Density functional theory (DFT) and Atoms-in-Molecules (AIM) analyses as well as Fourier transform Infrared, Raman, and UV spectra have been used to investigate the structure and vibrational spectra of bis(3,5-heptanedionato)copper(II) (Cu(HPD)2). To explore the effect of ethyl substitution with the methyl and t-But groups in the b-position, two different complexes have been chosen, namely, copper (II) acetylacetonate Cu(acac)2 and copper (II) 2,2,6,6-tetramethylheptane-3,5-dionate (Cu(TMHD)2), respectively. The experimental IR and Raman wavenumbers have been fully assigned, using the calculated ones. The calculated and experimental results are in good agreement. The metaleO bond strength was investigated by geometry calculations and spectroscopic results to realize the substitution effect. The metaleligand bond strength in Cu(HPD)2 is between the corresponding ones in Cu(THMD)2 and Cu(acac)2.

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