Zirconium and hafnium tert-butoxides and tert-butoxo-β-diketonate complexes – Isolation, structural characterization and application in the one-step synthesis of 3D metal oxide nanostructures

Long term storage of the pure commercial Zr(OtBu)4 in a sealed ampoule results in crystallization of a new high symmetry phase of Zr3O(OtBu)10 (1). Modification of Zr(OtBu)4 and Hf(OtBu)4 with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) produces dependent on the stoichiometry two types of derivatives, M(OtBu)2(thd)2 (2, 3) and M(OtBu)(thd)3 (4, 5) M = Zr(2, 4), Hf(3, 5), which have all been characterized by NMR and mass-spectral studies and for 4 and 5 also by complete X-ray single crystal studies. The latter failed for 2 and 3 in the view of their poor X-ray reflectivity. Addition of minor amounts of n-C5H11OH to 3 resulted in isolation of an unusual heteroleptic complex Hf2(OH)(OnC5H11)(OtBu)2(thd)4 (6). Thermal decomposition of compounds 1 and 3 in nitrogen atmosphere was studied for different thermal regimes by TGA-FTIR approach, revealing in all cases the formation of tetragonal ZrO2 and monoclinic HfO2 respectively, along with iso-butene, butanol and water for 1 and the same mixture including also Hthd for 3. Decomposition of 3 occurred always through intermediate melting, while higher heating rate for 1 permitted to achieve decomposition on in situ evaporation resulting in 3D hedgehog nanostructures according to SEM.

The paper reports structure and reactivity for tert-butoxide complexes of Zr(IV) and Hf(IV) in the solid state and solution. Thermal decomposition of Zr3O(OtBu)10 produces spontaneously the hedgehog type nanostructures.Figure optionsDownload as PowerPoint slideHighlights
► New modification of zirconium oxo-tert-butoxide was structurally characterized.
► Zirconium and hafnium t-butoxides were modified with Hthd β-diketonate ligand.
► Formed alkoxide β-diketonates belon to two families M(OtBu)2(thd)2 and M(OtBu)(thd)3.
► Unusual asymmetric byproduct Hf2(OH)(OnC5H11)(OtBu)2(thd)4 has been isolated and structurally characterized.
► Solution and solid state stability of tert-butoxide β-diketonates was investigated by NMR and mass-spectrometry.
► MOD treatment of the obtained precursors provides MO2 oxides with nano-hedgehog morphology for Zr3O(OtBu)10 as starting material.