Tuning Coordination Geometry of Nickel Ketoiminates and Its Influence on Thermal Characteristics for Chemical Vapor Deposition of Nanostructured NiO Electrocatalysts

Targeting Manganese Amidinate and ß-Ketoiminate Complexes as Precursors for Mn-Based Thin Film Deposition

With a focus on Mn based organometallic compounds with suitable physico-chemical properties to serve as precursors for chemical vapor deposition (CVD) and atomic layer deposition (ALD) of Mn-containing materials, systematic synthetic approaches with ligand variation, detailed characterization, and theoretical input from density functional theory (DFT) studies are presented. A series of new homoleptic all-nitrogen and mixed oxygen/nitrogen-coordinated Mn(II) complexes bearing the acetamidinate, formamidinate, guanidinate and ß-ketoiminate ligands have been successfully synthesized for the first time. The specific choice of these ligand classes with changes in structure and coordination sphere and side chain variations result in significant structural differences whereby mononuclear and dinuclear complexes are formed. This was supported by density functional theory (DFT) studies. The compounds were thoroughly characterized by single crystal X-ray diffraction, magnetic measurements, mass spectrometry and elemental analysis. To evaluate their suitability as precursors for deposition of Mn-based materials, the thermal properties were investigated in detail. Mn(II) complexes possessing the most promising thermal properties, namely Bis(N,N'-ditertbutylformamidinato)manganese(II) (IV) and Bis(4-(isopropylamino)pent-3-en-2-onato)manganese(II) (ßIII) were used in reactivity studies with DFT to explore their interaction with oxidizing co-reactants such as oxygen and water which will guide future CVD and ALD process development.

On the Fragmentation of Ni(II) β-Diketonate-Diamine Complexes as Molecular Precursors for NiO Films: A Theoretical and Experimental Investigation

NiO-based nanomaterials have attracted considerable interest for different applications, which have stimulated the implementation of various synthetic approaches aimed at modulating their chemico-physical properties. In this regard, their bottom-up preparation starting from suitable precursors plays an important role, although a molecular-level insight into their reactivity remains an open issue to be properly tackled. In the present study, we focused on the fragmentation of Ni(II) diketonate-diamine adducts, of interest as vapor-phase precursors for Ni(II) oxide systems, by combining electrospray ionization mass spectrometry (ESI-MS) with multiple collisional experiments (ESI-MSn) and theoretical calculations. The outcomes of this investigation revealed common features in the fragmentation pattern of the target compounds: (i) in the first fragmentation, the three complexes yield analogous base-peak cations by losing a negatively charged diketonate moiety; in these cations, Ni-O and Ni-N interactions are stronger and the Ni positive charge is lower than in the parent neutral complexes; (ii) the tendency of ligand electronic charge to migrate towards Ni further increases in the subsequent fragmentation, leading to the formation of a tetracoordinated Ni environment featuring an interesting cation-π intramolecular interaction.

Interplay between coordination sphere engineering and properties of nickel diketonate-diamine complexes as vapor phase precursors for the growth of NiO thin films

NiO-based films and nanostructured materials have received increasing attention for a variety of technological applications. Among the possible strategies for their fabrication, atomic layer deposition (ALD) and chemical vapor deposition (CVD), featuring manifold advantages of technological interest, represent appealing molecule-to-material routes for which a rational precursor design is a critical step. In this context, the present study is focused on the coordination sphere engineering of three heteroleptic Ni(II) β-diketonate-diamine adducts of general formula [NiL₂TMEDA] [L = 1,1,1-trifluoro-2,4-pentanedionate (tfa), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionate (fod) or 2,2,6,6-tetramethyl-3,5-heptanedionate (thd), and TMEDA = N,N,N',N'-tetramethylethylenediamine]. Controlled variations in the diketonate structure are pursued to investigate the influence of steric hindrance and fluorination degree on the chemico-physical characteristics of the compounds. A multi-technique investigation supported by density functional calculations highlights that all complexes are air-insensitive and monomeric and that their thermal properties and fragmentation patterns are directly dependent on functional groups in the diketonate ligands. Preliminary thermal CVD experiments demonstrate the precursors' suitability for the obtainment of NiO films endowed with flat and homogeneous surfaces, paving the way to future implementation for CVD end-uses.

A facile approach to C-functionalized β-ketoimine compounds via terminal alkylation of a tetralithiated intermediate

A series of C-functionalized β-ketoimine compounds at the terminal methyl groups of the β-ketoimine precursor L^phH₂ (L^ph = C₆H₄[NC(Me)CHC(Me)O]₂) were prepared. This convenient transformation was realized via straightforward double alkylation on the terminal C_α of a novel bis-dianionic β-ketoiminate lithium complex [L^ph'Li₄(THF)₄]₂ (L^ph' = C₆H₄[NC(Me)CHC(O)CH₂]₂) followed by hydrolysis.