Monomeric Sr Complexes Combined with Tetradentate Enaminolate Ligands for Containing Sr Thin-Film Deposition

New strontium complexes, Sr(ONO1)₂ (strontium-1-(bis(2-methoxyethyl)amino)-3,3-dimethylbut-1-en-2-olate) (1), Sr(ONO2)₂ (strontium-1-(bis(2-ethoxyethyl)amino)-3,3-dimethylbut-1-en-2-olate) (2), and Sr(ONO3)₂ (strontium-2-(bis(2-methoxyethyl)amino)-1-(dimethylamino)ethen-1-olate) (3), were successfully synthesized and characterized using tetradentate ligands. The molecular structures of 1-3 were elucidated by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), elemental analysis (EA), and single-crystal X-ray crystallography (XRC). All three complexes exhibited mononuclear structures, featuring nearly identical bicapped trigonal prismatic geometries. TGA revealed that 1, 2, and 3 retained residues of approximately 9.9, 11.9, and 34.5% at 450 °C, respectively. Notably, 1 showed volatility at 70 °C under 0.75 Torr and exhibited a vapor pressure of 0.1 Torr at 150 °C. The enthalpy of evaporation (ΔH_vap) for 1 was calculated to be 50.3 kJ/mol. Among the synthesized complexes, 1 demonstrated the highest thermal stability and is considered a promising precursor for atomic layer deposition (ALD) of strontium-containing oxide thin films.