Vibrational spectra, normal coordinate analysis, and conformation of bis(ɑ-cyanoacetylacetonato)Cu(II)

•The CuO bond strength in target complex is theoretically and experimentally studied.•We show CuO bond strength in Cu(CNacac)2 complex is higher than that in Cu(acac)2.•Variation of CC and CO bond lengths in target complex are interpreted by E(2).•Full vibrational band assignments for Cu(CNacac)2 complex are performed.•A normal coordinate analysis and PED calculations were carried out.

Ab initio calculations, Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses, and Fourier transform Raman (3200–350 cm−1) and infrared (4000–200 cm−1) spectral measurements have been made for bis(α-cyanoacetylacetonato)Cu(II), Cu(CNacac)2. The molecular structure and vibrational spectra of Cu(CNacac)2 is compared with those of bis(acetylacetonato)Cu(II), Cu(acac)2. The molecular electronic energies and the equilibrium geometries for all theoretically possible conformations are calculated. A normal coordinate analysis of the vibrational modes has been computed for the most stable conformation of Cu(CNacac)2, D2h symmetry. A complete assignment of the observed band frequencies has been proposed. The metal–O bond strength was investigated by geometry calculations, NBO, AIM, and spectroscopic results to realize the effect of cyano substitution at α-position. All theoretical and vibrational spectroscopic studies confirm stronger metal–ligand bond in Cu(CNacac)2 than that in Cu(acac)2.

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