Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3

Abstract

Cyclopentadienyl complexes Ba(C₅Me₅)₂(THF)₂ (1), Ba(C₅Me₅)₂(A) (A = THF, dien, trien, diglyme, triglyme) (2–5), Ba(Prⁱ₃C₅H₂)₂(THF)₂ (6), Ba(Bu^t₃C₅H₂)₂(THF) (7), Ba(Me₂NC₂H₄C₅Me₄)₂ (8) and Ba(EtOC₂H₄C₅Me₄)₂ (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2–5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-Ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO₃ thin film depositions by atomic layer deposition (ALD).