was identified, but not structurally characterised because of its instability, thus completing the exploration of the polymorph landscape of the title compound.