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

Abstract

High-yield synthesis of four new fluorinated enaminones LH₂ (R_fC(O)C₂H₂NH)₂C₂H₄ (R_f = 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.