We report application of nuclear inelastic scattering (NIS) spectroscopy to the compound tris(acetylacetonate)iron(III), [Fe(III)(acac)3] enriched in 57Fe. Experimental results are compared with the simulated spectrum based on the normal mode analysis of the isolated [57Fe(III)(acac)3] molecule using DFT calculations. Good agreement between the peak positions and intensities of the simulated and experimental spectra enables complete and reliable assignment of the Fe-selective vibrational modes. It is concluded that in the solid state E modes are enhanced by coupling with the lattice modes. Additionally, infrared and Raman spectra of [Fe(III)(acac)3] are calculated from DFT and compared with experiment thus demonstrating the complementarity of these three vibrational spectroscopic techniques.