Synthesis of volatile zinc precursors with pyrrolide-Imine ligands

Precursors for thin-film deposition have gained increasing research interest, driven by their industrial significance. Herein, we describe the synthesis and characterization of a family of Zn complexes for ZnO fabrication via CVD, ALD/ALE, and MLD. Four zinc complexes possessing pyrrole moieties, Zn(L1)₂ to Zn(L4)₂ (L1H = N-tert-butyl-1-(1H-pyrrol-2-yl)methanimine, L2H = N-tert-pentyl-1-(1H-pyrrol-2-yl)methanimine, L3H = N-neopentyl-1-(1H-pyrrol-2-yl)methanimine, and L4H = N-tert-octyl-1-(1H-pyrrol-2-yl)methanimine), were synthesized and characterized using various analytical methods, including nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HR-MS), and X-ray crystallography. The ligands acted as monoanionic bidentate ligands. Single-crystal X-ray diffraction revealed that complexes 2 and 4 were homoleptic monomeric conformers with distorted tetrahedral geometries, with calculated τ’₄ values of 0.744 and 0.738 for 2 and 4, respectively. Thermogravimetric analysis of all complexes showed a clear, single-step weight loss and exceptional volatility, with low residual masses of 0.35 − 4.41 % at 400 °C. The temperature at which a vapor pressure of 1 Torr was reached and the enthalpies of vaporization were calculated using the Clausius-Clapeyron equation, resulting in values of 148 °C and 105.11 kJ/mol for 2, and 169 °C and 101.31 kJ/mol for 4, respectively.