The Novel Crystal Structure with Zr₆O₄(OH)₄ Core and Hydrazine Carboxylate Ligands, and its Thermal Properties

Abstract

The title compound, [Zr₆(OH)₄O₄(N₂H₃COO)₁₂]·14H₂O, was prepared with a novel multi-step synthetic pathway. The structure contains a {Zr₆(μ₃-OH)₄(μ₃-O₄)}¹²⁺ core on which twelve hydrazine carboxylate anions are bound to form neutral coordination molecules. The coordination mode of carboxylate ligand is exclusively N,O-bidentate chelating, which is observed for the first time in this class of compounds. The title compound is also the first example of isolated Zr(IV) oxo clusters with cubic symmetry. The structure is stabilized with an extensive hydrogen bond network between coordination and water molecules, and amongst the solvent water molecules themselves. Thermogravimetric studies have shown that the prepared [Zr₆(OH)₄O₄(N₂H₃COO)₁₂]·14H₂O decomposed in several consecutive steps characterized by evolution of H₂O, CO, CO₂, N₂ and H₂, finally yielding ZrO₂. The decomposition mechanism is rather complex and includes the formation of a series of amorphous intermediates.