Study of Electronic Structure and Simulation of Molecular Rearrangements of MOCVD Precursors to Predict Their Thermal Stability Upon Evaporation on the Example of Heteroleptic Copper(II) Complexes

An approach for predicting stability of organometallic precursors during evaporation for chemical vapor deposition is considered on the example of isostructural heteroleptic copper complexes [Cu(acac)(hfac)]₂ (1) and [Cu(ki)(hfac)]₂ (2). The electron density distribution in binuclear molecules of 1 and 2 is studied by the density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS). It is established that the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of these complexes are characterized by the same composition and structure, their metal–ligand bonds and bridging Cu–O bonds in dimers have close energies, and their donor and central atoms have equal charges. It is shown that the differences between resistances of the studied heteroleptic complexes to the disproportionation upon condensed-phase heating, leading to the formation of homoleptic complexes, are determined by the kinetics of the process. We propose a mechanism of thermally activated ligand-exchange reaction as a series of rearrangements of dimeric complexes in crystals. It is shown from the calculated ΔE and ΔG values that 2 is thermally more stable than 1 due to the presence of an energy barriers it encounters at each stage of the process.