The synthesis, spectroscopic properties, and suitability for use as precursors in atomic layer deposition (ALD) processes are described for the ZrCp3 and HfCp3. ZrCp3 was prepared by a literature procedure entailing reduction of ZrCp4 with potassium graphite and was isolated as brown crystals in 34% yield. HfCp4 was isolated in 57% yield as yellow-brown crystals by a similar route employing reduction of HfCp4 with potassium graphite. ZrCp3 and HfCp3 showed broad paramagnetic resonances in the 1H NMR spectra that were centered at δ 6.2 and 6.0ppm, respectively, which are assigned to the cyclopentadienyl hydrogen atoms. Additionally, the 1H NMR spectra of the ZrCp3 and HfCp3 crystals revealed resonances arising from the diamagnetic complexes Cp3ZrH and Cp3HfH, which are proposed to arise from hydrolysis of ZrCp3 and HfCp3 by traces of water in the NMR solvent. The identities of ZrCp3 and HfCp3 were established by determination of their x-ray crystal structures, which exactly matched previously reported molecular structures. Thermogravimetric analyses of ZrCp3 and HfCp3 were conducted to assess their volatilities and thermal stabilities. ZrCp3 showed the onset of mass loss at about 125 °C and revealed a single-step evaporation up to about 225 °C, at which point decomposition limited further mass loss. Mass loss for HfCp3 started at about 150 °C and continued up to about 270 °C, at which point decomposition limited further mass loss. ZrCp3 and HfCp3 decomposed extensively during preparative sublimation experiments at 0.5 Torr, and do not appear to have promising properties as ALD precursors.
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