The effect of alkyl substituents in the β-side on the conformation, molecular structure, and copper-oxygen bond strength of bis(β-diketonato)copper(II) complexes by DFT results and experimental vibrational and UV spectra

The conformation, geometry, and relative energies of bis (2,6-dimethylheptane-3,5-dionato)copper(II), (Cu(DIMHD)₂), and bis (5,5-dimethylhexane-2,4-dionato)copper(II), Cu(DMHD)₂ have been assayed through using calculated results from atoms-in-molecules (AIM) analysis, time-dependent density functional theory (TD-DFT), natural bond orbital (NBO), and density functional theory (DFT). The electronic and vibrational spectra of these compounds have also been studied using experimental infrared, Raman, and ultraviolet (UV) spectra. All theoretical and empirical vibrational frequencies of the mentioned compounds have been assigned. The DFT was used to characterize the conformers of the complexes mentioned above, as well as the observed vibrational and UV spectra. Similar complexes, including copper (II) acetylacetonate Cu(AA)₂, bis(3,5-heptanedionato)copper(II) (Cu(HPD)₂), and copper (II) 2,2,6,6-tetramethylheptane-3,5-dionate (Cu(TMHD)₂), have been chosen to evaluate the influence of isopropyl (iPr) and tert-Butyl (t-Bu) groups substituents instead of methyl and ethyl groups. All experimental, spectroscopic, and DFT results confirmed that the O-Cu bond strength in Cu(DIMHD)₂ and Cu(DMHD)₂ is between Cu(TMHD)₂ and Cu(AA)₂ and close to Cu(HPD)₂.