Identification of cis/trans isomers of bis(acetylacetonato)nickel(II) complexes in solution based on electronic spectra

Electronic spectra of Ni(acac)2 were studied in acetone, DMF, and some other solvents for the purpose of identifying the cis/trans isomers from the spectra (acac− = acetylacetonate anion). The spectral components were investigated in the spin-allowed transition bands, and a relationship was found between the spectral pattern and the cis/trans isomers. According to this relationship, it was concluded that the cis isomer was formed in DMF and in N-methylformadide, whereas the trans isomer was formed in acetone and in pyridine. Based on the DFT computation, the cis-[Ni(acac)2(DMF)2] was found to be stabilized by intramolecular hydrogen bonds between acetylacetonate and DMF.