Fluorinated Cerium(IV) Enaminolates: Alternative Precursors for Chemical Vapor Deposition of CeO2 Thin Films

High-yield synthesis of four new fluorinated enaminones LH2 (RfC­(O)­C2H2NH)2C2H4 (Rf = CF3 (2a), C2F5 (2b), C3F7 (2c)) and (F3CC­(O)­C2H2NH)2C3H6 (2a′) as dianionic ligands is described. The ligands were characterized in solution (via nuclear magnetic resoannce (NMR)) as well as in the solid state (via X-ray diffraction (XRD)). The ligating ability of the enaminones was verified by reacting them with [Ce2(OiPr)8(HOiPr)2], which resulted in monomeric cerium­(IV) complexes [CeL2] (3a–c, 3a′) based on tetradentate chelation of the ligands. Cerium enaminolates were comprehensively analyzed by NMR spectroscopy, mass spectrometry, and single-crystal XRD studies to verify their monomeric nature. High stability under ambient conditions and high volatility makes them a potential precursor for the gas-phase synthesis of CeO2. Complexes 3a and 3b were applied as precursors in thermal and plasma-enhanced chemical vapor deposition to obtain crystalline ceria films with different surface morphologies. The purity and surface states of the films were analyzed by X-ray photoelectron spectroscopy, which revealed a high amount of Ce3+ on the subsurface of CeO2 films.