Nickel complexes based on amidine for applications in gas-assisted methods and photocatalysis

Abstract

The new nickel(II) complexes were investigated as potential precursors for gas-assisted methods: chemical vapor deposition and focused electron or ion beam induced deposition, which are techniques to produce nanomaterials. We report the conventional and mechanochemical ‘green’ synthesis of amidine-carboxylate [Ni₂(NH₂(NH)CR_f)₂(μ-O₂CR_f)₄] (R_f = CF₃, C₂F₅) and imidoylamidinate [Ni(NHC(CF₃)NC(CF₃)NH)₂] complexes with perfluorinated substituents and their characteristics. Infrared spectroscopy, electron impact mass spectrometry, and density-functional theory calculations were used to confirm the formation of dinuclear amidine-carboxylate and mononuclear imidoylamidinate complexes. Additionally, the structure of [Ni(NHC(CF₃)NC(CF₃)NH)₂]·(NH₄)(CF₃CONH)·(CF₃CONH₂)·H₂O was solved using single crystal X-ray diffraction. Thermal stability and volatility of the studied compounds were investigated using thermal analysis and sublimation experiments. These results show that [Ni₂(NH₂(NH)CC₂F₅)₂(μ-O₂CC₂F₅)₄] and [Ni(NHC(CF₃)NC(CF₃)NH)₂] sublimate over a range of 358–423 K under 10⁻² mbar pressure. Electron impact mass spectrometry of complexes and microscopy studies (SEM/EDX and TEM/EDX) reveal that [Ni₂(NH₂(NH)CC₂F₅)₂(μ-O₂CC₂F₅)₄] is the most sensitive to low- and high-energy electrons. For this compound, the nickel-based materials were grown on silicon, glass, and finally titania nanotubes using the chemical vapor deposition (CVD) process. Kinetic tests have shown that the modification of titania nanotubes with nickel strengthens this material's photocatalytic activity in methylene blue photodegradation. The obtained results indicate that the selected compound may be a promising precursor for vapor deposition techniques.